"Diurnal temperature variations significantly affect cucumber fruit growth"

Decreasing the temperature in heated greenhouses significantly reduces heat costs and CO2 emissions. However, the thermophile cucumber is known to be very sensitive to low temperatures. In particular, fruit growth decreases considerably as temperature declines. Nevertheless, reports show that cucumber can be grown successfully at low night temperatures.

To explain this phenomenon, it is necessary to investigate the effect of the diurnal temperature variation on fruit growth. Fruit-bearing cucumber plants were grown in two experiments, either at a constant low temperature during the light and dark phase of 15 or 16 °C or at an extremely low temperature during the dark phase of 10 or 11 °C with an increase to 24 or 25 °C during the middle of the light phase resulting in a daily average of 15 or 16 °C, respectively.

Introducing the diurnal temperature variation considerably increased fruit growth compared with cultivation at a constant temperature. The vegetative dry matter, however, was greater at a constant than at variable temperatures. Therefore, the total dry matter appeared to be unaffected by the treatments, meaning that photosynthesis was unaffected.

Model calculations indicate that the relationship between temperature and fruit growth is not linear in the low-temperature range. For practical applications, it can be concluded that short daily periods with high temperature can mitigate the negative effect of low night temperature on fruit growth and yield.

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