Variation in parameters related to leaf thickness in common bean (Phaseolus vulgaris L.)

Greater leaf thickness is usually associated with greater leaf carbon assimilation rate, but the tradeoff between thicker versus larger leaves also affects canopy structure and light interception. Many studies equate the ratio of dry leaf mass to area (leaf specific mass) with leaf thickness. This approximation has utility but ignores differences in true thickness due to variation in water or air content and other factors. To understand better variation in leaf thickness in common bean (Phaseolus vulgaris L.), 14 parameters related to thickness were compared for a diverse set of bean cultivars grown in three field environments in Colombia. The parameters included leaf thickness per se as measured anatomically or with a micrometer, leaf specific mass expressed on dry and fresh weight bases, leaf optical density measured at 670 nm, total leaf chlorophyll concentration expressed on a leaf area basis, leaf tissue density, and nitrogen concentration expressed on fresh and dry weight bases. Relative contributions of air, water, and dry matter to leaf thickness were also estimated. Most parameters showed large differences among lines, consistent with previous reports that cultivars from the Mesoamerican genepool have thicker leaves than those of the Andean genepool. Parameters varied greatly with environment and sampling date. The results support the need to control for leaf water content when studying leaf thickness. Furthermore, including mid and lateral rib tissue in leaf samples appeared to bias data sufficiently enough to double estimates of leaf thickness and specific mass. Based on time required for measurement and ability to detect cultivar differences, measuring leaf thickness with a micrometer and leaf optical density appeared the most promising for rapid characterization of leaf thickness. # 2004 Elsevier B.V. All rights reserved.