Limiting carbohydrates to trunk and roots improves bud fruitfulness, fruit set and yield in cv. Malbec

Abstract

Many commercial vineyards of Malbec, the most cultivated grapevine in Argentina, show unstable yield because of variations in bud fruitfulness and the occurrence of “shatter”, characterised by poor fruit set and fruitlet abscission. Shatter can be due to plant material, growing conditions and meteorological events. Among the parameters that determine fruit set efficiency and vine yield, the availability of carbohydrates (CH) plays an essential role. We previously showed that controlling CH partitioning by removing part of the phloem tissue through an annular incision at the base of the fruit shoots (shoot girdling) reduced shatter in Malbec. The objective of this research was to evaluate the partitioning of CH for the different sink organs of the aerial part of the plant when an interruption of phloem flux from leaves to storage organs is imposed by a girdle. Shoot and trunk girdling trials were conducted during the 2018 and 2019 growing seasons, respectively. At flowering, girdling was performed on different plant lots either at the base of the shoot (Base G), above the distal cluster of the shoot (Top G), to the trunk (Trunk G) or no girdling (Control). Most of the yield components were increased by Base G and Trunk G with no significant impact on vegetative growth or fruit quality. Total shoot biomass was not affected in Base G, while a 39 % reduction was observed in Top G, as compared to Control. The partitioning pattern within the shoot was modified by shoot girdling, and Base G favoured the accumulation of CH towards clusters at the expense of lateral shoots. Shoot girdling increased node diameter, bud fruitfulness and inflorescence dry weight of the shoot. Trunk-girdled vines showed an increase in fruit set and total yield at harvest, with no significant impact on vegetative growth. The restriction of CH flow to the trunk and roots by Base G and Trunk G at flowering increased yield components at harvest without affecting vegetative growth or grape quality. These results reinforce our hypothesis that the root system of the vines under study constitutes a strong sink during the flowering period that competes for CH.