Comparative Genomics of Pathogens Causing Brown Spot Disease of Tobacco: Alternaria longipes and Alternaria alternata

Rhizospheric microbiota of suppressive soil protect plants against Fusarium solani infection

BACKGROUND

Fusarium infection has caused huge economic losses in many crops. The study aimed to compare the microbial community of suppressive and conducive soils and relate to the reduction of Fusarium wilt.

RESULTS

High-throughput sequencing and microbial network analysis were used to investigate the differences in the rhizosphere microbiota of the suppressive and conducive soils and to identify the beneficial keystone taxa. Plant pathogens were enriched in the conducive soil. Potential plant-beneficial microorganisms and antagonistic microorganisms were enriched in the suppressive soil. More positive interactions and keystone taxa existed in the suppressive soil network. Thirty-nine and 16 keystone taxa were identified in the suppressive and conducive soil networks, respectively. Sixteen fungal strains and 168 bacterial strains were isolated from suppressive soil, some of which exhibited plant growth-promotion traits. Thirty-nine bacterial strains and 10 fungal strains showed antagonistic activity against F. solani. Keystone taxa Bacillus and Trichoderma exhibited high antifungal activity. Lipopeptides produced by Bacillus sp. RB150 and chitinase from Trichoderma spp. inhibited the growth of F. solani. Microbial consortium I (Bacillus sp. RB150, Pseudomonas sp. RB70 and Trichoderma asperellum RF10) and II (Bacillus sp. RB196, Bacillus sp. RB150 and T. asperellum RF10) effectively controlled root rot disease, the spore number of F. solani was reduced by 94.2% and 83.3%.

CONCLUSION

Rhizospheric microbiota of suppressive soil protects plants against F. solani infection. Antagonistic microorganisms in suppressive soil inhibit pathogen growth and infection. Microbial consortia consisted of keystone taxa well control root rot disease. These findings help control Fusarium wilt. © 2024 Society of Chemical Industry.

Characterization of antifungal properties of avocado leaves and majagua flowers extracts and their potential application to control Alternaria alternata

Plant extracts are used as an alternative to a wide range of foods against different types of fungal pathogens. In the present study, the extracts of avocado leaves (Persea americana) and majagua flowers (Talipariti elatum) were tested according to their antifungal activity against different fungi. The most promising extracts were those of majagua flowers that were applied lyophilized and in aqueous extract, being very effective against Alternaria alternata and reaching a 50 % in vitro reduction. Antifungal properties were also evaluated during infection of apples by A. alternata. A decrease in infection progression was confirmed with up to a 30 % reduction in disease incidence and a 20 % reduction in disease severity. Majagua extracts were also tested combined with edible pectin coatings, greatly increasing their effectiveness up 60 % reduction. Thus, extracts of majagua could provide a feasible alternative to control fungal pathogens during postharvest.

Fabrication of CuO nanoparticles composite ε-polylysine-alginate nanogel for high-efficiency management of Alternaria alternate

Although ε-poly-l-lysine (ε-PL) has a good potential as a green fungicide, high concentration is usually required during its controlling of plant disease. On the other hand, same problems also appeared in the study of CuONP based nano pesticides. In this manuscript, a new composite alginate nanogel (ALGNP) that containing CuONP and ε-PL was fabricated via in situ reduction of CuONP in nanogel and ε-PL surface coating. Based on the chelation of amide bond of ε-PL and Cu²⁺ released by CuONP, the synergy effect between Cu²⁺ and ε-PL layer of the nanogel make the nanogel (CuONP@ALGNP@PL) performed high anti-fungal activity under low Cu²⁺ and ε-PL concentration (Cu concentration was 40.09 μg/mL, ε-PL concentration was 11.90 μg/mL). Study showed that the nanogel could more significantly destroy the fungal cell membrane than CuONP@ALGNP and ALGNP@PL, also better than commercial fungicide CuCaSO₄ (Cu concentration was 120 μg/mL). Furthermore, CuONP@ALGNP@PL could seriously affect the spore production, spore germination rate and bud tube elongation length of Alternaria alternate. Moreover, CuONP@ALGNP@PL also inhibit Botrytis cinerea, Phytophthora, Thanatephorus cucumeris and Fusarium graminearum. These results showed that composite of CuONP and ε-PL based on nanogel can decrease the raw materials application amount, and achieve a high disease controlling ability, which provides a new perspective for preventing fungal diseases.

