INTERACTION BETWEEN WATERMELON MOSAIC VIRUS AND POWDERY MILDEW DISEASE ON SQUASH

Abstract

Squash (Cucurbita pepo L.) is subjected to the attack of different viral and fungal diseases. The most important diseases are watermelon mosaic virus and powdery mildew caused by Sphearotheca fuliginea that causes heavy losses in yield.

This work was carried out at the experimental farm and greenhouse at Faculty of Agriculture, Kafr El­ Sheikh, Tanta University to study the interaction between WMV-2 and S. fuliginea on squash plants. 1. WMV-2-infected squash plants were less susceptible to powdery mildew infection than virus­ free plants. The fungus attacked more leaves, stems and petioles on virus free plants grown either under greenhouse or field conditions as compared to virus infected ones. This indicated the existence of antagonism between WMV-2 and S. fuliginea. 2. On virus infected squash plants, the number of mildewed leaves was fewer than those on virus-free ones. These results also, indicated the existence of antagonism. The antagonism was more clear on the young leaves showing clear mosaic symptoms. Such leaves were less susceptible to fungal infection than healthy ones. 3. Extracts obtained from healthy, fungal or combined infection reduced the number of local lesions of WMV-2 and severity of virus symptoms on squash plants. Extracts of mildewed leaves showed stronger effect. 4. The extracts obtained from either single or combined infected leaves had an inhibitory effect