Drought stress is a common issue that affects agriculture production. The soybean plant is one of the drought-sensitive crops that could lose the yield of up to 40% under severe drought years. Improvements in drought tolerance have been one of the main objectives of breeding programs in soybean. In this study, 62 soybeans [Glycine max (L.) Merri.] germplasms including landraces and elite cultivars were evaluated by analyzing canopy and root morphological characteristics at seedling stage under polyethylene glycol (2.5 M PEG 8000, − 0.54 MPa) simulated drought stress. The results showed that the wilting index of sixty-two soybean germplasms showed significant polymorphism differences after 4 days PEG treatment. The lowest wilting index was 2.75 in Tiefeng 31, while the largest reached 9 in Fengdou 93 and Songzidou. The wilting index was positively correlated with plant height, electrolyte leakage, and negatively correlated with a dry weight of the above-ground part, stomatal conductance, and transpiration rate by regression analysis. The root system architecture (RSA) study showed root-canopy ratio, root length, number of the lateral roots, root surface area, and root volume were significantly negatively correlated with the wilting index and positively correlated with the root volume. Based on these results, sixty-two soybean germplasms were comprehensively evaluated for drought-tolerant cultivar by the principal component analysis (PCA). The results showed that Tiefeng 31 was the most drought-tolerant elite cultivar. However, Fengdou 93 was the most drought-sensitive elite variety. The drought tolerance screening results were consistent with the wilting index and RSA analysis, especially the root length. Both droughts tolerant and sensitive elite cultivar could be further used to breed drought-tolerant germplasms and to clarify the drought tolerance mechanism in soybean.

中文翻译：

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大豆（Glycine max L.）苗期枯萎指数和根系形态特征作为耐旱品种选择

干旱胁迫是影响农业生产的常见问题。大豆植物是对干旱敏感的作物之一，在严重干旱的年份可能会损失高达 40% 的产量。提高耐旱性一直是大豆育种计划的主要目标之一。在这项研究中，通过分析在聚乙二醇 (2.5 M PEG 8000, - 0.54 MPa) 模拟干旱胁迫下幼苗期的冠层和根系形态特征，评估了 62 个大豆 [Glycine max (L.) Merri.] 种质资源，包括地方品种和优良品种. 结果表明，PEG处理4天后，62份大豆种质的萎蔫指数表现出显着的多态性差异。萎蔫指数最低的是铁丰31号为2.75，最高的是凤斗93号和松子豆号为9号。通过回归分析，萎蔫指数与株高、电解质渗漏呈正相关，与地上部分干重、气孔导度和蒸腾速率呈负相关。根系结构（RSA）研究表明，根冠比、根长、侧根数、根表面积和根体积与萎蔫指数呈显着负相关，与根体积呈显着正相关。基于这些结果，通过主成分分析（PCA）对 62 个大豆种质进行了综合评价耐旱品种。结果表明，铁丰31是最耐旱的优良品种。然而，丰豆93是对干旱最敏感的优良品种。耐旱性筛选结果与萎蔫指数和RSA分析一致，尤其是根长。耐旱和敏感优良品种均可进一步用于培育耐旱种质和阐明大豆的耐旱机制。