Genetic Dissection of Drought Tolerance in Adapted x Exotic Crosses of Elite Maize (Zea mays L.) Inbred Lines.

Maize breeders exchange maize (Zea mays L.) germplasm as sources of favorable alleles to enhance performance of new maize varieties and hybrids under drought stress conditions. In the present study, we determined the combining abilities of 12 exotic maize inbred lines from CIMMYT and 12 adapted maize inbred lines from IITA for drought tolerance under controlled drought stress. These inbred lines in each group were separated into sets based on SSR-based genetic diversity and were intercrossed using a Design II mating scheme to generate 96 hybrids. These hybrids were evaluated in replicated trials under both controlled drought stress and well-watered conditions at Ikenne in Nigeria in 2010 and 2011. Mean grain yields of the hybrids under full irrigation ranged from 3,827 to 8,887 Kg/ha, whereas mean yields of the hybrids under drought stress varied from 444 to 3,022 Kg/ha. General combining ability (GCA) effects accounted for most of the variation observed for most traits recorded under both well-watered and drought stress conditions. Specific combining ability effects, though positive for grain yield in most crosses, were not significant. Among the 24 maize inbred lines, eight had significant and positive GCA effects for grain yield under full irrigation and five inbred lines had significant and positive GCA effects for grain yield and other important traits recorded under drought stress. Some of the good general combiners under well-watered conditions and drought stress had significantly positive GCA effects for normalized difference vegetation index at different growth stages.