Identification and characterization of cowpea aphid-borne mosaic virus isolates in Saudi Arabia

Cowpea (Vigna unguiculata subsp. unguiculata) plants showing mosaic, and other virus–like symptoms, were noticed in May 2009 in a field located in the Alahsa Governorate, (eastern Saudi Arabia). Systemic infections were observed on mechanically inoculated V. unguiculata subsp. unguiculata, V. unguiculata subsp. sesquipedalis, and Nicotiana benthamiana plants while local infections developed on inoculated leaves of Chenopodium quinoa, C. amaranticolor, and N. occidentalis. Latent infections were detected in inoculated Ocimum basilicum and Cajanus cajan. DAS-ELISA from the above plants gave positive reactions with Cowpea aphid-borne mosaic virus (CABMV) antibodies. The virus was transmitted by Aphis craccivora Koch. in a non-persistent manner and by infected cowpea seeds at a rate of ca. 5%. Electron microscopic examination of leaf-dip preparations from symptomatic cowpea leaves revealed flexuous particles, 750x12 nm. The virus was also identified molecularly by dot-blot hybridization and RT-PCR assays. The coat protein gene of each of the Saudi virus isolates was partially sequenced and compared with those of 18 CABMV strains from different countries. Phylogenetic analysis indicated that the Saudi virus isolates are virtually identical and had the highest nucleotide sequence identity (93.5%) with two CABMV strains from Morocco and one strain from Nigeria, and the lowest identity with two strains from Zimbabwe and a strain from Brazil. The partial nucleotide sequence of only one of these Saudi isolates was deposited in the GenBank under the accession number JQ638520 to represent all other isolates. This is the first report of the presence of CABMV in Saudi Arabia whose strain is denoted CABMV-SA.