Combining Ability of Inbred Lines Derived from Quality Protein Maize Populations

Abstract

Quality protein maize (QPM) with improved kernel quality over o2o2 soft genotypes was developed by introducing modifier genes and selecting for a hard, vitreous endosperm in o₂o₂ germplasm at the International Maize and Wheat Research Center (CIMMYT). Three QPM populations developed
by CIMMYT were used in the research. S0-plants of preferred morphological characters were selfpollinated to produce S1 until S3 lines. Ten S3 inbred lines were examined for the opaque-2 gene using the phi057 marker and a diallel cross was made. The experiment was conducted in a 7×7 simple lattice design at the National Corn and Sorghum Research Center, Thailand. The results showed that 10 inbred lines were detected with polymorphism the same as opaque-2 maize (o₂o₂) but were different from nonopaque-2 maize. The protein content in endosperm of these inbred lines ranged from 7.76 to 8.61% while those of opaque-2 and non-opaque-2 maize contained about 8.45 and 8.73%, respectively. However, the protein content of inbred lines, the diallel cross and check variety were not significantly different. Means of grain yield (t ha^-1) were 4.48 for the diallel cross (F1), 1.97 for inbred lines, 3.30 for opaque-2 and 6.61 for non-opaque-2 hybrid check. However, grain yield of the best diallel cross was 6.10 t ha^-1 which was not significantly different from the non-opaque-2 hybrid. Protein contents were not significant among the diallel cross, opaque-2 and non- opaque-2 hybrids. Tryptophan content in endosperm of the diallel cross was higher than non-opaque-2 hybrids. Inbred P10 had the best combination of GCA effects for grain yield. Moreover, inbred lines, P1, P7, P8 and P9 also gave positive GCA effects.