Assessment of drought stress sensitivity of kiwifruit rootstocks and grafting combinations through integrated physiological and phenotyping analysis

Kiwifruit has a high-water requirement and is sensitive to reduced water availability. Many kiwifruit growing areas are expected to face increasing water scarcity due to climate change. Although the effects of drought stress on kiwifruit have been widely studied, the sensitivity of different genotypes to drought remains poorly described. The present study evaluated the physiological and phenotypic drought responses of three kiwifruit rootstocks (‘Bounty71’, Actinidia macrosperma; ‘D1’ and ‘Hayward’, Actinidia chinensis var. deliciosa) and scion/rootstock combinations, in which a yellow-fleshed cultivar (‘Zesy002’, A. chinensis var. chinensis) was grafted on each rootstock. A pot experiment was conducted using non-destructive RGB imaging combined with leaf gas exchange measurements. Potted vines were subjected to continuous well-watered conditions or to a mild drought stress cycle, imposed by progressively reducing pot water availability (up to 65% field capacity), followed by five days of full re-watering. Based on physiological measurements, Hayward and D1 rootstocks were more affected by drought than Bounty71. Drought-induced physiological (reduced stomatal conductance and photosynthetic rate, increased intrinsic water use efficiency, and decreased instantaneous carboxylation efficiency) and phenotypic (changes in projected shoot area and leaf color) responses differed among genotypes, with Hayward identified as the most drought-sensitive. However, the complete recovery of both physiological and phenotypic parameters suggests the ability of all combinations to cope with short-term and mild drought. The results support the use of phenotypic tools combined with leaf gas exchange measurements for a comprehensive screening of drought sensitivity in kiwifruit genotypes.