Occurrence of viruses infecting melon in Xinjiang of China and molecular characterization of Watermelon mosaic virus isolates

Cucurbit viruses have been associated with important economic losses in Xinjiang of China. Therefore, a comprehensive survey and sample collection was performed during the 2013 and 2014 growing seasons from the major melon-growing locations in Xinjiang which is the largest area for melon production in China. Samples were analyzed using reverse transcription-polymerase chain reaction (RT-PCR) to detect Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), Cucumber mosaic virus (CMV), Papaya ringspot virus (PRSV), Squash mosaic virus (SqMV), Tomato ringspot virus (ToRSV), Moroccan watermelon mosaic virus (MWMV), Tomato spotted wilt virus (TSWV), Watermelon silver mottle virus (WSMoV), Cucumber green mottle mosaic virus (CGMMV), and Zucchini yellow fleck virus (ZYFV). We collected 492 melon samples with virus-like symptoms. Out of these, 94.5 % of the samples were infected by at least one of these viruses. WMV was the most prevalent virus detected. WMV, CMV, and ZYMV were detected in 77.0 %, 60.0 %, and 41.1 % of infected samples, respectively, and the infection rate of these three viruses changed significantly among melon cultivars. Other viruses analysed were not detected in any sample tested. The number of multiple infections was high (average 57.2 %), with the most common double infection WMV + CMV (17.8 %), closely followed by WMV + ZYMV (14.4 %). Statistical analysis of the potential association among viruses showed that there was a strong association between several viruses for multiple infections. An analysis of WMV genetic diversity suggested that all isolates obtained in this study clustered into group A and that purifying selection was restricting variability in the population.