Transcriptomic Analysis of Avocado Hass (Persea americana Mill) in the Interaction System Fruit-Chitosan-Colletotrichum

Application of chitosan nanopriming on plant growth and secondary metabolites of Pancratium maritimum L

BACKGROUND

Nanotechnology has demonstrated its vital significance in all aspects of daily life. Our research was conducted to estimate the potential of primed seed with chitosan nanoparticles in seed growth and yield by inducing plant secondary metabolism of Pancratium maritimum L. one of the important medicinal plants. Petri dish and pot experiments were carried out. Seeds of Pancratium maritimum L. were soaked in Nano solution (0.1, 0.5, 1 mg/ ml) for 4, 8, 12 h. Germination parameters (germination percentage, germination velocity, speed of germination, germination energy, germination index, mean germination time, seedling shoot and root length, shoot root ratio, seedling vigor index, plant biomass and water content), alkaloids and antioxidant activity of Pancratium maritimum L. were recorded and compared between coated and uncoated seeds.

RESULTS

Our results exhibited that chitosan nanopriming had a positive effect on some growth parameters, while it fluctuated on others. However, the data showed that most germination parameters were significantly affected in coated seeds compared to uncoated seeds. GC-MS analysis of Pancratium maritimum L. with different nanopriming treatments showed that the quantity of alkaloids decreased, but the amount of pancratistatin, lycorine and antioxidant content increased compared with the control.

CONCLUSIONS

Applying chitosan nanoparticles in priming seeds might be a simple and effective way to improve the quantity of secondary metabolites of Pancratium maritimum L. valuable medicinal plant.

Effect of Elicitor Treatments on Quality Attributes in Blueberry: Implications of Cultivar and Environmental Conditions

Elicitors of plant defence responses can trigger defence mechanisms that are able to protect plant tissues from biotic or abiotic stresses. Since one defence response involves the activation of secondary metabolites' biosynthesis, the purpose of this study was to evaluate the effect of chitosan and melatonin pre-harvest treatments on the quality and the nutritional parameters of the fruits of blueberry (Vaccinium corymbosum L.). Across the two years of experiment, three different cultivars (cv.s. 'Cosmopolitan', 'Hortblue Poppins' and 'Legacy') were treated with 1% chitosan or 100 µM melatonin every two weeks during the ripening season and ripe fruits were progressively harvested and analysed. The treatment with both elicitors had only slight effects on dry matter, soluble solids content, titratable acidity and pH, with a cultivar-dependent response. On the other hand, elicitors significantly affected the levels of phenylpropanoid and antioxidant compounds in all cvs. in both years, with a higher accumulation of total anthocyanins and phenolics and the enhancement of the antioxidant capacity, with positive effects on the nutraceutical quality of fruits. The anthocyanin profile in terms of both absolute concentrations and the relative proportion of single anthocyanins was affected by both harvest year and cv., highlighting the role of the genetic background in the plant response to environmental conditions (with particular reference to summer heat stress) and to elicitor treatments.

Global Transcriptome Analysis of the Peach (Prunus persica) in the Interaction System of Fruit-Chitosan-Monilinia fructicola

The peach (Prunus persica L.) is one of the most important stone-fruit crops worldwide. Nevertheless, successful peach fruit production is seriously reduced by losses due to Monilinia fructicola the causal agent of brown rot. Chitosan has a broad spectrum of antimicrobial properties and may also act as an elicitor that activate defense responses in plants. As little is known about the elicitation potential of chitosan in peach fruits and its impact at their transcriptional-level profiles, the aim of this study was to uncover using RNA-seq the induced responses regulated by the action of chitosan in fruit-chitosan-M. fructicola interaction. Samples were obtained from fruits treated with chitosan or inoculated with M. fructicola, as well from fruits pre-treated with chitosan and thereafter inoculated with the fungus. Chitosan was found to delay the postharvest decay of fruits, and expression profiles showed that its defense-priming effects were mainly evident after the pathogen challenge, driven particularly by modulations of differentially expressed genes (DEGs) related to cell-wall modifications, pathogen perception, and signal transduction, preventing the spread of fungus. In contrast, as the compatible interaction of fruits with M. fructicola was challenged, a shift towards defense responses was triggered with a delay, which was insufficient to limit fungal expansion, whereas DEGs involved in particular processes have facilitated early pathogen colonization. Physiological indicators of peach fruits were also measured. Additionally, expression profiles of particular M. fructicola genes highlight the direct antimicrobial activity of chitosan against the fungus. Overall, the results clarify the possible mechanisms of chitosan-mediated tolerance to M. fructicola and set new foundations for the potential employment of chitosan in the control of brown rot in peaches.

