Rhizobitoxine-induced chlorosis and the soybean response

Abstract

This study was conducted to understand the soybean response to rhizobitoxine-induced chlorosis. This study consisted of four objectives: (1) to study the inheritance of soybean susceptibility to rhizobitoxine, (2) to locate molecular markers associated with rhizobitoxine susceptibility in the soybean genome, (3) to screen important soybean ancestors to determine how common rhizobitoxine susceptibility might be in modern cultivars, and (4) to determine if rhizobitoxine-producing strains affect soybean yield in field grown soybeans.

Based on chi-square analysis, the F2 progeny segregated in a 9 susceptible to 7 resistant ratio, indicating that two genes are responsible for the soybean response to rhizobitoxine-induced chlorosis. This ratio was confirmed in the screening of the F2:3 population. In addition, results from F1 plants revealed that the genes for susceptibility to rhizobitoxine-induced chlorosis are dominant to genes for resistance.

SSR markers were used to locate genes responsible for rhizobitoxine-induced chlorosis. 455 total markers were screened and 141 (31%) were polymorphic for the parents Brim and CNS. A gene was identified by marker Satt 657 on LG F that was found to be highly significant and explained 32% of the phenotypic variation among F2 plants. The other gene was not found and further work is needed to determine its location.

The results of the ancestor soybean screening revealed that the frequency of alleles that are susceptible to rhizobitoxine-induced chlorosis are more common in southern soybean ancestors than in northern soybean ancestors. It was also reported that soybean ancestors that are resistant to rhizobitoxine-induced chlorosis can potentially pass on susceptible alleles to progeny.

A field study on the affects of rhizobitoxine-producing strains on yield of soybean showed that these strains can reduce yields 8-13% when compared to non-rhizobitoxine producing strains. These results are similar to earlier reports that rhizobitoxine-producing strains lower yields in field grown soybean.