Spatio-Temporal Variation in the Phyllospheric Microbial Biodiversity of Alternaria Alternata-Infected Tobacco Foliage

Phyllospheric microbial composition of tobacco (Nicotiana tabacum L.) is contingent upon certain factors, such as the growth stage of the plant, leaf position, and cultivar and its geographical location, which influence, either directly or indirectly, the growth, overall health, and production of the tobacco plant. To better understand the spatiotemporal variation of the community and the divergence of phyllospheric microflora, procured from healthy and diseased tobacco leaves infected by Alternaria alternata, the current study employed microbe culturing, high-throughput technique, and BIOLOG ECO. Microbe culturing resulted in the isolation of 153 culturable fungal isolates belonging to 33 genera and 99 bacterial isolates belonging to 15 genera. High-throughput sequencing revealed that the phyllosphere of tobacco was dominantly colonized by Ascomycota and Proteobacteria, whereas, the most abundant fungal and bacterial genera were Alternaria and Pseudomonas. The relative abundance of Alternaria increased in the upper and middle healthy groups from the first collection time to the third, whereas, the relative abundance of Pseudomonas, Sphingomonas, and Methylobacterium from the same positions increased during gradual leaf aging. Non-metric multi-dimensional scaling (NMDs) showed clustering of fungal communities in healthy samples, while bacterial communities of all diseased and healthy groups were found scattered. FUNGuild analysis, from the first collection stage to the third one in both groups, indicated an increase in the relative abundance of Pathotroph-Saprotroph, Pathotroph-Saprotroph-Symbiotroph, and Pathotroph-Symbiotroph. Inclusive of all samples, as per the PICRUSt analysis, the predominant pathway was metabolism function accounting for 50.03%. The average values of omnilog units (OUs) showed relatively higher utilization rates of carbon sources by the microbial flora of healthy leaves. According to the analysis of genus abundances, leaf growth and leaf position were the important drivers of change in structuring the microbial communities. The current findings revealed the complex ecological dynamics that occur in the phyllospheric microbial communities over the course of a spatiotemporal varying environment with the development of tobacco brown spots, highlighting the importance of community succession.

Comparative genomic analysis reveals cellulase plays an important role in the pathogenicity of Setosphaeria turcica f. sp. zeae

Setosphaeria turcica f. sp. zeae and S. turcica f. sp. sorghi, the two formae speciales of S. turcica, cause northern leaf blight disease of corn and sorghum, respectively, and often cause serious economic losses. They have obvious physiological differentiation and show complete host specificity. Host specificity is often closely related to pathogen virulence factors, including secreted protein effectors and secondary metabolites. Genomic sequencing can provide more information for understanding the virulence mechanisms of pathogens. However, the complete genomic sequence of S. turcica f. sp. sorghi has not yet been reported, and no comparative genomic information is available for the two formae speciales. In this study, S. turcica f. sp. zeae was predicted to have fewer secreted proteins, pathogen-host interaction (PHI) genes and carbohydrate-active enzymes (CAZys) than S. turcica f. sp. sorghi. Fifteen and 20 polyketide synthase (PKS) genes were identified in S. turcica f. sp. zeae and S. turcica f. sp. sorghi, respectively, which maintained high homology. There were eight functionally annotated effector protein-encoding genes specifically in S. turcica f. sp. zeae, among which the encoding gene StCEL2 of endo-1, 4-β-D-glucanase, an important component of cellulase, was significantly up-regulated during the interaction process. Finally, gluconolactone inhibited cellulase activity and decreased infection rate and pathogenicity, which indicates that cellulase is essential for maintaining virulence. These findings demonstrate that cellulase plays an important role in the pathogenicity of S. turcica f. sp. zeae. Our results also provide a theoretical basis for future research on the molecular mechanisms underlying the pathogenicity of the two formae speciales and for identifying any associated genes.

