Molecular insights into the variability and pathogenicity of Fusarium odoratissimum, the causal agent of Panama wilt disease in banana

Fusarium wilt or Panama disease of banana caused by the hemibiotroph fungus, Fusarium odoratissimum, also known as F. oxysporum f.sp. cubense Tropical Race 4 is a serious threat to banana production worldwide. Being the world's largest grower and the origins of bananas in its northeast region, India is particularly vulnerable to this deadly fungus. In the present study, a total of 163 Fusarium isolates from infected banana were characterized for their pathogenic traits. Considering the variability in the Fusarium, the contaminated banana plants were collected from five districts of Uttar Pradesh and Bihar, two major primary infection states of India. All the isolates were screened using universal and specific primers to identify the F. odoratissimum strains. The identified F. odoratissimum strains were subjected to in vivo pathogenicity assessment using the susceptible banana cultivar 'Grand Naine'. The identified six most virulent strains were further characterized for their pathogenicity via in vivo bipartite interaction in terms of biochemical assays. Assessment of in vivo pathogenicity through qRT-PCR for three pathogenesis responsive genes, Six 1a (Secreted in xylem), Snf (Sucrose non-fermenting) and ChsV (Chitinase V), ascertained that the identified F. odoratissimum strains exhibit both intra- and inter-specific variability. The variability of F. odoratissimum strains signifies its importance for the assessment of spread of infection at specific sites to enable efficient management strategy of Fusarium wilt in banana.

Discovery of gene regulation mechanisms associated with uniconazole-induced cold tolerance in banana using integrated transcriptome and metabolome analysis

BACKGROUND

The gibberellic acid (GA) inhibitor, uniconazole, is a plant growth regulator commonly used in banana cultivation to promote dwarfing but also enhances the cold resistance in plants. However, the mechanism of this induced cold resistance remains unclear.

RESULTS

We confirmed that uniconazole induced cold tolerance in bananas and that the activities of Superoxide dismutase and Peroxidase were increased in the uniconazole-treated bananas under cold stress when compared with the control groups. The transcriptome and metabolome of bananas treated with or without uniconazole were analyzed at different time points under cold stress. Compared to the control group, differentially expressed genes (DEGs) between adjacent time points in each uniconazole-treated group were enriched in plant-pathogen interactions, MAPK signaling pathway, and plant hormone signal transduction, which were closely related to stimulus-functional responses. Furthermore, the differentially abundant metabolites (DAMs) between adjacent time points were enriched in flavone and flavonol biosynthesis and linoleic acid metabolism pathways in the uniconazole-treated group than those in the control group. Temporal analysis of DEGs and DAMs in uniconazole-treated and control groups during cold stress showed that the different expression patterns in the two groups were enriched in the linoleic acid metabolism pathway. In addition to strengthening the antioxidant system and complex hormonal changes caused by GA inhibition, an enhanced linoleic acid metabolism can protect cell membrane stability, which may also be an important part of the cold resistance mechanism of uniconazole treatment in banana plants.

CONCLUSIONS

This study provides information for understanding the mechanisms underlying inducible cold resistance in banana, which will benefit the production of this economically important crop.

Investigating aluminum toxicity effects on callose deposition, oxidative stress, and nutrient homeostasis in banana genotypes

Aluminum (Al) toxicity poses a significant challenge to agricultural productivity, particularly in acidic soils. The banana crop, predominantly cultivated in tropical and subtropical climates, often grapples with low pH and Al toxicity. This study seeks to explore the differential responses of two banana genotypes with varying Al tolerance (Baodao and Baxi) to Al exposure (100 and 500 µM) for 24 h. Microscopic analysis uncovered distinctive structural modifications in root cells, with Baodao displaying more severe alterations in response to Al stress. There was higher superoxide (O2-.) and hydrogen peroxide (H2O2) production and lipid peroxidation in Baodao indicating enhanced oxidative stress and membrane damage. Al accumulation in root tips was higher in Baxi than Baodao, while the roots of Baodao had a higher accumulation of callose. Nutrient content analysis revealed alterations in ion levels, highlighting the impact of Al exposure on nutrient uptake and homeostasis. In summary, Al differentially affects callose deposition, which, in turn, leads to Al uptake and nutrient homeostasis alteration in two contrasting banana genotypes. This intricate interplay is a key factor in understanding plant responses to aluminum toxicity and can inform strategies for crop improvement and soil management in aluminum-stressed environments.

Regulatory landscape and public perception for gene-edited bananas in the Southeast Asian region

Banana is a premier fruit crop in many parts of the world especially Southeast Asia. The demand for banana has contributed to significant national income to primary banana producers in the SEA region such as the Philippines, Indonesia, Thailand, Vietnam, and Malaysia. However, the widely traded banana industry is plagued by numerous threats including pests and diseases, post-harvest issues and extreme climate vulnerability. To address these challenges, new breeding techniques such as gene editing have been explored for breeding programs to develop improved banana varieties. The first gene-edited non-browning banana has been deregulated in the Philippines recently, and more regulatory applications are expected to submit for approvals soon. Hence, it is timely to review the policy options for gene editing that have been adopted and discussed in the Southeast Asian countries and highlight the implications of differing regulatory approaches to gene editing for trading activities. Positive stakeholders' perceptions and public acceptance are key factors in allowing the benefits of gene editing and thus appropriate outreach strategies are important to gain acceptance and avoid the "GMO stigma" that may be associated with gene-edited products.

Improvement of cross-linked films based on chitosan/diepoxy-poly (ethylene glycol) incorporating trans-cinnamaldehyde essential oil: Preparation, properties, and application in banana storage

In this study, development of bioactive coatings containing 1 % (w/v) chitosan (CS), 0.6 % (w/v) diepoxy-polyethylene glycol (PEG), and trans-cinnamaldehyde (CIN) was achieved. The physicochemical and biological properties of the coatings were investigated. The tensile strength, light transmission, water vapor permeability (WVP), and antibacterial properties were enhanced by the incorporation of CIN. The CIN-containing films appeared compact and rough, as observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the quality attributes of the bananas were evaluated at room temperature for 24 days, and the results showed that the CS/PEG/CIN coating delayed the respiration peak, weight loss, sugar content loss, and maintained firmness, color, total soluble solids (TSS), titratable acid (TA), and the appearance of the bananas. Principal component analysis (PCA) revealed that the bioactive coating significantly affected the respiration rate and weight loss of bananas.

Identification of S-adenosyl-l-homocysteine hydrolase from banana fruit as a novel plant panallergen

Banana allergy is often associated with the pollen and latex allergies, which led us to the hypothesis that some yet unidentified banana allergen could provide a basis of the latex-pollen-fruit syndrome. S-adenosyl-l-homocysteine hydrolase (SAHH) was recently identified in the literature as a novel plant allergen. This study aimed to assess the allergenic potential of the naturally occurring banana SAHH (nSAHH) and its recombinant homolog produced in E. coli (rSAHH). nSAHH showed IgE reactivity with a serum pool of twelve banana-allergic persons, while rSAHH displayed IgE reactivity in ten out of the twelve tested patients. Five linear B-cell epitopes were identified on the rSAHH surface, exhibiting ≥ 90 % sequence homology with relevant plant SAHH allergens. Our findings have elucidated SAHH as a novel plant panallergen, underlying the cross-reactivity between plant-derived food and respiratory allergens, confirming our initial hypothesis.

Unveiling the dynamic expression of PR-1 during Musa spp. infection by Fusarium oxysporum fsp. Cubense: a cloning and characterization study

BACKGROUND

Pathogen-related proteins (PR) are pivotal in plant defense, combating diverse biotic and abiotic stresses. While multiple gene families contribute to banana resistance against Fusarium oxysporum f sp. cubense (Foc), Pseudocercospora eumusae, and Pratylenchus coffeae, the significance of PR-1 genes in defense is paramount.

METHODS

Three PR-1 genes, up-regulated under diverse biotic stresses, were cloned from both resistant and susceptible cultivars of Foc, P. eumusae, and P. coffeae. Molecular characterization, phylogenetic analysis, and docking studies with the Foc TR4 CP gene were conducted.

RESULTS

Through transcriptomic and real-time studies, three PR-1 genes (Ma02_g15050, Ma02_g15060, and Ma04_g34800) from Musa spp. were identified. These genes exhibited significant up-regulation in resistant cultivars when exposed to Foc, P. eumusae, and P. coffeae. Cloning of these genes was successfully performed from both resistant and susceptible cultivars of Foc race 1 and TR4, P. eumusae, and P. coffeae. Distinct characteristics were observed among the PR-1 genes, with groups 1 and 2 being acidic with signal peptides, and group 3 being basic without signal peptides. All cloned PR-1 proteins belonged to the CAP superfamily (PF00188). Phylogenetic analysis revealed clustering patterns for acidic PR-1 proteins, and KEGG orthology showed associations with vital pathways, including MAPK signaling, plant hormone signal transduction, and plant-pathogen interaction. Secondary and tertiary structure analyses confirmed sequence conservation across studied species. Docking studies explored interactions between the cerato-platanin (CP) gene from Foc TR4 and Ma02_g15060 from banana, suggesting the potential hindrance of PR-1 antifungal activity through direct interaction.

CONCLUSIONS

The findings underscore the crucial role of cloned PR-1 genes in banana plant defense mechanisms against a broad spectrum of biotic stresses. These genes, especially those in groups 1 and 2, hold promise as candidates for developing stress-tolerant banana cultivars. The study provides valuable insights into the molecular aspects of banana defense strategies, emphasizing the potential applications of PR-1 genes in enhancing banana resilience.

