Relationship between Maize Single Crosses and their Parent Inbred Lines for N Content in the Grain

The main objectives of this investigation were: a) to determine the N content of maize (Zea mays L.) parental inbred lines and their single-cross progenies when grown at high levels of N sufficiency; and b) to determine the relationship between the N content of inbreds and of their single-cross progenies. Such information is basic to the characterization of hybrids with respect to their N content at maximum yields relative to N and to the possible use of the N content of maize grain in N-sufficiency diagnoses. Also, such information is useful to breeders who are interested in developing inbred lines and hybrids that have high protein content. There have been few investigations of the relationship between the N or crude protein content of grain of maize inbred lines and their hybrid progenies. The average N content in the main of 29 inbred lines grown at Ames, Iowa, for 3 years (1974-1976) ranged from 1.45% N for B73 to 2.27% N for W64A, and the average for all lines was 1.80%. For 52 single crosses grown near Martinsburg, Iowa, in 1976, involving 15 inbred lines, N content ranged from 1.35% to 1.80% and averaged 1.53%, whereas for 49 single crosses grown near Grundy Center, Iowa, in 1976, involving 52 hybrids and 17 inbred lines, N content ranged from 1.39% to 1.85%, and averaged 1.63%. The simple correlation coefficients between the hybrids and the means of the two parents for N content were 0.84** for the Martinsburg experiment and 0.65** for the Grundy Center experiment. There was no evidence of dominance in the inheritance of crude protein content in either experiment, and the r-values indicated that gene action was primarily additive for N content. This means the proximate values for N or crude protein content of single crosses can be predicted reasonably well from the mean percent N of the two parents. A classification of hybrids according to N content of the inbreds showed consistent average differences in N content between types. It can, therefore, be considered a useful way for the general characterization of hybrids until more information is obtained for more specific characterization.