Effects of high night temperature and spikelet position on yield-related parameters of rice (Oryza sativa L.) plants

In subtropical rice-growing regions, occurrence of seasonally high night temperatures (HNT) during the critical stages of development reduces rice (Oryza sativa L.) yield and quality. A study was conducted to determine the effects of night temperatures and spikelet position in the panicle on multiple rice yield-determining parameters, including number of productive tillers, spikelet sterility, and grain length, width and weight. Plants were grown under ambient night temperature (ANT) (27 °C) or HNT (32 °C) in the greenhouse. They were subjected to a HNT through use of continuously controlled infrared heaters, starting from 2000 h until 0600 h. High night temperatures decreased yield (90%) by affecting spikelet sterility (61%), and grain length (2%), width (2%), and weight. High night temperature increased grain nitrogen concentration (44%), which was inversely related to grain weight. The increase in spikelet sterility under HNT was associated with decreased pollen germination (36%) and increased respiration rates (28%) and relative membrane injury (86%), but not with photosynthesis (production). In addition to HNT, position of the spikelet in the panicle also played an important role in determining its weight and nitrogen concentration. The spikelets at the tip of the panicle weigh more than the spikelets at the base of the panicle.