Scaling of Leaf Area and Mass in a Recombinant Inbred Population of the Common Bean (Phaseolus vulgaris L.).

A key aspect of the resource economy of plants lies in the relationship between leaf surface area and unit dry mass investment, the specific leaf area (SLA). In many species, SLA declines with increasing leaf size, presumably due to higher synthesis and maintenance costs. In order to assess if SLA changes with leaves of increasing size in the common bean (Phaseolus vulgaris L.), we explore the relationship between leaf area (LA) and dry mass (DM) using the power function DM=α∙LA^β. The population under study consisted of 177 recombinant inbred lines (RILs) of the cross between Jamapa, a Mesoamerican indeterminate landrace, and Calima, an Andean determinate cultivar, grown in two sites (Palmira and Popayan) with contrasting temperature regimes in southwestern Colombia during 2011-2012. Data collected consisted of the leaf area and dry weight of the first trifoliate leaf of three plants harvested at weekly intervals between the V1 (first trifoliate unfurled) and R1 (anthesis) stages of development. Major axis regression was utilized in order estimate the slopes (β) of the log-transformed power function log(DM)=log(α) +β∙log(LA) of the RILs grown in both sites. Results suggest the log-transformed power function explains the DM-LA relationship well, capturing at least 80% of the variation in over 95% of the RIL × site combinations studied. Slope values were strongly influenced by the environment, as indicated by the absence of genotypes with β<1 in Palmira, and only 4 genotypes with β>1 in Popayan. On average, genotypes in Palmira with β>1 had a lower SLA than genotypes with β=1, while in Popayan no differences were detected between groups with varying β. Our results suggest that while environmental factors strongly influence the hypothesized allometric relationship between leaf mass and area, genetic variation for this trait exists in the common bean. Furthermore, this relationship appears to be unrelated to plant growth habit.