Photosynthesis in Peanut (Arachis) Genotypes¹

Research was undertaken to assess the variation in photosynthetic capacity within the genus Arachis and to determine associations between photosynthesis and other leaf characteristics. Photosynthetic rates of attached leaves of thirty-one peanut genotypes, including six wild (Arachis L.) species and twenty-four genotypes of the cultivated species, Arachis hypogaea L., were measured by gas exchange. Genotypes of A. hypogaea showed a range in photosynthetic rates from 24 to 37 mg CO₂ dm^-2 hr^-1. Florunner, a recently developed US cultivar, consistently had higher photosynthetic rates than most other peanut genotypes. The rates were approximately 41 and 30 mg CO₂ dm^-2 hr^-1 in two pot experiments and a field test, respectively. Wild species had generally lower photosynthetic rates than did A. hypogaea. A. pintoi Krap. et Greg. had the lowest rate of photosynthesis and the lowest specific leaf weight in the three experiments. Photosynthetic rate was positively correlated, though weakly, with percent nitrogen and chlorophyll content of leaves in two out of three experiments. Specific leaf weight was positively correlated with photosynthesis in only one out of three experiments. Stomatal frequency and photosynthetic rates were negatively correlated. The relationship between photosynthesis and leaf characteristics is discussed.