Prevention of Lettuce Tipburn by Supplying Air to Inner Leaves

Abstract

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 CO2 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 mmol m2sl, and light period was 14 hours. The CO2 concentration was 1500 mmol mol1. 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.