Impact of Vat resistance in melon on viral epidemics and genetic structure of virus populations

Abstract

Cultivar choice is at the heart of cropping systems and resistant cultivars should be at the heart of disease management strategies whenever available. They are the easiest, most efficient and environmentally friendly way of combating viral diseases at the farm level. Among the melon genetic resources, Vat is a unique gene conferring resistance to both the melon aphid Aphis gossypii and the viruses it carries. The ‘virus side’ of this pleiotropic phenotype is seldom regarded as an asset for virus control. Indeed, the effect of Vat on virus epidemics in the field is expected to vary according to the composition of aphid populations in the environment and long-term studies are needed to draw a correct trend. Therefore, the first objective of the study was to re-evaluate the potential of Vat to reduce viral diseases in melon crops. The second objective was to investigate the potential of Vat to exert a selection pressure on virus populations. We monitored the epidemics of Cucurbit aphid-borne yellows virus (CABYV), Cucumber mosaic virus (CMV), Watermelon mosaic virus (WMV) and Zucchini yellow mosaic virus (ZYMV) in two melon lines having a common genetic background, a resistant line (R) and a susceptible line (S), in eight field trials conducted in southeastern France between 2011 and 2015. Vat had limited impact if any on WMV epidemics probably because A. gossypii is not the main vector of WMV in the field, but a favorable impact on CMV, yet of variable intensity probably related to the importance of A. gossypii in the total aphid population. Vat had a significant impact on CABYV epidemics with mean incidence reduction exceeding 50% in some trials. There was no effect of Vat on the structure of virus populations, both for the non-persistent WMV transmitted by numerous aphid species and for the persistent CABYV transmitted predominantly by A. gossypii.