Photosynthetic Light Response Curve and Photosynthetic Performance of Cacao (Theobroma cacao L.) Genotypes Grown Under Full Sun Field Conditions

The cultivation of <i>Theobroma cacao</i> L. in full sun conditions is expanding, but little is known about the physiological response of different genotypes under high irradiance in the field. This study evaluated the photosynthetic light response curve and physiological performance of eleven genotypes (BN-34, CSE-70, VT-05, FL-89, NSV-04, PS-13 19, NSV-410, CP-49, CEPEC-2002, VEM-20, and SJ-02) grown in full sun in Linhares, ES, Brazil. Parameters derived from gas exchange and hyperbolic modeling were used. Variability was observed among genotypes. The VT-05 genotype showed the best performance, with a high maximum CO₂ assimilation rate (<i>P</i>_nmax = 10.92 µmol CO₂ m^-2 s^-1), low dark respiration (R_d = 0.157 µmol CO₂ m^-2 s^-1), reduced light compensation point (Γ = 2.73 µmol photons m^-2 s^-1), and high water use efficiency (WUE = 4.65 µmol CO₂ mmol^-1 H₂O). Genotypes PS-13 19, CP-49, VEM-20, NSV-04, and CSE-70 also stood out with high WUE and instantaneous carbon use efficiency (EiC = µmol CO₂ µmol^-1 photons), indicating good performance under high light conditions. In contrast, BN-34 and NSV-10 showed low photosynthetic efficiency, lower EiC values, and higher vapor pressure deficits (Vpd = kPa), suggesting lower adaptability to full sun conditions.