Chitosan, chitosan derivatives, and chitosan-based nanocomposites: eco-friendly materials for advanced applications (a review)

For many years, chitosan has been widely regarded as a promising eco-friendly polymer thanks to its renewability, biocompatibility, biodegradability, non-toxicity, and ease of modification, giving it enormous potential for future development. As a cationic polysaccharide, chitosan exhibits specific physicochemical, biological, and mechanical properties that depend on factors such as its molecular weight and degree of deacetylation. Recently, there has been renewed interest surrounding chitosan derivatives and chitosan-based nanocomposites. This heightened attention is driven by the pursuit of enhancing efficiency and expanding the spectrum of chitosan applications. Chitosan's adaptability and unique properties make it a game-changer, promising significant contributions to industries ranging from healthcare to environmental remediation. This review presents an up-to-date overview of chitosan production sources and extraction methods, focusing on chitosan's physicochemical properties, including molecular weight, degree of deacetylation and solubility, as well as its antibacterial, antifungal and antioxidant activities. In addition, we highlight the advantages of chitosan derivatives and biopolymer modification methods, with recent advances in the preparation of chitosan-based nanocomposites. Finally, the versatile applications of chitosan, whether in its native state, derived or incorporated into nanocomposites in various fields, such as the food industry, agriculture, the cosmetics industry, the pharmaceutical industry, medicine, and wastewater treatment, were discussed.

Transcriptomic data exploring the effect of agave fructans on the induction of the defense system in avocado fruit

The effect of 20% high degree polymerized agave fructans (HDPAF) on the induction of the defense system in avocado fruits was investigated by transcriptomic analysis at 1, 24 and 72 h after treatment, and the effect of HDPAF on respiration rate and ethylene production was also analyzed. Transcriptomic profiling revealed 5425 differentially expressed genes (DEGs), 55 of which were involved in the pathways related to plant defense response to pathogens. Key genes were associated with phenylpropanoid biosynthesis, mitogen-activated protein signaling, plant hormone signaling, calcium ion signal decoding, and pathogenesis-related proteins. Dysregulated genes involved in ethylene biosynthesis were also identified, and the reduction in ethylene production by HDPAF was corroborated by gas chromatography, where three days of delayed peak production was observed compared to that in water-treated fruits. These results help to understand the mechanism of induction of the avocado defense system by applying HDPAF and support the application of HDPAF as an efficient postharvest treatment to extend the shelf life of the fruit.

Induced Resistance in Fruit and Vegetables: A Host Physiological Response Limiting Postharvest Disease Development

Harvested fruit and vegetables are perishable, subject to desiccation, show increased respiration during ripening, and are colonized by postharvest fungal pathogens. Induced resistance is a strategy to control diseases by eliciting biochemical processes in fruits and vegetables. This is accomplished by modulating the progress of ripening and senescence, which maintains the produce in a state of heightened resistance to decay-causing fungi. Utilization of induced resistance to protect produce has been improved by scientific tools that better characterize physiological changes in plants. Induced resistance slows the decline of innate immunity after harvest and increases the production of defensive responses that directly inhibit plant pathogens. This increase in defense response in fruits and vegetables contributes to higher amounts of phenols and antioxidant compounds, improving both the quality and appearance of the produce. This review summarizes mechanisms and treatments that induce resistance in harvested fruits and vegetables to suppress fungal colonization. Moreover, it highlights the importance of host maturity and stage of ripening as limiting conditions for the improved expression of induced-resistance processes.

