High temperature injuries in fruit vegetables (a preliminary report)

Covering plants with plastic film has been common practice in vegetable growing for early and late markets. Temperature inside of the cover rises higher than 40°C in clear days if ventilating is neglected. Therefore injuries due to high temperature are frequently observed in vegetable crops under the plastic coverings.In this preliminary study on high temperature injury in fruit vegetables, young plants of tomato, cucumber and egg-plant were exposed to artificially controlled high temperatures and their subsequent behaviors were observed.High temperature about 50°C induced necrosis in leaves and stems of these fruit vegetables, especially in their young portions, in relatively short time.Plants exposed to 45°C for 3 hours each in successive five days showed no visible injury in their leaves and stems, and their growth was as well as that of the control plants, though their leaf color was slightly lighter than that of the control plants, and in egg-plant, development of purple pigment in flowers and leaves was depressed. Nevertheless, in tomato, percentage of fruit setting was significantly lowered, while hormone spray was effective to counteract this disorder. In cucumber, male flowers had not come to bloom since a few days after the end of the treatment.Germination tests of pollen on artificial media revealed that percentage of germinating pollen of these fruit vegetables was decidedly decreased by the treatment. This is assumed to be one of the causes of poor setting of fruits and deformed fruit-formation which are often found in the plants growing under plastic covers.