A proline-rich biostimulant enhances grapevine (Vitis vinifera L.) water tolerance to reduced irrigation volumes

In organic viticulture, tools that prevent climate change-induced losses are urgently needed. Summer stresses diminish photosynthetic gains and lead to reduced biomass accumulation and crop formation. This study seeks to assess the use of an organic biostimulant consisting of proline-rich yeast derivatives (SYD) on pot-grown grapevines cv. Chardonnay as a priming strategy to enhance vine water status. Well-watered vines (WW-C) were compared to those vines with reduced irrigation at 80% of daily evapotranspiration for 43 days, with (WS1-T) and without (WS1-C) foliar SYD applications. Additionally, a group of vines received only 40% of daily evapotranspiration along with foliar SYD applications (WS2-T). The soil moisture content clearly mirrored the three irrigation levels (WW, WS1, and WS2). However, WS1-T vines maintained a higher midday leaf water potential than WS1-C. WS1-T and WW-C vines exhibited similar stomatal conductance and assimilation rates, while WS1-C showed lower stomatal conductance than WS1-T. On DOY 201, WS1-T leaves accumulated nearly twice the proline concentration compared to WS1-C. Meanwhile, WS2-T had stomatal conductance and leaf assimilation rates comparable to WS1-C vines. At harvest, the yield of WS1-T vines was similar to WW-C (1.75 vs. 1.82 kg), but grapes showed higher soluble solids concentrations and lower average titratable acidity while no differences were observed between WS1-C and WS2-T vines in terms of titratable acidity. The application of proline rich SYD therefore improved the grapevine physiological and productive performance, effectively compensating for modulations in irrigation and represents a powerful tool for the adaptation of organic vineyard to climate change pressures.