Application of depolymerized chitosan in crop production: A review

Currently, chitosan (CHT) is well known for its uses, particularly in veterinary and agricultural fields. However, chitosan's uses suffer greatly due to its extremely solid crystalline structure, it is insoluble at pH levels above or equal to 7. This has sped up the process of derivatizing and depolymerizing it into low molecular weight chitosan (LMWCHT). As a result of its diverse physicochemical as well as biological features which include antibacterial activity, non-toxicity, and biodegradability, LMWCHT has evolved into new biomaterials with extremely complex functions. The most important physicochemical and biological property is antibacterial, which has some degree of industrialization today. CHT and LMWCHT have potential due to the antibacterial and plant resistance-inducing properties when applied in crop production. This study has highlighted the many advantages of chitosan derivatives as well as the most recent studies on low molecular weight chitosan applications in crop development.

Insights into the domestication of avocado and potential genetic contributors to heterodichogamy

The domestication history of the avocado (Persea americana) remains unclear. We created a reference genome from the Gwen varietal, which is closely related to the economically dominant Hass varietal. Our genome assembly had an N50 of 3.37 megabases, a BUSCO score of 91%, and was scaffolded with a genetic map, producing 12 pseudo-chromosomes with 49,450 genes. We used the Gwen genome as a reference to investigate population genomics, based on a sample of 34 resequenced accessions that represented the 3 botanical groups of P. americana. Our analyses were consistent with 3 separate domestication events; we estimated that the Mexican group diverged from the Lowland (formerly known as "West Indian") and Guatemalan groups >1 million years ago. We also identified putative targets of selective sweeps in domestication events; within the Guatemalan group, putative candidate genes were enriched for fruit development and ripening. We also investigated divergence between heterodichogamous flowering types, providing preliminary evidence for potential candidate genes involved in pollination and floral development.

Transcriptomics and Metabolomics Reveal the Possible Mechanism by which 1-MCP Regulates the Postharvest Senescence of Zizania latifolia

To understand the mechanism governing the postharvest senescence of Zizania latifolia, and the regulatory mechanism induced by 1-methylcyclopropene (1-MCP) during storage at 25°C, physiobiochemical and conjoint analyses of the transcriptome and metabolome were performed. The results indicated that 1-MCP treatment engendered changes in the expression of genes and metabolites during the postharvest storage of Z. latifolia. The 1-MCP treatment maintained a good visual appearance, preserved the cell structure, and membrane integrity of Z. latifolia by keeping the expression of membranes-related lipolytic enzymes (and related genes) low and the amount of phosphatidylethanolamine high. Compared to the control group, 1-MCP treatment enhanced the activities of antioxidant enzymes, resulting in a decrease of reactive oxygen species (ROS) and malondialdehyde (MDA) contents, and thus inhibition of oxidative damage and loss of membrane integrity. In addition, 1-MCP treatment retarded the senescence of Z. latifolia by down-regulating the expression of ethylene biosynthesis-related genes and promoting up-regulation of brassinosteroid insensitive 1 (BRI1) kinase inhibitor 1, calmodulin (CaM), glutathione reductase, jasmonate amino acid synthase, and mitogen-activated protein kinase (MAPK)-related genes. Moreover, 1-MCP retarded Z. latifolia senescence by inducing the activity of ATP-biosynthesis related genes and metabolites. Our findings should facilitate future research on the postharvest storage of Z. latifolia, and could help delay senescence and prolong the storage time for commercial applications.

Recent advances and future perspective of essential oils in control Colletotrichum spp.: A sustainable alternative in postharvest treatment of fruits

The world population growth has raised concerns about food security. Agricultural systems are asked to satisfy a growing demand for food with increasingly limited resources, and simultaneously still must reduce the impacts on the environment. This scenario encourages the search for safe and sustainable production strategies. Reducing losses in the production process can be one of the main ways to guarantee food safety. In fruticulture, it is estimated that more than 50% of the production can be lost between harvest and the final consumer due to postharvest diseases caused by phytopathogenic fungi. The fungi of the genus Colletotrichum are opportunistic and are associated with several diseases, being the anthracnose the most relevant in terms of the quality and yield losses in fruit species around worldwide. To control these diseases, the use of synthetic fungicides has been the main instrument utilized, however, because of their phytotoxicity to human health, the environment, and strong selection pressure imposed by continuous applications, the fungicides have caused resistance in the pathogen populations. So reducing the excessive application of these products is indispensable for human health and for sustainable Agriculture. Towards this purpose, research has been carried out to identify the phytopathological potentiality of essential oils (EOs) extracted from plants. Therefore, this review aims to contribute to the formation of knowledge bases, about the discoveries, recent advances, and the use of EOs as a strategy to alternatively control fungal disease caused by Colletotrichum spp. in postharvest fruits. Here, we provide valuable information exploring the application potential of essential oils as commercially useful biorational pesticides for food preservation, contributing to sustainable production and global food security.

