Tolerance to CMV, WMV and ZYMV based on zucchini variety trials in Flanders

One of the major threats for zucchini production in temperate and tropical regions are caused by Cucumber mosaic virus (CMV, Cucumovirus), Zucchini yellow mosaic virus (ZYMV, Potyvirus), Watermelon mosaic virus (WMV, Potyvirus) and Papaya ringspot virus (PRSV, Potyvirus). The symptoms caused by these viruses include mosaic, mottling, chlorosis and leaf distortion on the plant and serious malformations and discoloration of the fruits. This results in a decreased production and unmarketable fruits. Due to the non‐persistent transmission by aphids and the mechanical transmission during cultivation of these viruses, one of the most successful control strategies would be the cultivation of tolerant varieties. To investigate virus tolerance of the cultivars that are regularly grown in Flanders, variety trials were organized during the 2013 growth season. Eight varieties were
mechanically inoculated at the five to eight true leafs stage with local isolates of CMV, WMV or ZYMV.
Symptom development on leafs and fruits were followed up during cultivation. The trial was treated with insecticides to avoid spread of the viruses by aphids, and knifes were sterilized to avoid spread during harvest. The results show a clear difference in tolerance between the varieties in both development of leaf‐ and fruit symptoms. Tolerance was not virus‐specific. The experiment also showed the different symptoms caused by CMV compared to WMV and ZYMV. These results show that selection for tolerant varieties can be one of the major strategies to control losses caused by these viruses. Despite the strict measures taken to avoid spread of the viruses, WMV and ZYMV were able to spread throughout the field by the end of the trial. This shows the importance of very strict hygiene measures during cultivation and the immediate removal of infected plants. In future experiments, the survival and disinfection of material will be evaluated to address this issue.