Evaluation of iron deficiency chlorosis in soybeans ( Glycine max)

Iron is an important micronutrient required for healthy plant growth. Significant yield reductions can result if the plant does not have proper levels of iron to maintain certain cellular functions. Iron deficiency chlorosis (IDC) is a major abiotic stress that affects soybeans grown on high-pH calcareous soils, primarily in the North Central region of the USA (Hansen et al., 2003). The degree of chlorosis depends on many aspects such as soil pH, temperature, and free carbonate levels. This research project studied the genetic control of IDC using conventional breeding and biotechnology methods. Specifically, three studies were conducted to gain a comprehensive view of genetic control of IDC in soybean to enhance development of IDC tolerant soybean cultivars for soybean producers, by i) genomic analysis of a long-term recurrent selection program, ii) mapping of QTLs using a recombinant inbred line population, and iii) phenotypic characterization of the Arabidopsis FRO2 gene on calcareous soils in a soybean background. Results from the recurrent selection analysis revealed clear signatures of selection at 4 important loci for IDC. Loss of genetic diversity was extensive as only 44% of markers polymorphic in the founders remained polymorphic in the most advanced cycle 10. The linkage mapping analysis revealed 4 significant (LOD \u3e 3.11) loci on separate chromosomes. Together these loci account for 27% of the phenotypic variation. There were no statistically significant interactions among these QTLs. Gene models related to IDC located within 600 kilobases of the significant marker include previously identified genes such as NRAMP2 and bHLH038. Evaluation of soybean with AtFRO2 on high-pH calcareous soil environments revealed no significant differences in IDC tolerance compared to wild-type. There were no significant differences among individual NILs differing for FRO2 in 2012 or 2013. Averaged over genotypes, the FRO2+ NIL class was not significantly different than the FRO2- class in either 2012 or 2013. This data provides support that the reduction of ferric iron to ferrous may not be the rate-limiting step in the iron uptake pathway in soybeans