Levels of phytoalexins in leaves of vines affected by GLSD at diffrent degree of severity

The foliar symptom expression in grapevine leaf stripe disease (GLSD) causes quantitative and qualitative yield losses correlated with the severity of the symptoms. A preliminary investigation of symptom formation dynamics assessing the amount of resveratrol in leaves collected at different symptoms severity and phenological growth stages showed a higher presence of trans-resveratrol in symptomatic leaves. The present study extended the investigations to the dynamics of other phytoalexins (including transresveratrol), recorded in leaves of grapevines in two vineyards in the Abruzzo region of central Italy. The levels of substances were observed in leaves collected from symptomatic, asymptomatic and healthy vines. For symptomatic leaves, four categories depending on the extent of symptoms were considered: 1) 5% chlorosis; 2) 20% chlorosis; 3) 40% chlorosis + necrosis, 4) 65% chlorosis + necrosis. The leaves were collected at the "berries beginning to touch," "berries developing color" and "berries ripe for harvest" stages. For each phytoalexin, results showed a pattern similar to what was preliminarily observed for trans-resveratrol, with a progressive increase in phytoalexin levels, increasing associated with the increased severity of leaf symptoms. It was particularly evident at the "berries beginning to touch" and "berries ripe for harvest" stages. A laboratory assay was also performed: petioles of healthy leaves were immersed in culture filtrates of Phaeomoniella chlamydospora (Pch), before and after immersion in different concentrations of trans-resveratrol or pterostilbene, to evaluate possible effcts on the leaf lamina. The addition of trans-resveratrol and pterostilbene did not influence the effect of Pch fitrates. Overall, our results seemed to exclude the involvement of phytoalexins in the alteration in the formation of the leaf lamina that lead to the foliar symptoms