Genotypic variation in photosynthesis in cacao is correlated with stomatal conductance and leaf nitrogen

Abstract

Variation in photosynthetic parameters was observed between eight contrasting cacao (Theobroma cacao) genotypes. Net photosynthetic rate (PN) ranged from 3.4 to 5.7 μmol(CO2) m−2 s−1 for the genotypes IMC 47 and SCA 6, respectively. Furthermore, genotypic differences were detected in quantum efficiency ranging from 0.020 to 0.043 μmol(CO2) μmol−1(photon) for UF 676 and AMAZ 15/15, respectively. Differences in PN were correlated with both stomatal conductance (gs) and leaf nitrogen per unit area. Some variation in water use efficiency was observed between genotypes, both intrinsic (PN/gs) and instantaneous (PN/transpiration rate). Both measures of water use efficiency were a negative function of specific leaf area. Evidence was found for a trade-off mechanism between cacao genotypes in photosynthesis and leaf structure. High photosynthetic rate, expressed on a mass basis was associated with smaller leaves. Furthermore, thinner leaves were compensated for by a higher nitrogen content per unit mass.