Transcriptome analysis reveals putative pathogenesis genes in Alternaria panax during infecting Panax notoginseng leaves

BACKGROUND

Alternaria panax is the causative agent of black spot disease in Panax notoginseng, which causes significant yield loss. However, the molecular mechanisms underlying its pathogenicity remain mostly unknown.

OBJECTIVE

We sequenced the transcriptome of A. panax during infecting P. notoginseng leaves using next-generation RNA-seq to understand the molecular aspects of black spot disease.

METHODS

In this study, we sequenced the A. panax transcriptome during infecting P. notoginseng leaves through next-generation sequencing to explore the pathogenesis genes that may be responsible for black spot disease on P. notoginseng.

RESULT

The de novo transcriptome assembly of A. panax produced 23,036 unigenes, of which 18,096 genes were functionally annotated by at least one protein database. GO enrichment analysis and KEGG pathways of differentially up-regulated genes suggest that most genes are associated with metabolic processes, catalytic activity, starch, and sucrose metabolism during infection. Many pathogenesis-associated genes, including genes encoding secreted proteins, candidate secreted effectors, cell wall degrading enzymes, transcription factors, and transporters, were up-regulated in A. panax during infection. In addition, the secondary metabolite biosynthesis genes, including cytochrome P450, and nonribosomal peptide synthetases, were also identified in this study.

CONCLUSIONS

Differential gene expression analysis has confirmed that A. panax infection was mainly present in the middle and final stages. The findings show that these pathogenesis-associated genes in A. panax may be critical for the P. notoginseng black spots disease.

Genetic Structure and Triazole Antifungal Susceptibilities of Alternaria alternata from Greenhouses in Kunming, China

Alternaria alternata is an opportunistic human fungal pathogen and a ubiquitous phytopathogen capable of causing diseases to >100 agricultural crops and ornamental plants. To control plant diseases caused by A. alternata, triazole fungicides have been widely used both in open crop and vegetable fields and in indoor growth facilities such as greenhouses. At present, the effect of fungicide use on triazole resistance development in A. alternata populations is not known. Here, we isolated 237 A. alternata strains from nine greenhouses around metropolitan Kunming in Yunnan, southwest China, determined their genotypes using 10 short tandem repeat markers, and quantified their susceptibility to four triazoles (difenoconazole, tebuconazole, itraconazole, and voriconazole). Abundant allelic and genotypic diversities were detected among these A. alternata strains. Significantly, over 17% of the strains were resistant to difenoconazole, and both known and new drug-resistance mutations were found in the triazole target gene cyp51. Our findings of high-level genetic variation of A. alternata in greenhouses coupled with high-frequency fungicide resistance call for greater attention to continued monitoring and to developing alternative plant fungal disease management strategies in greenhouses. IMPORTANCE Alternaria alternata is among the most common fungi in our environments, such as indoor facilities, the soil, and outdoor air. It can cause diseases in >100 crop and ornamental plants. Furthermore, it can cause human infections. However, our understanding of its genetic diversity and antifungal susceptibility is very limited. Indeed, the critical threshold values for resistance have not been defined for most antifungal drugs in this species. Greenhouses are known to have heavy applications of agricultural fungicides. In this study, we analyzed strains of A. alternata from nine greenhouses near metropolitan Kunming in southwestern China. Our study revealed very high genetic diversity and identified strains with high MIC values against two agricultural and two medical triazole antifungals within each of the nine greenhouses. Our study calls for greater attention to this emerging threat to food security and human health.

Analysis of Phyllosphere Microorganisms and Potential Pathogens of Tobacco Leaves

