Comparação dos métodos genealógicos e duplo-haplóide para seleção de genótipos elites e estudo da herança genética de altura de planta e espiga em milho

Abstract

The maize (Zea mays L.) is a species of the grass family. It is the third most cultivated cereal in the world, behind only to wheat and rice. The increasing of knowledge of the physiology and genetics of culture, the refinement of breeding techniques and the introduction of new technologies within the research programs has enhanced the production and productivity of maize, so that the production could reach 51.3 million tons in the 2010/2011 in Brazil. Phenotypic characteristicsassociated with genetic factors are commonly studied in maize. Plant height and ear height are important characteristics for maize since they are associated with resistance to lodging and grain yield. Because of its importance, several studies have been done trying to understand the genetic basis of it. The technology of double-haploid (DH) to obtain homozygous lines have been increasingly used in maize breeding programs for production of commercial hybrids. With the improvement and development of techniques for obtaining DH lines, several studies have been conducted to evaluate the efficiency and effectiveness of this method within programs especially compared to other methods. This work seeks to contribute to the clarification of questions about the use of double-haploid lines in maize breeding programs, by comparing two methods of breeding, pedigree method and double haploid, to identify superior lines of maize that produce hybrids of high grain yield, combined with low plant height and ear insertion. Also was aimed to compare genetic heritability and five maize populations obtained by both methods. To develop this study we used eight inbred lines of maize, from Du Pont in Brazil - Pioneer Seeds Division, which were crossed within their groups for the development of five populations, - three of the SSS heterotic group (AxB, AxC, DxE) and two NSS (FxG, FxH). After the crossing, populations were selfed to obtain segregating generations. These populations were conducted by two methods of breeding, the pedigree and the double-haploid. To compare the methods of generation hybrid lines F3 (pedigree) and F3 DH were crossed with a tester presenting high capacity combinatorial for producing testcross (F3-TC and F3-DH). The experiments with segregating populations were conducted at the research station of DuPont (Pioneer) at Coxilha-RS city. The experiments of hybrid F3-TC and F3-DH were conducted in three cities in Rio Grande do Sul state, Carazinho, Cruz Alta and Condor. The variables evaluated in the field were: plant height and ear height in F2, F3, DH-D1 and DH-D2 and their hybrids F3-TC and F3-DH, as well as yield of these hybrids. The study showed no difference between DH and pedigree methods in the identification of superior lines for grain yield in hybrid combinations. For characteristics of moderate to high heritability, such as plant height and ear height, the DH method had advantages over the pedigree. Moreover, the frequency distributions revealed that plant height and ear height are characteristic of high heritability, broad transgressive segregation and high heterosis in F2. The use of double haploid versus lines segregating in the study of inheritance of plant height and ear height reveals different aspects of genotypic variability for these characteristics and in general narrow and broad sense heritability of greater magnitude.