Characterization of Genetic Basis on Synergistic Interactions between Root Architecture and Biological Nitrogen Fixation in Soybean.

Yongqing Yang,Dong Liu,Wandong Qi,Qingsong Zhao,Mengchen Zhang,Chunyan Yang,Hong Liao,Xinxin Li,Wenqin Ai

doi:10.3389/fpls.2017.01466

Abstract

Soybean [Glycine max (L.) Merr] is an important legume crop and its yield largely depends on root architecture (RA) and biological nitrogen fixation (BNF). However, the relationship between RA and BNF, and its genetics behind remain unclear. Here, two soybean genotypes contrasting in RA and their 175 F9:11 recombinant inbred lines (RILs) were evaluated in field. The shallow-root parent, JD12, had better nodulation and higher yield than the deep-root parent, NF58. Strong correlations between shoot dry weight (SDW) and RA or BNF traits existed in the RILs, and the shallow-root group had more and heavier nodules, as well as higher SDW. After inoculating with rhizobia, roots became shallower and bigger, showing strong synergistic interactions between RA and BNF. In total, 70 QTLs were identified for the 21 tested traits. Among them, qBNF-RA-C2, qBNF-RA-O, and qBNF-RA-B1, were newly identified QTLs for BNF and/or RA traits in soybean, which co-located with the QTLs for SDW detected presently, and with the QTLs for yield identified previously. The results together suggest that there are synergistic interactions between RA and BNF, and the QTLs identified here could be used for breeding new soybean varieties with higher yields through optimization of RA traits and BNF capacity.

Highlights

Soybean [Glycine max (L.) Merr.] is an economically and ecologically important crop that provides protein and oil for food and feed, and serves as a key source of green manure in agroecosystems due to its having the highest capacity of biological nitrogen fixation (BNF) observed among leguminous crops (Coale et al, 1985; Kumudini et al, 2008)
The two parental genotypes did not significantly differ in total root length (TRL) and root dry weight (RDW) (Supplementary Figure S1), suggesting that the better growth of JD12 might be attributed to its shallow root architecture (RA)
The importance of legume breeding in increasing BNF has been highlighted for several decades, yet understanding of the genetics underlying BNF and variations of associated traits under different environmental conditions remains limited (Kouchi et al, 2010; Pandey et al, 2016)

Summary

Introduction

Soybean [Glycine max (L.) Merr.] is an economically and ecologically important crop that provides protein and oil for food and feed, and serves as a key source of green manure in agroecosystems due to its having the highest capacity of biological nitrogen fixation (BNF) observed among leguminous crops (Coale et al, 1985; Kumudini et al, 2008). It is estimated that BNF provides 50–70 million tons of N for agricultural systems each year, and, might be the most important source of N for agro-ecosystems (Herridge et al, 2008). A large proportion of the N2 fixed by nodules in soybean is available for the growth of subsequent crops in rotation systems, and thereby, makes the soybean-rhizobia symbiosis an efficient way to sustain agricultural development (Qin et al, 2012; Udvardi and Poole, 2013; Pandey et al, 2016). Breeding elite soybean cultivars that optimize BNF could be an important component of producing high yielding crops while maintaining agriculture sustainability

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