Mechanical fruit zone leaf removal and deficit irrigation practices interact to affect yield and fruit quality of Cabernet Sauvignon grown in a hot climate

Abstract

Context and purpose of this study – Cabernet Sauvignon is the top red wine cultivar in CA, however, the hot climate in Fresno is not ideal for Cabernet Sauvignon, particularly for berry color development. Fruit-zone leaf removal and irrigation were studied previously to have the significant effect on grape yield performance and berry quality. But the timing of leaf removal and the timing of irrigation are still inconclusive. Also, mechanical fruit-zone leaf removal is relatively new in CA. Our study aims to identify the interactive effect of mechanical fruit-zone leaf removal and irrigation on Cabernet Sauvignon’s yield performance and fruit quality and find the ideal timing of leaf removal and irrigation to maximize the berry color while maintaining the sustainable yield level.

Materials and Methods – A two-way (2×3) factorial split block design, replicated in five times, was implemented in Madera for three seasons of 2018 to 2020. Two levels of irrigation were regulated deficit irrigation (RDI) and sustained deficit irrigation (SDI). Irrigation from RDI was maintained at 50% ETc from berry set to veraison and 80% ETc from veraison to harvest and irrigation from SDI was maintained at 80% ETc from berry set to harvest. Three timings of mechanical fruit-zone leaf removal were: 1) bloom, 2) berry set, 3) no leaf removal. Six adjacent vines were used as an experimental unit and a total of 180 vines were included for this experiment. Vine water status, fruit-zone PAR, and leaf gas exchange were collected in the season and yield performance and berry primary and secondary metabolites were measured at harvest.

Results – RDI increased berry anthocyanins by 14% in comparison of SDI and bloom and berry set mechanical fruit-zone leaf removal increased berry anthocyanins by 19% and 13% compared to no leaf removal. However, no interactive effect of leaf removal and irrigation on berry anthocyanins was found in our study. RDI significantly reduced the berry size and led to 15% yield decrease compared to SDI. No yield reduction was caused by either bloom or berry set leaf removal. Both RDI and leaf removal can be applied to improve berry anthocyanins. However, given the significant yield reduction from RDI, leaf removal, particularly at bloom, coupled with SDI should be preferred to increase berry anthocyanins without reducing the yield.