Parâmetros genéticos e índices de seleção no desenvolvimento de genótipos de soja visando caracteres agronômicos e resistência à Sclerotinia sclerotiorum

Abstract

The soybean [Glycine max (L.) Merrill] is the most important crop cultivated in Brazil, and is one of the most relevant commodities of the international agricultural trade. Currently, Brazil is the world’s top producer followed by the United States and Argentina. The brazilian rise in soybean cultivation is intrinsically linked to the success in studies related to the area of soybean genetic improvement. The main objective of any breeding program is to identify, among the segregating populations, the few genotypes with the best genetic combinations, including grain quality, grain yield, adaptation and disease resistance. In this regard, an efficient estimation of genetic parameters such as variance components, heritability and selection gain can result in a more efficient selection process to obtain promising genotypes from segregating populations. One of the main factors that can limit the worldwide soybean production is the occurrence of diseases. Soybean white mold (WM), caused by Sclerotinia sclerotiorum (Lib.) de Bary, is considered the one of most destructive disease affecting soybean crops. Currently, there are no cultivars genetically resistant to S. sclerotiorum available. However, several studies have demonstrated that individual cultivars can differ in susceptibility, thus representing a key element for breeding programs. Genetic resistance is one of the main alternatives in the control of plant diseases, because in addition to being more economically viable, compared to the use of fungicides, it is easy to use, less aggressive to the environment, to the farmer and to the consumer. Therefore, to effectively develop soybean genotypes resistant to white mold and with superior agronomic traits, it is necessary to be cautious in the selection of parents. In addition, soybean breeding also targets a set of characters related to morpho agronomic traits that give the genotypes high grain yield, adaptability and stability. This thesis is divided into three chapters. Chapter I presents the literature review, which discusses the current situation in soybean breeding, genetics resistance to WM and production. In chapter II, the aim of the study was to develop soybean genotypes with resistance to white mold, while maintaining other desirable agronomic traits. And in chapter III, the objective was to estimate genetic parameters and analyze selection strategies in the development of soybean genotypes, in the F3 and F4 progenies, to identify the genotypes that present superior agronomic characters, such as in production and early cycle, and specifically in F4, to identify genotypes with resistance to the fungus Sclerotinia sclerotiorum.