Characterization of bean common mosaic virus isolates infecting three leguminous bean crops from South and Southeast Asia

Bean common mosaic virus (BCMV) is causing economically important diseases in leguminous crops worldwide. In this study, BCMV isolates from country bean (CB; Lablab purpureus), yard-long bean (YLB; Vigna unguiculata), and rajma bean (RB; Phaseolus vulgaris) collected from Bangladesh, Nepal, and Cambodia were characterized. Samples that tested positive for BCMV in serological assays were subjected to high-throughput sequencing to generate near-full-length genome sequences. In pairwise comparisons of the polyprotein open reading frame, 13 BCMV isolates from Bangladesh, Cambodia, and Nepal showed sequence identity of 92.1 to 98.8% at the nucleotide and 94.2 to 99% at the amino acid level among themselves and with corresponding sequences of BCMV reported previously. In phylogenetic analyses using the global BCMV sequences, they segregated into five distinct lineages, with RB isolates from Nepal clustering with US1/NL1-clade of common bean isolates from different countries, YLB isolates aligning with blackeye cowpea strain sequences reported from China, and CB isolates from Nepal and Bangladesh clustering with soybean isolates from China. One YLB isolate from Nepal was identified as a putative recombinant. None of the BCMV sequences aligned with isolates representing the RU1 or PStV clades. In grow-out tests, seed samples from local markets showed a 14.3 to 38.1% transmission efficiency rate of BCMV with CB seed lots and 9.5 to 33.3% with YLB seed lots.