Grain yield, photosynthesis and water relations in two contrasting maize landraces as affected by high temperature alone or in combination with drought

On a global basis, high temperature in conjugation with coincident drought poses the most important environmen¬tal constraint to plant survival and to crop productivity. Two experiments were conducted to investigate the effect of drought, heat, and the combined stresses on stress-tolerant C-3014 and stress-susceptible C-3015 maize landraces. The objective of the first experiment was to compare the effects of drought, heat, or the combined stresses on photosynthesis and water relations on two contrasting maize landraces under controlled conditions; the objective of the second experiment was to determine the effects on drought and heat stress on agronomic traits and grain yield in field. Results indicated that dry matter production, RWC, and Ψ was significantly reduced by the combination of high temperature and drought by 66, 38, and 105% respectively, which was greater and more severe than the reduction under drought or heat alone. In tolerant genotype the Ψ was reduced in 84%, how¬ever in the susceptible genotype the reduction was in 126%. The combined stresses also significantly decreased the A and gs in C-3015 more rapidly than C-3014. Under field, the combined stresses caused a severe decline in all agronomic traits, but the response was higher in the susceptible than tolerant genotype. The field evaluation confirmed the observation in controlled conditions, that C-3014 is more tolerant to high temperature and water stress combined, than C-3015