Foliar Application of Ascophyllum nodosum Extract Mitigates High-Temperature Stress in Different Grapevine Genotypes (Vitis spp.)

Abstract

Increasing heat stress, exacerbated by climate change, negatively affects the physiological and vegetative development of grapevines. In this study, the physiological and vegetative responses of four grapevine genotypes (Vitis spp.) to foliar application of seaweed (Ascophyllum nodosum L.) extract were evaluated under prolonged high-temperature conditions (44.0 ± 4.0 °C) in a climate-controlled glasshouse. Stomatal conductance (gs) responded in a genotype- and date-dependent manner. The gs consistently decreased in the 1103 P rootstock at all measurement dates by 5-23%. In contrast, the gs increased in 41 B by 11-13% and in ‘Isabella’ by 16% at specific dates. When the glasshouse temperature reached 48 °C, seaweed treatment led to decrease in leaf temperature in all genotypes by 0.7-2.1 °C. Seaweed application increased the leaf chlorophyll index in all genotypes from the second measurement onwards by 6-24%. Seaweed application also reduced electrolyte leakage (from 42-52% to 30-37%) and enhanced the leaf relative water content (from 49-66% to 71-82%). Improvements were also recorded in leaf area, leaf thickness, leaf fresh and dry weight, shoot length, shoot diameter and pruning residue weight. These results indicate that foliar seaweed application alleviated the adverse effects of prolonged high-temperature stress and elicited genotype-specific responses in Vitis genotypes. As the study was conducted in a glasshouse over a single season without a non-stressed control, recommendations for practical use in viticulture require confirmation in multi-season vineyard trials.