GRAPEVINE YELLOWS IN ITALY : PAST, PRESENT AND FUTURE

Following the discovery and description by the middle of the past century in France of an epidemic grapevine disease called Flavescence doree (FD), comparable disorders known with the general name of Grapevine Yellows (GY) were reported from all major grape-growing countries of the world, where they constitute a serious threat to viticulture. In Italy, FD and Bois noir (BN), the two most important diseases of the GY group, have been recorded since the 1970's, both representing a major concern for grapevine growers. FD is caused by phytoplasmas of the 'elm yellows' or 16SrV taxonomic group and is transmitted by the leafhopper Scaphoideus litanus in the persistent-propagative manner. Severe FD epidemics started about two decades ago and are still in progress in the main viticultural districts of northern Italy, i.e. Liguria (Italian Riviera), Lombardy, Piedmont and Veneto. The disease incidence may exceed 50% and the economic losses can be very high. BN is caused by phytoplasmas of the 'Stolbur' or 16S-XIIA group transmitted in the persistent-propagative manner by the planthopper Hyalesthes obsoletus. Other hopper species may also act as vectors since the disease has been observed to spread actively in geographic areas where H. obsoletus does not occur. Currently, the presence of FD seems limited to northern Italy, i.e. the Po Valley and a few regions south to it, like Marche, Tuscany and Umbria (central Italy). Its vector, however, has occasionally been found also in regions further south. BN occurs throughout the country and its incidence, initially believed to be negligible by comparison with that of FD, has recently attained economically important levels in some districts. FD and BN are symptomatologically undistinguishable from one another, molecular diagnosis is therefore necessary for the proper identification of the agent. Since 2000, compulsory control measures against FD are enforced in Italy by a govermental decree. These consist mainly in the elimination of infected vines, the use of healthy material for new plantations, and insecticide sprays against S. titanus. Thanks to these measures, a sharp decrease of FD incidence has been registered in the last few years in all affected areas of the country. Research on GY in Italy is now focusing mostly on epidemiological aspects (e.g. new potential insect vectors), new control practices such as genetic resistance to either FD or BN, or both, use of thermotherapy on propagation material, and investigation of the possible role of symbiotic micro-organisms present in host plants and insect vectors as antagonists of the phytoplasma agents of GY.