Characterization of a soybean (<i>Glycine max</i> L. Merr.) germplasm collection for root traits

Root systems that improve resource uptake and penetrate compacted soil (hardpan) are important for improving soybean (Glycine max L. Merr.) productivity in optimal and sub-optimal environments. The objectives of this research were to evaluate a soybean germplasm collection of 49 genotypes for root traits, determine whether root traits are related with plant height, shoot dry weight, chlorophyll index, and seed size, and identify genotypes that can penetrate a hardpan. Plants were maintained under optimal growth conditions in a greenhouse. Single plants were grown in mesocosms, constructed of two stacked columns (top and bottom columns had 25 and 46 cm height, respectively, and 15 cm inside diameter) with a 2-cm thick wax layer (synthetic hardpan; penetration resistance, 1.5 MPa at 30°C) in between. Plants were harvested at 42 days after planting. Significant genetic variability was observed for root traits in the soybean germplasm collection, and genotypes that penetrated the synthetic hardpan were identified. Genotypes NTCPR94-5157, NMS4-1-83, and N09-13128 were ranked high and PI 424007 and R01-581F were ranked low for most root traits. Shoot dry weight and chlorophyll index were positively related with total root length, surface area, and volume, and fine root length (Correlation coefficient, r ≥ 0.60 and P-value < 0.0001 for shoot dry weight and r ≥ 0.37 and P-value < 0.01 for chlorophyll index]. Plant height was negatively correlated with total root surface area, total root volume, and average root diameter (|r| ≥ 0.29, P-value < 0.05). Seed size was not correlated with any root traits. The genetic variability identified in this research for root traits and penetration are critical for soybean improvement programs in choosing genotypes with improved root characteristics to increase yield in stressful or optimum environments.能够提升养分吸收能力并穿透紧实土壤（硬盘层，hardpan）的根系，对于在最优与亚最优环境下提升大豆（Glycine max L. Merr.）的产量至关重要。本研究的目标为：评估包含49份基因型的大豆种质资源群体的根系性状，明确根系性状与株高、地上部干重、叶绿素指数以及种子大小之间的关联，并筛选出能够穿透硬盘层的基因型。 试验在温室最优生长条件下开展，单株种植于堆叠式中宇宙栽培柱体系（mesocosms）中：该体系由两个上下堆叠的柱体构成，上柱高度25 cm、下柱高度46 cm，内径均为15 cm，两柱之间设置有2 cm厚的蜡质层（人工模拟硬盘层；30℃下穿透阻力为1.5 MPa）。于播种后42天收获植株。 本大豆种质资源群体的根系性状存在显著的遗传变异，同时筛选出了能够穿透人工模拟硬盘层的基因型。在多数根系性状上，基因型NTCPR94-5157、NMS4-1-83与N09-13128表现优异，而PI 424007与R01-581F则表现较差。 地上部干重与叶绿素指数均与总根长、总根表面积、总根体积以及细根长呈显著正相关（地上部干重的相关系数r≥0.60，P值<0.0001；叶绿素指数的相关系数r≥0.37，P值<0.01）。株高则与总根表面积、总根体积以及平均根直径呈显著负相关（|r|≥0.29，P值<0.05）。种子大小与所有根系性状均无显著相关性。 本研究中鉴定出的根系性状与穿透能力的遗传变异，对于大豆育种项目至关重要——可用于筛选具备优良根系特性的基因型，从而在胁迫或最优环境下提升大豆产量。