Epidemiology of four Cucurbit viruses affecting zucchini production in Flanders (Belgium)

Cucumber mosaic virus (CMV, Cucumovirus), Zucchini yellow mosaic virus (ZYMV, Potyvirus), Watermelon mosaic virus (WMV, Potyvirus) and Papaya ringspot virus (PRSV, Potyvirus) are an increasing threat for cucurbit cultivation in temperate and tropical regions. They are transmitted in a non-persistent manner by a variety of aphid species and easily infect large areas in a limited time span. The symptoms, including mosaic, mottling, leaf distortion and chlorosis, not only result in a decreased yield but also seriously affect fruit quality. Since zucchini production in Flanders (Belgium) increased 5 to 10 times during the last decade, the economic impact of the damage caused by these viruses gained importance as well. To obtain insights into the epidemiology of the viruses, we performed preliminary virus screenings from 2007 to 2009, followed by a more intensive survey from 2010 to 2012. During this survey a clear shift in virus occurrence was observed between the different culture years. From 2007 to 2012, the importance of ZYMV gradually decreased while CMV became more important and is currently the most prevalent virus in Flanders, followed by WMV, ZYMV and PRSV. The viral shift did not only occur over the years, but also within a single growing season. Additionally, a substantial part of mixed virus infections were observed. Based on the results of this survey, inoculation experiments were set up to study introduction pathways and survival of the viruses and to assess the influence of mixed infections and cultivar choice on symptom development, yield and fruit quality. The results of this thorough epidemiological study of the zucchini viruses, together with a simultaneously performed epidemiological study of the aphid vector will result in a more sustainable control strategy of this emerging problem.