Possible cause of reduction in yield of rice under night temperature

Minimum nighttime temperature has been rising in the past and is continuing up to the present. The predicted increases in night temperature will have negative impact on rice crop production and on the livelihood of rice farmers. The first evidence of rice yield decrease associated with increasing nighttime temperature has been reported using historical data sets. Most of the studies previously conducted imposed night temperature treatments either at the vegetative or the reproductive growth phases. However, very limited information is available on the crucial stage of the onset of HNT that caused yield reduction. A strong limitation on growth or sink size may be occurring if treatment is applied at different stages, an approach that had not been done but may prove potentially valuable. The authors conducted an experiment in controlled-growth chambers using three rice cultivars to examine the possible cause of the observed yield reduction in rice and identify the critical stage of HNT treatment that would cause such reduction. Rice seedlings were grown under two temperature treatments: 30/21 deg C (low) and 30/25 deg C (high) day/night temperatures. At the end of the vegetative stages plants grown under these two temperatures were further subdivided and exposed to different times of HNT treatment. The temperature treatments significantly reduced the total spikelets and increased percentage spikelet degeneration. High night temperature treatment at an early reproductive phase produced the lowest number of spikelets per panicle and had significantly higher percentage of degenerated spikelets (35.9%) compared to the other HNT treatments. This study provides supportive evidence of sink size reduction by HNT due to increased spikelet degeneration, which might partly explain the low harvest index and biomass previously reported under HNT that caused the yield reduction.