Genomic Approaches for Improvement of Tropical Fruits: Fruit Quality, Shelf Life and Nutrient Content

The breeding of tropical fruit trees for improving fruit traits is complicated, due to the long juvenile phase, generation cycle, parthenocarpy, polyploidy, polyembryony, heterozygosity and biotic and abiotic factors, as well as a lack of good genomic resources. Many molecular techniques have recently evolved to assist and hasten conventional breeding efforts. Molecular markers linked to fruit development and fruit quality traits such as fruit shape, size, texture, aroma, peel and pulp colour were identified in tropical fruit crops, facilitating Marker-assisted breeding (MAB). An increase in the availability of genome sequences of tropical fruits further aided in the discovery of SNP variants/Indels, QTLs and genes that can ascertain the genetic determinants of fruit characters. Through multi-omics approaches such as genomics, transcriptomics, metabolomics and proteomics, the identification and quantification of transcripts, including non-coding RNAs, involved in sugar metabolism, fruit development and ripening, shelf life, and the biotic and abiotic stress that impacts fruit quality were made possible. Utilizing genomic assisted breeding methods such as genome wide association (GWAS), genomic selection (GS) and genetic modifications using CRISPR/Cas9 and transgenics has paved the way to studying gene function and developing cultivars with desirable fruit traits by overcoming long breeding cycles. Such comprehensive multi-omics approaches related to fruit characters in tropical fruits and their applications in breeding strategies and crop improvement are reviewed, discussed and presented here.

Non-Chemical Treatments for the Pre- and Post-Harvest Elicitation of Defense Mechanisms in the Fungi-Avocado Pathosystem

The greatest challenge for the avocado (Persea americana Miller) industry is to maintain the quality of the fruit to meet consumer requirements. Anthracnose is considered the most important disease in this industry, and it is caused by different species of the genus Colletotrichum, although other pathogens can be equally important. The defense mechanisms that fruit naturally uses can be triggered in response to the attack of pathogenic microorganisms and also by the application of exogenous elicitors in the form of GRAS compounds. The elicitors are recognized by receptors called PRRs, which are proteins located on the avocado fruit cell surface that have high affinity and specificity for PAMPs, MAMPs, and DAMPs. The activation of defense-signaling pathways depends on ethylene, salicylic, and jasmonic acids, and it occurs hours or days after PTI activation. These defense mechanisms aim to drive the pathogen to death. The application of essential oils, antagonists, volatile compounds, chitosan and silicon has been documented in vitro and on avocado fruit, showing some of them to have elicitor and fungicidal effects that are reflected in the postharvest quality of the fruit and a lower incidence of diseases. The main focus of these studies has been on anthracnose diseases. This review presents the most relevant advances in the use of natural compounds with antifungal and elicitor effects in plant tissues.

Chitosan Can Induce Rosa roxburghii Tratt. against Sphaerotheca sp. and Enhance Its Resistance, Photosynthesis, Yield, and Quality

Powdery mildew caused by Sphaerotheca sp. is the most serious disease of Rosa roxburghii cultivation. In this study, the foliar application of chitosan induced Rosa roxburghii Tratt. against Sphaerotheca sp. and its effects on the disease resistance, growth, yield, and quality of R. roxburghii were investigated. The results show that the foliar application of 1.0%~1.5% chitosan could effectively control Sphaerotheca sp. of R. roxburghii with the inducing control efficacy of 69.30%~72.87%. The foliar application of 1.0%~1.5% chitosan significantly (p < 0.01) increased proline, soluble sugar, flavonoids, superoxide dismutase (SOD), and polyphenoloxidase (POD) activities of the R. roxburghii leaf and decreased its malonaldehyde (MDA), as well as reliably enhanced its photosynthetic rate and chlorophyll. Moreover, the foliar application of 1.0%~1.5% chitosan notably improved single fruit weight, yield, vitamin C, soluble solid, soluble sugar, total acidity, soluble protein, flavonoids, and SOD activity of R. roxburghii fruits. This study highlights that chitosan can be used as an ideal, efficient, safe, and economical inductor for controlling powdery mildew of R. Roxburgh and enhancing its resistance, growth, yield, and quality.

