Grapevine yellows in Southern Italy (Apulia)
As serious outbreaks of grapevine yellows ressembling those of flavescence dorée (EPPO A2 quarantine pest) were observed in Southern Italy (Apulia), investigations on the etiology and epidemiology of the diseases were carried out by field surveys, transmission trials and electron microscopy. It was found that yellows infection occurred throughout the most important grape-growing areas of Apulia (excepted the northern part of the region), especially on native cultivars but not on cv. Chardonnay which is increasingly cultivated. It was noted that symptomatic vines were very often situated on the edges of the vineyards and bait plants placed near symptomatic vines became infected, both suggesting that the diseases are spread by vectors. Several potential insect vectors of MLOs were captured in diseased vineyards, but Scaphoideus titanus (vector of grapevine flavescence dorée MLO) was never found. During transmission experiments with dodder, it was possible to transmit MLO-like bodies from infected vines to periwinkle. In electron microscopy, MLOs were observed in the phloem of artificially infected periwinkles, in naturally infected weeds and in one infected grapevine. The authors concluded that these grapevine yellows observed in Apulia should be classified as a Mediterranean yellows and not as flavescence dorée MLO, because of the absence of Scaphoideus titanus and the edge distribution of the infected plants, suggesting that the inoculum source came from outside the vineyard. In addition, it has previously been demonstrated (RS 93/178) that MLOs found on Apulian vines belong to the aster yellows and not to the elm yellows group (which include grapevine flavescence dorée MLO).
Sources
Di Terlizzi, B.; Castellano, M.A.; Alma, A.; Savino, V. (1994) Present status of grapevine yellows in Apulia.
Phytopathologia mediterranea, 33 (2), 125-131.