EARLY-SEASON GROWTH IN RELATION TO REGION OF DOMESTICATION, SEED SIZE, AND LEAF TRAITS IN COMMON BEAN

In common bean (Phaseolus vulgaris L.) large-seeded lines (which are p redominately of Andean background) have a smaller relative growth rate (RGR) during early season growth (up to 30 days after sowing) than do lines with small seed size (which are predominately of Mesoamerican b ackground). Growth analyses, single-leaf gas exchange, and internal le af anatomy were studied during vegetative growth for 16 lines of commo n bean (9 Andean and 7 Mesoamerican) at Palmira and Popayan, Colombia, and for 14 Lines at Gainesville, Florida, to determine the basis for the smaller RGR of large-seeded Andean lines. Pooled analyses across s ites revealed that RGR, net assimilation rate (NAR), single-leaf carbo n exchange rates (CER), specific leaf weight (SLW), specific leaf N (S LN), leaf thickness, and mesophyll-cell surface area per unit leaf are a (A(m)/A) exposed to air were all smaller for large-seeded Andean lin es than for small-seeded Mesoamerican lines. Relative growth rate was positively correlated (P < 0.10) with CER at all three sites. We postu late that the smaller RGR of the large-seeded Andean lines is a functi on of their slower CER, which result from thinner leaves with less pho tosynthetic apparatus per unit leaf area.