Effect Of Grapevine Leafroll-associated Virus-3 On Grape And Wine Quality Of Vitis Vinifera L.cv Cabernet Gernischet

Grapevine leafroll disease（GLD）is the most widespread and influential virus disease in the global growing region of grape.Grapevine leafroll virus-3（GLRaV-3）is one of the major viruses that could cause GLD.Vines infected with leaf roll disease have rewound,thickened and brittle leaves,and the leaves of red varieties gradually turn red and those of white varieties yellow,resulting in a significant reduction in yield,lower tree vigor,reduced photosynthetic rate,and a significant reduction in sugar content,anthocyanin and phenolic content of berries.Vitis vinifera L.cv Cabernet Gernischet is gradually increasing in cultivation in China,but is also very susceptible to leaf roll disease.No systematic studies have been conducted in China on the effect of leafroll disease on the fruit and wine quality of Cabernet Gernischet.This experiment was conducted to investigate the effects of leaf roll on grape and wine quality,and to solve GLD of Cabernet Gernischet in China.The main results of this experiment are as follows:1.Infection with GLRaV-3 virus significantly affected the leaf photosynthetic characteristics and water use status of vines.Grapevine leaf curl reduced photosynthesis in susceptible leaves.Compared with normal leaves,net photosynthetic rate,transpiration rate,stomatal conductance and maximum photochemical efficiency of PSII（Fv/Fm）decreased in susceptible leaves,and intercellular CO₂concentration increased,and the leaves gradually became redder as the vines grew and developed during the growing season.The petiole water potential was higher in diseased vines compared to normal leaves,while water utilization decreased.2.Infection with GLRaV-3 virus significantly reduced the sugar and phenolic content of the grape and delayed maturation.There was little variation in berry cross and longitudinal diameter and grain weight in susceptible plants,but reducing sugars and soluble solids content,antioxidant activity and titratable acid content were significantly lower in susceptible grapes at commercial harvest.The total amount of anthocyanin in the fruit of susceptible plants at commercial harvest was significantly lower than that of normal fruit,with dimethyllanthin-3-O-glucoside showing the same trend as dimethyllanthin-3-O-（6-O-acetylated）-glucoside,which accounted for a larger proportion.Total flavonols decreased more rapidly during fruit ripening in susceptible plants,and quercetin-3-O-glucoside was highest at the commercial harvesting stage.Grapevine leaf roll disease caused a decrease in the percentage of fruit proanthocyanidin trihydroxy subunits,molecular mass,and%G,but there was interannual variability in the effect on total proanthocyanidin content as well as average polymerization.3.Infection with GLRaV-3 resulted in down-regulation of VvCHS3,VvCHI,VvGST4,VvOMT,and VvUFGT expression and significant up-regulation of VvMYBPA2 expression in fruit at the transient stage,and significant down-regulation of VvCHS3,VvLDOX,VvANR,and VvUFGT genes in grapes at the commercial harvesting stage.4.Infection with GLRaV-3 reduced the phenolic content of the wine,but had a minor effect on the total amount of aromatic substances.The total phenolic content of total phenols,total flavonoids,total tannins,total anthocyanins and total flavan-3-ols was significantly lower in wines made from diseased grapes than in normal wines,and the results of HPLC for anthocyanins,flavonols and proanthocyanidin monomer fractions were similar.The antioxidant activity of the wines from the affected plants was significantly lower than that of the normal wine samples.There was inter-annual variability in the effect of leaf roll disease on the total aroma compounds of Serpentine Dragon Pearl wines,and the content of aroma substances varied significantly between the two wine samples,with ethyl lactate,diethyl succinate and phenylethanol being higher than in the normal wine samples.In conclusion,GLRaV-3 infection of Cabernet Gernischet vines in the eastern foothills of the Helan Mountains had a greater impact on the quality of grapes and wines,especially in reducing the sugar and anthocyanin content of grape,which resulted in lighter color,lower anthocyanin content and sensory quality of wine samples made from diseased plants,but at the same time increased the acid content of riped berries.