Physiological responses of crimson seedless (Vitis vinifera) grapevines to altered micro climatic conditions and different water treatments in the Breede River Valley of South Africa

Abstract

Context and purpose of the study – Challenging conditions created by limited water supply and changes in the climate require an understanding of the physiological status of table grapes along the whole value chain. This is critical to develop tools for regulatory management of growth balances and grape quality. This study aimed to determine the impact of different amounts of water and an altered micro-climate (complete covering of vineyards with plastic) on the physiological reaction of the grapevine during the growth season.

Material and Methods – Two trials, an open field (OF) trial and a trial underneath overhead plastic covering (OPC), were conducted in a Crimson Seedless / Ramsey vineyard in the Breede River Valley of South Africa. The plastic covering to alter micro climatic conditions was installed after budbreak. The sides of the vineyard remained open. Vines were trained onto a Pergola trellis system, micro-irrigated (32 L/h) and spaced 1.75 m x 3.0 m on a stony loam-sand soil. The trial layout design was a randomised complete block with water regime as main factor and grape ripeness level as split strip-plot factor. Four water treatments were applied from after budbreak until the end of harvest. The treatments included a control treatment (100% water application, calculated using evapotranspiration and crop factor), and respectively 80%, 70%, and 55% less than the control. The water treatments were replicated six times under OF conditions and four times under OPC conditions. Grapes were harvested at three dates. Physiological variables (photosynthetic activity, transpiration rate, stem water potential, and light intensity) were measured from berry set until the end of the harvest period (three harvest dates). Micro climatic variables were measured continuously in the vineyard.

Results – For OF and OPC, stem water potential (SWP), and the photosynthetic and transpiration rates were decreased by 55% and 70% water compared to 100% water application. For all treatments, the light intensity underneath the OPC was decreased compared to the light conditions in OF conditions. For OF and OPC, light intensity tended to increase when only 70% and 55% water was applied. Relative humidity was increased by OPC and fell well within the optimal relative humidity range of 60 – 70% for photosynthesis.