Identification and Validation Of Iron Deficiency Chlorosis Quantitative Trait Loci Using Linkage Mapping In a Soybean Population.

Iron deficiency chlorosis (IDC) is an important abiotic stress prevalent on calcareous soils.  Growing tolerant  genotypes remains the most cost effective management strategy for producers, so research to understand the genetics and physiology of IDC tolerance is important to improve efficiency and effectiveness of breeding and selection. Linkage mapping and association mapping studies in soybean have identified approximately 42 quantitative trait loci (QTL), explaining close to 70% of the phenotypic variance. Further linkage mapping is needed to validate and refine the positions of most these QTL. A population of 320 F₆-derived recombinant inbred lines (RILs) was developed and phenotyped for foliar IDC symptoms based on a visual rating score of chlorosis severity. The tolerant parent is derived from a recurrent selection program for improved IDC score on high-pH soil while the susceptible parent was selected from among elite lines in a cultivar development program.  The RILs were evaluated in short-row plots in 7 replications of an augmented incomplete block design on high-pH soil.  The mean IDC scores for RILs ranged from 2.2 to 7.5, with a significant difference between the tolerant parent (3.2) and the susceptible parent (6.8) and a power of 0.85 to identify a 1 unit difference in mean IDC score as significant. Selective genotyping of the top and bottom 20% tails was performed using genotyping-by-sequencing. Linkage mapping was performed using R/QTL software to identify regions significant for IDC tolerance. Results from the QTL analysis will be presented. Markers associated with IDC tolerance can be used for marker assisted selection by breeders.