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 reirrigated. 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.

Effects of interstocks on the growth and fruit quality of 'Fuyu' Japanese persimmon (Diospyros kaki Thunb.) were investigated to select an effective dwarfing interstock of this species. The performance of four interstocks (Ac-1, Ac-2, Y clones, and a seedling of Diospyros rhombifolia) was evaluated in combination with 'Aogaki' (D. kaki) seedling rootstocks and 'Fuyu' scions over a six-year period. Ac-1 and Y interstocks moderately reduced the tree size without influencing yield efficiency (yield per unit of crown area). In contrast, Ac-2 and D. rhombifolia interstocks reduced both tree size and fruit yield (kg/tree), and many of these trees died within a few years after planting. Annual fluctuations and no consistent trends were observed in the fruit weight among control and interstock trees. These results show the possibility of dwarfing 'Fuyu' trees by using Ac-1 and Y as interstock.

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Japanese apricot (Prunus mume Siebold & zucc.) fruits of 'Nanko' have softer flesh than those of 'Gojiro'. Therefore, there are differences in the processability of these cultivars. We investigated the characteristics of cell-wall polysaccharide degradation that significantly affects fruit firmness in these 2 cultivars at unripe, ripe, and drop stages. Fruit firmness of 'Gojiro' was maintained during unripe and ripe stages and decreased after the ripe stage, while that of 'Nanko' decreased constantly and was lower than that of 'Gojiro' at ripe and drop stages. Amount of the pectin and the hemicellulose substances decreased commonly in 'Gojiro' and 'Nanko' in the process of fruit softening, in addition, decrease in mol wt of these polysaccharides significantly synchronized with decrease in fruit firmness, suggesting that degradation of the pectin and the hemicellulose cause the softening of Japanese apricot fruits. The amount of neutral sugar (NS) and uronic acid (UA) in the pectin fraction and NS in the hemicellulose fraction in 'Nanko' decreased more than in 'Gojiro'. Moreover, the cellulose content of 'Nanko' decreased during the fruit-softening process. These results suggest that higher degradation of pectin, hemicellulose, and cellulose in 'Nanko' fruits would result in softer fruits than 'Gojiro'.

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With the continuing trend of global warming, the adverse impact of high temperature and the inevitably accompanying drought stress on the growth of Japanese apricot trees (Prunus mume Siebold et Zucc.) are of concern. Therefore, the effects of these factors on photosynthesis and carbohydrate translocation were analyzed. An investigation was conducted at average daytime temperatures of 24°C, 30°C, and 34°C under both irrigated and drought conditions. The 34°C temperature was higher than the open air temperature by 5°C. Stable isotope 13 C was administered to trees to determine carbohydrate positioning. Under the drought stress condition, the photosynthetic rate declined accompanied by temperature elevation, and at the highest temperature of 34°C, 13C concentrations in the twigs and roots were lower than those in the irrigated trees at 24°C. Two-way analysis of variance revealed a trend of 13 C translocation to the young organs above ground, and old organs, while roots were affected by water status, temperature, and their combination, respectively. In the irrigated trees, the photosynthetic rate reduction was not detected, even at higher temperatures. However, translocation incompetence reflecting a decline in 13 C concentration in the roots was observed at 34°C. These results indicate that the permissible diurnal average temperature during summer for the growth of Japanese apricot trees is approximately up to 30°C, and in the temperature range around this irrigation is helpful to facilitate regular functioning of carbohydrate translocation under drought stress conditions.

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