Objective  Tolerance to deficient supply of phosphorus of soybean varieties at seedling stage was determined, and viable identification indicators selected to aid the breeding and resource utilization of soybean germplasms in southwest China.

  Method   Ten soybean germplasms were treated by varying degrees of phosphorus stress along with a blank control in a hydroponic experiment. Nineteen morphological, physical, and biochemical properties on the seedlings, including plant height, leaf area, shoot and root biomass, root length, root volume, root surface area, chlorophyll content, photosynthetic rate, and transpiration rate, were monitored during the treatment for the index selection. The low-phosphorus tolerance coefficient on each indicator was then used to finalize the selection based on the analyses of factor, membership function, cluster, and grey correlation.

  Result  The Grey correlation analysis showed that the shoot fresh weight, transpiration rate, shoot dry weight, stomatal conductance, leaf area, plant height, stem diameter, and root volume closely related to the tolerance of a soybean plant. The cluster analysis grouped the 10 soybean varieties into highly tolerant, moderately tolerant, and weakly tolerant categories.

  Conclusion  Among the tested varieties Tiefeng No.31 and Dian 86-4 exhibited the strongest phosphorus absorption and utilization ability at seedling stage. The shoot fresh weight, transpiration rate, shoot dry weight, stomatal conductance, leaf area, plant height, stem diameter, and root volume were the choice indicators for evaluating the tolerance to deficient phosphorus supply of soybean plants at seedling stage.