Differential responses of grapevine cv. Malbec and Merlot reproductive performance to shoot girdling and tipping at flowering

CARRILLO N.; BERLI F.; MILLS L.; KELLER M.

Cádiz

Conferencia; XLIV World Congress of Vine and Wine, XXI General Assembly of the OIV; 2023

OIV

The sink organs of Vitis vinifera, shoot tips, young leaves, inflorescences, clusters, trunk and roots, are in permanent competition for the supply of carbohydrates from the adult leaves. Their relative strength changes during the different phenological stages of the plant and is sensitive to different factors. The final productivity of the vine is determined by the number of clusters and their weight, which in turn is composed by the number of berries and their size. Some varieties, such as Malbec and Merlot, are susceptible to shatter, which is characterized by a low percentage of fruit set and the abscission of flowers and fruits, resulting in loose clusters with few berries. Carbohydrate (CH) availability for inflorescences and clusters plays an essential role among the factors determining fruit set efficiency and yield. This research attempted to modify the flow of carbohydrates between the sink organs by the technique of shoot girdling and shoot tipping. The trial was conducted at IAREC-WSU experimental field during the 2018 season. The plants evaluated correspond to Malbecand Merlot varieties and are trained in a bilateral cordon with drip irrigation. Different strategies to modify the plant´s source to sink ratio were evaluated in order to assess their impact on yield. The treatments applied were as follows: Control, Girdling the base of shoots, Girdling above the clusters, Double girdling and Shoot tipping. The treatments were applied just before flowering on 5 randomly selected shoots on each plant. The number of flowers per inflorescence, the percentage of fruit set,the percentage of aborted ovaries, the number of berries per cluster, cluster and berry weight, vegetative growth prior to veraison and variables related to leaf gas exchange were measured. The results obtained show that there is a strong varietal character in the behavior of the sink organs. Malbec showed marked responses to girdling and tipping treatments, while Merlot showed less plasticity. Girdling at the base of the shoots increased the percentage of fruit set and reduced thepercentage of aborted ovaries in Malbec with respect to the control. While in Merlot, no differences were observed for these variables. When analyzing the gas exchange of the leaves located below and above the girdles, it was observed that in Malbec, leaf 4 of shoots girdled at the base significantly increased net photosynthesis, stomatal conductance and transpiration withrespect to the control. While leaves 4 and 8 of shoots girdled above the clusters strongly decreased photosynthesis, stomatal conductance and transpiration. In Merlot, some differences were observed between leaves from shoots girdled at the base and those from shoots girdled above the clusters, but none with respect to the control. The girdling treatments did not cause differences in shoot growth and leaf area of leaves below and above the clusters in Malbec. In Merlot, the number of leaves per shoot decreased compared to the control when girdled at the base and at the top, but the final shoot length did not change. The trial showed that there is a strong varietal character in the determination of yield. The sink organs of Malbec and Merlot show different relative strengths to attract carbohydrates, mainly the inflorescences and possibly also the roots and trunk.