Use of water stress in forcing Kyoho grapevines to produce two crops per year

The use of post-harvest water stress as a management practice in producing two crops of grapes annually was investigated using three-year-old own-rooted Kyoho grapevines. The vines were established under a restricted rooting-zone culture (ca. 30 L/vine). Five weeks after harvesting the first crop, vines were subjected to water stress treatments by completely cutting off irrigation. Control vines received normal watering throughout the year. Though vines in all the treatments produced a second crop, the severe water stress lasting for 16 days was effective in inducing early budbreak, enhancing blooming, and increasing fruitfulness, cluster size, berry set, and berry growth, compared to continuously well-watered vines. The mild water stress of 10 days was less effective. There was an apical dominance tendency in budbreak and a growth potential gradient favoring the upper shoots during the second cycle. Fruits from the two cycles did not differ significantly in their quality. The study shows the potential of water stress as a management practice, especially in increasing the productivity of warm-regions grapevines.