Effect of Initiation Timing of Drought Stress on Carbohydrate Content and Vegetative Growth in Japanese Apricot (Prunus mume Sieb. et Zucc.) 'Nanko'

The effects of initiation timing of drought stress on the carbohydrate content and growth of Japanese apricot (Prunus mume Sieb. et Zucc.) 'Nanko' tree were investigated. Three-year-old trees were subjected to drought stress for three months in May ('Spring') and August ('Summer'), respectively. Irrigation was started immediately after drought stress treatment had finished. The starch concentration in the roots of stressed trees increased in both 'Spring' and 'Summer' two months after starting drought stress treatment and rapidly decreased just after starting irrigation in 'Spring'; however, it still temporarily increased in 'Summer'. These different results were attributed to seasonal changes in the carbohydrate demand. The dry matter weight of each tree organ in February of the following year was suppressed by drought stress, particularly in 'Spring'. This result indicates that, if a tree suffers drought stress in spring, vegetative growth is suppressed more seriously than in summer and tree growth, declined by suffering from severe and long-term drought stress, will hardly recover even the tree is re-irrigated. The total starch in all organs of the drought-stressed trees in February of the following year was significantly less than that in well-irrigated trees. These results indicate that severe drought stress for three months inhibits not only current tree growth but also the accumulation of carbohydrates that is necessary for the following year's growth. Hence, irrigation to avoid a fatal growth decline due to severe drought stress is needed during the current growth stage, especially in the early growth stage in spring.