The effect of a daily low temperature pulse on growth and development of greenhouse cucumber and tomato plants during propagation

Abstract

Thermomorphological responses of young cucumber and tomato plants to a low temperature pulse (LTP) given at the start of the daily light span were examined using a ‘walk in’ growth chamber. Four LTP levels consisting of 0, 2, 6 and 10°C for cucumber and 0, 3, 6 and 9°C for tomato, were combined factorially with exposure durations of 7, 14 or 21 days for cucumber and 7, 14, 21, 28 or 35 days for tomato. LTP treatments were terminated at transplanting. Plant height at transplanting decreased as LTP magnitude and time of exposure increased. A LTP of 10°C from cotyledon expansion to the end of propagation (8–29 days after sowing), reduced the plant height in cucumber 24%. A LTP of 9°C from cotyledon expansion to the end of propagation (10–45 days after sowing), reduced plant height in tomato by 36%. The height reduction was mainly owing to a decrease in internode length. However, a reduction in development was observed too, which may be credited for approximately 20% of the total height decrease. Petiole length was affected by the LTP magnitude and duration of exposure in the same way as plant height and internode length. Large and early LTP application delayed flowering in tomato. Consequently, time to first harvest was delayed. However, delayed flowering did not occur when the temperature pulse was given during the last part of propagation. For tomato, a 20% reduction in plant height could be attained with a LTP of 9°C during only the last week of propagation. For cucumber, a LTP of 6°C was necessary to obtain a significant height reduction. LTP did not affect early yield and quality in cucumber or in tomato.