ZUCCHINI YELLOW MOSAIC-VIRUS

Zucchini yellow mosaic potyvirus (ZYMV), first isolated in Italy in 19 73, described in 1981, and then identified in all continents within a decade, is one of the most economically important viruses of cucurbit crops. It is efficiently aphid-transmitted in a nonpersistent manner a nd it is also seed-home in zucchini squash, which could have contribut ed to its rapid spread worldwide. Biological variability has been obse rved among ZYMV isolates, concerning host range, symptomatology and ap hid transmissibility. More recent studies also revealed a serological and molecular variability. The survival of ZYMV in areas where cucurbi ts are not grown throughout the year remains to be elucidated, because very few natural over-wintering hosts have been identified so far. Pa rtial control of ZYMV can be achieved by limiting transmission of the virus to the crops by aphids, using adapted cultural practices. Cross- protection with a mild strain has been shown to be effective against m ost ZYMV isolates. Resistance genes found in cucurbit germplasms as cu rrently being introduced into cultivars with good agronomical characte ristics. Pathogen-derived resistance strategies using the expression o f ZYMV genes in transgenic plants have also been developed and appear promising. Nevertheless, the high biological variability of ZYMV justi fies a careful evaluation of the deployment of genetic control strateg ies in order to increase their durability.