Photosynthetic Traits of Selected Peanut Genotypes^1,2

These studies were undertaken to identify photosynthetic traits of the cultivated peanut (Arachis hypogaea L.) that might be used in breeding programs designed to increase yield. Net photosynthesis (Pn), CO₂ compensation point (Γ), stomatal diffusion resistance to water vapor and stomatal frequency were measured on 32 diverse genotypes. Pn was measured on 3 and 4 week old plants in a semi-closed compensating system, Γ by initial introduction of CO₂-free air and equilibration thereof, and stomatal resistance with a diffusion porometer; photorespiration and mesophyll diffusion resistance to CO₂ were calculated. At high light (1400 μE m⁻²s⁻¹PAR) eight genotypes had Pn rates of 20 to 30, seventeen 31 to 40 and seven 41 to 43 mg CO₂ dm⁻²h⁻¹. At any given light level tested Pn rates of a given genotype were significantly different from other genotypes. Only three genotypes showed any tendency toward photosaturation at 1400 μE m⁻²s⁻¹PAR. Photosynthetic rate and photorespiration were positively correlated (r = 0.92, P<.001). Stomatal density for the 32 genotypes averaged 168 and 154 mm⁻²on adaxial and abaxial surfaces. Neither stomatal density nor stomatal resistance to water vapor diffusion was correlated with Pn. In all instances, resistance to water vapor diffusion of the adaxial surface was less than that of the abaxial surface. Pn was negatively correlated (r = −0.98, P<.001) with mesophyll resistance which suggests that somewhere within the residual resistance system lies the reason(s) for differences in Pn amongst the genotypes tested.