Combining ability in medium-maturity maize genotypes adapted to mid-altitude and lowland tropical environments

Abstract

Maize (Zea mays L.) is grown in different agro-ecological zones in the semi-arid tropical regions. Breeding for high production requires information on the combining ability and the magnitude of useful genetic variances among adapted genotypes. This study was conducted to determine the combining ability among tropical lowland and mid-altitude medium-maturity maize genotypes, provide information to clarify the relationship among them and identify suitable lines for distribution to growers. Six mid-altitude adapted maize inbred lines and six lowland adapted maize inbred lines were crossed in a full diallel mating system. The resulting 132 crosses, excluding the parental lines were evaluatedin four environments for grain yield, days to silking, plant height, ear height, ear weight and grain moisture at harvest. The subdivision of treatment effects in the general (GCA) and specific (SCA) combining ability were performed according to Griffing’s diallel analysis method 3, model 2. Both GCA and SCA were significant for all traits. The reciprocal meansquares were significant for ear height, ear weight, grain moisture and grain yield. Both additive and nonadditive gene effects were involved in combining ability between maize germplasm from different ecologies. Additive genetic effects were more important than nonadditive effects in controlling expression of the various traits evaluated. Positive GCAeffects for yield were observed with the lines EXP124, NCREGP1103, NCREGP28, and TZUT57 among the lowland and the lines TZMI308, 87036 among the mid-altitude lines. Crosses involving parents of different adaptation ecologies yielded hybrids with good agronomic performances and high estimates of SCA for all assessed traits. Crosses with atleast one mid-altitude female parent were better than lowland x lowland and mid-altitude x mid-altitude crosses in all environments. Mid-altitude maize germplasm may hold potential for use as source populations for both mid-altitude and lowland ecologies. These results emphasize the need to exploit the full potential of interpopulation crosses ofmaize genotypes.