First Report of Bulb Rot Disease of Banana Caused by Klebsiella variicola in China

Banana (Musa spp.) is an economically important fruit and food crop globally as well as in China. In March 2023, a bulb rot disease was observed on more than 20% of cultivated dwarf bananas in a plantation in Wuming County of Guangxi Province, a major hub of banana production in China. Infected plants showed crackles at the basal part of stem and were relatively dwarf, while yellowing of the leaves was not observed. When the rhizomes were cut open, water-soaked lesions with a yellow or black margin can be seen in the bulb. In severe infections, the internal tissue became dry or wet rot, and there was typical dark-brown cavity formation in the bulb. The rot was limited to the bulb. To isolate the causal agent, dissected diseased tissues (5×5 mm) were surface sterilized with 75% ethanol (30 s) and 2% NaClO (3 min), followed by three rinses with sterile water. The sterilized sections were soaked in 2 mL of sterile water and shaken for 5 min in a vortex oscillator. The suspension was streaked on Luria-Bertani (LB) agar medium, and incubated at 28℃ for 24 h. Single colonies were re-streaked three times to obtain purified isolation. Twelve pure bacterial cultures with similar morphology were isolated from three plants taken from the field. The bacterial colonies were yellowish white, mucoid, round, and raised with translucent surfaces on the LB agar plate. Three strains Gxkv1, Gxkv2 and Gxkv3 were selected for further analyses. The 16S rDNA gene (GenBank Accession OR461756, PP094726 and PP109349) were amplified using primer pair 27F/1492R (Frank et al. 2008). Comparing 16S sequences against GenBank showed 99.86%-100% sequence identity to Klebsiella variicola strain (MZ475068) for the three isolates Gxkv1 (1,398/1,398 bp), Gxkv2 (1,398/1,396 bp) and Gxkv3 (1,398/1,398 bp). A multilocus phylogenetic analysis was conducted by neighbor-joining method (1,000 bootstrap values) based on three housekeeping gene sequences of gyrA (GenBank Accession No. OR515493, PP105747, PP105748), rpoB (OR515494, PP105751, PP105752 ) and infB (OR515495, PP105749, PP105750) genes which were amplified by gyrA-A/gyrA-C, CM31b/CM7 and infB867F/infB1819R primer sets, respectively (Rosenblueth et al. 2004). The results of phylogenetic analysis showed the three strains belong to the K. variicola clade. A pathogenicity test was conducted on six healthy 3-month-old dwarf banana plants by spraying 10 mL of bacterial suspensions of Gxkv1 (108 CFU/mL) into the rhizome which wounded with a sterilized needle; another six healthy control plants were sprayed with 10 mL of sterile water. Following inoculation, the plants were placed in a greenhouse at 28-32°C. After 30 days, all inoculated plants showed symptoms similar to those observed in the field, while the control plants remained healthy. Bacteria were successfully reisolated from the symptomatic tissues and identified to be K. variicola by PCR mentioned above. K. variicola has been reported to cause rhizome rot of banana in India (Loganathan et al. 2021), and to cause plantain soft rot in Haiti (Fulton et al. 2021). Besides, previous reports from China only showed K. variicola causing banana sheath rot (Fan et al. 2015, Sun et al. 2023). To our knowledge, this is the first report of bulb rot disease of banana caused by K. variicola in Guangxi Province, China. This finding will provide important information for studying the epidemiology and management of this pathogen.

Dataset from transcriptome profiling of Musa resistant and susceptible cultivars in response to Fusarium oxysporum f.sp. cubense race1 and TR4 challenges using Illumina NovaSeq

In this investigation, the study focused on the RNAseq data generated in response to Fusarium oxysporum f.sp. cubense (Foc) race1 (Cavendish infecting strain VCG 0124), targeting both resistant (cv. Rose, AA) and susceptible cultivars (Namarai, AA), and Tropical Race 4 (TR4, strain VCG 01213/16), involving resistant (cv. Rose, AA) and susceptible cultivars (Matti, AA). The respective contrasting cultivars were independently challenged with Foc race1 and TR4, and the root and corm samples were collected in two replications at varying time intervals [0th (control), 2nd, 4th, 6th, and 8th days] in duplicates. The RNA samples underwent stringent quality checks, with all 80 samples meeting the primary parameters, including a satisfactory RNA integrity number (>7). Subsequent library preparation and secondary quality control steps were executed successfully for all samples, paving the way for the sequencing phase. Sequencing generated an extensive amount of data, yielding a range of 10 to 31 million paired-end raw reads per sample, resulting in a cumulative raw data size of 11-50 GB. These raw reads were aligned against the reference genome of Musa acuminata ssp. malaccensis version 2 (DH Pahang), as well as the pathogen genomes of Foc race 1 and Foc TR4, using the HISAT2 alignment tool. The focal point of this study was the investigation of differential gene expression patterns of Musa spp. upon Foc infection. In Foc race1 resistant and susceptible root samples across the designated day intervals, a significant number of genes displayed up-regulation (ranging from 1 to 228) and down-regulation (ranging from 1 to 274). In corm samples, the up-regulated genes ranged from 1 to 149, while down-regulated genes spanned from 3 to 845. For Foc TR4 resistant and susceptible root samples, the expression profiles exhibited a notable up-regulation of genes (ranging from 31 to 964), along with a down-regulation range of 316-1315. In corm samples, up-regulated genes ranged from 57 to 929, while down-regulated genes were observed in the range of 40-936. In addition to the primary analysis, a comprehensive secondary analysis was conducted, including Gene Ontology (GO), euKaryotic Orthologous Groups (KOG) classification, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and investigations into Simple Sequence Repeats (SSRs), Single Nucleotide Polymorphisms (SNPs), and microRNA (miRNA). The complete dataset was carefully curated and housed at ICAR-NRCB, Trichy, ensuring its accuracy and accessibility for the duration of the study. Further, the raw transcriptome read datasets have been successfully submitted to the National Center for Biotechnology Information - Sequence Read Archive (NCBI-SRA) database, ensuring the accessibility and reproducibility of this valuable dataset for further research endeavors.

Postharvest melatonin and chitosan treatments retain quality of 'Williams' bananas during ripening

The effect of postharvest dipping treatments with 0.5 mM melatonin (MT) and 1% chitosan (CT) either alone or in combination on quality of pre-climacteric 'Williams' bananas during ripening at ambient conditions were investigated. MT or CT treatments delayed ripening by retaining greener peel, higher firmness, titratable acidity (TA), but lower total soluble solids (TSS) and TSS/TA, weight loss, browning and electrolyte leakage than the control. Total phenol (TPC) and flavonoid contents (TFC) in both peel and pulp increased up to 6 days and then decreased and was higher in treated fruit than the control. Vitamin C content decreased up to 3 days, then increased and was higher in treated fruit than control. MT and CT combination exhibited the highest TPC, TFC and vitamin C contents compared to other treatments. Radical scavenging capacity (RSC) of peel and pulp increased up to 6 days, then decreased and was higher in treated fruit than the control. The treated fruit exhibited lower polyphenoloxidase (PPO) and hydrolytic enzymes but higher peroxidase (POD) activities in both peel and pulp than the control. Postharvest treatments with 0.5 mM MT and 1% CT alone or in combination could be used to retain quality of 'Williams' bananas during ripening.

Comparative transcriptomic and weighted gene co-expression network analysis to identify the core genes in the cultivars of Musa acuminata under both infected and chemical perturbated conditions

Banana is a high nutrient crop, which ranks fourth in terms of gross value production. Fusarium wilt of banana, caused by Fusarium oxysporum f. sp. cubense tropical race 4 (FocTR4), is considered the most destructive disease leading to the complete loss of production of the Cavendish cultivars Berangan, Brazilian and Williams, which are vulnerable to the infection of FocTR4. However, the treatment with benzothiadiazole, a synthetic salicylic analog, is aimed to induce resistance in plants. Thus, the treatments pertaining to the banana plants subjected to the Foc infection within the chosen cultivars were compared with chemically treated samples obtained at different time intervals for a short duration (0-4 days). The integrated omics analyses considering the parameters of WGCNA, functional annotation, and protein-protein interactions revealed that many pathways have been negatively influenced in Cavendish bananas under FocTR4 infections and the number of genes influenced also increased over time in Williams cultivar. Furthermore, elevation in immune response and resistance genes were also observed in the roots of the Cavendish banana.

Inducing mutation and ascertaining lethal dosage of in vitro cultures of banana cv. Ney Poovan to ethyl methane sulfonate

In vitro mutation breeding in vegetatively propagated crops like banana offers a benefit in screening for beneficial variants in plant cells or cultured tissues. An attempt was made to induce mutants and determine the lethal dose, as it is the prerequisite to optimize the concentration and duration of the mutagen used to recover a larger population in mutation research. Shoot tip cultures were treated for 2 and 4 h at six different EMS concentrations ranging from 80 mM to 160 mM, whereas proliferating multiple shoots were exposed for 30 and 60 min at six different EMS concentrations ranging from 8 mM to 40 mM. Survival percentage, shoot length, and number of shoots reduced linearly and significantly as concentration and duration increased in both shoot tips and proliferating multiple buds. The probit curve-based analysis of mortality of treated explants revealed that the LD50 was 155.83 mM for 2 h and 113.72 mM for 4 h, respectively for shoot tip cultures, whereas for proliferating multiple buds, the LD50 value was adjusted to 39.11 mM for 30 min and 30.41 mM for 60 min. 160 mM EMS for 4 h resulted in a shorter shoot, a longer rooting duration, a lesser number of roots, and decreased root development. In proliferating multiple shoots, the smallest shoot, longest rooting duration, least number of roots, and shortest root were observed in 40 mM EMS for 60 min. Similar reductions in growth parameters were observed in proliferating multiple shoots at higher exposure to EMS for a longer duration.

Application of pesticide application measures to reduce residue based on the metabolic transfer law of imidacloprid in banana leaves and soil

An investigation of the metabolism and transfer of imidacloprid (IMI) in banana plants and soil was performed using high-resolution mass spectrometry. Results indicated the presence of eight IMI metabolites in soil and leaves that resulted from hydroxylation of the imidazolidine ring, the reduction and loss of nitro groups, and oxidative cleavage of methylene bridges. Six metabolites, including 4/5-hydroxy IMI (4/5-hydroxy), IMI olefin (olefin), and 6-chloronicotinic acid (6-CNA), were detected in the fruits following leaf treatment, while only three were detected after soil treatment. Quantitative analysis showed that the total amount of imidacloprid and its metabolites transferred from leaves to fruits was higher than that transferred from soil to fruits. Therefore, leaf transfer was considered the main means by which IMI and its metabolites transferred to banana fruits. We found that adjuvants tank-mixed with IMI could reduce the total concentration of pesticide transfer from leaves to fruits, especially reducing the amount of metabolites transformed from the reduction and loss of nitro groups and oxidative cleavage of methylene bridges, thus reducing the pesticide residue in fruits and achieving the purpose of reducing the safety risk.