In the tobacco phyllosphere, some of the microbes may have detrimental effects on plant health, while many may be neutral or even beneficial. Some cannot be cultivated, so culture-independent methods are needed to explore microbial diversity. In this study, both metagenetic analysis and traditional culture-dependent methods were used on asymptomatic healthy leaves and symptomatic diseased leaves of tobacco plants. In the culture-independent analysis, asymptomatic leaves had higher microbial diversity and richness than symptomatic leaves. Both asymptomatic and symptomatic leaves contained several potentially pathogenic bacterial and fungal genera. The putative bacterial pathogens, such as species of Pseudomonas, Pantoea, or Ralstonia, and putative fungal pathogens, such as species of Phoma, Cladosporium, Alternaria, Fusarium, Corynespora, and Epicoccum, had a higher relative abundance in symptomatic leaves than asymptomatic leaves. FUNGuild analysis indicated that the foliar fungal community also included endophytes, saprotrophs, epiphytes, parasites, and endosymbionts. PICRUSt analysis showed that the dominant functions of the bacterial community in a symptomatic leaf were cellular processes and environmental information processing. In the other five foliar samples, the dominant functions of the bacterial community were genetic information processing, metabolism, and organismal systems. In the traditional culture-dependent method, 47 fungal strains were isolated from 60 symptomatic tobacco leaf fragments bearing leaf spots. Among them, 21 strains of Colletotrichum (29%), Xylariaceae (14%), Corynespora (14%), Pestalotiopsis (10%), Alternaria (10%), Epicoccum (10%), Byssosphaeria (5%), Phoma (5%), and Diaporthe (5%) all fulfilled Koch’s postulates and were found to cause disease on detached tobacco leaves in artificial inoculation tests. Symptoms on detached leaves caused by three strains of Corynespora cassiicola in artificial inoculation tests were similar to the original disease symptoms in the tobacco field. This study showed that the combined application of culture-dependent and independent methods could give comprehensive insights into microbial composition that each method alone did not reveal.

Draft Genome Sequence of Alternaria longipes Causing Tobacco Brown Spot

Alternaria is a cosmopolitan fungal genus associated with diverse hosts. Tobacco brown spot caused by Alternaria longipes is one of the most destructive diseases of tobacco. A. longipes can also infect many other plants, some animals and even humans. Here, we report a genome assembly of A. longipes CBS 540.94 using Oxford Nanopore Technologies. A total of 15 contigs were assembled, and the genome size was 37.5 Mb with contig N50 of 4.33 Mb. This genome resource will provide information for further research on comparative genomics of the genus Alternaria and be a valuable resource in investigations of the molecular interactions of pathogen and hosts.

Highly sensitive time-resolved fluoroimmunoassay for the quantitative onsite detection of Alternaria longipes in tobacco

AIMS

Alternaria longipes is a causal agent of brown spot of tobacco, which remains a serious threat to tobacco production. Herein, we established a detection method for A. longipes in tobacco samples based on the principle of time-resolved fluoroimmunoassay, in order to fulfil the requirement of rapid, sensitive and accurate detection in situ.

METHODS AND RESULTS

A monoclonal antibody against A. longipes was generated, and its purity and titration were assessed using western blot and ELISA. The size of europium (III) nanospheres was measured to confirm successful antibody conjugation. The method described here can detect A. longipes protein lysates as low as 0.78 ng ml-1 , with recovery rates ranging from 85.96% to 99.67% in spiked tobacco. The specificity was also confirmed using a panel of microorganisms.

CONCLUSIONS

The fluorescent strips allow rapid and sensitive onsite detection of A. longipes in tobacco samples, with high accuracy, specificity, and repeatability.

SIGNIFICANCE AND IMPACT OF THE STUDY

This novel detection method provides convenience of using crude samples without complex procedures, and therefore allows rapid onsite detection by end users and quick responses towards A. longipes, which is critical for disease control and elimination of phytopathogens.

A New Leaf Blight Disease Caused by Alternaria jacinthicola on Banana in China

A leaf blight disease with an incidence level of about 50% was found on Robusta banana in Guangdong province of China in September 2020. The early symptom appeared as pale gray to black brown, irregular, small, necrotic lesions mainly on the top 3–5 leaves. Severely infected leaves were withered and necrotic. Two representative fungus strains, strain L1 and strain L2, were isolated from affected banana leaves, and morphological and molecular identification analysis confirmed that the two fungi were both Alternaria jacinthicola. Many Alternaria species have been reported to cause wilting, decay, leaf blight and leaf spots on plants and lead to serious economic losses in their production, including A. alternata, causing leaf blight and leaf sport diseases on banana. The Koch’s postulates of A. jacinthicola causing the leaf blight disease was further fulfilled, which confirmed that it is the causal agent of this disease. To our knowledge, this is the first report of A. jacinthicola causing leaf blight on banana in China.

