Establishment of temporary heat treatment for controlling disease and insect damage by non-ventilation in combination with heat stress tolerant varieties in summer greenhouse cucumber

1) Cucumber plants require the use of multiple chemicals to protect them against disease and insects. In order to reduce the amounts of chemicals, temporary heat treatment using heat stress tolerant varieties was developed as a substitute for chemical spraying of summer greenhouse cucumbers. 2) The chlorophyll fluorescence generated from photosystem II was measured in 25 varieties of 17 vegetables using a pulse amplitude modulation (PAM) chlorophyll fluorescence meter before and after high-temperature treatment at 45 deg C. The decrease in Phi II = (Fm-Ft)/Fm with high-temperature treatment depended on whether the vegetables were treated with heat treatment. 3) The integrated Phi II values for five hours after the start of the 45 deg C treatment were calculated in 25 vegetable varieties. The scatter plot of the integrated Phi II of non-heat-treated varieties (natural high-temperature stress tolerance) and the ratio of the integrated Phi II in heat-treated / non-heat-treated samples (high-temperature acclimation ability) explained the responses of the vegetables to high temperature. 4) Five cucumber varieties were cultivated under different temperature conditions by altering window operations. The measured Phi II suggested that the best temperature for estimating high-temperature stress tolerance and acclimation ability was 50 deg C. 5) Twenty-two cucumber varieties were cultivated under heat treatment or control conditions. The Phi II values were measured at 50 deg C. High-temperature stress tolerance and acclimation ability were estimated on a scatter plot using the integrated Phi II values. 6) High-temperature stress tolerance was highly correlated with fruit yield in five varieties of summer cucumber. This suggests that the integrated Phi II value measured with a PAM chlorophyll fluorescence meter is useful for screening high-tolerance varieties. 'Taisho' was the most suitable variety for heat treatment. In this variety, heat treatment increased the yield remarkably. 7) Three heat treatments were compared: fully open, setting the ventilation temperature to 45 deg C from 4:30 until 10:30 (short treatment: 1 hour at 45 deg C on a fine day), and setting the ventilation temperature at 45 deg C from 4:30 until 13:00 (long treatment: 3 hours at 45 deg C on a fine day). The yield was sufficient with the short treatment. The results of the long treatment depended on the time of the year. 8) Daily heat treatment from 4:30 until 10:30 strongly suppressed diseases and insects without chemical spraying. The yield was the same as with chemical protection. By contrast, chemical protection was absolutely necessary for continuous growth in the fully open control. 9) To avoid disrupting labor in the morning, the effect of heat treatment at lunch time (11:30-13:20) was estimated. This suggests that pesticides should be used against mites. 10) The salicylic acid (SA) content was analyzed by capillary electrophoresis using the leaves of 22 varieties treated with heat treatment and controls. The SA levels were higher in heat-treated leaves than in controls in 18 varieties. The increased SA levels suggested that SA acts as a signal transducer for inducing disease resistance. 11) The time course of SA content was estimated in leaves after being soaked into hot water at 45 deg C for two minutes. Free SA increased 2.8 times after 12 hours and total SA did 21.4 times after 24 hours. This result suggested plant resistance activation was induced in one day after high temperature stress treatment. 12) To examine whether heat treatment induced disease resistance, an inoculation test was conducted using Cladosporium cucumerinum. Infection was suppressed in leaves soaked in water at 45 deg C for two minutes from 1 to 4 days after treatment. This effect was especially marked in 'Tsubasa', 'Natsusuzumi', and 'Shimoshirazu-jibai'. 13) If the greenhouse air temperature was close to the ventilation temperature (45 deg C) when the solar irradiation was strong, shading eliminated the need to keep the windows closed. Thermal sheets could be used to provide shade. 13) An effective heat treatment for cucumber was as follows. A. Daily heat treatment suppressed disease and insects; furthermore, it induced shoot growth and disease resistance at the beginning of the harvest. B. Heat treatment should be repeated at 8- to 14-day intervals to maintain yield. 14) Chemical protection should be used as soon as possible when the weather is not suitable for heat treatment.