PT - JOURNAL ARTICLE AU - Alexander D. Levin AU - Mark A. Matthews AU - Larry E. Williams TI - Impact of Preveraison Water Deficits on the Yield Components of 15 Winegrape Cultivars AID - 10.5344/ajev.2020.19073 DP - 2020 Mar 13 TA - American Journal of Enology and Viticulture PG - ajev.2020.19073 4099 - http://www.ajevonline.org/content/early/2020/03/05/ajev.2020.19073.short 4100 - http://www.ajevonline.org/content/early/2020/03/05/ajev.2020.19073.full AB - Accurate information regarding crop reproductive development and yield formation in response to water deficits is needed for informed vineyard irrigation management decisions, particularly when water supply is limiting. Fifteen red wine grape cultivars, grown in the San Joaquin Valley of California, were subjected to two regulated deficit irrigation (RDI) treatments for four years to determine yield component responses to water deficits (no applied water) preveraison (ED) and postveraison (LD), and in the fifth year were kept well-watered to determine carryover effects. In the first four years, early water deficits (ED) consistently and significantly reduced yields compared to the control (sustained deficit; SD, applied water at 50% of estimated ETc throughout the growing season) across all years and cultivars, but the late (postveraison) deficit (LD) treatment vines were not different from the control. The reduction in yield with ED was primarily due to a significant reduction in berry fresh weight (FW), and clusters/vine, with little change in berries/cluster. Neither flowers/cluster nor percent berry set were affected by the treatments, though flowers/cluster varied significantly among cultivars. Berries/cluster increased linearly with flowers/cluster until saturation at ~150 berries/cluster as percent berry set declined at ~250 flowers/cluster. In the fifth year, yields of the two RDI treatments recovered somewhat due to increases in berry FW and a small, but significant, increase in clusters/vine. These results show that berry size, due to a reduction in FW, is the most sensitive yield component to water deficits, followed by clusters/vine, and berries/cluster, with sensitivity maximum preveraison and few differences among cultivars.