|Montes-R, Consuelo - UNIV DE CAUCA, COLUMBIA|
Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2004
Publication Date: January 10, 2005
Citation: White, J.W., Montes-R, C. 2005. Variation in parameters related to leaf thickness in common bean (phaseolus vulgaris l.). Field Crops Research. 91:7-21. Interpretive Summary: Greater leaf thickness is usually associated with greater leaf photosynthesis, but the tradeoff between thicker vs. larger leaves also affects canopy structure and light interception. Thicker leaves are also thought to be ecologically adaptive for conditions of drought, high light, and cooler temperatures. Understanding leave thickness varies thus is important for agricultural research ranging from crop improvement to crop response to elevated temperatures and CO2, to potential for carbon sequestration in rangeland. This paper describes research analyzing different approaches for characterizing leaf thickness in common bean. The results confirmed widely recognized associations among lead thickness per se, indicators of tissue density, and nitrogen content, among other traits. However, they also showed substantial variation due to environmental differences. Two major methodological issues emerged concerning the need to standardize leaf water contents when measuring thickness and to clearly differentiate whether the whole leaf is being considered or only the flat leaf blade tissues, where the bulk of photosynthesis occurs. Because of the wide use of measures of leaf thickness in agricultural research, these results potentially could have substantial impact on research procedures. Specifically for bean research, the results suggest means to improve selection for higher-yielding large-seeded cultivars (such as kidney-types), which should lead to lower prices to consumers for the usually much-preferred large-seeded types.
Technical Abstract: Greater leaf thickness is usually associated with greater leaf carbon assimilation rate, but tradeoff between thicker vs. 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 potential 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.), 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 content expressed on a leaf area basis, leaf tissue density, and nitrogen concentrations 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, it appears that including mid and lateral rib tissue in leaf samples induced a bias sufficiently large 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 structure.