Investigation of root phenotype in soybeans (Glycine max L.) using imagery data

Roots are the most essential plant part owing to the uptake of water and nutrients. Therefore, phenotyping of root features is vital for improving soybean cultivars. This study evaluated the root morphological and architectural traits of six soybean cultivars using two-dimensional (2D) root imaging. The cultivars were selected from a previous experiment, based on 6 root phenotypes (total root length [TRL], surface area [SA], average diameter [AD], number of tips, number of forks, and main total length [MTL]) in 372 soybean cultivars, (3 each from the highest 5% and lowest 5%). When plants reached two trifoliate leaves stage, both root and shoot parts were harvested and analyzed. According to the analysis of variance, significant variability was observed between the two groups (highest 5% and lowest 5%) for root and shoot morphological traits, but no significant difference was found regarding most root architectural traits. Among three root phenotypes (TRL, SA, and RV [root volume]), IT 21595 and IT 165432 were the highest and lowest, respectively. TRL exhibited a significant positive correlation with other root and shoot morphological traits, such as SA, RV, leaf area, leaf length, and leaf width. Contrastingly, AD showed a significant negative correlation with those parameters. TRL and SA of all the cultivars were classified based on root diameter classes (0–0.5 mm, 0.5–1.0 mm, and 1.0–1.5 mm). A segment of TRL < 0.5-mm root diameter was observed from 74.0 to 75.6% in the highest 5% cultivars and 63.7–75.3% in the lowest 5% cultivars. A segment of SA < 0.5-mm root diameter was observed from 42.0 to 46.9% in the highest 5% cultivars and a relatively reduced ratio (34.5–44.7%) in the lowest 5% cultivars. Conclusively, this research highlighted the characterization of root morphological and architectural traits and some soybean cultivars.