First report of black leaf streak disease in bananas caused by Pseudocercospora fijiensis on Mauritius island

Pseudocercospora fijiensis, the causal agent of the black leaf streak disease of bananas (plants in the genus Musa) (BLSD), is considered to be the major economic threat to export-banana cultivation (de Bellaire, Fouré, Abadie, & Carlier, 2010). The disease has a worldwide distribution throughout the humid tropical regions and has been previously reported in the Southwestndian Ocean (SWIO) area: in 1993 in Mayotte and Comoros islands (DR Jones & Mourichon, 1993), in 2000 in Madagascar (Jones, 2003; Rivas, Zapater, Abadie, & Carlier, 2004) and in 2018 in Reunion Island (Rieux et al., 2019). In Mauritius, the presence of Pseudocercospora fijiensis was suspected in 1996 (Soomary & Benimadhu, 1998) but has never been confirmed, as symptoms could have been confounded with Pseudocercospora musae or Pseudocercospora eumusae, two causal agents of others leaf spot diseases of banana which were previously described in Mauritius in 1959 (Orieux & Felix, 1968) and 2000 (Carlier, Zapater, Lapeyre, Jones, & Mourichon, 2000), respectively. In March 2022, typical BLSD symptoms were observed at relatively low prevalence in a Cavendish crop located in the "Balance John" area (site S1 on Fig. S1-A) of Mauritius island. Typical early symptoms (stages 2) were 1- to 4-mm long brown streaks at the abaxial leaf surface, and typical older streaks (stages 3 and 4) were also observed (Fig. S1-B). These symptoms were mixed with symptoms of ELSD caused by P. eumusae. Since both species cannot be clearly distinguished only on the description of symptoms, conidial sporulation on stages 2 was checked in the laboratory (Ngando et al., 2015) since P. eumusae does not produce conidia on these young stages. In April 2022, banana leaves bearing symptoms of leaf spot diseases were collected in 7 different sites (Fig. S1-A). All leaf fragments were sent to the CIRAD laboratories where molecular diagnosis was performed following the protocol developed by Arzanlou et al. (2007). In brief, genomic DNA was extracted from ground leaf fragments displaying symptoms using the DNeasy® Plant Mini Kit (Qiagen®, Courtaboeuf, France). At each site, a total of 6 lesions cut from 6 different leaves were pooled. The DNA extracts were added as templates for real-time PCR assay designed to specifically detect the presence of P. fijiensis, P. musae and P. eumusae using MFbf/MFbrtaq/MFbp, MEbf/MEbrtaq/FMep and MMbf/Mmbrtaq/FMep primers and probes, respectively (Arzanlou et al., 2007). Both positive and negative controls were included in the assay and every sample reaction was duplicated. P. fijiensis was detected from 2 out of 7 sites (S2 and S7, see Fig.S2-B). P. eumusae was detected at all sites while P. musae was found in one site only (S6). Interestingly, our results also showed coinfection by P. fijiensis - P. eumusae & P. musae - P. eumusae on several sites. The presence of P. fijiensis was further confirmed by several investigations performed on conidia isolated from S2 samples including i) morphological observations of conidia displaying P. fijiensis type description (Pérez-Vicente, Carreel, Roussel, Carlier, & Abadie (2021), Fig. S2-A), ii) DNA sequencing of 16S ribosomal gene with ITS1 & ITS4 primers (GenBank accessions Nos. OR515818-OR515810) with BLAST results displaying percentages of identity > 99.70% with type strains and iii) Koch's postulates were fulfilled by artificial inoculation of detached leaf pieces as described in Pérez-Vicente, Carreel, Roussel, Carlier, & Abadie (2021) (Fig. S2-D). In brief, for the artificial inoculation, symptoms obtained after inoculation of both a strain isolated in Mauritius (S2-MAU) and a positive control (T+) were compared and shown to be typical of P. fijiensis species for the 3 replicates. To the best of our knowledge, this is the first official report of P. fijiensis and BLSD in Mauritius Island. This revelation holds significant importance for both the agricultural and scientific communities, shedding light on the potential spread and impact of this devastating pathogen in previously unaffected regions. From a global perspective, this discovery underscores the interconnectedness of agricultural ecosystems and the need for vigilance in monitoring and responding to emerging plant diseases in an increasingly interconnected world (Vega et al. 2022). Future investigations will be required to monitor the spread of BLSD on the island, describe the genetic structure of populations and identify routes of invasion at the SWOI scale.

Identification of Zimbabwe's locally grown banana (Musa Spp.) cultivars using morphology and genome-targeted sequencing

BACKGROUND

Banana production is increasingly under threat due to harsh weather conditions as a result of climate change and different diseases. As such there is a need for the preservation and the characterization of the banana cultivar population for the purposes of crop improvement. The identification of collected banana germplasm in Zimbabwe was conducted based on the Inter-transcribed spacer region as well as morphology. The study was conducted with the aim of distinguishing one cultivar from another towards genetic conservation as well as banana improvement.

RESULTS

ITS 1 and ITS 4 region targeting primers were used to amplify the DNA from twelve cultivars as well as sequence. Blast results identified five Musa groups which are Musa balbisiana (BB), Musa ABB, Musa AB hybrid, Musa acuminata (AAA), and Musa acuminata subsp. Malaccensis (AA). Phylogenetic analysis was done on the sequences under study and a maximum likelihood tree was generated to determine relationships between the sequences. Further identification was done using the inflorescence, bract, and male bud and fruit characteristics of each cultivar complementing the molecular evaluation.

CONCLUSION

Genetic and morphological identification of locally grown bananas was therefore successful. An important step towards identifying pure lines suitable for breeding.

Rasthali

BACKGROUND

The GHMP kinase gene family encompasses ATP-dependent kinases, significantly involved in the biosynthesis of isoprenes, amino acids, and metabolism of carbohydrates. Banana is a staple tropical crop that is globally consumed but known for high sensitivity to salt, cold, and drought stresses. The GHMP kinases are known to play a significant role during abiotic stresses in plants. The present study emphasizes the role of GHMP kinases in various abiotic stress conditions in banana.

METHODS AND RESULTS

We identified 12 GHMP kinase (MaGHMP kinase) genes in the banana genome database and witnessed the presence of the conserved Pro-X-X-X-Gly-Leu-X-Ser-Ser-Ala domain in their protein sequences. All genes were found to be involved in ATP-binding and carried kinase activity confronting their biological roles in the isoprene (27%) and amino acid (20%) biosyntheses. The expression analysis of genes during cold, drought, and salt stress conditions in tissue culture grown banana cultivar Rasthali plants showed a significant involvement of MaGHMP kinase genes in these stress conditions. The highest expression of MaGHMP kinase3 (8.5 fold) was noted during cold stress, while MaGHMP kinase1 (25 fold and 40.01 fold) showed maximum expression during drought and salt stress conditions in leaf tissue of Rasthali.

CONCLUSION

Our findings suggested that MaGHMP kinase1 (MaHSK) and MaGHMP kinase3 (MaGlcAK) could be considered promising candidates for thwarting the abiotic stresses in banana.

Molecular characterization of vermicompost-derived IAA-releasing bacterial isolates and assessment of their impact on the root improvement of banana during primary hardening

The hardening step of micropropagation is crucial to make the in vitro raised plants mature and further enhancing their survivability in the external environment. Auxin regulates various root physiological parameters in plant systems. Therefore, the present study aimed to assess the impact of three vermicompost-derived IAA-releasing microbial strains, designated S1, S2, and S3, as biofertilizers on in vitro raised banana plantlets during primary hardening. The High-Performance Thin-Layer Chromatography (HPTLC) analysis of these strains revealed a higher IAA content for S1 and S2 than that of S3 after 144 h of incubation. In total, seven different treatments were applied to banana plantlets, and significant variations were observed in all plant growth parameters for all treatments except autoclaved cocopeat (100%) mixed with autoclaved vermicompost (100%) at a 1:1 ratio. Among these treatments, the application of S3 biofertilizer: autoclaved cocopeat (1:1), followed by S2 biofertlizer: autoclaved cocopeat (1:1), was found to be better than other treatments for root numbers per plant, root length per plant, root volume, and chlorophyll content. These findings have confirmed the beneficial effects of microbial strains on plant systems and propose a link between root improvement and bacterial auxin. Further, these strains were identified at the molecular level as Bacillus sp. As per our knowledge, this is the first report of Bacillus strains isolated from vermicompost and applied as biofertilizer along with cocopeat for the primary hardening of banana. This unique approach may be adopted to improve the quality of plants during hardening, which increases their survival under abiotic stresses.

Ubiquitylome analysis reveals the involvement of ubiquitination in the cold responses of banana seedling leaves

Low temperature is a crucial environmental factor limiting the productivity and distribution of banana. Ubiquitination (Kub) is one of the main posttranslational modifications (PTMs) involved in plant responses to abiotic stresses. However, little information is available on the effects of Kub on banana under cold stress. In this study, we used label-free quantification (LFQ) to identify changes in the protein expression and Kub levels in banana seedling leaves after chilling treatment. In total, 4156 proteins, 1089 ubiquitinated proteins and 2636 Kub sites were quantified. Western blot assays showed that Kub was abundant in leaves after low-temperature treatment. Our results show that the proteome and ubiquitylome were negatively correlated, indicating that Kub could be involved in the degradation of proteins in banana after chilling treatment. Based on bioinformatics analysis, low-temperature stress-related signals and metabolic pathways such as cold acclimation, glutathione metabolism, calcium signaling, and photosynthesis signaling were identified. In addition, we found that transcription factors and chromatin remodeling factors related to low-temperature stress were ubiquitinated. Overall, our work presents the first systematic analysis of the Kub proteome in banana under cold stress and provides support for future studies on the regulatory mechanisms of Kub during the cold stress response in plants. SIGNIFICANCE: Banana is a typical tropical fruit tree with poor low-temperature tolerance,however, the role of PTMs such as Kub in the cold response of banana remains unclear. This study highlights the fact that the effects of low-temperature on proteome and ubiquitylome in the banana seedling leaves, we discussed the correlation between transcriptome and proteome, ubiquitylome and proteome, and we analyzed the expression and the changes of ubiquitination levels of low-temperature related proteins and pathway after chilling treatment, and we found that transcription factors and chromatin remodeling factors related to low-temperature stress were ubiquitinated. This study provides new insights into the ubiquitination pathway of banana under cold stress.