Distinct and essential roles of bZIP transcription factors in the stress response and pathogenesis in Alternaria alternata

The ability to cope with environmental abiotic stress and biotic stress is crucial for the survival of plants and microorganisms, which enable them to occupy multiple niches in the environment. Previous studies have shown that transcription factors play crucial roles in regulating various biological processes including multiple stress tolerance and response in eukaryotes. This work identified multiple critical transcription factor genes, metabolic pathways and gene ontology (GO) terms related to abiotic stress response were broadly activated by analyzing the transcriptome of phytopathogenic fungus Alternaria alternata under metal ions stresses, oxidative stress, salt stresses, and host-pathogen interaction. We investigated the biological functions and regulatory roles of the bZIP transcriptional factor (TF) genes in the phytopathogenic fungus A.alternata by analyzing targeted gene disrupted mutants. Morphological analysis provides evidence that the bZIP transcription factors (Gcn4, MeaB, Atf1, the ER stress regulator Hac1, and the all development altered-1 gene Ada1) are required for morphogenesis as the colony morphology of these gene deletion mutants was significantly different from that of the wild-type. In addition, bZIPs are involved in the resistance to multiple stresses such as oxidative stress (Ada1, Yap1, MetR) and virulence (Hac1, MetR, Yap1, Ada1) at varying degrees. Transcriptome data demonstrated that the inactivation of bZIPs (Hac1, Atf1, Ada1 and Yap1) significantly affected many genes in multiple critical metabolism pathways and gene ontology (GO) terms. Moreover,the ΔHac1 mutants displayed reduced aerial hypha and are hypersensitivity to endoplasmic reticulum disruptors such as tunicamycin and dithiothreitol. Transcriptome analysis showed that inactivation of Hac1 significantly affected the proteasome process and its downstream unfolded protein binding, indicating that Hac1 participates in the endoplasmic reticulum stress response through the conserved unfolded protein response. Taken together, our findings reveal that bZIP transcription factors function as key regulators of fungal morphogenesis, abiotic stress response and pathogenesis, and expand our understanding of how microbial pathogens utilize these genes to deal with environmental stresses and achieve successful infection in the host plant.

Distribution of the potential pathogenic Alternaria on plant leaves determines foliar fungal communities around the disease spot

Plant leaves are colonized by a remarkably diverse fungal microbiome, which contributes to host plant growth and health. However, responses of foliar fungal community to phytopathogen invasion and measures of the fungal community taken to resist or assist pathogens remain elusive. By utilizing high-throughput sequencing of internal transcribed spacer (ITS) amplicons, we studied the relationships between the foliar fungal community around the disease spot and the pathogen of brown spot disease. The pathogenic Alternaria was found to follow a dramatically decreased trend from the disease spot to its surrounding fungal communities, whose community structure also diverged substantially away from the disease spot community. With the increase of pathogenic Alternaria, diversity indexes, including Shannon, Pielou and Simpson, showed a trend of increasing first and then decreasing. Total network links and the average path distance exhibited strong negative and positive correlations with Alternaria, respectively. Five keystone members showed direct interactions with pathogenic Alternaria. Members of Botryosphaeria, Paraphoma and Plectosphaerella might act as key 'pathogen facilitators' to increase the severity and development of brown spot disease, while Pleospora and Ochrocladosporium might be important 'pathogen antagonists' to suppress the expansion of pathogenic Alternaria. Our study provides new insights in developing new strategies for leaf disease prediction or prevention.

Dual species dynamic transcripts reveal the interaction mechanisms between Chrysanthemum morifolium and Alternaria alternata

BACKGROUND

Chrysanthemum (Chrysanthemum morifolium) black spot disease caused by Alternaria alternata is one of the plant's most destructive diseases. Dual RNA-seq was performed to simultaneously assess their transcriptomes to analyze the potential interaction mechanism between the two species, i.e., host and pathogen.

