Atypical symptoms of grapevine leafroll disease, caused by grapevine leafroll-associated viruses (GLRaVs), were observed on leaves of grapevine cultivar ‘Merlot’, grown in a vineyard in Goriška Brda. On the 28.8.2017, the leaves from seven vines were sampled, five of which exhibited atypical symptoms of GLRaV, one with typical symptoms of GLRaV-3 and one had no visual signs of disease (control or K). Ten leaves per treatment were cut off from leaf veins (Ž) and leaf surface (L) and labelled as: GLRaV-2_Ž, GLRaV-2_L, GLRaV-3_Ž, GLRaV-3_L, K_Ž and K_L. In vines with atypical symptoms (red discoloration of veins and red blotches on leaf surface) GLRaV-2 was identified. Obtained results lead to conclusion that the virus has an impact on the content of phenolic compounds in leaf veins and surface, since the highest content of total analysed phenolics at GLRaV-2 was 3832 mg/100 g in L and 2534 mg/100 g in Ž. Significant differences in the content of total analysed phenolics were between GLRaV-2 and GLRaV-3 in Ž (2534 mg/100 g and 1374 mg/100 g, respectively). In L of GLRaV-2 (3832 mg/100 g) significantly higher content of total and individual phenolic compounds were determined than in Ž (2534 mg/100 g). Among individual phenolics, the highest measured content belonged to derivatives of quercetin, and at GLRaV-2, their contents were 1040 mg/100 g in Ž and 1590 mg/100 g in L. The highest content of anthocyanins was measured in Ž at GLRaV-2 (22.9 mg/100 g), while the highest content at GLRaV-3 belonged to L (110 mg/100 g). The results confirm that phenolic compounds in different parts of the leaves react differently to infection, which causes grapevine leafroll disease.
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