Cordon height and deficit irrigation practices interact to affect yield and fruit quality of Cabernet Sauvignon and petite Sirah grown in a hot climate

Abstract

Context and purpose of this study – Cabernet Sauvignon and Petite Sirah are the top red wine cultivars in CA, however, the hot climate in Fresno is not ideal for red Vitis Vinifera, particularly for berry color development. Mechanical pruning and irrigation were studied previously to significantly affect grapevine yield performance and berry quality. But there is lack of studies on cordon height and irrigation on mechanical pruned vineyard system. Recently, mechanical pruning started to gain growers’ interests in CA due to the vineyard labor shortage. Our study aims to identify the interactive effect of cordon height and irrigation on two wine cultivars’ yield performance and fruit quality and find the ideal cordon height and irrigation to maximize the berry color while maintaining the sustainable yield level.

Materials and Methods – A two-way (2×2) factorial split block design, replicated in three times, was implemented in Fresno for two seasons of 2021 and 2022, and the same experimental design was applied for both Cabernet Sauvignon and Petite Sirah. Six years’ old field grown vines were trained in bilateral cordon and spur pruned system with no catch wire. Two cordon heights were 1.3 m and 1.7 m above the vineyard floor. Two irrigation treatments were regulated deficit irrigation (RDI) and sustained deficit irrigation (SDI). RDI was maintained at 60% ETc from berry set to veraison and 80% ETc from veraison to harvest and SDI was maintained at 80% ETc from berry set to harvest. Five adjacent vines were used as an experimental unit and a total of 120 vines were included for this experiment. Vines were hand pruned in the first three years and box pruned with 10 cm spur height in the following three years. Temperature dataloggers were located at the fruit-zone and fruit-zone PAR were measured monthly. Vine water status and leaf gas exchange were measured in the season and yield performance and berry primary and secondary metabolites were measured at harvest.

Results – RDI reduced Cabernet Sauvignon berry weight and Petite Shira cluster weight compared to SDI as a summary across two years. But neither cordon heights nor irrigation treatments significantly affected the yield. High cordon increased leaf area per vine by 24% for Cabernet Sauvignon but not for Petite Shira, whereas high cordon increased leaf area to fruit ratio for Petite Shira but not for Cabernet Sauvignon. High cordon might offer benefits on cooler fruit-zone, higher Brix and berry anthocyanins compared to low cordon in the hot climate.