RESULTS

C. morifolium and A. alternata were subjected to dual RNA-seq at 1, 12, and 24 h after inoculation, and differential expression genes (DEGs) in both species were identified. This analysis confirmed 153,532 DEGs in chrysanthemum and 14,932 DEGs in A. alternata, which were involved in plant-fungal interactions and phytohormone signaling. Fungal DEGs such as toxin synthesis related enzyme and cell wall degrading enzyme genes played important roles during chrysanthemum infection. Moreover, a series of key genes highly correlated with the early, middle, or late infection stage were identified, together with the regulatory network of key genes annotated in the Plant Resistance Genes database (PRGdb) or Pathogen-Host Interactions database (PHI-base). Highly correlated genes were identified at the late infection stage, expanding our understanding of the interplay between C. morifolium and A. alternata. Additionally, six DEGs each from chrysanthemum and A. alternata were selected for quantitative real-time PCR (qRT-PCR) assays to validate the RNA-seq output.

CONCLUSIONS

Collectively, data obtained in this study enriches the resources available for research into the interactions that exist between chrysanthemum and A. alternata, thereby providing a theoretical basis for the development of new chrysanthemum cultivars with resistance to pathogen.

Draft Genome Sequence of Cumin Blight Pathogen Alternaria burnsii

The fungal genus Alternaria consists of highly diverse species. They can be isolated readily from soil, water, and many plants, and even from animals and humans. Alternaria burnsii is a small-spored species of section Alternaria. It has been reported as a pathogen, an endophyte, and a saprophyte, and can also be found in indoor air. It causes cumin blight, a destructive disease on cumin (Cuminum cyminum), and also causes other serious diseases, such as pumpkin seed rot, date palm leaf spot, wheat leaf spot, and gray spot of Notopterygium incisum. In this study, we sequenced and assembled the first genome of A. burnsii isolate CBS 107.38. The draft genome can be used as a reference for the further study of related pathogens and comparative genomics of Alternaria species.

Effects of ε-poly-l-lysine on vegetative growth, pathogenicity and gene expression of Alternaria alternata infecting Nicotiana tabacum

Microbial secondary metabolites produced by Streptomyces are applied to control plant diseases. ε-poly-l-lysine (ε-PL) is a non-toxic food preservative, but the potential application of ε-PL as a microbial fungicide in agriculture has rarely been reported. In this study, Alternaria alternata (A. alternata) was used to reveal the effect and mode of action for ε-PL on the plant pathogenic fungi. The results showed that ε-PL effectively inhibited necrotic-lesion development caused by A. alternata on tobacco. Mycelial growth was also significantly inhibited in vitro by 100 μg/ml ε-PL using in vitro analysis. Moreover, 25 μg/ml ε-PL inhibited spore germination and induced abnormal morphological development of A. alternata hyphae. To clarify the molecular-genetic antifungal mechanisms, we selected several crucial genes involved in the development and pathogenesis of A. alternata and studied their expression regulated by ε-PL. Results of real-time quantitative PCR showed that a mycelium morphology and pathogenic process related cyclic adenosine monophosphate protein (cAMP) dependent protein kinase A (PKA), Alternaria alternata cAMP-dependent protein kinase catalytic subunit (AAPK1) and the early infection-related glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were down-regulated after ε-PL treatment. The results provide novel insights for the application of ε-PL in the control of plant diseases caused by A. alternata.

Genomics Evolutionary History and Diagnostics of the Alternaria alternata Species Group Including Apple and Asian Pear Pathotypes

The Alternaria section alternaria (Alternaria alternata species group) represents a diverse group of saprotroph, human allergens, and plant pathogens. Alternaria taxonomy has benefited from recent phylogenetic revision but the basis of differentiation between major phylogenetic clades within the group is not yet understood. Furthermore, genomic resources have been limited for the study of host-specific pathotypes. We report near complete genomes of the apple and Asian pear pathotypes as well as draft assemblies for a further 10 isolates representing Alternaria tenuissima and Alternaria arborescens lineages. These assemblies provide the first insights into differentiation of these taxa as well as allowing the description of effector and non-effector profiles of apple and pear conditionally dispensable chromosomes (CDCs). We define the phylogenetic relationship between the isolates sequenced in this study and a further 23 Alternaria spp. based on available genomes. We determine which of these genomes represent MAT1-1-1 or MAT1-2-1 idiomorphs and designate host-specific pathotypes. We show for the first time that the apple pathotype is polyphyletic, present in both the A. arborescens and A. tenuissima lineages. Furthermore, we profile a wider set of 89 isolates for both mating type idiomorphs and toxin gene markers. Mating-type distribution indicated that gene flow has occurred since the formation of A. tenuissima and A. arborescens lineages. We also developed primers designed to AMT14, a gene from the apple pathotype toxin gene cluster with homologs in all tested pathotypes. These primers allow identification and differentiation of apple, pear, and strawberry pathotypes, providing new tools for pathogen diagnostics.

