Panicle emergence pattern and grain yield of rice plants in response to high temperature stress

Abstract

The timing of panicle emergence in rice (Oryza sativa L.) is an important trait. We studied the effects of increasing temperatures during growing seasons on the emergence of first panicle, consequent emerging panicle numbers, and grain yields in rice plant using temperature gradient chambers (TGCs) located in a part of Japan with a humid subtropical climate. Four japonica varieties, Koshihikari, Akitakomachi, Hitomebore, and Nipponbare, were exposed to different temperatures in the TGCs. The number of days from transplanting to heading (DTH) differed among temperatures. Increasing temperatures both accelerated and delayed the timing of heading. Extreme temperatures (>40℃ daily maximum) increased the DTH, whereas moderately high temperatures decreased or did not change the DTH. Increasing temperatures after heading affected the number of panicles emerging. The final panicle number increased with temperature in Koshihikari and Akitakomachi. In these varieties, spikelet fertility and mean grain weight of early-emerging panicles were lower at higher temperatures because of the occurrence of grain sterility. However, the grain numbers and grain weights of lateemerging panicles were greater under higher temperatures, and total grain yields were not significantly different among the temperature treatments. We concluded that late-emerging panicles recouped the yield of rice plants, compensating for grain sterility.

Field survey on rice spikelet sterility in an extremely hot summer of 2018 in Japan

“…Furthermore, the occurrence of sterility may influence on the source-sink balance, which leads to compensatory effects, such as changing the grain size distribution. It has been also reported that the late-emerging panicles can compensate for the failure to fertility of the early-emerging panicles, resulting in no reduction of the yield (e.g., Maruyama et al, 2015). Conversely, this means that even if HISS increases due to global warming and the resulting increasingly frequent heat waves, its effects on rice yield would not be directly detected by yield monitoring such as the monitoring that is done under Japan's national Crop Survey.…”

Increasing canopy photosynthesis in rice can be achieved without a large increase in water use—A model based on free‐air CO2 enrichment

“…Our study suggests that if a Takanari‐like rice variety was cultivated under approximate [CO 2 ] in 2050 (200 μmol/mol over present‐day [CO 2 ]), we could feasibly maintain the cost for water at the same level as for cultivating common cultivars like Koshihikari at current [CO 2 ]. Even if air temperature increased alongside [CO 2 ] in the future, a 14‐day simulation of Takanari in E‐CO 2 with air temperature increased by 2°C results in an ET of 3.9 ± 1.4 mm/day, which is still approximately the same level of ET of Koshihikari in A‐CO 2 , although the simulation did not consider the temperature effects on phenology and downregulation of photosynthesis (Adachi et al., ; Maruyama et al., ).…”