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Summary. Grapevine leaf stripe disease (GLSD) is a tracheomycosis caused by Phaeomoniella chlamydospora and Phaeoacremonium minimum. Impacts on yields of grapes were correlated with the incidence and severity of GLSD symptoms on vine canopies. In 2012 and 2013, vines in two vineyards were treated with nine applications of a mixture of leaf fertilizers containing calcium, magnesium and seaweed extracts. At different growth stages, leaves were sampled from treated and control plots of healthy, GLSD-asymptomatic, or GLSD-symptomatic vines and contents were measured of the phytoalexins íraws-resveratrol, ŕraws-e-viniferin, ŕraws-ô-viniferin and iraws-pterostilbene. Grape ripening was also monitored from veraison to harvest during both vintages. The treatments caused significant reductions in canopy symptom expression. Increased phytoalexin contents were measured from 'fruit set' to 'berries developing colour' stages. Traws-resveratrol peak was recorded in asymptomatic diseased vines at the 'berries pea-sized' stage, and ŕraws-e-viniferin and rraws-ð-viniferin increased at the 'berries beginning to touch' stage, compared to the contents recorded in untreated asymptomatic vines. From 'berries developing colour' to harvest, all treated vines had lower amounts of phytoalexins than the control ones. At harvest, treated healthy and symptomatic vines produced berries with similar amounts of total sugars compared to untreated vines. Treated asymptomatic vines produced berries with greater amounts of total sugars compared to the untreated vines. These results indicate that increased phytoalexin content recorded from 'fruit set' to 'berries beginning to touch' in asymptomatic vines treated with the mineral/seaweed mixture may reduce symptoms of GLSD.
Key words: leaf fertilizers, GLSD, leaf symptoms, maturation.
Introduction
Grapevine trunk diseases are considered the most destructive diseases in grape growing areas worldwide. The most important and common trunk disease in European vineyards is grapevine leaf stripe disease (GLSD) of the esca complex (Surko et al., 2008; 2009). GLSD is caused mainly by Phaeomoniella chlamydospora and Phaeoacremonium spp., of which P. minimum is the most frequently isolated. These tracheomycotic fungi colonize the woody tissues inside grapevines, producing black streaking and brown or red-brown necrosis (Marchi et al., 2001; Calzarano and Di Marco, 2007; Surico, 2009). The most common hypothesis for the formation of the characteristic symptoms of the disease is based on phytotoxic substances produced by the pathogens, that are transported through the host vascular tissues into the leaves (Sparapano et ah, 1998; Evidente et...