Soybean PI 416937 Root System Contributes to Biomass Accumulation in Reciprocal Grafts

Abstract

Soybean [Glycine max (L.) Merr.] plant introduction PI 416937 (PI4) has an extensive fibrous‐like root system that contributes to enhanced drought and Al tolerance. The root system of PI4 appears to be more highly nodulated than standard southern U.S. cultivars, and thus has potential for enhanced N2 fixation. Genetic transfer of PI4 root system to soybean cultivars may lead to increased seed N at harvest through increased biomass or seed protein concentration. This hypothesis has not been tested. The objective of this study was to determine the influence of PI4 root system on plant productivity and protein accumulation in soybean seedling reciprocal grafts grown to maturity in the field. In three experiments, grafts were initiated 5 d after greenhouse planting by transversely severing the hypocotyl 2 cm below the apical meristem and transferring wedge‐cut scions to severed root stock. Plants were then transplanted and grown in the field. PI 416937 maintained its superior root fibrosity in graft combination with other genotype scions. In Exp. 2, at the end of the season, plants of non‐PI4 scions grafted to PI4 root stock averaged significantly higher in root fibrosity score (8.2) than the mean of their self‐grafts (6.0); however, when PI4 scions were grafted to root stock from other genotypes, the root fibrosity score decreased significantly (6.6) compared with PI4 self graft (8.4). Thus, grafting revealed that the root system itself, rather than the scion of PI4, regulates expression of the fibrous‐like rooting trait. Seed protein concentration did not increase significantly for genotype scions grafted to PI4 root stock. In Exp. 3, ‘Lee 74’ or N85‐492 grafted to PI4 root stock had significantly higher seed dry weight (161.1 g plant−1 for Lee 74 grafted to PI4 vs. 96.4 g plant−1 for the self‐graft; 129.5 g plant−1 for N85‐492 grafted to PI4 vs. 79.4 g plant−1 for the self‐graft). The fibrous‐like root system of PI4 enhances seed biomass when grafted to some non‐PI4 genotypes. The genetic transfer of the PI4 rooting trait to elite germplasm through applied breeding may lead to the development of more productive soybean lines.