Production of pycnidia and pycnidiospores by Macrophomina phaseolina is not often seen in vitro. The objective of this study is to develop a simple and effective technique to obtain pycnidiospores of M. phaseolina isolates in vitro and to evaluate germination rates and pathogenicity of pycnidiospores. We found M. phaseolina isolates can produce pycnidia on oatmeal agar (OMA) under ultraviolet light with 365 nm wavelength (UV). For evaluating the effect of OMA and UV on growth of M. phaseolina, combinations of two agar media and three lighting conditions were tested. The results confirm that all six M. phaseolina isolates produced pycnidia only on OMA under UV. The pycnidiospores produced on OMA under UV had germination rates higher than 90%. In pathogenicity tests, inoculation with the pycnidiospores showed symptoms later than inoculation with hypha-colonized toothpicks. Significant differences in the pathogenicity is detected between isolates Mp2014003 and Mp2014024 when inoculation is done with the pycnidiospores (P < 0.001), but not when hypha-colonized toothpicks are used as inoculum (P = 0.091). This study provides a new method for obtaining pycnidiospores of M. phaseolina for future investigations.

Background: Corynespora leaf spot is a common leaf disease occurring in sesame, and the disease causes leaf yellowing and even shedding, which affects the growth quality of sesame. At present, the mechanism of sesame resistance to this disease is still unclear. Understanding the resistance mechanism of sesame to Corynespora leaf spot is highly important for the control of infection. In this study, the leaves of the sesame resistant variety (R) and the sesame susceptible variety (S) were collected at 0–48 hpi for transcriptome sequencing, and used a combined third-generation long-read and next-generation short-read technology approach to identify some key genes and main pathways related to resistance. Results: The gene expression levels of the two sesame varieties were significantly different at 0, 6, 12, 24, 36 and 48 hpi, indicating that the up-regulation of differentially expressed genes in the R might enhanced the resistance. Moreover, combined with the phenotypic observations of sesame leaves inoculated at different time points, we found that 12 hpi was the key time point leading to the resistance difference between the two sesame varieties at the molecular level. The WGCNA identified two modules significantly associated with disease resistance, and screened out 10 key genes that were highly expressed in R but low expressed in S, which belonged to transcription factors (WRKY, AP2/ERF-ERF, and NAC types) and protein kinases (RLK-Pelle_DLSV, RLK-Pelle_SD-2b, and RLK-Pelle_WAK types). These genes could be the key response factors in the response of sesame to infection by Corynespora cassiicola. GO and KEGG enrichment analysis showed that specific modules could be enriched, which manifested as enrichment in biologically important pathways, such as plant signalling hormone transduction, plant-pathogen interaction, carbon metabolism, phenylpropanoid biosynthesis, glutathione metabolism, MAPK and other stress-related pathways. Conclusions: This study provides an important resource of genes contributing to disease resistance and will deepen our understanding of the regulation of disease resistance, paving the way for further molecular breeding of sesame.

Sesame (Sesamum indicum L.) is a very important oilseed crop and cultivated on 11.7 million hectares, producing 6.02 million tons of seeds with an average seed yield of 512 kg ha–1 in the world (Ya...

Introduction: Corynespora leaf spot caused by Corynespora cassiicola is one of the most serious foliar diseases of sesame. Mycoviruses can infect various groups of fungi and have certain potential biocontrol value. However, the number of mycovirus reported in C. cassiicola is relatively scarce. Methods: Seven strains of C. cassiicola isolated from Sesamum indicum were subjected to metatranscriptomic sequencing. Viral diversity was further assessed and validated through RT-PCR, followed by sequence alignment and phylogenetic analysis. Results: A total of 19 viruses were identified across the seven strains, distributed among 12 families. +ssRNA viruses were identified, belonging to Botourmiaviridae (four viruses), Deltaflexiviridae (one virus), Fusariviridae (two viruses), Narnaviridae (two viruses), Ambiguiviridae (two viruses), and Potyviridae (one virus). −ssRNA viruses were assigned Mymonaviridaeto (two viruses), and Mycophioviridae (one virus). dsRNA viruses were found, including Chrysoviridae (one virus), Partitiviridae (one virus), Totiviridae (one virus), and Polymycoviridae (one virus). Discussion: This study uses metatranscriptome technology to expand our understanding of the diversity of mycoviruses in C. cassiicola and provides a rich resource for future studies on mycovirus diversity and taxonomy.