Description of Xanthocytophaga agilis sp. nov. and Xanthocytophaga flavus sp. nov. of the new genus Xanthocytophaga gen. nov and the proposal of Rhodocytophagaceae fam. nov. within the order Cytophagales

Four Gram-staining-negative, aerobic, yellow-pigmented and rod-shaped bacteria, named strains BD1B2-1T, NT2B1T, YF14B1 and DM2B3-1, were isolated from four rhizosphere soil samples of banana in China. Comparison of the 16S rRNA gene sequences showed that all these strains were most closely related to an invalidly published species, 'Rhodocytophaga rosea' 172606-1, with similarities ranging from 87.7 to 88.0%. According to the phylogenomic analysis, the four strains were clustered in an independent lineage and closely related to the genus Rhodocytophaga. The genomic sizes of these strains were approximately 9.49-9.77 Mbp with the DNA G + C contents of 38.8-39.0 mol%. They all contained C16:1 ω5c, iso-C15:0 and iso-C17:0 3-OH as the major fatty acids and menaquinone 7 as the only respiratory quinone. They all had phosphatidylethanolamine as the major polar lipids. Based on phenotypic and phylogenomic characteristics, the four strains should represent two novel species within a novel genus, for which the names Xanthocytophaga agilis gen. nov., sp. nov. (BD1B2-1T = GDMCC 1.2890T = JCM 35374T) and Xanthocytophaga flavus sp. nov. (NT2B1T = GDMCC 1.2889T = JCM 35375T) are proposed; the former is assigned as the type species of the novel genus Xanthocytophaga gen. nov. In addition, based on the phenotypic and phylogenomic data, we proposed to reclassify the existing genus Rhodocytophaga in the family Cytophagaceae into a novel family Rhodocytophagaceae fam. nov. The novel family consists of the type genus Rhodocytophaga and the novel genus Xanthocytophaga.

Genome-wide characterization of 2OGD superfamily for mining of susceptibility factors responding to various biotic stresses in Musa spp

Bananas are an important staple food and cash crop, but they are vulnerable to a variety of pests and diseases that substantially reduce yield and quality. Banana diseases are challenging to control and necessitate an integrated strategy, and development of resistant cultivars is one of the effective ways of managing diseases. Lasting disease resistance is the main goal in crop improvement and resistance mediated by a single resistant (R) gene mostly lack durability. However, long-term resistance can be obtained by inactivating susceptibility factors (S), which facilitate pathogen infection and proliferation. Identification and inactivation of susceptibility factors against the major pathogens like Fusarium oxysporum f. sp. cubense (Foc), Pseudocercospora eumusae and Pratylenchus coffeae in banana will be an effective way in developing banana varieties with more durable resistance. Downy mildew resistance 6 (DMR6) and DMR-like oxygenases (DLO1) are one such susceptibility factors and they belong to 2-oxoglutarate Fe(II) dependent oxygenases (2OGD) superfamily. 2OGDs are known to catalyze a plethora of reactions and also confer resistance to different pathogens in various crops, but not much is known about the 2OGD in Musa species. Through a comprehensive genome-wide analysis, 133 and 122 potential 2OGDs were systematically identified and categorized from the A and B genomes of banana, respectively. Real time expression of dmr6 and dlo1 genes showed positive correlation with transcriptome data upon Foc race1 and TR4 infection and examination of expression pattern of Macma4_04_g22670 (Ma04_g20880) and Macma4_02_g13590 (Ma02_g12040) genes revealed their involvement in Foc race1 and TR4 infections, respectively. Further the expression profile of 2OGDs, specifically Macma4_04_g25310 (Ma04_g23390), Macma4_08_g11980 (Ma08_g12090) and Macma4_04_g38910 (Ma04_g36640) shows that they may play a significant role as a susceptibility factor, particularly against P. eumusae and P. coffeae, implying that they can be exploited as a candidate gene for editing in developing resistant cultivars against these diseases. In summary, our findings contribute to a deeper comprehension of the evolutionary and functional aspects of 2OGDs in Musa spp. Furthermore, they highlight the substantial functions of these family constituents in the progression of diseases. These insights hold significance in the context of enhancing the genetic makeup of bananas to attain extended and more durable resistance against pathogens.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01380-y.

Dataset of banana leaves and stem images for object detection, classification and segmentation: A case of Tanzania

Banana is among major crops cultivated by most smallholder farmers in Tanzania and other parts of Africa. This crop is very important in the household economy as well as food security since it serves as both food and cash crops. Despite these benefits, the majority of smallholder farmers are experiencing low yields which are attributed to diseases. The most problematic diseases are Black Sigatoka and Fusarium Wilt Race 1. Black Sigatoka is a disease that produces spots on the leaves of bananas and is caused by an air-borne fungus called Pseudocercospora fijiensis, formerly known as Mycosphaerella fijiensis. Fusarium Wilt Race 1 disease is one of the most destructive banana diseases that is caused by a soil-borne fungus called Fusarium oxysporum f.sp. Cubense (Foc). The dataset of curated banana crop image is presented in this article. Images of both healthy and diseased banana leaves and stems were taken in Tanzania and are included in the dataset. Smartphone cameras were used to take pictures of the banana leaves and stems. The dataset is the largest publicly accessible dataset for banana leaves and stems and includes 16,092 images. The dataset is significant and can be used to develop machine learning models for early detection of diseases affecting bananas. This dataset can be used for a number of computer vision applications, including object detection, classification, and image segmentation. The motivation for generating this dataset is to contribute to developing machine learning tools and spur innovations that will help to address the issue of crop diseases and help to eradicate the problem of food security in Africa.

High temperature elevates carotenoid accumulation of banana fruit via upregulation of MaEIL9 module

Banana is a good source of carotenoids, which are bioactive metabolites with health beneficial properties for human. However, the molecular mechanism of carotenoid accumulation in banana fruit is largely unclear. In this study, we found that high temperature elevated carotenoid production in banana pulp, which is presumably due to upregulation of a subset of carotenogenic genes as well as a carotenoid biosynthesis regulator MaSPL16. Moreover, an ethylene signaling component MaEIL9 was identified, whose transcript and protein contents were also induced by high temperature. In addition, MaEIL9 positively regulates transcription of MaDXR1, MaPDS1, MaZDS1 and MaSPL16 through directly targeting their promoters. Overexpression of MaEIL9 in tomato fruit substantially increased the expression of carotenoid formation genes and elevated carotenoid content. Importantly, transiently silencing MaEIL9 in banana fruit weakened carotenoid production caused by high temperature. Taken together, these results indicate that high temperature induces carotenoid production in banana fruit, at least in part, through MaEIL9-mediated activation of MaDXR1, MaPDS1, MaZDS1 and MaSPL16 expression.

Three R2R3-MYB transcription factors from banana (Musa acuminata) activate structural anthocyanin biosynthesis genes as part of an MBW complex

OBJECTIVE

Bananas are one of the most popular fruits in the world, providing food security and employment opportunities in several developing countries. Increasing the anthocyanin content of banana fruit could improve the health-promoting properties. Anthocyanin biosynthesis is largely regulated at the transcriptional level. However, relatively little is known about the transcriptional activation of anthocyanin biosynthesis in banana.

RESULTS

We analysed the regulatory activity of three Musa acuminata MYBs that were predicted by bioinformatic analysis to transcriptionally regulate anthocyanin biosynthesis in banana. MaMYBA1, MaMYBA2 and MaMYBPA2 did not complement the anthocyanin-deficient phenotype of the Arabidopsis thaliana pap1/pap2 mutant. However, co-transfection experiments in A. thaliana protoplasts showed that MaMYBA1, MaMYBA2 and MaMYBPA2 function as components of a transcription factor complex with a bHLH and WD40 protein, the so called MBW complex, resulting in the activation of the A. thaliana ANTHOCYANIDIN SYNTHASE and DIHYDROFLAVONOL 4-REDUCTASE promoters. The activation potential of MaMYBA1, MaMYBA2 and MaMYBPA2 was increased when combined with the monocot Zea mays bHLH ZmR instead of the dicot AtEGL3. This work paves the path towards decoding the MBW complex-mediated transcriptional activation of anthocyanin biosynthesis in banana. It will also facilitate research towards increased anthocyanin content in banana and other monocot crops.

Flow patterns and pathways of legacy and contemporary pesticides in surface waters in tropical volcanic catchments

Severe water pollution issues due to legacy and contemporary pesticides exist in tropical regions and are linked to cash crops requiring intensive plant protection practices. This study aims to improve knowledge about contamination routes and patterns in tropical volcanic settings to identify mitigation measures and analyse risk. To this aim, this paper analyses four years of monitoring data from 2016 to 2019 of flow discharge and weekly pesticide concentrations in the rivers of two catchments grown predominantly with banana and sugar cane in the French West Indies. The banned insecticide chlordecone, applied in banana fields from 1972 to 1992, was still the major source of river contamination, while the currently used herbicide glyphosate, its metabolite aminomethylphosphonic acid (AMPA), and postharvest fungicides also exhibited high contamination levels. A value of 0.5 of the Gustafson Ubiquity Score (GUS) was shown to separate contaminant and noncontaminant pesticides, indicating a high vulnerability to pollution by pesticides in this tropical volcanic context. The patterns and routes of river exposure to pesticides differed markedly between the pesticides in accordance with the hydrological behaviour of volcanic islands and the history and nature of pesticide uses. Concerning chlordecone and its metabolites, observations confirmed previous findings of a main subsurface origin of river contamination by this compound but also showed large erratic short-term variations, suggesting the influence of fast surface transport processes such as erosion for legacy pesticides with large sorption capacity. Concerning herbicides and postharvest fungicides, observations have suggested that surface runoff and fast lateral flow in the vadose zone control river contamination. Accordingly, mitigation options need to be considered differently for each type of pesticide. Finally, this study points out the need for developing specific exposure scenarios for tropical agricultural contexts in the European regulation procedures for pesticide risk assessment.

