Two field trials were established in 1996 and 1997 to assess genotypic variability of four cassava ( Manihot esculanta
) cultivars for adaptability in the inland valley in terms of leaf chlorophyll content and tuberous root yield, using a 4 x 4 Latin square design with four replications arranged along the toposequence. Leaf chlorophyll a, b and ab contents and root yield of the improved cultivars were similar, but were significantly greater than those of Isunikankiyan, the local cultivar. Plants in the valley fringe had the highest concentrations of the three chlorophyll components and root yield. Leaf chlorophyll a and ab contents and root yield were significantly higher in 1996 than in 1997, due partly to favourable weather conditions in 1996. However, the reverse was the case for leaf chlorophyll b content, suggesting that chlorophyll b concentration may increase under stressful conditions. Root yield in all cultivars increased with increase in concentration of the three leaf chlorophyll components, but chlorophyll a and ab were more correlated with yield than chlorophyll b. Correlation between chlorophyll contents and root yield were strongest for TMS 91/02324 with the highest root yield, and weakest for Isunikankiyan, the lowest yielder. Root yield of the four cultivars and concentrations of the three chlorophyll components decreased linearly as the groundwater table depth became shallow. Therefore, selection of cassava cultivars that can maintain high leaf chlorophyll contents under moisture stress can lead to high root yield when combined with other yield determinants in inland valleys.