Molecular characterization of a newly introduced whitefly-transmitted crinivirus and assessment of its synergistic interaction with other viruses in cucumber -

Abstract

Whitefly-transmitted viruses pose a real threat to worldwide vegetable production. In the past decade, a number of viruses have emerged due to an unprecedented high whitefly population. Two important whitefly-transmitted virus genera infect cucurbits, the Begomovirus, single-stranded (ss) DNA viruses and the Crinivirus, positive ssRNA viruses. Several emerging viruses such as the begomovirus, Squash leaf curl virus (SLCV)) and the crinivirus, Cucurbit yellow stunting disorder virus (CYSDV) are already present in Lebanon. Cucurbit chlorotic yellows virus (CCYV), a newly-introduced virus was detected and characterized in this study. CCYV incidence varied from about 20 to 80percent in protected cucumber. A high rate of CCYV and CYSDV co-infections occurred. The genetic variability of CCYV was examined based on sequences of four genes. A very low genetic variability was observed with highly homogeneous inter-populations. Phylogenetic analyses placed CCYV in the CYSDV cluster within the genus Crinivirus. Moreover, Cucumber vein yellowing virus (CVYV), a whitefly-transmitted Ipomovirus was reported at a very low incidence. CVYV showed a high inter-population genetic variability. A multiplex reverse-transcription polymerase chain reaction (RT-PCR) and TaqMan®-based quantitative real-time (qRT-PCR) assays were designed for differentiation between CCYV and CYSDV. The assays were highly specific and 100 times more sensitive than RT-PCR. The qPCR assay developed for SLCV showed a higher sensitivity compared to PCR. SLCV concentration was higher in the stems and roots as compared to the leaves. Field experiments of mixed virus infections were conducted to assess the losses induced by single, double and triple infections of CCYV, CYSDV and SLCV. Single infection by CYSDV induced significant yield and height reduction, while SLCV infection did not lead to any height or yield reduction. Co-infection by two viruses, CCYV, CYSDV or SLCV did not lead to synergistic interaction. However, triple infected plants with CCYV, CYSDV