Poor soil fertility is a major problem in many common bean growing regions of Africa, leading to sub-optimal yields.  One of the limiting soil macronutrients is potassium (K).  Potassium deficient plants have reduced leaf area, lowered photosynthetic capacity, and limited yield potential.  Because we are interested in developing new, higher yielding bean cultivars for African farmers, we have worked to identify K-efficient Andean bean lines (more tolerant of limited K supply) that could be deployed directly, or used in bean breeding programs.  For these experiments, diverse Andean bean lines were selected to assess expansive leaf growth (leaf area) in response to limited availability of K.  Plants were grown hydroponically on a complete nutrient solution until full expansion of the unifoliate leaves.  Plants were then maintained on control K (1.2 mM), 300 µM K, or 50 µM K.  After 10 days, first and second trifoliolate leaves were removed, scanned on a photocopier, and areas of trifoliolate leaves were measured using a tool in Photoshop.  Relative to the 1.2 mM K controls, leaf area of first trifoliolates was reduced by as little as 10% to as much as 60% in a range of Andean lines grown on 50 µM K, and from as little as 0% to as much as 69% in second trifoliolates.  Similarly, the leaf area of first trifoliolates was reduced by as little as 0% to as much as 48% in the same Andean lines grown on 300 µM K (relative to controls), and from 0% to 60% in second trifoliolates.  Our results demonstrate that broad genetic diversity exists for K efficiency in Andean bean lines.  Genome-wide association mapping will be conducted in an attempt to find quantitative trait loci associated with enhanced K efficiency.  The identification of K-efficient lines and the potential for K-efficiency molecular markers will help us develop new bean varieties for K-limited soils in Africa.  This work was funded in part by the USDA Agricultural Research Service through Cooperative Agreement No. 58-6250-0-008 and by USAID as part of Feed the Future, the U.S. Government’s Global Hunger and Food Security Initiative.