Transcriptome analysis reveals key defense-related genes upon SA induction in Cocos nucifera L

BACKGROUND

Salicylic acid (SA) is an important regulator of genes involved in plant defense and pathogen-triggered systemic acquired resistance (SAR). Coconut is an important crop affected by several pathogens. Reported evidence suggests SA involvement in defense responses, including SAR in coconut.

OBJECTIVE

To identified differentially expressed genes in leaf and root tissues of coconut plantlets, as a result of SA, that might be involved in coconut defense responses.

METHODS

Comparative transcriptomic analysis by RNA-Seq of leaf and root tissues from in vitro coconut plantlets unexposed and exposed to SA 2.5 mM for 48 h. And in silico validation of gene expression by qRT-PCR.

RESULTS

We identified 4615 and 3940 differentially expressed unigenes (DEUs) in leaf and root tissues respectively. Our GO analysis showed functional categories related to the induction of defense responses, such as "systemic acquired resistance" and highly enriched hormone categories, such as abscisic acid. The most abundant KEGG pathway in our results was "Biosynthesis of antibiotics". Our findings support that exogenous application of SA to plantlets induced the activation of PRs, RGAs, ICS2, NLTP2, PER4, TRXM and some WRKYs mediated by NPR1-dependent pathways. Also, we found DEUs, such as BZR1, HSL1, and WHY2 that support that SA could regulate defense-related genes through NPR1-independent pathways.

CONCLUSION

The present study of massive data analysis carried out on coconut plantlets exposed to SA, generates valuable information that increases our understanding of defense molecular mechanisms in coconut and open new venues for research for the improvement of management of coconut diseases.

Chitosan stimulates secondary metabolite production and nutrient uptake in medicinal plant Dracocephalum kotschyi

BACKGROUND

A wide variety of secondary metabolites are synthesized from primary metabolites by plants which have a vast range in pharmaceutical, food additive and industrial applications. In recent years, the use of elicitors has opened a novel approach for the production of secondary metabolite compounds. Dracocephalum kotschyi is a valuable herb due to pharmaceutical compounds like rosmarinic acid, quercetin and apigenin. In the current study, foliar application of chitosan (0, 100, 400 mg L-1 ) as an elicitor was used.

RESULTS

After chitosan treatment, the amounts of hydrogen peroxide (H2 O2 ) increased and the plant was able to increase the activities of enzymatic (guaiacol peroxidase, catalase and phenylalanine ammonium lyase) and non-enzymatic (total phenols and flavonoids) defensive metabolites. Also, foliar spray of chitosan promoted nutrient absorption which led to the accumulation of macroelements in the plant.

CONCLUSIONS

Chitosan was found to be a very effective elicitor for improving rosmarinic acid and quercetin content (up to 13-fold). Also, the content of apigenin (anticancer flavonoid) showed 16-fold enhancement compared to the control. Therefore, the treatment of D. kotschyi leaves with chitosan caused a very large increase in the induction and production of important pharmaceutical compounds such as rosmarinic acid and quercetin. © 2020 Society of Chemical Industry.

Transcriptomics and metabolomics reveal the induction of flavonoid biosynthesis pathway in the interaction of Stylosanthes-Colletotrichum gloeosporioides

Colletotrichum, a hemibiotrophic fungal pathogen with a broad host range, causes a yield-limiting disease called anthracnose. Stylo (Stylosanthes) is a dominant pasture legume in tropics and subtropics, and anthracnose is one of its most destructive disease. Resistance mechanisms against anthracnose in stylo are poorly understood, thus hindering the development of resistant varieties. We performed time-resolved leaf transcriptomics, metabolomics and in vitro inhibition assay to investigate the defense responses against Colletotrichum gloeosporioides in stylo. Transcriptomics demonstrated that flavonoid biosynthetic genes were significantly induced during the infection. Consistently, metabolomics also showed the increased accumulation of flavonoid compounds. In vitro assays showed that phloretin and naringenin inhibited the mycelial growth, and apigenin, daidzein, quercetin and kaempferol suppressed conidial germination of Colletotrichum strains. Together, our results suggest that stylo plants cope with C. gloeosporioides by up-regulation of genes and compounds in flavonoid biosynthesis pathway, providing potential targets for resistance breeding.

