First Report of Lettuce Mosaic Virus Infecting Pea in Taiwan

Pea (Pisum sativum L.) is the fourth largest leguminous vegetable in cultivated area in Taiwan. In 2016 and 2017, pea plants with unfamiliar symptoms of foliar vein banding and mottling were collected from Miaoli (ML) and Changhua (CH) counties. These symptomatic plants also had shortened internodes and malformed pea pods. Enzyme-linked immunosorbent assay on five plants using antibodies against three viruses (cucumber mosaic virus, peanut mottle virus, and pea seed-borne mosaic virus) known to infect pea in Taiwan proved negative. Inoculation of sap extract from ML and CH samples on Chenopodium quinoa resulted in the development of chlorotic lesions on inoculated and upper leaves after 8 days. Lesions from two isolates were singly screened and reinoculated three times on C. quinoa and subsequently inoculated onto Nicotiana benthamiana and pea cultivar Farmer 162 for propagation. All inoculated pea plants showed symptoms similar to field samples from ML and CH. In a host range test, ML and CH samples caused mosaic symptoms on lettuce. Because potyviruses and tobamoviruses often cause systemic chlorotic lesions in C. quinoa, two sets of degenerate genus-specific primers against potyvirus (Chen et al. 2006) and tobamovirus (Letschert et al. 2002), respectively, were used in reverse transcription PCR (RT-PCR) to test these propagated pea samples. Only the former gave positive results, generating a 1.4-kb amplicon of expected size. Cloning and sequencing studies on two amplicons (GenBank accession nos. MH844631 and MH844632) revealed that their coat protein (CP) genes were highly homologous to the sequences of lettuce mosaic virus (LMV) isolates in the GenBank and showed nucleotide sequence identities from 87.1 to 97.5% to LMV isolates from France (KJ161185) and India (JQ794776), respectively. As for the two isolates from ML and CH, their CP genes shared 97.1 and 97.5% in their nucleotide and amino acid sequence identities, respectively. To assess the incidence of LMV in pea fields, a specific primer pair (LCP-f, 5′-ATCCCCGAAYATAAATGGAACAT-3′; and LCP-r, 5′-TTTAAATGCCWACACACGCCTTTA-3′) was designed and used in RT-PCR for field surveillance. Five original samples and 17 additional pea samples exhibiting similar symptoms from Nantou and Yunlin counties were all confirmed to be positive for LMV, giving an expected 457-bp amplification product. To our knowledge, this is the first report of LMV infecting pea in Taiwan. It is likely that the virus in the field may have come directly from infected pea seeds or from surrounding lettuce, because LMV has been reported previously in Taiwan (Chen et al. 1995). Our study suggests that LMV is a new threat for pea production in Taiwan.