EFFICIENCY OF SECONDARY TRAITS FOR IMPROVING MAIZE FOR LOW-NITROGEN TARGET ENVIRONMENTS

Consideration of secondary traits could improve selection efficiency u nder stress conditions, This study assesses the value of secondary tra its for improving lowland tropical maize (Zea mays L.) for low-N targe t environments, Nineteen experiments grown with no N applied at CIMMYT , Mexico, between 1986 and 1995 were analyzed for grain yield, anthesi s-silking interval (ASI), number of ears per plant, leaf chlorophyll c oncentration, and an estimate of leaf senescence, Broad-sense heritabi lities of traits, genetic: correlations between secondary traits and g rain yield, and predicted response of grain yield to selection for sin gle or multiple traits were calculated, Multiple traits were combined using an unrestricted selection index (Smith-Hazel index), Broad-sense heritabilities averaged 0.46 for grain yield, 0.52 for ASI, 0.44 for ears per plant, 0.35 for leaf chlorophyll concentration, and 0.60 for leaf senescence, Genetic correlations of secondary traits with grain y ield averaged -0.47 for ASI, 0.78 for ears per plant, 0.24 for leaf ch lorophyll concentration, and 0.42 for leaf senescence. Direct selectio n for grain yield was superior to selection for single secondary trait s in most experiments, When information on all traits was combined in a Smith-Hazel index, selection efficiency improved by 14% on average o ver selection for grain yield alone, Among secondary traits, ears per plant and leaf senescence discriminated high-yielding genotypes the be st. Leaf chlorophyll concentration, and in some instances ASI, provide d information on environmental variation within experiments, We conclu de that secondary traits can increase the efficiency of selection for grain yield in maize breeding programs targeting low-N environments.