Carbohydrate reserve status of Malbec grapevines after several years of regulated deficit irrigation and crop load regulation

Abstract

Background and Aims Regulated deficit irrigation (RDI) and bunch thinning are two viticultural practices applied worldwide. There is limited knowledge, however, about their combined effects on carbohydrate dynamics and accumulation. We evaluated during year 3 and 4 of the experiment the effect of 4 consecutive years of RDI and bunch thinning on carbohydrate status, vegetative and reproductive variables. Methods and Results From 2006/07 to 2009/10, we imposed four levels of water supply [100, 60, 38 and 25% of reference evapotranspiration (ETo)] and two crop loads (100 and 50% of the bunches). We compared shoot length, flowers per inflorescence and yield in 2009/10. We also measured pruning mass and the concentration of non-structural carbohydrates in dormant wood in the winters of 2009 and 2010. Starch concentration in the trunk was reduced by severe water deficit (25 and 38% ETo) and improved by bunch thinning. Pruning mass, shoot length, flowers per inflorescence and yield were affected in vines with water applied at 25 and 38% of ETo. Conclusions Severe water stress and high crop load reduced trunk starch concentration with no interaction between both factors, whereas the concentration of total non-structural carbohydrate was not affected. Vegetative growth and yield were reduced after 4 years of severe water stress. Significance of the Study We provide evidence that starch concentration and carbon partitioning can be manipulated through common viticultural practices, such as irrigation and crop load.