Effects Of Higher Nighttime Temperature On Irrigated Rice Yield And Grain Quality Under Tropical Condition

Minimum night temperatures are increasing at a much faster pace compared with maximum day temperatures and this trend is projected to continue into the future. As of now, crop model estimation, as well as controlled environment studies have recorded a significant negative impact of higher minimum night temperature on rice yields and quality. Limited information is available on the effect of high night temperature on the physiological mechanism of contrasting rice genotypes under field conditions. So our trial was carried out in temperature controlled chambers under field conditions using two of most contrasting entries (highly toleracnt-N22, Highly susceptible-Gharib) for physiological characterization. Both field and laboratory analyses were undertaken to estimate the impact of higher night temperature (HNT) on grain yield and yield components; quantify nitrogen and non-structural carbohydrate partitioning at key developmental stages in response to HNT; determine the impact of HNT on flowering pattern, rate and duration of grain filling along different sections of panicle and grain quality. The main conclusions are as follows:1. Higher night temperature reduced grain yield by21.8%in the sensitive Gharib, whereas N22was not affected significantly. Regarding to yield components,1000-grain weight of Gharib was greatly decreased by7.9%and HNT decreased spikelets per panicle by15.3%and increased seed set by7.6%in N22; however, these traits were not affected in Gharib. On the other hand,1000-grain weight was the only one factor significantly related to the grain yield in Gharib.(correlation coefficient r=0.909**)2. Higher night temperature led to a shortness of duration of two varieties especially after flowering. SPAD reading of Gharib under HNT decreased faster than the control, while N22kept same pace between HNT and control treatment. Leaf area index and total aboveground dry weight at heading stage of two varieties were not affected by HNT. However, total aboveground dry weight at maturity of Gharib significantly decreased by13.5%, while N22was unsignificantly influenced. Moreover, HNT induced significant increase in plant height of N22.3. The initial grain-filling rate of three positions along with panicles were substantially increased with HNT compared with control in N22and Gharib. For N22, the maximum, and mean grain-filling rate were went up with HNT for the three positions However, maximum and mean grain-filling rate of Gharib were reduced under HNT compared to control, particularly those at the bottom of the panicle. The active grain-filling duration in both N22and Gharib were shortened under HNT. Overall NSC and nitrogen content in Gharib were reduced significantly at15DAF and physiological maturity (P<0.05), while they were relatively unaffected in N22. The percent NSC and N in the panicles at15DAF were higher at28℃than those at22℃in both entries under HNT compared with control. However, the exact opposite accumulation of NSC and N in panicles in both entries exposed to28℃were recorded during physiological maturity.4. Higher night temperature at reproductive stage had significant effects on grain quality of Gharib while N22were unaffected. In Gharib, brown and milled rice yield, grain width, protein content were reduced greatly under HNT compared to control and increased in chalkiness with the>75%category.