Effects of Air Temperature and Air Flow Rate Control on the Tipbum Occurrence of Leaf Lettuce in a Qosed-type Plant Factoiy System

摘要

This study aimed to establish a practical method to reduce tipbum symptoms on leaf lettuce cultivars in a closed plant factory system, focusing on air temperature conversion at specific plant growth stages and artificial air flow application strategies using pre-screened tipbum-sensitive cultivars. Inter-conversion effect of day temperature among 18, 22, and 25°C, 12 days after transplanting on tipbum occurrences, were compared with stable day temperature condition. Horizontal air flow rates were controlled at 0.28 (Low), 0.55 (Medium), and 1.04 m-s~(-1) (High). Tipbum occurrences were highly variable depending on the lettuce cultivars tested. Following the initial screening of 28 leaf lettuce cultivars under 3 different light intensity conditions(ranging from 150 to 250 pmol-m~(-1)s~(-2)), two cultivars exhibiting relatively higher percentages of tipbum were selected for the following air temperature and air flow treatments. None of the temperature treatments effectively reduced tipbum symptom,while adjusting the temperature to a lower day temperatures at 12 days after transplanting only had a minor effect on lettuce growth and tipbum occurrence. In contrast, stable horizontal 24-hour air flow rates above 0.28 m s~(-1) effectively reduced tipbum symptom, with no significant differences being found among the tested air flow rates, while above 65% of tipbumed plants were found in the control plot of 0.08 m s~(-1) flow rate. When stable air flow was applied, compared to the control, there was anincrease in the absolute calcium content and a decrease in the calcium content difference between the inner and outer lettuce leaves. This calcium balance change may have occurred due to the enhanced transpiration in the inner parts of plants. This study showed that stable horizontal air flow application along cultivation beds is more effective than air temperature control in decreasing tipbum symptoms in a closed plant factory system.