Mapping quantitative trait loci (QTL) for plant nitrogen isotope ratio in soybean

Authors: BAZZER, SUMANDEEP - University Of Arkansas; Ray, Jeffery - Jeff; Smith, James - Rusty; FRITSCHI, FELIX - University Of Missouri; PURCELL, LARRY - University Of Arkansas

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2020
Publication Date: 11/15/2020
Citation: Bazzer, S.K., Ray, J.D., Smith, J.R., Fritschi, F.B., Purcell, L.C. 2020. Mapping quantitative trait loci (QTL) for plant nitrogen isotope ratio in soybean. Euphytica. https://doi.org/10.1007/s10681-020-02726-3.
DOI: https://doi.org/10.1007/s10681-020-02726-3

Interpretive Summary: Soybean meets a large portion of its nitrogen need through biological nitrogen fixation, a process through which nitrogen in the air is incorporated into compounds that can be used by plants. The purpose of this study was to determine regions in the soybean genome that are associated with nitrogen fixation. In this study, nitrogen isotope ratios were used as a measure of biological nitrogen fixation in a genetically segregating soybean population grown in multiple field environments. A total of 10 genomic regions were putatively identified on seven chromosomes as being associated with nitrogen fixation. These identified regions may be used in marker-assisted selection by plant breeders for enhancing nitrogen fixation in soybean. The study also provides additional information to the research community of soybean geneticists and physiologists on which genes might potentially be involved in nitrogen fixation.

Technical Abstract: Soybean (Glycine max (L.) Merr.) meets a large portion of its nitrogen (N) need via biological N2 fixation, which is highly sensitive to drought stress. Nitrogen isotope ratios between 15N and 14N (d15N) can be used as a metric for relative differences among soybean genotypes for N2 fixation, as d15N is negatively associated with N2 fixation. This study evaluated the genetic basis of d15N using a mapping population of 196 F6-derived recombinant inbred lines (RILs) developed from a cross between PI 416997 and PI 567201D that was assessed in multiple environments. There was a wide range of d15N in all environments and narrow-sense heritability for d15N was 35% when estimated across environments. Analysis of variance of d15N showed significant effects of genotype and environment, whereas the genotype × environment interaction was not significant (P<0.05). Inclusive composite interval mapping for individual environments identified 10 additive QTLs on seven chromosomes with additive effects ranging from 0.02 to 0.13‰ and that individually explained phenotypic variation from 1.72 to 9.34%. In total, eight QTL × environment interactions were found, and several genomic regions were involved in QTL × QTL interactions that were not identified as additive QTLs. These identified QTLs were co-localized with genomic regions associated with N2 fixation and other physiological traits identified in previous studies. A search for candidate genes resulted in detection of genes for nodulation and N-metabolism underlying many additive and epistatic QTLs. These identified regions may serve as potential targets for enhancing N2 fixation in soybean.