Parâmetros genéticos, fenotípicos e coeficiente de caminhamento em duas populações de milho (Zea mays L.)

Abstract

Two maize populations were evaluated in respect to their genetic potential for breeding improved lines for yield and yield components through selection. The two populations identified as EPACE-M-21 described as yellow-dented and CMS-451 as a white-dented grain, were experimentally grown at the Federal University of Ceará Experimental Farm, in Pentecoste, Ceará, Brazil. For each population 100 random select progenies were sown under irrigation in August 1994 in a square 10 x10 lattice design. At harvesting, a random sample of 20 progenies was taken from each population experiment. Each of the 20 progenies was measured for: ear weight, diameter and length, height, ear insection height from the ground, grain weight and number per ear and average weight per 100 seeds. Simple correlation coefficients among the great majority of the characters investigated were found to be highly significative. Genetic coefficients of variation were also high indicating enough genetic variabillity for a successful improvement through selection for most traits in both populations. Components of additive genetic variances were higher for ear weight and number of grains per ear. Estimates of strict sense heritabilliy coefficients were higher for ear height, ear length and ear weight. Expected genetic advances expressed as percent of the mean per generation of mass selection were found to be higher than those expected for selection within half sib progenies. Path analysis applied to a causal system in which ear weight was the dependent variable showed that among all independent variables the number of grains per ear was the one that yielded the highest direct and indirect path coefficients with the dependent variable. Experimental precision as measured by the coefficients of variation were relativery low for all studied traits. This was taken as being due to environmental circunstances such as lack of uniformity of the irrigation process and other cultural pratices.