VEGETATIVE COMPATIBILITY AND CONVERSION TO HYPOVIRULENCE AMONG ITALIAN ISOLATES OF CRYPHONECTRIA-PARASITICA

A total of 850 virulent isolates of Cryphonectria parasitica were isol ated from natural cankers on European chestnut trees growing in variou s Italian regions. Vegetative-compatibility (v-c) group membership was tested using the merge-barrage method. In all, 19 vegetative-compatib ility groups were found, and, for each of these, a representative isol ate (v-c tester) was identified; 49% of the Isolates were compatible w ith the tester of only one v-c group, whereas 51% were compatible with the testers of more than one v-c group; 3% of the isolates showed com patibility with seven v-c groups. The coincidence between vegetative i ncompatibility and failure of conversion occurred in only a few cases; 42% of the converts were stable with respect to their morphological c haracteristics ana presence of cytoplasmic ds-RNA. The results obtaine d in Italy suggest that, for an efficient biocontrol programme, it is preferable to evaluate the tendency of a population to be converted ra ther than evaluating the v-c group membership.