Effects of Increasing Temperatures on Spikelet Fertility in Different Rice Cultivars based on Temperature Gradient Chamber Experiments

<jats:title>Abstract</jats:title><jats:p>Spikelet sterility in rice (<jats:italic><jats:styled-content style="fixed-case">O</jats:styled-content>ryza sativa </jats:italic><jats:styled-content style="fixed-case">L</jats:styled-content>.) induced by high temperatures is a major concern given global warming predictions. We studied differences among eight rice cultivars in spikelet fertility at five different temperature levels in temperature gradient chamber (<jats:styled-content style="fixed-case">TGC</jats:styled-content>) experiments. Six japonica and two indica cultivars were exposed to high‐temperature gradients in <jats:styled-content style="fixed-case">TGC</jats:styled-content>s during the 2005 flowering season. Spikelet sterility increased with temperature in <jats:styled-content style="fixed-case">TGC</jats:styled-content>s and differed among cultivars because of both variations in temperature tolerance and timing of heading. The correlation between spikelet fertility of individual panicles and both air temperature and panicle temperature during flowering was analyzed to compare tolerances among cultivars. The temperature (<jats:italic><jats:styled-content style="fixed-case">T</jats:styled-content></jats:italic><jats:sub>75</jats:sub>) at which spikelet fertility was 75 % of maximum ranged from 34 to 39 °C air temperature and differed significantly among cultivars. Indica varieties had higher <jats:italic><jats:styled-content style="fixed-case">T</jats:styled-content></jats:italic><jats:sub>75</jats:sub> values than japonica varieties. The <jats:italic><jats:styled-content style="fixed-case">T</jats:styled-content></jats:italic><jats:sub>75</jats:sub> values based on panicle temperature also differed among cultivars, but the difference between indica and japonica varieties were less significant. We concluded that the higher temperature tolerances of indica cultivars in our experiments could be attributed to lower spikelet temperatures, and cultivars with similar spikelet temperatures still had different heat tolerances due to differences in pollination ability.</jats:p>