Molecular breeding approaches for production of disease-resilient commercially important tobacco

Tobacco is one of the most widely cultivated nonfood cash crops, a source of income, model organism for plant molecular research, a natural pesticide and of pharmaceutical importance. First domesticated in South Americas, the modern-day tobacco (Nicotiana tabacum) is now cultivated in more than 125 countries to generate revenues worth billions of dollars each year. However, the production of this crop is highly threatened by the global presence of devastating infectious agents, which cause huge fiscal loss. These threats have been battled through breeding for acquiring disease resilience in tobacco plants, first, via conventional and now with the use of modern molecular breeding approaches. For efficacy and precision, the characterization of the genetic components underlying disease resistance is the key tool in tobacco for resistance breeding programs. The past few decades have witnessed significant progress in resilience breeding through advanced molecular techniques. The current review discusses history of tobacco breeding since its time of origin till date, highlighting the most widely used techniques and recent advances in molecular research and strategies for resistance breeding. In addition, we narrate the budding possibilities for the future. This review will provide a comprehensive and valuable information for the tobacco growers and researchers to deal with the destructive infectious diseases.

Genome Sequence Resource for Stemphylium vesicarium, Causing Brown Spot Disease of Pear

Stemphylium vesicarium is the causal agent of several plant diseases as well brown spot of pear (BSP), which is one of the most economically important fungal diseases in European pear-production areas. In addition to the relevance of the economic impact, conidia spread widely from plant material infected by the pathogen can trigger respiratory allergy. Here, we report the first genome of a S. vesicarium strain, 173-1a13FI1M3, isolated from pear and sensitive to the mostly used fungicide classes currently authorized in Europe against BSP. The availability of this draft genome could represent a first important step in understanding the physiology and the infection mechanism of the pathogen. Furthermore, this contribution could be fundamental in order to design more effective and sustainable strategies to control the disease.

Nitric oxide and ROS mediate autophagy and regulate Alternaria alternata toxin-induced cell death in tobacco BY-2 cells

Synergistic interaction of nitric oxide (NO) and reactive oxygen species (ROS) is essential to initiate cell death mechanisms in plants. Though autophagy is salient in either restricting or promoting hypersensitivity response (HR)-related cell death, the crosstalk between the reactive intermediates and autophagy during hypersensitivity response is paradoxical. In this investigation, the consequences of Alternaria alternata toxin (AaT) in tobacco BY-2 cells were examined. At 3 h, AaT perturbed intracellular ROS homeostasis, altered antioxidant enzyme activities, triggered mitochondrial depolarization and induced autophagy. Suppression of autophagy by 3-Methyladenine caused a decline in cell viability in AaT treated cells, which indicated the vital role of autophagy in cell survival. After 24 h, AaT facilitated Ca2+ influx with an accumulation of reactive oxidant intermediates and NO, to manifest necrotic cell death. Inhibition of NO accumulation by 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) decreased the level of necrotic cell death, and induced autophagy, which suggests NO accumulation represses autophagy and facilitates necrotic cell death at 24 h. Application of N-acetyl-L-cysteine at 3 h, confirmed ROS to be the key initiator of autophagy, and together with cPTIO for 24 h, revealed the combined effects of NO and ROS is required for necrotic HR cell death.

