Epidemics of aphid-transmitted viruses in melon crops in Spain

A survey of mosaic diseases in fields of open air grown melon was done in three provinces of Spain over 3 years. The incidence of the mosaic-inducing viruses Cucumber mosaic virus (CMV), Watermelon mosaic virus-2 (WMV-2), Papaya ringspot virus watermelon strain (PRSV-W) and Zucchini yellow mosaic virus (ZYMV) was assessed. The only viruses present in the three provinces during the 3 years studied were CMV and WMV-2, but their incidence differed according to year and region. For each epidemic, disease progress curves (DPC) were obtained, all of them well described by the Gompertz model. With the five descriptive variables of the model, a principal component analysis was done and two principal components, representing a severity factor and a time factor were found. Cluster analyses done with these two principal components, grouped the epidemics into 6 clusters that did not correlate with year, virus or province. Correlation analyses between epidemics caused by WMV-2 and CMV and climatic variables were done. Although the temperature in the spring months was the main factor associated with the severity of the epidemics caused by these two viruses, other differential correlations were found. Spatial evolution of CMV and WMV-2 epidemics was also different suggesting different aphid species acting as vectors for the viruses.