Abstract

8 cassava genotypes were evaluated under growth chambers (15/10, 20/15, 25/20 and 32/22°C day/night temperature respectively) and field conditions (Ibadan: 27B ± 5°C and Jos plateau: 18 ± 5°C) from 1993 to 1996. In a growth chamber study, none of the tested genotypes survived after 3 week at 15/10°C, low temperature regimes by 20/15 and 25/20°C had significantly (P < 0.05) reduced leaf stomatal conductances compared to high temperature, 32/22°C. the abaxial stomatal conductance ranged from 0.13 to 0.63 mol ms-¹. The total dry biomass per plant was higher at ambient than at lower temperature (20/15°C). In a field study, stomatal conductances were significantly higher at Ibadan compared to Jos plateau. The leaf stomatal conductance ranged from 5.6 to 21.0 mol ms-¹. Genotypic variations were observed by stomatal conductances depending on temperature regimes and locations. At 20/15°C and Jos plateau, TMS 91934, Danwaru, TMS 30572 and TME1 had the highest leaf stomatal conductances. This result showed that high stomatal conductances contributed to the tolerance of TMS 91934, TMS 30572 and TME1 to low temperatures, these genotypes had the highest total dry biomass compared to other evaluated genotypes. The correlation of dry biomass with stomatal conductances (r = 0.77, n = 8) suggest that high stomatal conductances are important physiological characteristics of cassava genotypes tolerant to low temperatures.

Key words: Low temperature, stomatal, tolerance, cassava genotypes.