First Report of Capsicum chlorosis orthotospovirus Infecting Zucchini (Cucurbita pepo) in China.

Abstract

Capsicum chlorosis orthotospovirus (CaCV), mostly transmitted by Frankliniella occidentalis (Thripidae, Frankliniella), a tentative species in the genus Orthotospovirus, family Tospoviridae, was first identified in tomato in Australia in 2002 (McMichael et al. 2002). To date, CaCV has been reported to infect peanut (Chen et al. 2007) and tomato (Huang et al. 2010; Yin et al. 2016) in China. During a survey of zucchini (Cucurbita pepo L.) viral diseases in October 2015, about 30% of fruits had chlorosis and rugged symptoms in Shouguang City, Shandong Province, China. The symptomatic fruits of zucchini were collected and tested for virus identification using high-throughput small RNA sequencing. Small unique RNA reads (17 to 28 nt) were assembled into contigs using Velvet 1.0.5 software. BLASTn searches of the resultant contigs in the National Center for Biotechnology Information databases identified about 40 contigs matching four viruses (watermelon mosaic virus, capsicum chlorosis orthotospovirus, watermelon silver mottle virus, and peanut bud necrosis virus) with 86 to 100, 100, 96, and 83% sequence identity, respectively. Among them, one contig nucleotide sequence (50 bp) had 100% identity with the corresponding regions of CaCV M segment genome (KX078566). To confirm this, reverse transcription polymerase chain reaction was conducted with a primer pair CaCV-F (5′-ACTTTCCATCAACCTCTGT-3′) and CaCV-R (5′-GTTATGGCCATATTTCCCT-3′) in eight symptomatic zucchini samples. An expected 812-bp fragment, partial sequence of GN/GC gene on the M RNA, was amplified in one-half of symptomatic zucchini samples and not in a healthy sample. The fragment was purified and sequenced, and the sequence was deposited in GenBank (accession no. MG244190). The nucleotide identity of the amplified fragment was 99% with CaCV-Hainan isolate from Arachnis labrosa (KX078566) and Qld-3432 isolate from pepper in Australia (KM589494), 98% with isolate from Taiwan (KC953854), and 97% with isolate from India (KX499515). The presence of CaCV in the eight symptomatic zucchini samples was verified by using ELISA with CaCV-specific polyclonal antibody (DSMZ, Germany). The infection of pepper (Krishnareddy et al. 2008), tomato (Premachandra et al. 2005), groundnut (Vijayalakshmi et al. 2016), and waxflower (Melzer et al. 2014) with CaCV was previously reported from Australia, Thailand, India, and the United States. No natural infection of zucchini or other cucurbit crops by CaCV has been reported. To our knowledge, this is the first report of CaCV infection of zucchini in China. This study suggests that CaCV may be more widely distributed in China than previously thought.