Characterization of novel French bean leaf curl virus and betasatellite associated with leaf curl disease of French bean (Phaseolus vulgaris L.)

Leaves from French bean plants with severe leaf curl (ten samples) and from asymptomatic plants from 10 fields (FB1-10) in the Western Ghat region of Karnataka, India were collected. Virus isolate FB01 from French bean was shown to be transmitted by whitefly Bemisia tabaci cryptic species Asia I. DNA was isolated from the samples (ten field samples and one sample infected with FB01 via whitefly) and subjected to PCR to confirm begomovirus infection using specific primers. All 11 were positive for the expected 1.2-kb amplicon. The sequence analysis of the 1.2-kb amplicon showed that all isolates shared more than 98% nucleotide identity. Further, the complete genome from isolate FB01 was amplified and sequenced and shown to share a maximum nucleotide identity (89.3%) with Ageratum yellow vein Sri Lanka virus. As per the ICTV species threshold for begomoviruses, the virus is considered as a new species, with the proposed name French bean leaf curl virus (FbLCV). The samples were subjected to PCR using specific primers for DNA B, betasatellite and alphasatellite; only betasatellites were amplified. The detected betasatellite shared maximum nucleotide identity (92.6%) with Synedrella yellow vein betasatellite. Recombination analysis indicated that FbLCV and betasatellite were recombinants. The significance of these findings are discussed.