Evaluation of Advanced Drought Tolerant Maize (Zea mays L.) Hybrids for Grain Yield and Other Agronomic Traits Under Combined Drought and Heat Stress.

Drought and high temperature are two major environmental factors limiting maize productivity in sub-Saharan Africa. An increase in temperature above 30⁰ C reduces yield by 1% under optimal rain-fed and by 1.7% under drought conditions. Integrated approaches that improve the performance of genotypes to alleviate negative impacts of these stresses are essential to sustain productivity. The objective of this study was to evaluate the performance of maize hybrids and identify those combining high grain yields with tolerance to combined drought and heat stress. Forty-eight advanced 3-ways cross drought tolerant hybrids were evaluated under drought stress at elevated temperature during the dry season in Nigeria. The trial was subjected to severe drought stress when day temperature ranged from 35 to 42⁰ C and night temperature varied from 22 to 27⁰ C. Highly significant (P<0.001) differences were observed among the hybrids for all measured traits. Mean grain yield of hybrids varied from 0 kg ha^-1 for three commercial hybrids to 3240 kg ha^-1 for the best advanced 3-way cross hybrid. Grain yield was strongly and positively correlated with number of ears per plant, but negatively associated with tassel blast, barren plants, ear aspect scores, days to anthesis silking interval, and the first leaf death scores. The top eight hybrids produced 11% to 54% more grain yields than the best commercial hybrid (Oba Super 2) and had yield advantages of 135% to 227% over the local check. These hybrids consistently maintained relatively high number of ear per plant under combined drought and heat stress. The hybrids also maintained green leaves and fresh tassel contributing to less damage of reproductive tissues compared to susceptible hybrids. These hybrids will further be evaluated under combined heat and drought stress to confirm the consistency of their performance before sharing with partners in West and Central Africa.