Inheritance of rhizobitoxine‐induced chlorosis in soybean

Abstract

There are two species of Bradyrhizobium that nodulate soybean [Glycine max (L.) Merr.] and fix nitrogen (N): B. japonicum and B. elkanii. Bradyrhizobium elkanii is endemic to soils in the southeastern region of the United States. Some strains of B. elkanii produce rhizobitoxine (RT), a toxin that causes chlorosis on newly developing trifoliates of some field‐grown soybean, in root nodules. Some soybean genotypes 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 cultivars. 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 nine susceptible to seven resistant, indicating that there are two genes responsible for the soybean resistance to RI chlorosis. This ratio was confirmed in F2:3 population screening. One hundred forty‐one simple sequence repeat (SSR) markers polymorphic in both a susceptible parent and a resistant parent were used to locate the genes responsible for resistance to chlorosis. A gene found near marker Satt 657 on linkage group (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.