First Report of Tomato yellow leaf curl virus Infecting Cowpea in China.

Tomato yellow leaf curl virus (TYLCV) is a devastating pathogen of tomato that causes significant yield losses in many tropical and subtropical regions (1). In China, this virus was first found in 2006 on tomato in Shanghai (2). In October 2008, chlorotic yellow leaves of cowpea (Vigna sinensis) were observed in Qingpu, Shanghai, China with 15 to 20% incidence in plants in high tunnels. Large populations of whiteflies were observed in association with the diseased cowpea. The disease agent was transmitted to cowpea (and tomato) by whiteflies, which resulted in chlorotic yellow leaves on cowpea (yellow leaf curl symptoms on tomato) that were identical to those observed in the field. On the basis of the suspected insect vector, symptomology, and severe epidemics of tomato yellow leaf curl disease (TYLCD) in Shanghai in recent years, Tomato yellow leaf curl virus was suspected as the causal agent. Total DNA was extracted from four symptomatic cowpea samples. PCR was performed with specific primers V416 (5'-CAAGGCACAAACAAGCGACG-3') and C1287 (5'-CTCAACTTCCGAATTTGGACGAC-3') to amplify a 872-bp DNA fragment of the viral coat protein (CP) gene and an amplicon of the expected size was obtained in all four samples but not from healthy leaf samples. The PCR products were sequenced and the sequences were identical among samples. Primers TYLCV-F (5'-CAGGAGGCAGCCAAGTATGAG-3') and TYLCV-R (5'-ACTAATGCCTGTTCYTTCATTCC-3') (Y = C or T/U) were designed on the basis of the sequence (Accession No. HM804856) and reported (Accession No. FM163463) CP gene to amplify the full-length viral DNA of cowpea isolate (CN:SH:Cowpea:08). The sequence was determined to be 2,781 nucleotides long (Accession No. GU434143). A comparison of the sequence with those in GenBank shows that the cowpea isolate has the highest nucleotide sequence identity (99%) with TYLCV isolate XH2 from tomato in Xinghua, Jiangsu, China (Accession No. GU111505). To our knowledge, this is the first report of TYLCV infecting cowpea in China and also the first report in the world. References: (1) H. Czosnek and H. Laterrot. Arch. Virol. 142:1391, 1997. (2) J. B. Wu et al. Plant Dis. 90:1359, 2006.