Isolation and characterization of different promising fungi for biological waste management of polyurethanes

As a highly resistant polymer family, polyurethanes (PU) are responsible for increasing environmental issues. Then, PU biodegradation is a challenging way to develop sustainable waste management processes based on biological recycling. Since the metabolic diversity of fungi is a major asset for polymer degradation, nearly thirty strains were isolated from sampling on six different PU wastes-containing environments. A screening of the fungi on four thermoplastic PU (TPU) with different macromolecular architectures led to the selection of three strains able to use two polyester PU as sole carbon source: Alternaria sp., Penicillium section Lanata-Divaricata and Aspergillus section flavi. Weight loss, FT-IR, Scanning Electron Microscopy and Size Exclusion Chromatography analyses revealed that these three fungi degrade slightly and similarly a fatty acid dimer-based TPU while variability of degradation was noticed on a polycaprolactone-based TPU. On this last TPU, robust analysis of the degraded polymers showed that the Penicillium strain was the best degrading microorganism. Membrane enzymes seemed to be involved in this degradation. It is the first time that a strain of Penicillium of the section Lanata-Divaricata displaying PU biodegradation ability is isolated. These newly discovered fungi are promising for the development of polyester PU waste management process.

Dissipation and translocation of saisenxin in tobacco and soil under conventional field and controlled laboratory conditions

The aim of this investigation was to investigate the fate and translocation characteristics of saisenxin (SSX), a novel organic zinc fungicide, in the environment and tobacco plants under conventional field and laboratory conditions. A rapid and sensitive analytical technique based on high-performance liquid chromatography was used for determination of SSX, in soil samples and tobacco leaf, stem and root samples. The method had satisfactiry linearity (R2 = 0.9999) and the limits of detection and of quantitation of the target compound were 0.06 and 0.20 mg kg-1, respectively. The average recoveries were in the range of 89.74-94.24% in soil, leaf, stem and root samples, with relative standard deviations of <8%. For conventional field trials, the half-life (t1/2) of SSX was 5.9-6.5 days in soil and 4.8-5.3 days in tobacco leaves; the corresponding values under controlled laboratory conditions were extended to 7.1 and 7.6 days. The translocation factor (TF) values were in the range of 0-2.25 and 0-0.25 for foliage and root irrigation treatments, respectively. The TFs of SSX in tobacco indicated that tobacco had a high ability to transfer SSX upward.

Occurrence, biochemistry and biological effects of host-selective plant mycotoxins

Host-selective mycotoxins (HSTs) are various secondary metabolites or proteinaceous compounds secreted by pathogenic necrotrophic fungi that feed off on dead tissues of certain plants. Research on the HSTs has not only fundamental but also practical importance. On one hand they are implicated in the onset of devastating crop diseases. On the other hand, they have been studied as a good model for revealing the intricate mechanisms of plant-pathogen interactions. At the cellular level, HSTs target different compartments and in most instances induce programmed cell death (PCD) by a wide range of mechanisms. Often the responses provoked by HSTs resemble the effector-triggered immunity used by plant cells to combat biotrophic pathogens, which suggests that HST-producing fungi exploit the plants' own defensive systems to derive benefits. Although by definition HSTs are active only in tissues of susceptible plant genotypes, it has been demonstrated that some of them are able to influence animal cells as well. The possible effects, like cytotoxicity or cytostasis, can be harmful or beneficial and thus HSTs may either pose a health risk for humans and livestock, or be of prospective use in the fields of pharmacology, medicine and agriculture.

Recent advances in tenuazonic acid as a potential herbicide

Tenuazonic acid (TeA), belonging to tetramic acids that are the largest family of natural products, is a mycotoxin produced by members of the genus Alternaria and other phytopathogenic fungi. TeA has many desirable bioactivities. In the past two decades, several studies have addressed its phytotoxic activity. Because it can cause brown leaf spot and kill seedlings of mono- and dicotyledonous plants, TeA is regarded as a potential herbicidal agent. TeA blocks electron transport beyond Q_A by interacting with D1 protein and is a PSII inhibitor. The chloroplast-derived oxidative burst is responsible for TeA-induced cell death and plant necrosis. Based on the model of molecular interaction between TeA and D1 protein, a series of its derivatives with stable herbicidal activity have been designed, evaluated and patented. Recently, some chemical synthetic approaches of TeA and its derivatives have been successfully developed. This paper will mainly focus on new developments regarding TeA's herbicidal activity, mode of action, biosynthesis and chemical synthesis, and characterization of new derivatives.