We sequenced and compared the genomes of the Dothideomycete fungal plant pathogens Cladosporium fulvum (Cfu) (syn. Passalora fulva) and Dothistroma septosporum (Dse) that are closely related phylogenetically, but have different lifestyles and hosts. Although both fungi grow extracellularly in close contact with host mesophyll cells, Cfu is a biotroph infecting tomato, while Dse is a hemibiotroph infecting pine. The genomes of these fungi have a similar set of genes (70% of gene content in both genomes are homologs), but differ significantly in size (Cfu >61.1-Mb; Dse 31.2-Mb), which is mainly due to the difference in repeat content (47.2% in Cfu versus 3.2% in Dse). Recent adaptation to different lifestyles and hosts is suggested by diverged sets of genes. Cfu contains an α-tomatinase gene that we predict might be required for detoxification of tomatine, while this gene is absent in Dse. Many genes encoding secreted proteins are unique to each species and the repeat-rich areas in Cfu are enriched for these species-specific genes. In contrast, conserved genes suggest common host ancestry. Homologs of Cfu effector genes, including Ecp2 and Avr4, are present in Dse and induce a Cf-Ecp2- and Cf-4-mediated hypersensitive response, respectively. Strikingly, genes involved in production of the toxin dothistromin, a likely virulence factor for Dse, are conserved in Cfu, but their expression differs markedly with essentially no expression by Cfu in planta. Likewise, Cfu has a carbohydrate-degrading enzyme catalog that is more similar to that of necrotrophs or hemibiotrophs and a larger pectinolytic gene arsenal than Dse, but many of these genes are not expressed in planta or are pseudogenized. Overall, comparison of their genomes suggests that these closely related plant pathogens had a common ancestral host but since adapted to different hosts and lifestyles by a combination of differentiated gene content, pseudogenization, and gene regulation.

No abstract

Plant pathogenic fungi adapt quickly to changing environments including overcoming plant disease resistance genes. This is usually achieved by mutations in single effector genes of the pathogens, enabling them to avoid recognition by the host plant. In addition, horizontal gene transfer (HGT) and horizontal chromosome transfer (HCT) provide a means for pathogens to broaden their host range. Recently, several reports have appeared in the literature on HGT, HCT and hybridization between plant pathogenic fungi that affect their host range, including species of Stagonospora/Pyrenophora, Fusarium and Alternaria. Evidence is given that HGT of the ToxA gene from Stagonospora nodorum to Pyrenophora tritici-repentis enabled the latter fungus to cause a serious disease in wheat. A nonpathogenic Fusarium species can become pathogenic on tomato by HCT of a pathogenicity chromosome from Fusarium oxysporum f.sp lycopersici, a well-known pathogen of tomato. Similarly, Alternaria species can broaden their host range by HCT of a single chromosome carrying a cluster of genes encoding host-specific toxins that enabled them to become pathogenic on new hosts such as apple, Japanese pear, strawberry and tomato, respectively. The mechanisms HGT and HCT and their impact on potential emergence of fungal plant pathogens adapted to new host plants will be discussed.

Nanotechnology can offer green and eco-friendly alternatives for plant disease management. Apart from being eco-friendly, fungi are used as bio-manufacturing units, which will provide an added benefit in being easy to use, as compared to other microbes. The non-pathogenic nature of some fungal species in combination with the simplicity of production and handling will improve the mass production of silver nanoparticles. Recently, a diverse range of fungi have been screened for their ability to create silver nanoparticles. Mycosynthesis of gold, silver, gold–silver alloy, selenium, tellurium, platinum, palladium, silica, titania, zirconia, quantum dots, usnic acid, magnetite, cadmium telluride and uraninite nanoparticles has also been reported by various researchers. Nanotechnological application in plant pathology is still in the early stages. For example, nanofungicides, nanopesticides and nanoherbicides are being used extensively in agriculture practices. Remote activation and monitoring of intelligent nano-delivery systems can assist agricultural growers of the future to minimize fungicides and pesticides use. Nanoparticle-mediated gene transfer would be useful for improvement of crops resistant to pathogens and pest. This review critically assesses the role of fungi in the synthesis of nanoparticles, the mechanism involved in the synthesis, the effect of different factors on the reduction of metal ions in developing low-cost techniques for the synthesis and recovery of nanoparticles. Moreover, the application of nanoparticles in plant disease control, antimicrobial mechanisms, and nanotoxicity on plant ecosystem and soil microbial communities has also been discussed in detail.

