INHIBITION OF THE PATHOGENICITY OF THE GR APEVINE FLAVESCENCE DOREE PHYTOPLASMA BY HOST INSECT AND PLANT-EXTRACTS

We have tested the effect of host plant extracts (Catharanthus roseus, Vicia faba and Vitis vinifera) and host insect extracts (Euscelidius variegatus) on the pathogenicity of the Flavescence doree (FD) phytopl asma. This pathogenicity was assessed by microinjection into healthy l eafhoppers, followed by FD transmission onto healthy V faba. We first present results on phytoplasma extraction. Data from infectious leafho pper extracts suggest that males were a better source of extraction th an females. The extraction of phytoplasma from V faba showed an inhibi tory effect. Then, in order to study the inhibitory effect of plant an d vector extracts on phytoplasma pathogenicity we incorporated healthy extracts of these hosts into a preservation medium. We detected vario us degrees of toxicity according to the amount of extract with both pl ants and insects. In addition, insects showed differences in relation to their stages of development and sex. C roseus, a tropical plant, wa s the least toxic of all healthy host plants. It is interesting to not e that this plant is known to be an experimental host for numerous cas es of yellowing with extractible or non-extractible phytoplasma.