Efeito xÃnia em hÃbridos comerciais de milho visando ao aumento da produtividade / Xenia effect in commercial maize hybrids aiming at increased yields.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The xenia effect in maize yield components was investigated in five field experiments conducted in two counties within the state of Minas Gerais, Lavras and RibeirÃo Vermelho, in the growing seasons 2004/05 and 2005/06. Aiming at a possible practical use of this effect in commercial cultivation, four experiments were conduct as close as possible to those on commercial fields, especially regarding natural pollination and the genotypes commonly used by farmers. Three single cross commercial hybrids were used (P 30F90, A 2555 and DKB 333 B), which allowed all possible crosses among them, including the reciprocals. In the fifth experiment controlled pollination was manually performed with the same hybrids, with 100% and 50% foreign pollen. The selfpollinated were differentiated from crossed grains through molecular markers (microsatellites). The experimental design consisted of systematic schemes with 50 m long row plots. In the experiments with open ollination, data were collected as randomized samples in 3 m long subplots, and from sets of 3 plants where controlled pollination had been performed. The xenia effect on ear yield, grain yield, weight of 100 grains, individual grain weight, and grain density was estimated according to the experiment through diallel analyses, analyses of variance according to the model âamong and withinâ, contrast tests with one degree of freedom, and the âtâ test for unpaired data means. Xenia effects were observed in all possible crosses involving the three hybrids, but they varied in magnitude, according to the specific hybrid combinations and the situation of receptor/pollinator of the genotype involved. Maternal effect was observed in 71% of the cases in which xenia effect was statistically significant. Marked effects of the environment (site and year) and interactions of these factors with the genotypes indicated lack of consistence and repeatability of some of the observed effects, which impairs any extrapolation of the phenomenon. In the most systematic and consistent cases of specific open-pollinated crosses, the mean xenia effect reached 17.8%, resulting in a grain increase of 1.302 kg ha-1. Under these conditions, a mean effect of 12.6% (varying from 7.4 to 16.5%) was also observed for individual grain weight. In the controlled crosses with 100% foreign pollen the mean xenia effect on the weight of 100 grains was 13.1% and 8.7% on the individual grain weight, although increments of 15.4% and 16.6%, respectively, were observed in these traits in the most favorable crosses. Crosses based on 100% foreign pollen led to mean increments of around 7.3% in the weight of 100 grains, compared with the mixture with only 50% foreign pollen, demonstrating the influence of a greater pressure of foreign pollen in the increase of this trait. No consistent effects were observed on grain density.

ASSUNTO(S)

maize marcador molecular milho molecular markes hybrids hibridaÃÃo produtividade. melhoramento vegetal yield

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