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  • Author or Editor: Kunihisa Morinaga x
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Relationship between root system and shoot pruning was studied by three different pruning times (February, June, and August) and intensity (heavy, medium, and light) using satsuma mandarin trees (Citrus unshiu Marc.). Root weight, respiratory rate of fine root, and CO2 concentration in root zone were measured on the 90th day after starting each pruning treatment. The weight of fine root was more severely influenced by pruning intensity than by pruning time. Fine root of heavy pruned trees showed lower respiratory rate than those of medium- and light-pruned trees. Heavy-pruned trees showed the highest CO2 concentration level in root zone. Influence of high root temperature on root respiration was investigated using `Kyoho' grape (Vitis vinifera L. × V. Iabrusca L.), kiwifruit (Actinidia deliciosa), and satsuma mandarin trees. Respiratory rate of grape root increased more rapidly than those of mandarin and kiwifruit under high root temperature. Respiratory rate of mandarin root given immersion treatment in stagnated water began to decrease significantly at the 70th hour after starting the treatment. Photosynthesis of the trees decreased by 85% at the same time.

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Mechanisms of sugar accumulation in response to drought stress in Satsuma mandarin (Citrus unshiu Marc.) fruit were investigated. Predawn leaf water potentials averaged -0.35MPa for well-watered, -0.60 MPa for moderately drought-stressed, and -1.00 MPa for severely drought-stressed glasshouse-grown 3-year-old trees. Fruit peel turgor and fruit growth of the moderately drought-stressed trees recovered to a similar value to that of the well-watered trees. Photosynthetic rates and stomatal conductance of both moderately and severely drought-stressed trees were significantly lower than those of the well-watered plants. However, the total sugar content per fruit of moderately drought-stressed trees was the highest among the drought treatments. A 13C-labeling experiment showed that 13C distribution in fruit grown under the moderately drought-stressed condition was the highest. These findings indicate that sugar accumulation in fruit was caused by an increase in translocation of photosynthates into fruit, especially into the juice sacs, under drought stress.

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