Leaf Temperature Drop Measured by Thermography and Occurrence of Leaf Browning Injury in Saintpaulia

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The relationship between the rate of temperature drop, observed by infrared video thermography, and leaf browning injury was investigated in <I>Saintpaulia</I>. The severity of leaf injury increased largely during the immersion of leaf (20°C) in water (5°C) for 10s, whereas no further increase in the severity of injury was observed thereafter. During 3s of leaf immersion at various temperatures of water, leaf injury was induced only when the rate of temperature drop was more than 3°C/s. In the case of decreasing leaf temperature from various initial temperatures (40°C, 35°C, 30°C), leaf injury was observed at smaller temperature difference between leaf and water when the initial leaf temperature was high. The rate of temperature drop was high when the leaf temperature at 33°C as dropped to 20°C (3.5°C/s) rather than from 23°C to 10°C (3.2°C/s), resulting in 53% and 32% injury on the leaf, respectively. The temperature drop of coated leaves following immersion in 7°C water showed a lower rate of temperature drop than uncoated leaves, resulting in 1/30 times of the injury in uncoated leaves. In addition, the severity of the injury decreased as the size of a water droplet decreased due to the slow drop in leaf temperature. The results suggest that a gradual drop in leaf temperature inhibits leaf injury even though the temperature difference between water and leaf is large.
日本生物環境工学会の論文