The current research deals with the formulation and characterization of bio-based oil-in-water nanoemulsion. The formulated eugenol oil nanoemulsion was characterized by dynamic light scattering, stability test, transmission electron microscopy and thin layer chromatography. The nanoemulsion droplets were found to have a Z-average diameter of 80 nm and TEM study reveals the spherical shape of eugenol oil nanoemulsion (EON). The size of the nanoemulsion was found to be physically stable up to more than 1-month when it was kept at room temperature (25°C). The TEM micrograph showed that the EON was spherical in shape and moderately mono or di-dispersed and was in the range of 50-110 nm. Three concentrations of the nanoformulation were used to evalute the anti-fusarium activity both in vitro and in vivo experiments. SDS-PAGE results of total protein from the Fusarium oxysporum f. sp. vasinfectum (FOV) isolate before and after treatment with eugenol oil nanoemulsion indicate that the content of extra cellular soluble small molecular proteins decreased significantly in EON-treated fungus. Light micrographs of mycelia and spores treated with EON showed the disruption of the fungal structures. The analysis of variance (ANOVA) for Fusarium wilt incidence indicated highly significant (p = 0.000) effects of concentration, genotype, and their interaction. The difference in wilt incidence between concentrations and control was not the same for each genotype, that is, the genotypes responded differently to concentrations. Effects of three EON concentration on germination percentage, and radicle length, were determined in the laboratory. One very interesting finding in the current study is that cotton genotypes was the most important factors in determining wilt incidence as it accounted for 93.18 % of the explained (model) variation. In vitro experiments were conducted to evaluate the potential phytotoxic effect of three EON concentrations. Concentration, genotype and concentration x genotype interaction were all highly significant sources of variation in seed germination; however, interaction was the first in importance as a source of variation followed by the concentration, while genotype was the least important source of variation. These results suggest the potential use of eugenol oil nanoemulsion for protecting seedcotton from Fusarium wilt infection.

Rhizoctonia root-rot disease causes severe economic losses in a wide range of crops, including Vicia faba worldwide. Currently, biosynthesized nanoparticles have become super-growth promoters as well as antifungal agents. In this study, biosynthesized selenium nanoparticles (Se-NPs) have been examined as growth promoters as well as antifungal agents against Rhizoctonia solani RCMB 031001 in vitro and in vivo. Se-NPs were synthesized biologically by Bacillus megaterium ATCC 55000 and characterized by using UV-Vis spectroscopy, XRD, dynamic light scattering (DLS), and transmission electron microscopy (TEM) imaging. TEM and DLS images showed that Se-NPs are mono-dispersed spheres with a mean diameter of 41.2 nm. Se-NPs improved healthy Vicia faba cv. Giza 716 seed germination, morphological, metabolic indicators, and yield. Furthermore, Se-NPs exhibited influential antifungal activity against R. solani in vitro as well as in vivo. Results revealed that minimum inhibition and minimum fungicidal concentrations of Se-NPs were 0.0625 and 1 mM, respectively. Moreover, Se-NPs were able to decrease the pre-and post-emergence of R. solani damping-off and minimize the severity of root rot disease. The most effective treatment method is found when soaking and spraying were used with each other followed by spraying and then soaking individually. Likewise, Se-NPs improve morphological and metabolic indicators and yield significantly compared with infected control. In conclusion, biosynthesized Se-NPs by B. megaterium ATCC 55000 are a promising and effective agent against R. solani damping-off and root rot diseases in Vicia faba as well as plant growth inducer.

Leaf mold of tomato is caused by the biotrophic fungus Cladosporium fulvum which complies with the gene-for-gene system. The disease was first reported in Japan in the 1920s and has since been frequently observed. Initially only race 0 isolates were reported, but since the consecutive introduction of resistance genes Cf-2, Cf-4, Cf-5 and Cf-9 new races have evolved. Here we first determined the virulence spectrum of 133 C. fulvum isolates collected from 22 prefectures in Japan, and subsequently sequenced the avirulence (Avr) genes Avr2, Avr4, Avr4E, Avr5 and Avr9 to determine the molecular basis of overcoming Cf genes. Twelve races of C. fulvum with a different virulence spectrum were identified, of which races 9, 2.9, 4.9, 4.5.9 and 4.9.11 occur only in Japan. The Avr genes in many of these races contain unique mutations not observed in races identified elsewhere in the world including (i) frameshift mutations and (ii) transposon insertions in Avr2, (iii) point mutations in Avr4 and Avr4E, and (iv) deletions of Avr4E, Avr5 and Avr9. New races have developed by selection pressure imposed by consecutive introductions of Cf-2, Cf-4, Cf-5 and Cf-9 genes in commercially grown tomato cultivars. Our study shows that molecular variations to adapt to different Cf genes in an isolated C. fulvum population in Japan are novel but overall follow similar patterns as those observed in populations from other parts of the world. Implications for breeding of more durable C. fulvum resistant varieties are discussed.

Plant diseases are among the major factors limiting crop productivity. A first step towards managing a plant disease under greenhouse and field conditions is to correctly identify the pathogen. Current technologies, such as quantitative polymerase chain reaction (Q-PCR), require a relatively large amount of target tissue and rely on multiple assays to accurately identify distinct plant pathogens. The common disadvantage of the traditional diagnostic methods is that they are time consuming and lack high sensitivity. Consequently, developing low-cost methods to improve the accuracy and rapidity of plant pathogens diagnosis is needed. Nanotechnology, nano particles and quantum dots (QDs) have emerged as essential tools for fast detection of a particular biological marker with extreme accuracy. Biosensor, QDs, nanostructured platforms, nanoimaging and nanopore DNA sequencing tools have the potential to raise sensitivity, specificity and speed of the pathogen detection, facilitate high-throughput analysis, and to be used for high-quality monitoring and crop protection. Furthermore, nanodiagnostic kit equipment can easily and quickly detect potential serious plant pathogens, allowing experts to help farmers in the prevention of epidemic diseases. The current review deals with the application of nanotechnology for quicker, more cost-effective and precise diagnostic procedures of plant diseases. Such an accurate technology may help to design a proper integrated disease management system which may modify crop environments to adversely affect crop pathogens.