Preferential transmission of two criniviruses by whitefly influences their seasonal prevalence in melon

Cucurbit chlorotic yellows virus (CCYV) and cucurbit yellow stunting disorder virus (CYSDV), two closely related viruses (Crinivirus; Closteroviridae) transmitted semi-persistently by whitefly (Bemisia tabaci), are significant production constraints in cucurbit growing regions of California and Arizona. Our recent study demonstrated altered seasonal prevalence of CCYV and CYSDV between spring and fall melon (Cucumis melo) growing seasons. To understand this, melon plants (cv Topmark) were singly inoculated with either CCYV or CYSDV, or simultaneously co-inoculated with both CCYV and CYSDV using 50 viruliferous whiteflies per each virus in clip cages. Samples from systemically infected leaves were taken from multiple positions along the vine every 3 days and assayed with single-step multiplex RT-qPCR to measure titer. Results indicated preferential transmission and establishment does not appear to be strongly correlated with virus accumulation in melon plant, but rather timing of infection exerts a much greater influence on which virus becomes dominant inoculated plants. Results suggest differences in seasonal prevalence of CYSDV and CCYV is partially dependent upon sequence of introduction and alternate hosts may greatly influence which virus is most prevalent during a production season. Understanding prevalence is critical to determining virus management.