Yield stability of selected rice breeding lines and donors acrossconditions of mild to moderately severe drought stress

Although mild to moderately severe drought stress may have less of an effect on rice grain yield thansevere drought stress during reproductive stage, its prevalence across rice farmers’ fields at the globallevel may be more economically significant. In this study, field experiments were conducted on selectedgenotypes with known tolerance to severe reproductive-stage drought in order to identify those thatwould produce high and stable grain yield across seasons and soil moisture conditions varying fromwell-watered to mild and moderately severe drought stress. Mild stress generally occurred during wetseasons and moderate stress happened during dry seasons. The drought stress was mild enough suchthat the time to flowering was similar under drought stress and well-watered conditions in either sea-son. However, significant grain yield reductions were incurred even at mild drought levels. Using anAMMI1 biplot analysis, IR83142-B-7-B-B, Binuhangin, IR77298-14-1-2-13, IR70215-70-CPA-3-4-1-3 andIR77298-14-1-2 were identified as the genotypes with the highest and most stable grain yields in bothwell-watered and mild to moderately severe drought stress environments. In a characterization of traitsconferring drought tolerance among the highest yielding genotypes under mild to moderate droughtstress, genotypes Binuhangin and IR70215-70-CPA-3-4-1-3 stood out for multiple physiological traitsunder drought. However, no direct correlations among genotypes between stomatal conductance, nor-malized difference vegetation index (NDVI) or root dry weight with grain or total dry matter yield wereobserved under any soil moisture level. These results reflect the complex interaction of drought responsetraits contributing to grain yield. The genotypic variation and physiological responses observed in thisstudy point to the potential of developing varieties targeted to mild and moderate drought stress usingyield as the selection criterion.

尽管在生殖生长期，轻至中度干旱胁迫对水稻籽粒产量的影响弱于重度干旱胁迫，但这种胁迫在全球稻农田块中的普遍发生，其经济影响可能更为显著。本研究针对已被证实可耐受生殖期重度干旱胁迫的选定基因型开展田间试验，旨在筛选出在不同生育季、以及从充分供水到轻至中度干旱胁迫的各类土壤水分条件下，均能实现高产且籽粒产量稳定的基因型。轻度干旱胁迫通常发生在湿季，中度干旱胁迫则多出现于旱季。本试验设置的干旱胁迫强度适中，使得两个生育季内，干旱胁迫与充分供水条件下的抽穗期均无显著差异。但即便在轻度干旱胁迫水平下，水稻籽粒产量仍出现了显著降低。通过AMMI1双标图分析，筛选出IR83142-B-7-B-B、Binuhangin、IR77298-14-1-2-13、IR70215-70-CPA-3-4-1-3以及IR77298-14-1-2这5个基因型，它们在充分供水以及轻至中度干旱胁迫环境下，均表现出最高且最稳定的籽粒产量。针对轻至中度干旱胁迫下高产基因型的抗旱相关性状进行表征分析时发现，Binuhangin与IR70215-70-CPA-3-4-1-3这两个基因型在干旱胁迫下的多项生理性状表现突出。但在任一土壤水分条件下，未观测到不同基因型的气孔导度、归一化差分植被指数（Normalized Difference Vegetation Index, NDVI）或根干重，与籽粒产量或总干物质产量之间存在直接相关性。上述研究结果反映了影响籽粒产量的干旱响应性状之间存在复杂的互作关系。本研究中观测到的基因型差异与生理响应，表明以籽粒产量为筛选指标，培育适配轻至中度干旱胁迫的水稻品种具备潜在应用价值。