A legume survey in Story County was conducted to characterize legume viruses present in Iowa and potentially problematic to soybeans. Symptomatic (chlorosis, leaf curl, or vein banding) and non-symptomic leaves were selected from Apios americana, Cyamopsis tetragonolobus, Desmodium spp., Glycine max, Lablab purpureus, Lotus japonicus, Phaseolus coccineus, Phaseolus vulgaris, Vicia faba, Vigna ungulculata, and Chenopodium quinoa (an indicator species), and sent to Agdia Inc. for their Crop Screen: “Bean (Soybean)” tests. Cowpea mosaic virus (in L. purpureus), Southern bean mosaic virus (in A. americana), Soybean dwarf virus (in L. purpureus), and Tobacco streak virus (in Desmodium spp.) were identified. In addition, P. vulgaris was found positive in the serological Potyvirus group test, and was further characterized using reverse transcription (RT)-PCR using total RNA (Qiagen RNeasy extraction kit) from symptomatic leaves. A ~1-kb fragment of virus genome was amplified using degenerate primers, forward: 5′ TGYGTNGAYGAYYTYAAYAA 3′ (3) and reverse: 5′ TCRTARAARTCRAAIGCRTAICKIG 3′ (2). The closest GenBank BLAST hits for the sequence were BCMV strain NL1 (GenBank Accession No. AY112735) and BCMV MS1 (EU761198), both at 97% identity. RNA sequencing using an Illumina HiSeq 2500 (100 base paired ends) allowed construction of a nearly complete viral sequence from positions 38 to 10,037 nt (KM023744). This showed 99% similarity to BCMV-NL1 (AY112735) and 98% similarity to BCMV MS1 (EU761198). The BCMV isolate was recovered on the P. vulgaris cv. Taos Red and tested against a panel of Phaseolus, Glycine, and other hosts. Symptomatic hosts (vein-banding, mosaic, stunting, and leaf curl) were P. vulgaris cvs. Starlight, Tohono O'odham vaya Amarillo, Black Valentine Stringless, Sutter Pink, Hidatsa red, Stringless Green Refugee, Burpees Stringless Improved Bush, Princess d'Artois, Princess Double de Holland, and Dubelle Witte. Asymptomatic hosts included P. vulgaris cvs. Sierra, Great Northern Tara, Tara, and Vigna radiata. Non-host plants were P. vulgaris cvs. Michelite 62, Great Northern UI 31, Great Northern UI 123, Pure Gold Wax, Top Crop, Redlands Greanleaf B, Red Mexican UI 34, Imuna, Monroe, Pinto UI 114, Widusa, Othello, Sacramento, Red Kidney, Provider, Black Turtle Soup, Victor, and Witte boon, G. max cv. Williams, Cucumis sativus cv. Straight 8, Solanum lycopericum cv. Reine des Hatives, Vicia faba, Pisum sativum var. macrocarpon, V. unguiculata, and A. americana. The host range of the BCMV isolate on common bean differential species concurred with pathogenicity group I (1) and agreed with assignment as strain NL1. To our knowledge, this is the first complete characterization of a pathotype I strain NL1 of BCMV in the United States, combining biological typing and whole genome sequencing.
References: (1) R. E. Klein et al. Plant Dis. 76:1263, 1992. (2) H. Yamamoto et al. J. Gen. Plant Pathol. 74:97, 2008. (3) L. Zheng et al. PLoS One 3:e1586, 2008.
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