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Research Highlights

Research Highlights
Dissecting the Genetic and Molecular Basis of Abiotic Stress Tolerance in Fiskeby III Soybean for Advancing Breeding Outcomes

Experimental soybean lines that are nearly genetically identical, differing for only a few genes. The line in the background shows superior IDC tolerance to the line in the front, which has very yellow leaves with green veins. This is a classic symptom of iron deficiency.

By Robert Stupar, Ph.D., University of Minnesota

It is mid-June in western Minnesota, near the town of Benson. Jim Johnson is driving down back country roads, passing his fields of soybeans and corn after a few weeks of wet weather. The corn he is not so concerned about. The adequate rainfall has been perfect, and those fields look great. The soybeans have him worried, because Jim knows that in his higher pH soil, and with the steady moisture, they are at risk of iron deficiency chlorosis (IDC). He gets to one of his lower-lying soybean fields that does not drain as well and, sure enough, his beans are starting to turn bright yellow at the top trifoliates, with leaf veins remaining distinguishably green. At this point, Jim knows that there is not much he can do and is wondering just how bad his yield will be this year. 

While Jim is a fictitious character, he illustrates the very real problems of soybean growers in regions with high pH soils and high levels of calcium carbonates. IDC, often called “chlorosis,” occurs when soybeans cannot get enough iron from the soil. Iron is the fourth most abundant element so it is not missing, but instead is unavailable to plants due to the high soil pH. Iron is a crucial element of many biological processes, including chlorophyll production and photosynthesis. Yield-loss estimates due to IDC are over $100,000,000 annually. The best defenses against IDC are selecting a variety with good tolerance and field application of iron chelates at planting, but this is not always sufficient. 

This project, funded at the $157,612 level, will identify a particular IDC tolerance gene(s), and understand at the gene level how to develop varieties that are more tolerant to IDC. The list of potential genes responsible for tolerance has been narrowed from hundreds of possibilities to just a handful. To help identify which of the remaining genes causes IDC, expression of each of these genes in soybean plants is being reduced. Once identified, the specific gene(s) used in the plant and differences between varieties will be studied in order to create more efficient advances in breeding for more tolerant varieties. 

Enough is already known to start breeding the source of tolerance into a few elite University of Minnesota breeding lines. The source of the tolerance gene is a cultivar called Fiskeby III, a maturity group 00 variety developed in Sweden in the 1940s for edamame, which does not have the best agronomic qualities but does have high tolerance to many environmental stresses, including drought. 

In addition, the discovery pipeline used for understanding IDC is being applied to uncover the genes useful for drought tolerance, and to breed those genes into elite varieties. The results of this work will allow soybean growers to plant varieties that can better handle stresses such as IDC and drought. 

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.