Location: Soybean and Nitrogen Fixation ResearchTitle: Inheritance of rhizobitoxine induced chlorosis in soybean
|ROBINSON, KEITH - United States Patent And Trademark Office|
|BURTON, JOSEPH - North Carolina State University|
|ISRAEL, DANIEL - North Carolina State University|
|Carter Jr, Thomas|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2020
Publication Date: 5/5/2020
Citation: Robinson, K., Burton, J., Taliercio, E.W., Israel, D., Carter Jr, T.E. 2020. Inheritance of rhizobitoxine induced chlorosis in soybean. Crop Science. https://doi.org/10.1002/csc2.20193.
Interpretive Summary: There are two species of Bradyrhizobium which nodulate soybean, (Glycine max (L.) Merrill), and fix nitrogen (N), B. japonicum and B. elkanii. Strains of B. elkanii produce rhizobitoxine (RT) in root nodules, a toxin that causes chlorosis on newly developing trifoliates of some field grown soybean. Others are resistant to rhizobitoxine induced (RI) chlorosis. Sensitivity to RT may reduce yield when a sensitive soybean is nodulated by a toxin-producing strain of B. elkanii. Examination of F1 hybrids and F2 progeny derived from crosses between RT resistant and sensitive soybean varieties indicate that RT resistance is recessive and there are two independent genes controlling the trait. Further genetic analysis identified a locus near marker Satt657 on chromosome 13 for resistance to RT. A second locus was not identified. This insight can be used to breed RT resistance into elite soybean cultivars growing in the Southern US where B. elkanii predominates.
Technical Abstract: There are two species of Bradyrhizobium which nodulate soybean, (Glycine max (L.) Merrill), and fix nitrogen (N), B. japonicum and B. elkanii. B. elkanii is endemic to soils in the southeastern region of the United States. While B. elkanii has been shown to be a less efficient nitrogen fixer than B. japonicum on soybean, there is some evidence that it may be superior in water stressed environments. Strains of B. elkanii produce rhizobitoxine (RT) in root nodules, a toxin that causes chlorosis on newly developing trifoliates of some field grown soybean. Others are resistant to rhizobitoxine induced (RI) chlorosis. The objective of this research was to determine the inheritance of soybean resistance to RI chlorosis. Crosses were made between resistant and susceptible. Progeny were identified as susceptible, resistant, or segregating in the first, second and third self- pollinated generations. All F1 hybrids from crosses between resistant and susceptible soybean exhibited seedling chlorosis, indicating that genes for resistance to chlorosis are recessive. The F2 progeny segregated in a ratio of 9 susceptible to 7 resistant, indicating that there are two genes responsible for the soybean resistance to RI chlorosis. This ratio was confirmed in F2:3 populations screening. One hundred forty-one SSR markers polymorphic in both a susceptible parent and a resistant parent were used to locate the genes responsible for resistance to chlorosis. A quantitative trait locus (QTL) found near marker Satt 657 on LG F (chromosome 13)explained a statistically significant 32% of the phenotypic variation among F2 plants based on the p-value and R2 of a single factor ANOVA. The second gene was not located.