Silver Nanoparticles for Enhancing the Efficiency of Micropropagation of Banana (Musa acuminata L.)

Silver nanoparticles (AgNPs) have numerous applications in plant biotechnology. The unique biological activities of AgNPs in reducing microbial contamination and promoting in vitro plant growth have encouraged their use in the development of novel culture systems for the in vitro cultivation of several plant species. In this study, the influence of (80 nm-100 nm) AgNPs on the micropropagation of banana was examined by incorporating AgNPs into shoot multiplication and rooting media at concentrations of 3 mg/L-15 mg/L. Biometric parameters for shoot multiplication (number of shoots/explant, shoot length and leaf surface area) and root development (number of roots/explant and root length) were analysed. In addition, shoot chlorophyll content, proline content and the possible impact of lipid peroxidation on membrane stability of plantlets were estimated. The results showed that all concentrations of AgNPs stimulated shoot growth and enhanced root development. The highest response was observed in media supplemented with 12 mg/L AgNPs. This optimal level of AgNPs caused a threefold increase in shoot growth parameter and a similar increase in root numbers/shoot and root length. Treatment with AgNPs at 12 mg/L also increased chlorophyll and proline content of shoots by 25% and 120% over control, respectively. Although the application of AgNPs increased the level of lipid peroxidation in shoots, it however, had a limited influence on membrane stability index. These results suggested that the administration of AgNPs to culture media can be effectively utilised for the enhancement of banana micropropagation with minimal toxic effects.

cubense tropical race 4 using comparative proteomic analysis

Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense is a worldwide devastating fungal disease in the banana industry. The disease caused by Fusarium oxysporum f. sp. cubense is becoming more and more serious. The pathogen of Fusarium oxysporum f. sp. cubense tropical race 4 (Foc4) is the most harmful one. 'Guijiao 9' is a banana cultivar with good resistance to Foc4, which is identified by resistance screening of natural variant lines. It is of great significance to explore the resistance genes and key proteins of 'Guijiao 9' for banana cultivar improvement and disease resistance breeding. In this study, iTRAQ (isobaric Tags for Relative and Absolute quantitation) was used to analyze the xylem proteomic data of banana roots from the resistant variety 'Guijiao 9' and susceptible variety 'Williams', and the differences in protein accumulation profiles between these two varieties at 24, 48, and 72 h after infection with Foc4 were compared. The identified proteins were analyzed by the protein WGCNA (Weighted Gene Correlation Network Analysis), and the differentially expressed proteins (DEPs) were verified by qRT-PCR experiments. Proteomic analysis showed that there were differences in the protein accumulation profiles of the resistant cultivar 'Guijiao 9' and the susceptible cultivar 'Williams' after infection with Foc4, and there were differences in resistance-related proteins, biosynthesis of secondary metabolites, peroxidase, and pathogenesis-related proteins. The stress response of bananas to pathogens was affected by multiple factors. Protein co-expression analysis showed that there was a high correlation between the MEcyan module and resistance, and 'Guijiao 9' had a different resistance mechanism compared with 'Williams'. SIGNIFICANCE: 'Guijiao 9' is a banana variety with good resistance to Foc4, which is identified by screening the resistance of natural variant lines in the farmland where banana plants are seriously infected by Foc4. It is of great significance to excavate the resistance genes and key proteins of 'Guijiao 9' for banana variety improvement and disease resistance breeding. The aim of this paper is to identify the proteins and related functional modules controlling the pathogenicity differences of Foc4 by comparative proteomic analysis of 'Guijiao 9', so as to understand the resistance mechanism of banana to Fusarium wilt, and offer basis for the final identification, isolation and utilization of Foc4 resistance-related genes in banana variety improvement. The research results will also provide a basis for further understanding the host-pathogen interaction and revealing the resistance mechanism of bananas.

cubense, a banana wilt pathogen

Fusarium wilt of banana is a destructive widespread disease caused by Fusarium oxysporum f. sp. cubense (Foc) that ravaged banana plantations globally, incurring huge economic losses. Current knowledge demonstrates the involvement of several transcription factors, effector proteins, and small RNAs in the Foc-banana interaction. However, the precise mode of communication at the interface remains elusive. Cutting-edge research has emphasized the significance of extracellular vesicles (EVs) in trafficking the virulent factors modulating the host physiology and defence system. EVs are ubiquitous inter- and intra-cellular communicators across kingdoms. This study focuses on the isolation and characterization of Foc EVs from methods that make use of sodium acetate, polyethylene glycol, ethyl acetate, and high-speed centrifugation. Isolated EVs were microscopically visualized using Nile red staining. Further, the EVs were characterized using transmission electron microscopy, which revealed the presence of spherical, double-membrane, vesicular structures ranging in size from 50 to 200 nm (diameter). The size was also determined using the principle based on Dynamic Light Scattering. The Foc EVs contained proteins that were separated using SDS-PAGE and ranged between 10 and 315 kDa. Mass spectrometry analysis revealed the presence of EV-specific marker proteins, toxic peptides, and effectors. The Foc EVs were found to be cytotoxic, whose toxicity increased with EVs isolated from the co-culture preparation. Taken together, a better understanding of Foc EVs and their cargo will aid in deciphering the molecular crosstalk between banana and Foc.

Spatio-temporal change of selected soil physico-chemical properties in grevillea-banana agroforestry systems

In Africa, banana is mainly produced by smallscale farmers under complex production systems for both home consumption and income generation. Low soil fertility continually constraints its production and farmers are embarking on emerging technologies such as improved fallow, cover crops, integrated soil fertility management, agroforestry with fast growing tree species to address this challenge. This study aims at assessing the sustainability of grevillea-banana agroforestry systems by investigating the variability in their soil physico-chemical properties. Soil samples were collected in banana sole stands, Grevillea robusta sole stands and grevillea-banana intercrops in three agro-ecological zones during the dry and rainy seasons. Soil physico-chemical properties significantly differed among agroecological zones, cropping systems and between seasons. Soil moisture, total organic carbon (TOC), P, N, Mg decreased from the highland to the lowland zone, through the midland zone whereas soil pH, K and Ca showed the opposite trend. Soil bulk density, moisture, TOC, NH₄⁺-N, K and Mg were significantly higher in the dry season compared to the rainy season but total N was higher in the rainy season. Intercropping banana with grevillea trees significantly decreased soil bulk density, TOC, K, Mg, Ca and P. Soils under banana sole stands accumulated higher potassium, magnesium, calcium, phosphorus with a higher soil bulk density and pH compared to grevillea-banana intercrops and grevillea sole stands. This suggests that intercropping banana and grevillea trees increases the competition for these nutrients and requires careful attention for the optimization of their interactive benefits.

Histone demethylase MaJMJ15 is involved in the regulation of postharvest banana fruit ripening

Histone methylation plays important roles in plant development. However, the role of histone methylation in fruit ripening remains unclear. Here, a total of 16 Jumonji domain-containing proteins (JMJs) were identified from banana genome. During fruit ripening, expression of MaJMJ15 was significantly upregulated. Exogenous ethylene accelerated the upregulation whereas 1-methylcyclopropene delayed the process, suggesting that MaJMJ15 positively regulates banana fruit ripening. MaJMJ15 is an H3K27me3 site-specific demethylase. Transient overexpression of MaJMJ15 promoted banana fruit ripening. Moreover, the global H3K27me3 was decreased by MaJMJ15. Furthermore, MaJMJ15 directly targeted several key ripening-related genes (RRGs) in banana including NAC transcription factor 1/2 (MaNAC1/2), 1-aminocyclopropane-1-carboxylate synthase 1 (MaACS1), 1-aminocyclopropane-1-carboxylate oxidase 1 (MaACO1) and expansin 2 (MaEXP2), removed H3K27me3 from their chromatin, and activated their expression. Our data suggest that MaJMJ15 is an H3K27me3 demethylase, which is involved in the regulation of banana fruit ripening by activating expression of key RRGs via removal of H3K27me3.

Metapangenomics of wild and cultivated banana microbiome reveals a plethora of host-associated protective functions

BACKGROUND

Microbiomes are critical to plants, promoting growth, elevating stress tolerance, and expanding the plant's metabolic repertoire with novel defense pathways. However, generally microbiomes within plant tissues, which intimately interact with their hosts, remain poorly characterized. These endospheres have become a focus in banana (Musa spp.)-an important plant for study of microbiome-based disease protection. Banana is important to global food security, while also being critically threatened by pandemic diseases. Domestication and clonal propagation are thought to have depleted protective microbiomes, whereas wild relatives may hold promise for new microbiome-based biological controls. The goal was to compare metapangenomes enriched from 7 Musa genotypes, including wild and cultivated varieties grown in sympatry, to assess the host associations with root and leaf endosphere functional profiles.

RESULTS

Density gradients successfully generated culture-free microbial enrichment, dominated by bacteria, with all together 24,325 species or strains distinguished, and 1.7 million metagenomic scaffolds harboring 559,108 predicted gene clusters. About 20% of sequence reads did not match any taxon databases and ~ 62% of gene clusters could not be annotated to function. Most taxa and gene clusters were unshared between Musa genotypes. Root and corm tissues had significantly richer endosphere communities that were significantly different from leaf communities. Agrobacterium and Rhizobium were the most abundant in all samples while Chitinophagia and Actinomycetia were more abundant in roots and Flavobacteria in leaves. At the bacterial strain level, there were > 2000 taxa unique to each of M. acuminata (AAA genotype) and M. balbisiana (B-genotype), with the latter 'wild' relatives having richer taxa and functions. Gene ontology functional enrichment showed core beneficial functions aligned with those of other plants but also many specialized prospective beneficial functions not reported previously. Some gene clusters with plant-protective functions showed signatures of phylosymbiosis, suggesting long-standing associations or heritable microbiomes in Musa.

