ORIGINAL ARTICLE

Physiological Response of Rice Seedlings (Oryza sativa L.) Subjected to Different Periods of Two Night Temperatures

Night temperatures have shown an increase in rice-growing regions due to climate change in Colombia in recent years, causing a reduction in grain yield. The objective of this research was to study the effect of four different periods of exposure to two night temperatures (24°C vs. 30°C) on the physiological behavior of an Indica rice cultivar widely grown in Colombia. Fedearroz 60 (ʻF60ʼ) were grown under greenhouse conditions for forty-five days. After this period, 12 plants in each treatment was established in a growth chamber at 30°C from 18:00 to 24:00 to carry out the duration of the different periods of heat nighttime stress (4, 8, 12, and 16 days respectively). The control plants were kept in a greenhouse at 24°C. The results showed that leaf photosynthesis, carboxylation efficiency, and pigment content decreased in rice seedlings subjected to 30°C. Also, dark respiration and intercellular CO₂ concentration increased. These reductions in the variables as mentioned above were more severe during the first four days of exposure to 30°C than 24°C. In conclusion, these results suggest that these physiological variables may be useful to assess the tolerance of rice plants to high nighttime temperatures in plant breeding programs.