Intensified pollination and fertilization ameliorate heat injury in rice (Oryza sativa L.) during the flowering stage

Heat induces spikelet sterility during flowering in rice. Spikelet sterility in heat-stressed plants is associated with poor pollination due to insufficient pollen grain deposition and unsatisfactory fertilization from reduced pollen germination on the stigma. Measures aimed at facilitating pollen shedding and pollen germination will help to address the adverse effects of heat stress on spikelet fertility in rice during the flowering stage. Intensified pollination by artificially assisted pollen shedding combined with intensified fertilization by promoting pollen germination through chemical application (pH = 8.0, 10 % sucrose, 0.1 mM spermidine, 0.01 % myo-inositol, 0.01 % boric acid, 1 mu M 24-epibrassinolide, 1 mM KCl, 1 mM CaNO3, 1 mM CaCl2, 0.03 % casein enzymatic hydrolysate, 0.01 % ferric ammonium citrate, 10 mM -aminobutyric acid, and 1-2 drops of Tween 20) increased spikelet fertility significantly compared with that without intensified measures under heat treatments in controlled greenhouse conditions. Intensified pollination increased the percentage of anther dehiscence and the number of pollen grains on the stigma, and the chemical application increased the number of germinated pollen grains on the stigma, thus increasing the spikelet fertility and ultimately the grain yield. In open-field conditions, intensified pollination and fertilization measures increased the spikelet fertility, grain weight and quality significantly under elevated temperatures. The proposed methods of enhancing pollination and fertilization are simple and effective for ameliorating the adverse effects of heat stress on the grain yield and quality in rice. This study provides strategies for sustainable rice production under the high temperatures expected with future global warming.