Occurrence and distribution of tospovirus and thrips species infecting tomato crops in Thailand

Tospoviruses are single-stranded RNA viruses that cause severe damage to various economically important crops in Thailand and worldwide. Tospoviruses are transmitted by several species of thrips. In Thailand, four tospovirus species including Capsicum chlorosis virus (CaCV), Melon yellow spot virus (MYSV), Tomato necrotic ringspot virus (TNRV) and Watermelon silver mottle virus (WSMoV) have been identified in tomato, pepper and cucurbit production fields so far. In this study, we conducted a survey to determine the occurrence and distribution of tospoviruses and their thrips vectors collected from tomato fields in several regions of Thailand during December 2011 to April 2015. Tomato plant samples exhibiting tospovirus-like symptoms (n=385) were screened for tospoviruses using a plate-trapped antigen enzyme-linked immunosorbent assay (PTA-ELISA). RT-PCR was performed on ELISA-positive samples (n=121) using primers specific to the nucleocapsid protein (N) genes of CaCV, MYSV, TNRV and WSMoV. N gene sequencing was conducted in some samples for confirmation. Thrips collected from tomato fields were identified to the species level based on morphological characteristics (n=700). Our results showed that TNRV (44.6%) and CaCV (35.5%) were the two major tospoviruses detected in the examined tomato crops, while a low incidence of WSMoV infection (1.7%) was found. Mixed infections of CaCV and TNRV (16.6%), CaCV and MYSV (0.8%), and CaCV, TNRV and WSMoV (0.8%) were also observed. All thrips found in the tomato fields were identified as Ceratothripoides claratris. Thrips transmission assay confirmed that C. claratris was able to transmit CaCV and TNRV with efficiencies of 70 and 12%, respectively.