EFFECT OF TWO NOCTURNAL TEMPERATURES ON CHLOROPHYLL FLUORESCENCE PARAMETERS OF FLAG LEAVES AND PANICLE CHARACTERISTICS IN SEVEN RICE (ORYZA SATIVA L.) GENOTYPES

High night temperature periods have reduced rice crop yields in recent years in Colombia. One of the strategies used to address this situation has been selecting tolerant genotypes and identifying physiological variables that serve as selection criteria in breeding programs. The aim of this study was to determine the effect of two-night temperatures (24 degrees C vs. 30 degrees C) on the physiological and agronomic performance of seven rice genotypes (Fedearroz 50 (F50), Fedearroz 60 (F60), IR 1561, FLO 2764, LV447-1, CT19021 and LV1401). At milk growth stage, a group of six plants of each genotype was placed in a growth chamber between 18:00 and 24:00 h at 30 degrees C for a period of eight days (stressed plants). Meanwhile, another group of rice plants sorted by genetic material was kept under normal growth conditions (24 degrees C) in a shade house (Control Plants). Results showed that rice genotype F50 plants showed a lower rate of spikelet fertility compared to the other genotypes studied at 30 degrees C (p <= 0.05). Leaf photosynthetic pigments and chlorophyll alpha fluorescence parameters (Y(II), Y(NPQ), Y(NO) and Fv/Fm ratio) showed no differences between night temperatures; however, significance differences were found among genotypes. The above results suggest that Y(II), Y(NPQ), Y(NO) and Fv/Fm in rice plants at advanced phenological stages (milk stage) are not an effective tool to quantify the physiological behavior of rice genotypes under a high night temperature condition.