Heat Acclimation and De-acclimation for Pod Setting in Heat-tolerant Varieties of Common Bean (Phaseolus vulgaris L.)

Abstract

The effect of exposure to high temperature over a long period of time on pod setting of common bean (Phaseolus vulgaris L.) was investigated for heat-tolerant varieties (Haibushi and Ishigaki 2) and one heat-sensitive variety (Kentucky Wonder) in an air temperature-controlled phytotron. When the plants were transferred from a moderate daily mean air temperature (DMAT) (23.6°C) to a high DMAT, the pod setting ratio gradually decreased from 7 days after the initiation of the heat treatments. At 29.6°C, the ratio decreased to 0%-15% at 15 days after the transfer and it did not recover thereafter. On the other hand, at around 28°C, the low pod setting ratio recovered again from 15 days after the transfer for the heat-tolerant varieties. At about 30 days after the transfer, the ratio of pod setting increased to the level (around 80%) of that of the plants that were continuously kept at 23.6°C. The recovery was not caused by changes in environmental conditions, that is, day length, light intensity, etc. but by the heat acclimation of flower buds to the air temperature (around 28°C) . Heat acclimation appeared also at the same DMAT (around 28°C) but under different combinations of day and night temperatures (32.3°C/23.9°C and 30.4°C/25.7°C) . Heat acclimation was not evident in the heat-sensitive variety and it could not be observed even in the heat-tolerant varieties at 29.6°C. When heat-acclimated plants were transferred back to 23.6°C and were left for one month, heat acclimation disappeared.