Nanostructured chitosan edible coating loaded with α-pinene for the preservation of the postharvest quality of Capsicum annuum L. and Alternaria alternata control

Bell peppers are susceptible to postharvest diseases caused by the fungus Alternaria alternata that limit its commercialization. Nowadays, nanotechnology allows encapsulation of natural components such as terpenes. The objective of this work was to develop chitosan nanoparticles with α-pinene (P-CSNPs) and a nanostructured edible coating (EC-P-CSNPs). The P-CSNPs were characterized by TEM (Transmission Electron Microscopy), FTIR (Fourier-Transform Infrared Spectroscopy), DLS (Dynamic Light Scattering) and ζ potential. The P-CSNPs and the EC-P-CSNPs were applied to the bell peppers inoculated with A. alternata under cold storage for either 0, 7, 14 and 21 days at 12 ± 2 °C followed by a shelf-life period of 5 days at 20 ± 2 °C to assess their post-harvest quality. Nanoparticles size was 3.9 ± 0.5 nm and the ζ potential value was between 13.4 and 14.9 mV. The incorporation of α-pinene was corroborated by FTIR. Significant changes in weight loss were obtained for P-CSNPs and EC-P-CSNPs at percentage of 3 and 6% compared to the control. For firmness, color, total soluble solids, titratable acids, maturity index, total flavonoid content and antioxidant capacity, no differences were found. Total carotenes were higher in bell peppers without A. alternata. The chitosan nanoparticles and edible coating inhibited A. alternata during the cold storage period of bell pepper and preserved the physicochemical quality.

Funcionalización de los recubrimientos a base de quitosano para la conservación postcosecha de frutas y hortalizas

En años recientes, se ha buscado el desarrollo y aplicación de recubrimientos comestibles que sean seguros, biodegradables y con adecuadas propiedades tecnológicas y funcionales que ayuden a extender la vida de anaquel de frutas y hortalizas. El quitosano es uno de los biomateriales con mayor potencial para la elaboración de recubrimientos comestibles. Sin embargo, su principal desventaja es la alta permeabilidad al vapor de agua que exhibe, por lo que, una alternativa para mitigar esta limitante, es su funcionalización mediante la incorporación de compuestos orgánicos (aceites esenciales, extractos naturales, ácido ascórbico, hidrolizados de proteína, polisacáridos) e inorgánicos (SiO2, TiO2, ZnO, Ag y montmorillonita), además, de la adición de microorganismos (levaduras) a la matriz polimérica. El quitosano funcionalizado, aplicado a productos hortofrutícolas, ha mostrado mejores resultados (mayor vida de anaquel y cambios mínimos en parámetros de calidad) que los obtenidos al emplear quitosano sin funcionalizar. El objetivo de esta revisión es describir y discutir los beneficios y limitaciones de la funcionalización del quitosano y su aplicación en productos hortofrutícolas.

Transcriptome Analysis of Solanum Tuberosum Genotype RH89-039-16 in Response to Chitosan

Potato (Solanum tuberosum L.) is the worldwide most important nongrain crop after wheat, rice, and maize. The autotetraploidy of the modern commercial potato makes breeding of new resistant and high-yielding cultivars challenging due to complicated and time-consuming identification and selection processes of desired crop features. On the other hand, plant protection of existing cultivars using conventional synthetic pesticides is increasingly restricted due to safety issues for both consumers and the environment. Chitosan is known to display antimicrobial activity against a broad range of plant pathogens and shows the ability to trigger resistance in plants by elicitation of defense responses. As chitosan is a renewable, biodegradable and nontoxic compound, it is considered as a promising next-generation plant-protecting agent. However, the molecular and cellular modes of action of chitosan treatment are not yet understood. In this study, transcriptional changes in chitosan-treated potato leaves were investigated via RNA sequencing. Leaves treated with a well-defined chitosan polymer at low concentration were harvested 2 and 5 h after treatment and their expression profile was compared against water-treated control plants. We observed 32 differentially expressed genes (fold change ≥ 1; p-value ≤ 0.05) 2 h after treatment and 83 differentially expressed genes 5 h after treatment. Enrichment analysis mainly revealed gene modulation associated with electron transfer chains in chloroplasts and mitochondria, accompanied by the upregulation of only a very limited number of genes directly related to defense. As chitosan positively influences plant growth, yield, and resistance, we conclude that activation of electron transfer might result in the crosstalk of different organelles via redox signals to activate immune responses in preparation for pathogen attack, concomitantly resulting in a generally improved metabolic state, fostering plant growth and development. This conclusion is supported by the rapid and transient production of reactive oxygen species in a typical oxidative burst in the potato leaves upon chitosan treatment. This study furthers our knowledge on the mode of action of chitosan as a plant-protecting agent, as a prerequisite for improving its ability to replace or reduce the use of less environmentally friendly agro-chemicals.

