Identification of Quantitative Trait Loci (QTL) Affecting Seed Mineral Content in the Model Legume Medicago truncatula.

Increasing the amount of bioavailable micronutrients such as iron and zinc in plant foods for human consumption is a challenge especially in developing countries where plant foods comprise a significant portion of the diet.  Legume seeds have the potential to provide the essential nutrients required by humans.  However, the concentrations of minerals such as Fe and Zn are low when compared to other foods.  In order to increase the seed mineral concentration, it is important to understand the genetic basis for mineral concentration in the seeds and the rate limiting steps involved in the mineral distribution. To determine the loci governing seed mineral concentrations, content and average seed weight in legumes, 175 lines of Medicago truncatula RIL population (Jemalong-6 X DZA 315.16) were grown for seed harvest for subsequent seed mineral analysis using ICP-OES in 2004 and 2006.  QTL cartographer was used to identify quantitative trait loci (QTL) using composite interval mapping (CIM). Transgressive segregation was observed for nearly all the minerals suggesting that both parents carry alleles affecting mineral levels in seeds. Significant correlations between different minerals were observed for both years, which might indicate cosegregation of genes for traits. CIM identified a total of 45 significant QTL for all minerals in both years. Of the 45 QTL detected, one or more loci were detected for all minerals during both years. Colocation of QTL for several minerals was found in different regions for both years, which might indicate that common whole plant phenotypic traits such as transpiration efficiency or common transporters might be contributing to seed mineral levels. Our results also suggest that seed size is an important determinant in seed mineral concentration.