Leaf morphology, rather than plant water status, underlies genetic variation of rice leaf rolling under drought

Soil drying causes leaf rolling in rice, but the relationship between leaf rolling and drought tolerance has historically confounded selection of drought‐tolerant genotypes. In this study on tropical japonica and aus diversity panels (170–220 genotypes), the degree of leaf rolling under drought was more affected by leaf morphology than by stomatal conductance, leaf water status, or maintenance of shoot biomass and grain yield. A range of canopy temperature and leaf rolling (measured as change in normalized difference vegetation index [ΔNDVI]) combinations were observed among aus genotypes, indicating that some genotypes continued transpiration while rolled. Association mapping indicated colocation of genomic regions for leaf rolling score and ΔNDVI under drought with previously reported leaf rolling genes and gene networks related to leaf anatomy. The relatively subtle variation across these large diversity panels may explain the lack of agreement of this study with earlier reports that used small numbers of genotypes that were highly divergent in hydraulic traits driving leaf rolling differences. This study highlights the large range of physiological responses to drought among rice genotypes and emphasizes that drought response processes should be understood in detail before incorporating them into a varietal selection programme.土壤干旱会引发水稻叶片卷曲，但长期以来，叶片卷曲与耐旱性之间的复杂关联，始终干扰着耐旱基因型的选育工作。本研究针对热带粳稻（tropical japonica）和Aus稻（aus）多样性群体（包含170~220份基因型材料）开展实验，结果表明：干旱条件下的叶片卷曲程度，受叶片形态的影响显著大于气孔导度、叶片水分状况、地上部生物量维持及籽粒产量的影响。在Aus稻基因型中，观测到多种冠层温度与叶片卷曲程度的组合类型，其中叶片卷曲程度以归一化植被指数（normalized difference vegetation index）变化量（ΔNDVI）为衡量指标，这提示部分基因型在叶片卷曲状态下仍可维持蒸腾作用。关联作图分析显示，干旱条件下控制叶片卷曲评分和ΔNDVI的基因组区域，与此前报道的与叶片解剖结构相关的叶片卷曲基因及基因网络存在共定位现象。本研究所用的大型多样性群体中，相关性状的变异相对细微，这或许可以解释本研究与过往研究结论不一致的原因——过往研究仅采用了少数在调控叶片卷曲差异的水力性状上存在显著分化的基因型材料。本研究揭示了水稻基因型间对干旱的生理响应存在广泛差异，并强调在将耐旱相关性状纳入品种选育程序前，需先对干旱响应机制展开深入解析。