Responses of five Iranian grapevine cultivars to Partial Root-zone Drying: Implications for water savings and yield

Given the recent water scarcity crisis in Iran and worldwide, the implementation of management practices such as Partial Root-zone Drying (PRD) is essential to optimize water consumption in the agricultural sector. To investigate the effect of PRD on yield, fruit quality, and water use efficiency (WUE), a study was conducted over two consecutive years (2023–2024) on 8-year-old grapevines in a trellis vineyard located in Malayer (Hamedan province, Iran). A randomized complete block design was used with two irrigation regimes (Control; irrigating both sides and PRD; alternately irrigating one side of the vine at each time)×five commercial cultivars (‘Bidaneh Sefid’, ‘Shahani Peykani’, ‘Rasha’, ‘Askari’, and ‘Fakhri’). The results showed that PRD significantly increased leaf abscisic acid concentration (38.1–77.8%) and water use efficiency (40.2–92.1%), and significantly decreased berry length (7.9–12.6%), berry diameter (6.6–11.5%), titratable acidity (6.2–10.4%), berry sugar content (5.6–12%), vegetative growth (11.3–28%), chlorophyll index (6.9–36.9%), leaf relative water content (6.6–8.6%), midday leaf water potential (5.5–6.8%), berry weight (3.8–27%), cluster weight (7.9–21.9%), vine yield (7.3–29.9%) and yield index (3.9–29.8%) compared to the control. PRD irrigation achieved a 50% reduction in water use while the highest yield reduction (in ‘Askari’ cultivar) was 29.9%, demonstrating a substantial water-saving potential with a variable yield cost that was cultivar-specific. Therefore, considering the improvement in WUE (40.2–92.1%), applying deficit irrigation by the PRD method is recommended as a water-saving strategy for vineyards, with cultivar selection being a critical factor for success.