Mapping QTLs Associated with Root Growth and Architecture in Soybean.

Understanding root structure and function is critical to crop improvement in water limited environments. From a breeding standpoint, root traits are recognized as selection criteria to improve drought tolerance. However selection for root traits is a challenge because of the difficulty in measurement and their quantitative nature of inheritance. The identification of quantitative-trait loci (QTLs) is the first step towards the development of DNA markers for marker-assisted breeding and discovery of genes controlling root characteristics in soybean. Both the dynamics of root growth under well-watered conditions (constitutive root traits) and root growth response to drought stress (adaptive root traits) improve drought resistance by increasing water uptake from deeper soil layers. The objective of this study is to map the QTLs associated with tap root length, number of lateral roots, and root biomass in soybean (Glycine max (L.) Merr.) under well-watered conditions. We established a screening technique called “the cone system” using turface:sand medium. Using this system, thirty eight soybean germplasm including cultivars, plant introduction lines, and wild soybean were evaluated for tap root length and root biomass under well-watered conditions. We identified two parental lines of a mapping population developed at the University of Nebraska; Dunbar (Glycine max) and PI325682A (Glycine soja) with tap root length of 22 and 13 cm, respectively, 12 days after sowing. These parents also showed significant variation for tap root length (18 and 56 cm) 21 days after sowing in 2-foot tall tubes.  We are screening plants of BC2-F5-derived population of 277 recombinant inbred lines developed from Dunbar X PI326582A under controlled environmental conditions using the cone system. There are 204 SSRs, 35 SNPs, and 4 Classical (I/i, %/5, L1/l1, and L2/l2) markers mapped in the 277-RIL population. The phenotypic variation for root traits in this population and genetic mapping results will be presented.