The avocado genome informs deep angiosperm phylogeny, highlights introgressive hybridization, and reveals pathogen-influenced gene space adaptation

The avocado is a nutritious, economically important fruit species that occupies an unresolved position near the earliest evolutionary branchings of flowering plants. Our nuclear genome sequences of Mexican and Hass variety avocados inform ancient evolutionary relationships and genome doublings and the admixed nature of Hass and provide a look at how pathogen interactions have shaped the avocado’s more recent genomic evolutionary history.

The avocado, Persea americana, is a fruit crop of immense importance to Mexican agriculture with an increasing demand worldwide. Avocado lies in the anciently diverged magnoliid clade of angiosperms, which has a controversial phylogenetic position relative to eudicots and monocots. We sequenced the nuclear genomes of the Mexican avocado race, P. americana var. drymifolia, and the most commercially popular hybrid cultivar, Hass, and anchored the latter to chromosomes using a genetic map. Resequencing of Guatemalan and West Indian varieties revealed that ∼39% of the Hass genome represents Guatemalan source regions introgressed into a Mexican race background. Some introgressed blocks are extremely large, consistent with the recent origin of the cultivar. The avocado lineage experienced 2 lineage-specific polyploidy events during its evolutionary history. Although gene-tree/species-tree phylogenomic results are inconclusive, syntenic ortholog distances to other species place avocado as sister to the enormous monocot and eudicot lineages combined. Duplicate genes descending from polyploidy augmented the transcription factor diversity of avocado, while tandem duplicates enhanced the secondary metabolism of the species. Phenylpropanoid biosynthesis, known to be elicited by Colletotrichum (anthracnose) pathogen infection in avocado, is one enriched function among tandems. Furthermore, transcriptome data show that tandem duplicates are significantly up- and down-regulated in response to anthracnose infection, whereas polyploid duplicates are not, supporting the general view that collections of tandem duplicates contribute evolutionarily recent “tuning knobs” in the genome adaptive landscapes of given species.

Chitosan, a Biopolymer With Triple Action on Postharvest Decay of Fruit and Vegetables: Eliciting, Antimicrobial and Film-Forming Properties

Chitosan is a natural biopolymer from crab shells that is known for its biocompatibility, biodegradability, and bioactivity. In human medicine, chitosan is used as a stabilizer for active ingredients in tablets, and is popular in slimming diets. Due to its low toxicity, it was the first basic substance approved by the European Union for plant protection (Reg. EU 2014/563), for both organic agriculture and integrated pest management. When applied to plants, chitosan shows triple activity: (i) elicitation of host defenses; (ii) antimicrobial activity; and (iii) film formation on the treated surface. The eliciting activity of chitosan has been studied since the 1990's, which started with monitoring of enzyme activities linked to defense mechanisms (e.g., chitinase, β-1,3 glucanase, phenylalanine ammonia-lyase) in different fruit (e.g., strawberry, other berries, citrus fruit, table grapes). This continued with investigations with qRT-PCR (Quantitative Real-Time Polymerase Chain Reaction), and more recently, with RNA-Seq. The antimicrobial activity of chitosan against a wide range of plant pathogens has been confirmed through many in-vitro and in-vivo studies. Once applied to a plant surface (e.g., dipping, spraying), chitosan forms an edible coating, the properties of which (e.g., thickness, viscosity, gas and water permeability) depend on the acid in which it is dissolved. Based on data in literature, we propose that overall, the eliciting represents 30 to 40% of the chitosan activity, its antimicrobial activity 35 to 45%, and its film-forming activity 20 to 30%, in terms of its effectiveness in the control of postharvest decay of fresh fruit. As well as being used alone, chitosan can be applied together with many other alternatives to synthetic fungicides, to boost its eliciting, antimicrobial and film-forming properties, with additive, and at times synergistic, interactions. Several commercial chitosan formulations are available as biopesticides, with their effectiveness due to the integrated combination of these three mechanisms of action of chitosan.

