Fruit quality control using water management and simple water status detection methods in fruit tree leaves

　In fruit production, water status during the maturation season has a significant effect on fruit quality, influencing not only sugar but also organic acid and amino acid contents. Water management technology, therefore, is important for improving fruit quality and maintaining yield in Japan. This study firstly discusses extensive research into the effect of irrigation control on each component of grape fruit juice. Secondly, given that real time monitoring of leaf moisture content is essential to controlling water status, a simple estimation method is described. This method involved fixing a “water stress indicator” to the abaxial side of a leaf; the indicator changed color depending on the water status, which could then be evaluated. The water status was assessed against an indicator color scale, based on a property of cobalt （II） chloride that causes it to change color, from blue to light pink, through a hydration reaction between the indicator sheet and the water evaporating from the leaf to which the indicator sheet is affixed. By using this method, estimates were made of decreases under water stress conditions in the water evaporation rate from satsuma mandarin, grapes, peaches, and Japanese pear, based on the time required for the indicator sheet to change color. Thirdly, a new electrical sensor method to investigate water status in fruit tree leaves was developed, and used to measure electro pulse period; the relationship with transpiration rate was then evaluated using a leaf porometer. Pulse period was found to be consistently correlated with transpiration rate. The results indicate that the water status of fruit tree leaves can be estimated by measuring pulse period. This provides an accurate and quick method for detecting water stress, which could potentially be used for other crops that are particularly sensitive to water stress.

研究紹介 (Research Report)