EFFECT OF TEMPERATURE ON THE GROWTH OF INDIVIDUAL CUCUMBER FRUITS

In order to study the effect of temperature on the growth of individua l fruits in cucumber (Cucumis sativus L. cv. Corona), fruits were grow n at 17.5, 20, 25 and 30-degrees-C continuously or the fruit temperatu re was changed from 17.5 to 27.5-degrees-C or vice versa. Fruit develo pment appeared to be closely related to the temperature sum. When the growth of a fruit was not constrained by assimilate supply, a decrease in growing period with increasing temperature was more than compensat ed for by a strong increase in growth rate, resulting in an increase i n final fruit weight. However, when the growth of a fruit was constrai ned by assimilate supply, the increase in growth rate with increasing temperature was small and did not compensate for the decrease in growi ng period, resulting in a decrease in final fruit weight. Determinatio ns of cell number and size showed that the effect of temperature on fr uit growth was due to effects on cell expansion rather than on cell di vision, when growth was not constrained by assimilate supply. However, when assimilate supply did constrain fruit growth the number of cells per fruit decreased with increasing temperature, while the effect on cell size was negligible. In all stages of fruit development, the grow th rate of a cucumber fruit responded within one day to a change in te mperature. It was not irreversibly impaired by a low temperature (17.5 -degrees-C) during the early development of a fruit. A high temperatur e treatment (27.5-degrees-C), however, had a great effect on the growt h rate of a fruit after the temperature treatment had terminated. At a ll stages of fruit development (even before anthesis) a period of four days at 27.5-degrees-C resulted in a pronounced stimulation of the gr owth rate afterwards at 17.5-degrees-C.