Avocado rhizobacteria emit volatile organic compounds with antifungal activity against Fusarium solani, Fusarium sp. associated with Kuroshio shot hole borer, and Colletotrichum gloeosporioides

Recent studies showed that bacterial volatile organic compounds (VOCs) play an important role in the suppression of phytopathogens. The ability of VOCs produced by avocado (Persea americana Mill.) rhizobacteria to suppress the growth of common avocado pathogens was therefore investigated. We evaluated the antifungal activity of VOCs emitted by avocado rhizobacteria in a first screening against Fusarium solani, and in subsequent antagonism assays against Fusarium sp. associated with Kuroshio shot hole borer, Colletotrichum gloeosporioides and Phytophthora cinnamomi, responsible for Fusarium dieback, anthracnosis and Phytophthora root rot in avocado, respectively. We also analyzed the composition of the bacterial volatile profiles by solid phase microextraction (SPME) gas chromatography coupled to mass spectrometry (GC-MS). Seven isolates, belonging to the bacterial genera Bacillus and Pseudomonas, reduced the mycelial growth of F. solani with inhibition percentages higher than 20%. Isolate HA, related to Bacillus amyloliquefaciens, significantly reduced the mycelial growth of Fusarium sp. and C. gloeosporioides and the mycelium density of P. cinnamomi. Isolates SO and SJJ, also members of the genus Bacillus, reduced Fusarium sp. mycelial growth and induced morphological alterations of fungal hyphae whilst isolate HB, close to B. mycoides, inhibited C. gloeosporioides. The analysis of the volatile profiles revealed the presence of ketones, pyrazines and sulfur-containing compounds, previously reported with antifungal activity. Altogether, our results support the potential of avocado rhizobacteria to act as biocontrol agents of avocado fungal pathogens and emphasize the importance of Bacillus spp. for the control of emerging avocado diseases such as Fusarium dieback.

Chitosan biopolymer promotes yield and stimulates accumulation of antioxidants in strawberry fruit

Strawberry is a well-known source of natural antioxidants with excellent free radical scavenging capacity. This study determined the effects of chitosan application in field condition on plant growth, fruit yield and antioxidant activities in strawberry fruit. Foliar applications of chitosan on strawberry significantly increased plant growth and fruit yield (up to 42% higher) compared to untreated control. Increased fruit yield was attributed to higher plant growth, individual fruit weight and total fruit weight/plant due to the chitosan application. Surprisingly, the fruit from plants sprayed with chitosan also had significantly higher contents (up to 2.6-fold) of carotenoids, anthocyanins, flavonoids and phenolics compared to untreated control. Total antioxidant activities in fruit of chitosan treated plants were also significantly higher (ca. 2-fold) (p< 0.05) than untreated control. To the best of our knowledge, this is the first report of chitosan applied on field plants providing significant improvement of both yield and health benefiting biochemical contents in strawberry fruit. Further study on the elucidation of mechanisms involved with enhancement of growth, yield and biochemical contents by chitosan is needed to promote sustainable production of strawberry.

Recent Advances of Chitosan Applications in Plants

In recent years, the search for biological methods to avoid the application of chemical products in agriculture has led to investigating the use of biopolymers-based materials. Among the tested biomaterials, the best results were obtained from those based on the biopolymer chitosan (CHT). CHT, available in large quantities from the deacetylation of chitin, has multiple advantages: it is safe, inexpensive and can be easily associated with other compounds to achieve better performance. In this review, we have summarized the latest researches of the application of CHT on plant productivity, plant protection against the attack of pathogens and extension of the commercial life of detached fruits.