First Report of Cucumber vein yellowing virus on Cucumber in Lebanon.

Abstract

In a 2-year (2008 to 2009) wide-scale survey of viruses infecting cucurbits, a limited number of greenhouse-grown cucumber (Cucumis sativus) plants showed vein-yellowing symptoms. Greenhouses were infested with whiteflies and infection with Cucumber vein yellowing virus (CVYV) was suspected. CVYV is widely distributed in southern Europe in both open field and protected cucurbit crops (2). Total RNA was extracted from seven plants with vein yellowing symptoms using TRI Reagent (Sigma-Aldrich, St Louis, MO). RT-PCR tests using CVYV-specific primers (CV+/CV-) targeting the coat protein of CVYV (2) gave amplicons of the expected size from seven plants. The sequence of one representative isolate, CVYV-LB3 (GenBank Accession No. JF289167), showed 97, 95.6, and 95.2% pairwise nucleotide identity with isolates from Tunisia (EF538680), Israel (AF233429), and Jordan (JF460793), respectively. In 2012, CVYV like symptoms were not observed in greenhouses in the same areas. In early spring 2013, a total of 16 leaf samples with vein-yellowing symptoms were collected from the northern coastal areas (Jbeil, Amshit, Tabarja) and 11 samples showing only yellowing on older leaves from the southern coast (Jiyeh). CVYV was detected in all samples from the northern coast and in four samples from the southern coast. Four isolates from the North and two from the South were sequenced (KC990497 to KC990502) and showed high sequence variation. The pairwise nucleotide and amino acid identities between these isolates ranged from 95.1 to 100% and 98.5 to 100%, respectively. Pairwise nucleotide and amino acid identities of the isolates with CVYV-LB3 showed variable homology between 93.7 to 98.2% and 94.6 to 96.6%, respectively. The inter-population structure of CVYV in Lebanon showed high variability as compared to the homogenous Spanish population (4). For transmission tests, non-viruliferous whiteflies (Bemisia tabaci) were exposed for an 18-h acquisition access period on vein-yellowed leaves followed by a 24-h inoculation access period to healthy cucumber plants (5-leaf stage). In addition, leaves with vein-yellowing symptoms were ground in 0.1 M phosphate buffer (pH 7.0) and sap-inoculated on carborundum-dusted cucumber (cv. Delta) and squash (Cucurbita pepo cv. FarajF1) plants. Vein yellowing symptoms developed 9 to 11 days post-inoculation on all whitefly inoculated plants, while symptoms were delayed till 3 weeks post inoculation on seven out of eight sap-inoculated plants. All symptomatic plants were positive for CVYV by RT-PCR. Furthermore, surveyed plants were also tested for Cucurbit chlorotic yellows virus (CCYV) and Cucurbit yellow stunting disorder virus (CYSDV), two criniviruses reported previously in Lebanon, by RT-PCR (1). Double or triple infection of CCYV and CYSDV occurred in 18 out of 20 of the CVYV-infected plants. During the past 5 years, a limited number of cucumber plants showed CVYV symptoms. This indicates that CVYV occurrence is sporadic. However, its occurrence in mixed infection with criniviruses may have damaging economic implications to cucurbit production (3). To our knowledge, this is the first report of CVYV on cucurbits in Lebanon and its occurrence in co-infection with CCYV.