Morpho-physiological and phenological response of rice (Oryza sativa L.) genotypes to low temperature stress at reproductive stage

The yearly changes in atmospheric temperature are projected to negatively affect food production in several locations. Rice exposure to low-temperature stress can decrease plant growth in different stages, notably during the reproductive period. A field experiment was conducted in ARS Gangavathi, Karnataka. The experiment laid out in factorial randomized block design where four different rice genotypes (GNV-10-89, GNV-1801, GNV-1108 and BPT-5204) transplanted under two different dates of transplanting D1 (normal Kharif-15th September) and D2 (late Kharif-30th September). The low temperature during the reproductive stage was 14.1°C which inhibited the morphological, physiological, phenological and yield traits of rice crop. All the observations were recorded at the flowering stage (95 DAT). The results revealed that morphological traits like plant height, number of green leaves, number of productive tillers, total dry matter, total leaf area and root length were high in D1 than D2 (101.6 & 99.76 cm, 21.5 & 16.1 hill-1, 14.5 & 11.5 hill-1, 29.0 &21.1 g hill-1, 3.79 & 4.11 dm2 hill-1 and 14.6 & 18.2 cm), physiological traits such as photosynthetic rate (14.55 & 13.45 µ mole CO2 m-2 s-1) and Transpiration rate (12.86 & 11.01 m mole H2O m-2 s-1) similarly phenological traits, DPI (80.6 & 90.5 days), DF (98.3 & 102.3 days), DPM (116.7 & 127.2 days) and DHM (124.7 & 135.4 days). Reproductive traits like pollen viability (91.3 & 87.4 %) and spikelet fertility (84.3 & 75.9 %) and grain yield (7744.8 & 6531.3 kg ha-1). Among the genotypes GNV-10-89 (10270.9 kg ha-1) recorded the higher grain yield and lower was observed in BPT-5204 (3937.5 kg ha-1) these results conclude that the late Kharif transplanting was not suitable for this region as there was sharp drop-down of temperature (14.1°C) at a reproductive stage which leads to high spikelet sterility. By looking at the results obtained, among four genotypes GNV-10-89 recorded high grain yield followed by GNV-1108 these two genotypes are considered as moderately tolerant, GNV-1801 is moderately sensitive and BPT-5204 is sensitive to low-temperature stress.