Effects of high temperature on tomato summer fruit quality

Crop-scale and controlled environment experiments were carried out to explore the effects of short periods or pulses of high temperature on fruit quality defects, uneven ripening and softness for two standard round UK tomato cultivars Solairo and Espero. Elevated temperatures were achieved by manipulating glasshouse heat and vent set points. Heat pulses were applied over 3 or 7 d to explore the impacts of duration, in 1999, and magnitude for a range of mean temperatures 20.4 (control), 22.2, 24.2 and 25.9degreesC over 3 d in 2000. Fruit defects and yields were significantly increased in the week immediately following the end of a heat-pulse treatment. This demonstrated that 0 the development of uneven ripening and softness was confined to fruits between mature green and colour stage 4/5 and that ii) the potential commercial impact of these defects was compounded by the higher yields. Pulse durations of 7 d compared with 3 d exacerbated the incidence of uneven ripening and increased yield but had little additional effect on fruit softening. Strong positive linear relationships were found for the dependence between the key fruit defects and pulse magnitude in the range 20.4-25.9degreesC. The incidence of uneven ripening increased at a rate of 2.7 units of score and fruit firmness decreased by 0.07 N mm(-1) per degreesC rise in mean pulse temperature. Fruit detached at mature green and placed in controlled environment conditions at constant light and humidity with air temperatures of 20.2, 22.9 and 26.8degreesC exhibited similar incidences of defect compared with attached fruits sampled from the crop-scale experiments. Future studies could utilise the detached fruit model system to elucidate the mechanisms involved in high temperature induced softness and uneven ripening. To provide an estimate of commercial damage, relationships between percentage Class I uneven ripening fruits and pulse temperature and magnitude were formulated. A heat-pulse lasting 3 d and with a mean temperature of 23.0degreesC was sufficient to cause a 10% loss of Class I fruit. This temperature regime was lower than previously considered harmful by growers. Implications for predicting the likely impact of high temperature events are discussed.