Two field trials with two groups of cassava (Manihot esculenta Crantz) cultivars were conducted under rainfed conditions in seasonally dry and semiarid environments at the northern coast of Colombia, South America, to evaluate the genetic diversity in photosynthesis and productivity, and to determine their interrelationship. There were significant differences among cultivars in both environments, in average net photosynthetic rates (P N ) of upper canopy leaves and in final dry root yields. Both P N and dry root yields were much higher in the seasonally dry environment than in the semiarid one. Highly significant correlation (r 2 = 0.90, p < 0.001) between leaf P N and dry root yield was observed across environments, suggesting that selection in parental plants for high photosynthesis might lead to high yields if combined with other yield determinants, such as leaf area duration, high harvest index and strong root sink.