抄録
In order to develop an irrigation control system for applying optimum water stress to produce high-Brix tomato fruits with restricted root-zone hydroponics, a non-destructive evaluation method of water stress by measuring stem diameter (SD) was investigated. SD was continuously measured by using a laser sensor at internode between the 2nd and the 3rd leaves of tomato plant during the growing period. Relative stem diameter (RSD) was used as an index of a water stress, which is calculated from a percentage of SD toward maximum stem diameter (MSD) . When RSD is 100%, there is no water stress. And if the RSD is smaller than 100%, an intensity of water stress is bigger. RSD indicated a diurnal change which decreased to less than 100% after the sunrise and recovered to 100% from the evening to midnight. With a substrate drying, the relationship between RSD and leaf photosynthetic rate (Pr) was expressed as linear regression lines with high coefficient of correlation. The positive correlation between RSD in one plant grown in cultivation bed and relative water content (RWC) of leaves in other plants was investigated, except for the harvesting time of the double-truss cultivation. These results indicate that RSD is useful for an evaluation of water stress as an index for irrigation control in tomato cultivation, while a time constraint should be concerned in evaluating water stress by RSD measured at same stem position.
