Field and agroinoculation screening of national collection of urd bean (Vigna mungo) germplasm accessions for new sources of mung bean yellow mosaic virus (MYMV) resistance.

Yellow mosaic disease (YMD) is a major problem in Urd bean (Vigna mungo L.) in India, which causes huge yield losses. Breeding for wide spectrum and durable Mungbean yellow mosaic virus (MYMV) resistance and cultivating resistant cultivars is the most appropriate and effective approach. However, the task has become challenging with the report of at least two species of the virus, viz., Mungbean yellow mosaic virus (MYMV) and Mungbean yellow mosaic India virus (MYMIV) and their recombinants; the existence of various isolates of these species with varied virulence and rapid mutations noted in the virus as well as in the whitefly vector population. Thus the present study was carried out to identify and characterize novel and diverse sources of YMV resistance and develop linked molecular markers for breeding durable and broadspectrum resistant urdbean cultivars against YMV. Towards this goal, we have screened 998 accessions of urdbean national collection of germplasm against YMD Hyderabad isolate both in a field under the natural level of disease incidence and through agro inoculation in the laboratory using viruliferous clones of the same isolate. Ten highly resistant accessions identified through repeated testing have been characterized in terms of reported linked markers. We attempted to see diversity among the ten resistant accessions reported here using earlier reported resistance-linked SCAR marker YMV1 and SSR CEDG180 marker. SCAR marker YMV1 did not amplify with any of the 10 accessions. But with CEDG180, results suggested that 10 accessions shortlisted through field and laboratory tests do not carry PU31 allele and this shows that it may be likely to carry novel gene(s). Further studies are needed to genetically characterize these new sources.

Draft genome sequence of 'Candidatus Phytoplasma australasia', strain SS02 associated with sesame phyllody disease.

'Candidatus Phytoplasma' is an uncultivated, intracellular bacterial plant pathogen transmitted by phloem-feeding insect vectors. Among the group of phytoplasmas, the Peanut Witches' Broom or 16SrII group of phytoplasmas associated with various diseases cause severe crop losses every year in India. The 'Ca. Phytoplasma sp.' strain SS02 was associated with phyllody disease of sesame plants collected from New Delhi. The genome sequence of strain SS02 was obtained using its genomic DNA enrichment and hybrid assembly of sequences generated on Illumina and Oxford Nanopore Technologies MinION platforms. The hybrid assembly strategy generated a draft genome with 60 contigs totaling 553,228 bp of length with more than 400 × depth coverage and 95.21% of the estimated completeness. The SS02 genome draft sequence contains 465 protein-coding genes, 17 tRNA genes, and 3 rRNA genes. The availability of this draft genome also provided a foundation for genome-scale genotypic analyses.