Heat stress during the reproductive and grain-filling stages leads to severe yield losses in rice, especially in irrigated areas during the dry season in Thailand. Thus, breeding for heat-tolerant rice is one of the strategies for developing rice crops adapted to the effects of high temperature in major growing regions. M9962, a fast neutron-induced mutant, was identified as a heat-tolerant line that was then used as a donor parent and crossed with the Phisanulok 2 (PSL2) cultivar (the recurrent parent) in a backcross breeding programme. Heat tolerance scoring under controlled greenhouse and field conditions was based on the percentage of spikelet fertility. Yield trials for the BC2F7 and BC3F6 lines were subsequently conducted under field conditions at three locations and under controlled greenhouse conditions during the dry season of 2019 (DS2019). In the early generation, 210 plants of the BC1F1 population and 440 plants of BC2F1 population were evaluated for their heat tolerance, and the spikelet fertility distribution within the BC1F1, BC2F1 and BC3F1 populations showed a skewed-right pattern. In addition, most rice plants in every generation were heat sensitive. Finally, compared with PSL2, the four-candidate heat-tolerant lines exhibited a high percentage of spikelet fertility and high yield. In addition, the one candidate line, BC2F7-6-5-4-1-1-21 was most similar to PSL2 in terms of genetic background, plant type and grain quality. Thus, backcross breeding programmes via the spikelet fertility can be used as an indirect trait to select for heat tolerance.

中文翻译：

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回交育种提高泰国水稻 (Oryza sativa L.) 品种繁殖期的耐热性

生殖和灌浆阶段的热应激导致水稻严重减产，特别是在泰国旱季的灌溉区。因此，培育耐热水稻是在主要种植区开发适应高温影响的水稻作物的策略之一。M9962 是一种快速中子诱导的突变体，被鉴定为耐热品系，然后将其用作供体亲本，并在回交育种计划中与 Phisanulok 2 (PSL2) 栽培品种（轮回亲本）杂交。在受控温室和田间条件下的耐热性评分基于小穗生育率的百分比。BC 的产量试验2F7和公元前3F6随后，在 2019 年旱季（DS2019）期间，在三个地点的田间条件下和受控温室条件下进行了生产线。在早期世代，BC 的 210 株植物1F1BC 的人口和 440 株植物2F1评估种群的耐热性，以及 BC 内的小穗生育率分布1F1, 公元前2F1和公元前3F1人口呈现右倾模式。此外，每一代的大多数水稻都是热敏感的。最后，与 PSL2 相比，四候选耐热品系表现出较高的小穗生育率和高产率。此外，一个候选线，BC2F7-6-5-4-1-1-21在遗传背景、植物类型和籽粒质量方面与PSL2最相似。因此，通过小穗生育力的回交育种计划可以用作选择耐热性的间接性状。