Dynamics of Dry Matter and Mineral Allocation to Pod Walls Versus Seeds in Common Bean.

Common bean (Phaseolus vulgaris) is an important source of dietary nutrients, energy, and fiber.  Although its seeds store starch, protein, minerals and vitamins, we have yet to fully understand how the movement of minerals, amino acids, and sugars are regulated from the main plant to the seeds.  This movement of compounds from vegetative tissues and pod walls to the developing seeds determines not only the nutritional value of those seeds, but also impacts total harvest yield of the crop.  One aspect of this nutrient/yield phenomenon which has received only limited attention is the role of the pod wall in intercepting and re-routing nutrients and sugars from the main plant to the growing seeds.  Previous studies have shown that genetic variation exists for dry matter distribution between bean seeds and their pod walls.  Our analyses of various agronomic legumes shows beans averaging around 75% for this seed partitioning parameter, while chickpea and pea genotypes averaged 86% and 88%, respectively, with broad variation seen for each of these species.  Thus, with the variation already inherent in bean, along with the fact that some legumes have the capacity to partition more of their pod wall nutrients and biomass to seeds, we believe that significant genetic gains for this trait are possible in bean.  Interestingly, it is important to note that an improvement in this seed partitioning trait (as percent of total pod) would not require any additional photosynthetic output by the plant; it relies entirely on a redistribution of sugars, amino acids, and minerals that have already been delivered to (and/or synthesized within) the reproductive structure (pod wall pus seeds).  Detailed analyses of pod wall-to-seed nutrient and dry matter dynamics will be presented for a diverse set of bean germplasm.  The information will be used to discuss strategies for manipulating pod and seed nutrient allocation to enhance dry matter and nutritional yield in bean.  This work was supported by USAID as part of the Feed the Future Program.