The effect of shoot heterogeneity on the physiology and grape composition of Shiraz/Richter 99 grapevines

[摘要] ENGLISH ABSTRACT:The effect of shoot heterogeneity on vegetative and reproductive growth parameters, vinephysiology and grape composition was investigated in a ShirazlRichter 99 vineyard.Comparisons between underdeveloped (typically shorter and less ripened at véraison) andnormally developed shoots in both shaded (non-manipulated) and well-exposed (manipulated)canopies were made. Compared to underdeveloped shoots, normal shoots had a larger total leafarea, due to the higher occurrence of secondary shoots as well as larger leaves on primary andsecondary shoots. Since the photosynthetic activity of the leaves from normal shoots was higherthan those from underdeveloped shoots, higher levels of carbohydrates were produced andstored in the former. Starch was more evenly distributed over the length of the whole shoot innormally developed shoots compared to underdeveloped shoots. Normally developed shootswere longer and thicker in diameter than underdeveloped shoots. The larger clusters of thenormally developed shoots are evidence of their more favourable total leaf area per gram berrymass. Berries from the normally developed shoots were smaller at five weeks after véraison thanthose from underdeveloped shoots, displaying a higher skin to pulp ratio and therefore higheranthocyanin and total phenolic extraction potential for winemaking. The smaller clusters andfewer berries per cluster found for the underdeveloped shoots indicate an imbalance betweenvegetative and reproductive growth initiated during the vegetative growth phase and continuedduring the ripening period.The peculiar absence of statistically significant differences in grape composition betweennormally and underdeveloped shoots indicates that assimilates needed for berry ripening of thelatter originated in organs other than the leaves [e.g. from adjacent normal shoots and the rest ofthe permanent structure of the vine (cordon, trunk, roots)]. The larger differences in berry sizethat occurred between shoot types in the shaded compared to the well-exposed canopies may beevidence for this. The photosynthetic activity of shoots was lower in shaded than in exposedcanopies. The total carbohydrate production of the normal shoots in shaded canopies seemedinsufficient to supply in the ripening needs of the shoot itself, their own clusters as well as theripening of stem tissue and clusters of the underdeveloped shoots in the canopy. This isillustrated by the lower levels of starch that accumulated in the normal shoots from shadedcompared to that of exposed canopies. Vine shoot heterogeneity clearly leads to visible andphysiological imbalances that would impact negatively on grape and wine quality as well asproduction costs and should therefore be avoided on any terroir.

[发布机构] Stellenbosch University