Screening Maize for Drought Tolerance in the Rainforest Ecology of Sw Nigeria.

Drought stress, which occurs at any growth stage of maize (Zea mays L.) is a major abiotic constraint to maize production in the rainforest ecology of sw Nigeria. Breeding drought tolerant (DT) varieties is considered the most efficient strategy to overcome this constraint.  Maize breeders at CIMMYT and IITA have been using managed drought stress, involving controlled application of irrigation to select DT varieties. Screening under the completely rain-free dry season rainforest ecology of sw Nigeria could drastically reduce the cost of developing DT maize varieties. The objective of this study was to investigate the possibility of reliably screening and identifying DT maize germplasm during the dry season in the rainforest ecology of sw Nigeria. Two trials, respectively involving 30 and 50 maize varieties of different levels of drought tolerance were evaluated under field conditions for two years. Planting was done at the time flowering coincided with the occurrence of natural drought and continued for the rest of the growth cycle. The varieties were also evaluated under non-stress field conditions in the two years. A rank summation index (RSI) calculated from flowering, plant aspect and grain yield data was used to select the best and the worst 10 varieties under natural stress. The natural drought environment clearly differentiated the tolerant from the susceptible varieties as was done under managed drought stress imposed by IITA and CIMMYT scientists about similar growth stages of maize. This method is now being used to screen for drought tolerance at the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, Nigeria.