CONCLUSIONS

Metapangenomics revealed key taxa and protective functions that appeared to be driven by genotype, perhaps contributing to host resistance differences. The recovery of rich novel taxa and gene clusters provides a baseline dataset for future experiments in planta or in vivo bacterization or engineering of wild host endophytes.

A novel SNP panel developed for targeted genotyping-by-sequencing (GBS) reveals genetic diversity and population structure of Musa spp. germplasm collection

The Philippines is situated in the geographic region regarded as the center of diversity of banana and its wild relatives (Musa spp.). It holds the most extensive collection of B-genome germplasm in the world along with A-genome groups and several natural hybrids with A- and B-genome combinations. Management of this germplasm resource has relied immensely on identification using local names and morphological characters, and the extent of genetic diversity of the collection has not been achieved with molecular markers. A high-throughput and reliable genotyping method for banana and its relatives will facilitate germplasm management and support breeding initiatives toward a marker-based approach. Here, we developed a 1 K SNP genotyping panel based on filtering of high-quality genome-wide SNPs from the Musa Germplasm Information System and used it to assess the genetic diversity and population structure of 183 accessions from a Musa spp. germplasm collection containing Philippine and foreign accessions. Targeted GBS using SeqSNP™ technology generated 70,376,284 next-generation sequencing (NGS) reads with an average effective target SNP coverage of 340 × . Bioinformatics pipeline revealed 971 polymorphic SNPs containing 76.9% homozygous calls, 23.1% heterozygous calls and 4% with missing data. A final set of 952 SNPs detected 2,092 alleles. Pairwise genetic distance varied from 0.0021 to 0.3325 with most pairs of accessions distinguished with 250 to 300 loci. The SNP panel was able to detect seven (k = 7) genetically differentiated groups and its composition through Principal Component Analysis (PCA) with k-means clustering algorithm and Discriminant Analysis of Principal Components (DAPC). Accession-specific SNPs were also identified. The 1 K SNP panel effectively distinguishes between genomic groups and provides relatively good resolution of genome-wide nucleotide diversity of Musa spp. This panel is recommended for low-density genotyping for application in marker-assisted breeding and germplasm management, and could be further enhanced to increase marker density for other applications like genetic association and genomic selection in bananas.

First Report of Epicoccum latusicollum Causing Leaf Spot Disease on Banana in China

Banana (Musa acuminata) is one of the most important fruit crops in the world. In June 2020, a leaf spot disease was detected on M. acuminata (AAA Cavendish cv. Williams B6) in a commercial plantation (∼1.2 ha), Nanning, Guangxi province, China. The disease occurred on ~30% of plants. The first symptoms were round or irregular dark brown spots on the leaf surface, which progressively expanded into large, suborbicular or irregular-shaped dark brown necrotic areas. Finally, the lesions coalesced and resulted in leaf abscission. Fragments of tissues (~5 mm) were cut from six symptomatic leaves, surface disinfected (2 min in 1% NaOCl, and rinsed three times in sterile water), and incubated on potato dextrose agar (PDA) at 28°C for 3 days. The hyphal tips from emerging colonies were transferred onto fresh PDA plates to obtain pure cultures. From the 23 isolates, 19 exhibited similar morphology. The colonies on PDA and Oatmeal agar (OA) were villose, dense, white to grey. NaOH spot test resulted in a dark green discolouration on malt extract agar (MEA) cultures. After 15 days of incubation, pycnidia were observed, which were dark, spherical or flat spherical, 67.1 to 173.1 µm (n = 64) in diameter. Conidia were oval mostly, aseptate, hyaline, guttulate, 4.1 to 6.3 × 1.6 to 2.8 µm (n = 72). Morphological features were similar to Epicoccum latusicollum (Chen et al. 2017, Qi et al. 2021). The internal transcribed spacer (ITS), the partial 28S large subunit rDNA (LSU), beta-tubulin (TUB), and RNA polymerase II second largest subunit (RPB2) genes of the three representative isolates (GX128.6.3, GX132.14.1, GX140.4.3) were amplified and sequenced using the primers ITS1/ITS4 (White et al. 1990), LR0R/LR5 (Vilgalys and Hester 1990, Rehner and Samuels 1994), TUB2-Ep-F/TUB2-Ep-R (GTTCACCTTCAAACCGGTCAATG/AAGTTGTCGGGACGGAAGAGCTG), and RPB2-Ep-F/RPB2-Ep-R (GGTCTTGTGTGCCCCGCTGAGAC/TCGGGTGACATGACAATCATGGC), respectively. The ITS (OL614830-32), LSU (OL739128-30), TUB (OL739131-33), and RPB2 (OL630965-67) sequences were 99% (478/479, 478/479, and 478/479 bp), 99% (881/882, 867/868, and 877/878 bp), 99 to 100% (332/333, 333/333, and 333/333 bp), and 100% (556/556, 559/559, and 555/555 bp) identical to those of the ex-type E. latusicollum LC5181 (KY742101, KY742255, KY742343, KY742174) (Chen et al. 2017). A phylogenetic analysis confirmed the isolates as E. latusicollum. Therefore, based on morphological and molecular data, the isolates were identified as E. latusicollum. To verify pathogenicity, healthy leaves on 1.5 months old banana plants (cv. Williams B6) were stab-wounded using a needle and inoculated with either mycelial discs (5 mm) or aliquots of 10 μl conidial suspension (106 conidia/ml). Three leaves on each of six plants were inoculated. Each leaf had four inoculation sites, two were inoculated with a representative strain, and two treated with pollution-free PDA discs or sterile water served as controls. All plants were incubated in a greenhouse at 28°C (12-h photoperiod, 80% humidity). After seven days, leaf spot appeared on the inoculated leaves. No symptoms were detected on controls. The experiments were repeated three times showed similar results. To fulfill Koch's postulates, the Epicoccum isolates were consistently re-isolated from symptomatic tissue and confirmed by morphology and sequencing. To our knowledge, this is the first report of E. latusicollum causing leaf spot on banana in China. This study may provide the basis for control of the disease.

Musa spp. cultivars as a neutralising source against some toxic activities of Bothrops and Crotalus genus snake venoms

Accidents involving snakes from Bothrops spp. and Crotalus spp. constitute the most important cause of envenomation in Brazil and Argentina. Musa spp. (banana) have been reported to be used in popular medicine against snakebite by the members of the Canudos Settlement, located in Goiás. In this way, the aim of this work was to evaluate the antivenom effect of the Ouro (AA), Prata (AAB), Prata-anã (AAB) and Figo (ABB) cultivars against in vitro (phospholipase, coagulation and proteolytic) and in vivo (lethality and toxicity) activities caused by the venoms and toxicity (Artemia salina nauplii and Danio rerio embryos) of Musa spp. as well as the annotation of chemical compounds possibly related to these activities. From the in vitro antiophidic tests with the sap, we observed 100% inhibition of the phospholipase and coagulant activities with the cultivars Prata-anã and Figo against the venoms of B. alternatus and C. d. collineatus, B. diporus and B. pauloensis, respectively, and neutralisation of the lethality against the B. diporus venom. It was observed that the cultivars of Musa spp. did not show toxicity against Artemia salina nauplii and Danio rerio embryos. The sap analysis via HPLC-MS/MS allowed the annotation of the 13 compounds: abscisic acid, shikimic acid, citric acid, quinic acid, afzelechin, Glp-hexose, glucose, sucrose, isorhamnetin-3-O-galactoside-6-raminoside, kaempferol-3-glucoside-3-raminoside, myricetin-3-O-rutinoside, procyanidin B1 and rutin. Therefore, it can be seen that Musa spp. is a potential therapeutic agent that can act to neutralise the effects caused by snakebites.

Identification and expression of the CCO family during development, ripening and stress response in banana

Plant hormone abscisic acid (ABA) plays an important role in plant growth, development and response to biotic / abiotic stressors. Thus, it is necessary to investigate the crucial genes associated with ABA synthesis. Currently, the carotenoid cleavage oxygenases (CCOs) family that function as the key step for ABA synthesis are not well understood in banana. In this study, 13 MaCCO genes and 12 MbCCO genes, divided into NCED subgroup and CCD subgroup, were identified from the banana genome, and their evolutionary relationship, protein motifs, and gene structures were also determined. Transcriptomic analysis suggested the involvement of CCO genes in banana development, ripening, and response to abiotic and biotic stressors, and homologous gene pairs showed homoeologue expression bias in the A or B subgenome. Our results identified MaNCED3A, MaCCD1, and MbNCED3B as the genes with the highest expression during fruit development and ripening. MaNCED5 / MbNCED5 and MaNCED9A might respond to abiotic stress, and MaNCED3A, 3B, 6 A, 9 A, and MbNCED9A showed transcriptional changes that could be a response to Foc4 infection. These findings may contribute to the characterization of key enzymes involved in ABA biosynthesis, as well as to identify potential targets for the genetic improvement of banana.

Functional characterization of 5'-regulatory region of flavonoid 3',5'-hydroxylase-1 gene of banana plants

Generation of crops with broad-spectrum tolerance to biotic and abiotic stress conditions depends upon availability of genetic elements suitable for varied situations and diverse genotypes. Here, we characterize the 5'-upstream regulatory region of flavonoid 3'5'-hydroxylase-1 (F3'5'H-1) gene from banana and analyzed its tissue-specific and stress-mediated activation in genetic background of tobacco plants. MusaF3'5'H-1 is a stress-responsive gene as its expression is induced in banana after application of salicylic acid and methyl jasmonate while its transcript levels were drastically reduced in response to drought, high salinity and abscisic acid. P_MusaF3'5'H-1 harbours cis-elements associated with stress conditions and those responsible for tissue-specific expression. Transgenic lines harbouring P_MusaF3'5'H-1-GUS displays strong GUS expression in guard cells of stomata indicating guard cell preferred activity of P_MusaF3'5'H-1 while its activity was undetectable in roots. Drought and high salinity induce strong expression of GUS in transgenic tobacco lines and exposure to abscisic acid, salicylic acid and methyl jasmonate revealed distinct profiles of GUS expression in transgenic lines confirming involvement of F3'5'H-1 in plant stress responses. Fluorescent β-galactosidase assay revealed induction profiles of P_MusaF3'5'H-1 at different time points in transgenic lines exposed to salicylic acid and abscisic acid while strong suppression in GUS expression was observed after application of methyl jasmonate. The guard cell preferred activity of P_MusaF3'5'H-1 and stress-mediated expression profiles of MusaF3'5'H-1 indicated the suitability of P_MusaF3'5'H-1 for generating stress-enduring crops and analyzing guard cell functions.

