The Flavescence dorèe disease of grapevine (FD), first recorded in Italy in 1973, became of serious economic importance since the Eighties of the past century by spreading epidemically from the eastern to the western area of the Po Valley. Its outbreak was attributed to the appearance and rapid diffusion of new, more aggressive isolates of the phytoplasma agent such as those named FD-C and –D respectively. Measures to control the disease established with a Decree of the Italian Ministry of Agriculture (May 31st, 2000) consisted on eradicating the infected plants and spraying insecticides against its leafhopper vector, Scaphoideus titanus. In a few years, these yielded satisfactory results in the eastern (Friuli, Veneto) but not in the western area of north Italy, particularly in Piedmont. This is presently the region most severely affected by FD in the provinces of Asti and of Cuneo ( more locally) both of which are of outstanding importance for the production of world-wide appreciated red vines, e.g. Barolo, Barbera, Barbaresco. The failure to contain the FD spread in Piedmont so far is due to the fact that the practice of viticulture in this region is decreased drastically in the last few decades causing many vineyards to be abandoned and thus become ideal sites for the multiplication and spreading of both the disease and its insect vector.
Searching for alternative control means, attention has now been turned to genetic resistance and induced resistance. In the former case, work to detect resistance or tolerance genes is in progress in several Institutions and early results are being achieved. In the latter case, a peculiar procedure based on both field and laboratory work has been followed. Basically, non symptomatic vine plants were selected in heavily FD-affected vineyards, their root symbionts were identified and isolated in pure cultures. They were then tested experimentally for their capability to inhibit MLOs multiplication, either individually or in combination of two or more. The species/combinations of interest were then multiplied in the laboratory and used to produce biological fertilizers to be distributed to grapevine roots.
To allow the traditional viticulture to survive in north Italy it is really important that vine plants resistant to FD can be obtained. However, if this is the case and resistant cultivar become available, before growing them in the field it will be strictly necessary to reduce drastically the pool of infection represented by the abandoned, ‘wild’ vineyards, source of the pathogen and its vector. This will reduce the ‘natural infection pressure’ of FD which occurs now in great part of Piedmont. It may typically induce the selection of new, more virulent isolates of the pathogen which could overcome resistance and destroy in a short time all the work done.
Maurizio Conti - email@example.com