CHANGES IN CHEMICAL AND PHYSICAL QUALITY PARAMETERS OF MAIZE GRAIN DURING 3 DECADES OF YIELD IMPROVEMENT

Concern exists that the grain quality of maize (Zea mays L.) may decli ne due to breeding for increased yield. This study quantified chemical - and physical-quality parameters of maize grain for hybrids represent ing three decades of grain yield improvement in Ontario, Canada. Six h ybrids that were commercially important in Ontario from 1959 to 1988 w ere grown at two locations in southern Ontario during 1986 and 1987 at two plant densities. Grain contents of N, P, K, Ca, Mg, Zn, Cu, Mn, S e, lysine, tryptophan, and lipid were evaluated as chemical-quality pa rameters. Test weight, kernel density and weight, kernels exhibiting s tress cracks; and breakage susceptibility were examined as indications of physical quality. Concentrations of Mg, Cu, Mn, and Se were greate r in kernels of old hybrids than in more recent ones. Nitrogen concent ration was greater in grain of recent hybrids and levels of N, P, and Mn all were lesser at high than at low plant density. Concentrations o f lysine and tryptophan did not differ among hybrids. Differences in n utrient concentration were often greater among hybrids within an era t han among means for eras of hybrid release. Among physical-quality tra its, test weight, kernel density and kernel weight increased with more recent hybrids. These parameters were also higher with the lower plan t density. Breakage susceptibility of kernels, although not affected b y era of hybrid release, was less at low plant density. (C) 1998 Elsev ier Science B.V. All rights reserved.