Abstract
High nighttime temperatures impair rice yield. Additionally, heat stress periods have increased during the last years in the rice areas of the tropics. The aim of this study was to physiologically characterize six genotypes of rice (a commercial cultivar (ʻF60ʼ) and five selected lines (ʻIR 1561ʼ, ʻFLO 2764ʼ, ʻLV447-1ʼ, ʻCT19021ʼ, and ʻLV1401ʼ) subjected to two nighttime temperatures (24 and 30 °C), based on different physiological traits. When the collar formed on leaf 6 of the main stem, one group of six plants in each genotype was subjected to 30 °C from 18:00 to 24:00 hours for eight days, while the other group remained at 24 °C. Differences were found in the interaction between genotype and nighttime temperatures, where a high night temperature reduced leaf photosynthesis by approximately 50% in all genotypes compared to the controls (20 µmol vs. 10 µmol CO2 m-2 s-1, respectively). In general, higher plant respiration was also observed in almost all genotypes when the plants were exposed to 30 °C. However, rice plants of the genotype ʻF60ʼ showed a constant respiration under two different night temperatures. A high nighttime temperature increased the electrolyte leakage and malondialdehyde content only in the ʻLV1401ʼ plants. Plant growth and Fv/Fm ratio were separately conditioned by the night temperature or the genotype factor. A lower total plant dry weight was found at 30 °C (620.36 mg) than in rice plants exposed to 24 °C (254.16 mg). The Fv/Fm ratio was slightly diminished at a high nighttime temperature. These results suggest that physiological variables, such as leaf photosynthesis, plant respiration, malondialdehyde content and leaf photosynthetic pigments, can be considered markers for characterizing tolerant genotypes in earlier growth phases during plant breeding programs.
Highlights
Global warming has generated adverse weather conditions, such as heavy and prolonged periods of drought and more frequent periods of high temperatures, in several regions of the world in recent years (FAO, 2002)
Differences were found in the interaction between genotype and nighttime temperatures, where a high night temperature reduced leaf photosynthesis by approximately 50% in all genotypes compared to the controls (20 μmol vs. 10 μmol CO2 m-2 s-1, respectively)
These results suggest that physiological variables, such as leaf photosynthesis, plant respiration, malondialdehyde content and leaf photosynthetic pigments, can be considered markers for characterizing tolerant genotypes in earlier growth phases during plant breeding programs
Summary
Global warming has generated adverse weather conditions, such as heavy and prolonged periods of drought and more frequent periods of high temperatures, in several regions of the world in recent years (FAO, 2002). High night temperatures (HNT) cause plant responses at the biochemical, physiological and/or genetic level. A high night temperature can reduce the leaf photosynthesis rate and increase plant respiration (Mohammed and Tarpley, 2010). Earlier studies have shown that rice plants exposed to high night temperatures (35 °C) had low CO2 assimilation due to lower PSII efficiency and ribulose 1-5 bisphosphate carboxylase/oxidase activity (Yin et al, 2010). Several studies have shown that tolerant genotypes have a series of biochemical and physiological changes to cope with heat stress (Bita and Gerats, 2013; Kumar et al, 2016). The use of different biochemical and physiological traits has been helpful to screen, and select, genotypes that are tolerant to high night temperatures (Araus et al, 2008)
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