後藤 英司

Growing environments were controlled to prevent or reduce lettuce tipburn, a physiological disorder in inner developing leaves around a growing point caused by calcium deficiency. Lettuce (Lactuna sativa, L.) of butter head type was grown by hydroponics in a controlled-environment room which had heaters, humidifiers, a refrigerator, electric lamps, and a CO control apparatus. With air pumps and flexible pipes, room air was blown onto inner developing leaves totally or partially enclosed by the outer leaves. After transplanting, lettuce plants were exposed to various air supply conditions. Air temperature and RH were 24° C and 85%, respectively, in the light period, and 20°C and 85% in the dark. The PPF was 264 μmol m s , and light period was 14 hours. The CO concentration was 1500 μmol mol . Temperature of the nutrient solution was constant at 20°C, pH was 5.8-6.2, and EC was 150 mS/m. The effects of various conditions on tipburn development were studied in relation to growth rate. Air supply to inner leaves prevented tipburn completely up to 60 g f.w., though tipburn occurred at approximately 15 g. f. w. in the control. All-day air supply was more effective in preventing tipburn than air supply in the light period or the dark period alone. Air supply to inner developing leaves was proved effective in preventing tipburn without sacrificing a rapid growth rate. The reason for the effect was an increase in transpiration from the leaves encouraged water and calcium uptake by the root and increased calcium concentration in the leaves. 2 2 -2 -1 -1

Systems were developed for investigating optimal conditions for plant tissue culture using nutrient mist supply. A system in which a growth chamber and a mist generator were combined into a single unit operated reliably. An experiment that restricted the mist wafting region in the culture space resulted in better growth of potato nodal explants than that attained with a conventional culture method using agar media.