Effect of different drying techniques on the nutrient and physiochemical properties of Musa paradisiaca (ripe Nendran banana) powder

Musa paradisiaca (ripe Nendran) is the staple food of south India, especially Kerala. The present study analyzed the effect of different drying techniques, namely, freeze, spray and tray drying on the retention of nutrients especially micronutrients. Mineral content was determined by using Atomic absorption spectroscopy and Vitamin content was determined through High-performance liquid chromatography. This study aimed to analyze the availability of minerals and water-soluble vitamins in dried ripe banana powder. The micronutrient content of freeze-dried banana powder was observed to be with 486.92 ± 0.12 mg/100 g of potassium, 0.60 ± 0.005 mg/100 g of calcium, 3.10 ± 0.10 mg/100 g of sodium, 3.82 ± 0.02 mg/100 g of iron, 6.28 ± 0.04 mg/100 g of vitamin C and 0.606 ± 0.005 mg/100 g of vitamin B6. Along with micronutrient analysis, proximate, and various important physiochemical properties were also analyzed. The results showed that freeze-drying was the best technique to preserve nutrients present in ripe banana. Structure analysis of dried banana was done using scanning electron microscopy indicated that remarkable changes has occurred in both tray and spray dried banana when comparing to freeze dried banana. Data was analyzed by one-way ANOVA, found significantly differ at p < 0.05 with respect to drying methods.

Graphical abstract

Characterization of Hoplolaimus seinhorsti and Hoplolaimus pararobustus (Tylenchina: Hoplolaimidae) from banana, with phylogeny and species delineation in the genus Hoplolaimus

The morphological and molecular characterisations of two lance nematode species isolated from the rhizosphere of banana, Hoplolaimus seinhorsti and H. pararobustus, are provided based on an integrative study that includes light and scanning electron microscopy, phylogenetic analysis and two tree-based molecular species delimitation methods (GMYC and bPTP). Nineteen new sequences were obtained, including 5 partial 18S rRNA, 6 D2-D3 of 28S rRNA, 1 ITS rRNA and 7 COI mtDNA (the first COI sequences of H. seinhorsti and H. pararobustus), and an updated morphological character comparison of 37 Hoplolaimus species is presented. The tree-based molecular species-delimitation approaches employed gave markedly differing results, and also showed remarkable discrepancies among the investigated genes, although the bPTP output was found to agree well with established morphological species delimitations. Both species-delimitation approaches did, however, provide the same output for the COI mtDNA sequences, and the COI mtDNA gene sequence was also found to correspond better to established morphological species. It is therefore recommended by this paper as representing the most suitable barcode marker for Hoplolaimus species identification. This integrative study also resulted in the corrective reassignment of 17 gene sequences that were previously unidentified or incorrectly classified, as well as concluding that H. pararobustus consists of two cryptic species.

WRKY transcription factor MaWRKY49 positively regulates pectate lyase genes during fruit ripening of Musa acuminata

Fruit ripening is the last phase of fruit growth and development. The initiation and progression of fruit ripening are highly modulated by a plethora of key genes, such as transcription factor (TF) genes. The WRKY gene family is a large group of TFs that play important roles in various cellular processes; nevertheless, the role of WRKY TF on fruit ripening remains enigmatic. Here, we report that a banana WRKY TF, MaWRKY49 functions in ethylene-induced fruit ripening by modulating the expression of fruit softening-related genes. We found that the expression of MaWRKY49 is highly induced by ethephon and inhibited by 1-methylcyclopropene, which is synchronous with the ripening process. Moreover, based on transcriptome data on fruit ripening, two pectate lyase (PL) genes that are involved in fruit softening were determined, and their expression pattern is also consistent with the fruit ripening process. Yeast one-hybrid and dual-luciferase assay confirmed that MaWRKY49 activated the transcription of two PL genes. In addition, transient overexpression of MaWRKY49 in banana fruits can apparently accelerate fruit ripening processs. Taken together, our findings indicate that MaWRKY49 acts as a potential modulator of fruit ripening by direct regulation of PL expression. This work contributes to developing the technology for improving the shelf-life of banana fruit.

MusaNAC29-like transcription factor improves stress tolerance through modulation of phytohormone content and expression of stress responsive genes

Understanding the molecular mechanisms governed by genes and cross-talks among stress signaling pathways is vital for generating a broad view on stress responses in plants. Here, we analysed the effects of MusaNAC29-like transcription factor of banana on stress responses and report the quantitative modulation of phytohormone and flavonoid content and analysed the growth parameters and yield trait in transgenic banana plants. Expression of MusaNAC29-like transcription factor was strongly altered in responses to stress conditions and application of signaling molecules. Under control conditions, P_{MusaNAC29-like}-GUS is activated in cells bordering xylem vessel elements and is strongly triggered in other cells types after influence of salicylic acid and abscisic acid. Transgenic banana plants of cultivar Rasthali and Grand Naine overexpressing MusaNAC29-like transcription factor displayed superior tolerance towards drought and salinity stress. LC-MS analysis indicated elevated levels of jasmonic acid and salicylic acid while content of zeatin was significantly reduced in leaves of transgenic banana lines. Transgenic banana lines displayed increased levels of gallic acid, coumaric acid, naringenin, chlorogenic acid while levels of vanillic acid and piperine were significantly reduced. Expression of stress related genes coding for antioxidants, thiol peptidase proteins, cold-regulated proteins, late embryogenesis abundant proteins, ethylene-responsive transcription factors, bHLH proteins, jasmonate-zim-domain proteins and WRKY transcription factors were significantly induced in transgenic banana lines. Though MusaNAC29-like transcription factor improved stress tolerance, its overexpression resulted in retarded growth of transgenic lines resulting in reduced yield of banana fruits.

Post-harvested Musa acuminata Banana Tiers Dataset

Post-harvested Musa acuminata banana species from a local banana plantation in the Philippines are the subject of this article. All banana tier samples used were pre-classified into four classes by a local expert. These four classifications are extra class, class I, class II, and reject. There are six images captured per banana tier sample from the six different views. Each captured image underwent a three-step image transformation to finely extract the RGB numerical values while the size measurement feature was gathered through manual measurement. The dataset presented in this article provides a brief differentiation of the different classes of banana tiers for commercial use through image processing. This dataset can be useful in establishing an advanced intelligent system in a non-invasive approach through machine and deep learning techniques.

Genome-wide identification, characterization, and evolutionary analysis of NBS genes and their association with disease resistance in Musa spp

Banana is an important food crop that is susceptible to a wide range of pests and diseases that can reduce yield and quality. The primary objective of banana breeding programs is to increase disease resistance, which requires the identification of resistance (R) genes. Despite the fact that resistant sources have been identified in bananas, the genes, particularly the nucleotide-binding site (NBS) family, which play an important role in protecting plants against pathogens, have received little attention. As a result, this study included a thorough examination of the NBS disease resistance gene family's classification, phylogenetic analysis, genome organization, evolution, cis-elements, differential expression, regulation by microRNAs, and protein-protein interaction. A total of 116 and 43 putative NBS genes from M. acuminata and M. balbisiana, respectively, were identified and characterized, and were classified into seven sub-families. Structural analysis of NBS genes revealed the presence of signal peptides, their sub-cellular localization, molecular weight and pI. Eight commonly conserved motifs were found, and NBS genes were unevenly distributed across multiple chromosomes, with the majority of NBS genes being located in chr3 and chr1 of the A and B genomes, respectively. Tandem duplication occurrences have helped bananas' NBS genes spread throughout evolution. Transcriptome analysis of NBS genes revealed significant differences in expression between resistant and susceptible cultivars of fusarium wilt, eumusae leaf spot, root lesion nematode, and drought, implying that they can be used as candidate resistant genes. Ninety miRNAs were discovered to have targets in 104 NBS genes from the A genome, providing important insights into NBS gene expression regulation. Overall, this study offers a valuable genomic resource and understanding of the function and evolution of NBS genes in relation to rapidly evolving pathogens, as well as providing breeders with selection targets for fast-tracking breeding of banana varieties with more durable resistance to pathogens.

Cellulose from the banana stem: optimization of extraction by response surface methodology (RSM) and charaterization

Cellulose was extracted from the banana stem by chemical method and the factors affecting the extraction process such as concentration of NaOH and H₂O₂, as well as the assisted microwave time were investigated. Design-Expert software with Response Surface Methodology was used in the modeling and optimization of the cellulose extraction process. The results of XRD, FT-IR, SEM were also used to determine the physicochemical properties of cellulose obtained from the banana stem. The results of the modeling and optimization process of cellulose extraction showed the efficiency of the process and the high applicability of cellulose from the banana stem to create valuable industrial products.

Genome-wide identification and expression profiling of WUSCHEL-related homeobox (WOX) genes confer their roles in somatic embryogenesis, growth and abiotic stresses in banana

Plant-specific WUSCHEL-related homeobox (WOX) transcription factors are known to be involved in plant developmental processes, especially in embryogenesis. In this study, a total of thirteen WOX members were identified in the banana (Musa acuminata) genome (MaWOX) and characterized for in-silico analysis. Phylogenetic analysis revealed that these genes were divided into three clades (ancient, intermediate and modern) which reflected the evolutionary history of WOX families. Furthermore, modern clade members have shown higher variations in gene structural features and carried unique conserved motifs (motif 3 and motif 4) when compared to the members of other clades. The differential expression of all 13 MaWOX was observed in early (embryogenic cell suspension (ECS), multiplying ECS, germinating embryos, young leaflet and node of germinated plantlets) and late (unripe fruit peel and pulp, ripe fruit peel and pulp) developmental stages of banana cultivar Grand Naine. The maximum expression of MaWOX6 (18 fold) and MaWOX13 (120 fold) was found during somatic embryogenesis and in unripe fruit pulp, respectively. Moreover, numerous cis-elements responsive to drought, cold, ethylene, methyl jasmonate (MeJA), abscisic acid (ABA) and gibberellic acid (GA) were observed in all MaWOX promoter regions. The subsequent expression analysis under various abiotic stresses (cold, drought and salt) revealed maximum expression of the MaWOX3 (830 fold), MaWOX8a (30 fold) and MaWOX11b (105 fold) in salt stress. It gives evidence about their possible role in salt stress tolerance in banana. Hence, the present study provides precise information on the MaWOX gene family and their expression in various tissues and stressful environmental conditions that may help to develop climate-resilient banana plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03387-w.

