Response of S1 maize varieties and varietal hybrids to altitude and environments in Cameroon

SUMMARY S1 maize varieties and varietal hybrids were tested in six locations ranging in altitude from 236 to 1600 m in Cameroon. The grain yields of highland varieties were observed to increase with each increase in altitude while the yields of the lowland varieties decreased with increasing altitude. The highland × lowland S1 varietal crosses yielded the same as the lowland parental varieties in highland areas and better than highland parental varieties in lowland areas. Average yields of all varieties per location increased by about 1·1 t/km increase in altitude. Eberhart & Russell's (1966) stability method found no stable variety while Francis & Kannenberg's (1978) genotype-grouping technique found five highland × lowland crosses to be relatively stable. Number of days from planting to tasselling increased with increasing altitude by about 20 days/km increase in altitude. Highland and lowland varieties performed poorly outside their zones of adaptation because of high incidence of foliar diseases like leaf blights and rusts.