Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange
Abstract
Soybean production in most of the northern plain area is challenged by iron deficiency chlorosis (IDC), a physiological problem with plants grown in high pH calcareous soils. Planting tolerant varieties is the best approach to meet the challenge. Currently, the variety development is limited by lack of genetic resources and knowledge about mechanisms of resistance to IDC. The previous research in the Seed Molecular Biology Laboratory at SDSU developed a population of recombinant inbred lines (RILs) from a cross between a cultivated (Glycine max) and a wild (G. soja) soybean line. The objectives of this research were: 1) to evaluate the RIL population for genetic variability of the IDC trait and its relationship with plant iron (Fe) content, and 2) to generate a linkage map covering the wild soybean genome to map quantitative trait loci (QTL) associated with the IDC trait. A total of 207 RILs were grown in the same field (soil pH 8.0 - 8.3) with four replications to evaluate IDC symptoms using a 1 (most resistant) – 5 (most susceptible) scale at 3 or 4 time points of plant development in summers of 2012 and 2013. Plants from 25 RILs (5 for each of the 5 scales) were sampled to quantify soluble (Fe2+) and total Fe contents using atomic absorption spectrometry and inductively coupled plasma-optical emission spectrometry (ICP-OES). Simple sequence repeat (SSR) markers were screened for polymorphism between the cultivated and wild soybean lines to genotype the RILs to construct a linkage map. An interval-mapping program was used to scan for IDC QTL along the map. The IDC trait displayed continuous variation in the RIL population at each of the 3 or 4 time points. Both genotypic and environmental (year and field block) effects on IDC were significant. Estimated heritability for the IDC trait varied from 26 to 72%. The IDC scales were negatively correlated with the leaf soluble Fe content (r= -0.93) and positively correlated with the leaf total Fe content (r=0.94), demonstrating that the phenotypic variation in the IDC symptom was due to the lack of soluble Fe2+ in leaves. A framework linkage map was constructed with 164 markers and map consists of 36 linkage groups belonging to 20 soybean chromosomes. A total of 11 QTLs were associated with the IDC trait, with 5 of them being repeatable across the two years. Each QTL accounted for 7 to 16% of the total phenotypic variances. The parental line of wild soybean contributed the IDC-resistance allele to one QTL detectable in the two years. These 11 QTL were mapped on 8 chromosomes, with two QTL on chromosomes 18 co-located with the previously reported loci for the IDC trait in soybean. In summary, the IDC trait in the RIL population had a moderate level of heritability under the local field conditions and the genotypic variation was caused by the lack of soluble Fe in the leaf tissue. With the associated 11 putative QTLs, the alleles that enhance resistance to IDC distribute in both cultivated and wild soybean germplasm. The RIL population will be used to confirm the putative QTL in environments with different stress levels. The QTL repeatable in the two years could be used in breeding programs by backcrossing and marker-assisted selection techniques