Effects of nitrogen reduction combined with organic fertilizer on growth and nitrogen fate in banana at seedling stage

Nitrogen reduction combined with organic fertilizer is of considerable significance for the sustainable development of agriculture. A pot experiment using nitrogen reduction combined with organic fertilizer was conducted to explore the effects of different treatments on matter accumulation, physiological resistance, and fertilizer nitrogen fate in banana seedlings. Compared with conventional fertilization, a 20% reduction of nitrogen did not affect the dry weight, chlorophyll content, physiological resistance, and fertilizer utilization rate of banana seedlings, but significantly reduced the nitrogen leaching loss and increased the nitrogen soil residue. Compared with conventional fertilization, organic nitrogen substituting 20% or 30% of the nitrogen reduced by 20% significantly promoted dry matter accumulation and physiological resistance. Organic nitrogen substituting 30% of the 20% reduction of nitrogen increased the dry matter of the whole plant by 24.94%, the nitrogen uptake in the root by 30.87%, the chlorophyll content by 6.05%, the soluble sugar content by 16.88%, Peroxidase (POD) activity by 26.35%, Catalase (CAT) activity by 27.48%, and Super Oxide Dismutase (SOD) activity by 22.97%. Compared with conventional fertilization, all organic substitution treatments significantly reduced fertilizer nitrogen leaching loss, apparent loss, and increased nitrogen soil residue. Compared with the 20% reduction of nitrogen, organic nitrogen substituting 30% of the 20% reduction of nitrogen significantly increased nitrogen utilization by 16.34% and soil residue rate by 13.26%, and reduced nitrogen leaching loss by 35.46%. The results of the present study revealed that a 20% reduction of nitrogen fertilizer with a 30% organic substitution application promoted matter accumulation, enhanced the physiological resistance of banana seedlings, increased the utilization and residue of nitrogen fertilizer, and reduced nitrogen pollution.

Characterization of probiotic properties and development of banana powder enriched with freeze-dried Lacticaseibacillus paracasei probiotics

Lacticaseibacillus paracasei is one of the probiotic bacteria widely identified from fermented foods. The application of L. paracasei is commonly used in dairy and non-dairy products. To investigate the probiotic properties of L. paracasei cells including their acid, pepsin, pancreatin, and bile salt tolerances; adhesion ability; antipathogen activity; and antibiotic susceptibility, L. paracasei cells were incorporated into skim milk and lyophilized by freeze drying. Freeze-dried probiotic cells were add to green banana powder and low moisture additive food matrices and a storage analysis of the product was performed. The result showed that L. paracasei cells possessed potentially beneficial probiotic properties to survive stress in the gastrointestinal tract (GIT) and functional abilities as an anti-enteropathogenic agent; they were also safe to use and displayed antibiotic properties. Furthermore, the probiotic freeze-drying technique preserved high probiotic cell survivability (10¹¹ CFU/g). In term of prolonged storage (60 days), the powder product was stable and maintained probiotic survival (10⁷ CFU/g) while excluding non-probiotic growth. In conclusion, L. paracasei displayed probiotic properties in the GIT and was judged to be a highly acceptable product as a probiotics–banana rehydrated beverage.

Halotolerant rhizobacteria isolated from a mangrove forest alleviate saline stress in Musa acuminata cv. Berangan

Saline soils resulting from anthropogenic activity and climate change present a challenge to future food security. Towards addressing this, we isolated and characterized halotolerant bacteria from a Malaysian mangrove forest, and explored their effect on morpho-physiological and biochemical parameters of banana plantlets under salt stress. A total of 88 rhizobacterial and 16 endophytic bacterial isolates collected from the roots and rhizosphere of Rhizophora apiculata, Avicennia alba and Sonneratia alba, were found to tolerate up to 400 mM of sea salt. Based on best performance in multiple plant growth traits, three rhizobacterial strains RB1, RB3 and RB4 and three endophytic bacterial strains EB1, EB2 and EB3 were used for further analysis. The rhizobacterial strains were identified as Bacillus sp. and endophytic bacteria as Pseudomonas sp. based on 16 S rRNA gene sequence. SEM observation confirmed colonization of each strain on banana plantlet roots. When colonized plantlets were subjected to 90 mM salt and compared to uninoculated (control) and mock inoculated plants, improved plant growth was observed with each of the strains, especially with bacterial strains EB3 and RB3. Biochemical analysis of plantlets revealed that root colonization with EB3 and RB3 enhanced levels of plant chlorophyll (> 5-fold), carotenoid (> 2.85-fold) and proline (2.6-fold and 2.3-fold), while plantlets also showed reduced MDA content (0.45-fold and 0.51-fold), significantly reduced generation of ROS (0.23-fold and 0.47-fold) and lower levels of electrolyte leakage (0.77 and 0.51-fold). Antioxidant enzymes also showed enhanced activity with EB3 and RB3. Our results indicate that these halotolerant Bacillus and Pseudomonas strains from the mangrove have multifunctional plant growth promoting activity and can reduce salt stress in bananas. This data provides a reference for exploring halotolerant microbes from hypersaline environments to overcome salt stress in plants.

The Musa troglodytarum L. genome provides insights into the mechanism of non-climacteric behaviour and enrichment of carotenoids

BACKGROUND

Karat (Musa troglodytarum L.) is an autotriploid Fe'i banana of the Australimusa section. Karat was domesticated independently in the Pacific region, and karat fruit are characterized by a pink sap, a deep yellow-orange flesh colour, and an abundance of β-carotene. Karat fruit showed non-climacteric behaviour, with an approximately 215-day bunch filling time. These features make karat a valuable genetic resource for studying the mechanisms underlying fruit development and ripening and carotenoid biosynthesis.

RESULTS

Here, we report the genome of M. troglodytarum, which has a total length of 603 Mb and contains 37,577 predicted protein-coding genes. After divergence from the most recent common ancestors, M. troglodytarum (T genome) has experienced fusion of ancestral chromosomes 8 and 9 and multiple translocations and inversions, unlike the high synteny with few rearrangements found among M. schizocarpa (S genome), M. acuminata (A genome) and M. balbisiana (B genome). Genome microsynteny analysis showed that the triplication of MtSSUIIs due to chromosome rearrangement may lead to the accumulation of carotenoids and ABA in the fruit. The expression of duplicated MtCCD4s is repressed during ripening, leading to the accumulation of α-carotene, β-carotene and phytoene. Due to a long terminal repeat (LTR)-like fragment insertion upstream of MtERF11, karat cannot produce large amounts of ethylene but can produce ABA during ripening. These lead to non-climacteric behaviour and prolonged shelf-life, which contributes to an enrichment of carotenoids and riboflavin.

CONCLUSIONS

The high-quality genome of M. troglodytarum revealed the genomic basis of non-climacteric behaviour and enrichment of carotenoids, riboflavin, flavonoids and free galactose and provides valuable resources for further research on banana domestication and breeding and the improvement of nutritional and bioactive qualities.

From fruit growth to ripening in plantain: a careful balance between carbohydrate synthesis and breakdown

In this study, we aimed to investigate for the first time different fruit development stages in plantain banana in order gain insights into the order of appearance and dominance of specific enzymes and fluxes. We examined fruit development in two plantain banana cultivars during the period between 2-12 weeks after bunch emergence using high-throughput proteomics, quantification of major metabolites, and analyses of metabolic fluxes. Starch synthesis and breakdown are processes that take place simultaneously. During the first 10 weeks fruits accumulated up to 48% of their dry weight as starch, and glucose 6-phosphate and fructose were important precursors. We found a unique amyloplast transporter and hypothesize that it facilitates the import of fructose. We identified an invertase originating from the Musa balbisiana genome that would enable carbon flow back to growth and starch synthesis and maintain a high starch content even during ripening. Enzymes associated with the initiation of ripening were involved in ethylene and auxin metabolism, starch breakdown, pulp softening, and ascorbate biosynthesis. The initiation of ripening was cultivar specific, with faster initiation being particularly linked to the 1-aminocyclopropane-1-carboxylate oxidase and 4-alpha glucanotransferase disproportionating enzymes. Information of this kind is fundamental to determining the optimal time for picking the fruit in order to reduce post-harvest losses, and has potential applications for breeding to improve fruit quality.

Genome wide identification of MADS box gene family in Musa balbisiana and their divergence during evolution

MADS box gene family is transcription factor gene family that is involved in growth and development of eukaryotes. In plants the MADS box gene family is mainly associated with floral meristem identity and flower development, apart from being involved in nearly all the phases of plant growth. The MADS box gene family has also been shown to be involved during fruit development and ripening. In this study the MADS box gene family from Musa balbisiana was identified and the divergence of this gene family between Musa balbisiana and Musa acuminata studied. A total of 97 MADS box genes were identified from the genome of Musa balbisiana. Phylogenetic analysis showed that the MbMADS box genes were categorised into type I (α and γ; the β group was not distinguishable) and type II groups (MIKC^c and MIKC* and MIKC^c was further divided into 13 subfamilies). The typeII group has the largest number of genes and also showed the most expansion which could be correlated with the whole genome duplications. There were significant differences in the MADS box genes from Musa acuminata and Musa balbisiana during evolution that can be correlated with different floral phenotype and fruit ripening pattern. The divergence of the MADS RIN genes in Musa balbisiana as compared to Musa acuminata might play an important role in the slow ripening of Musa balbisiana fruits.