Avaliação de caracteres quantitativos através da análise dialética e mapeamento de QTLs em milho.

Abstract

The understanding about general-GCA and specific-SCC combining ability are key to identify the best combinations in an elite lineage group of a maize breeding program. In order to identify these relationships, a group comprising 10 lineages crossed with each other in a diallel design, including the reciprocal crosses, totalling 90 hybrids, were used. The hybrids were tested in three different environments, Pato Branco-PR, Campos Novos-SC and Frederico Westphalen-RS, representing the Southern Region of Brazil in the agricultural harvest of 2012/2013. For hybrid variance, additive were more important than non-additive effects. Parent 6 showed the highest estimated effect of GCA, with favorable alleles for increments of ear and grain weight. For these same traits, taking into account the SCC, the hybridization involving 1x2 parents promotes an increase in the environment 1. On the other hand, the hybridization involving 4x8 parents promotes a pronounced reduction of these traits. The expression of most traits analyzed were affected by environmental action and it indicates that the understanding of genetic and environmental factors is necessary for the development of new maize hybrids. For QTL mapping, 73 introgressed lines from the crossing between B73 and Gaspé Flint followed by backcross were used and evaluated under two field water regimes. The major traits analyzed were root architecture, plant morphological traits and yield components. Based in the genotyping analysis of the lines, it was possible to obtain a map in which 80% of the Gaspé Flint genome is introgressed in B73 comprising 329 independent bins. The software REST was employed to quantify the variables of the maize root system under field conditions and it was effective, fast and accurate. The QTL analyses indicate 25 probable regions mainly in the chromossomes 1, 2 and 4 for the root traits. Taking into account all of the 31 traits, 90 probable QTLs, distributed in all chromossomes, were found. For watering stress condition, it was possible to observe that roots with open angle, bigger area and dry mass, as well as superficial, reduces grain yield.