Leandro Vagno de Souza

Genetic variability and heterotic groups of Brazilian popcorn populations

The development of successful advanced lines and cultivars in maize is dependent on parental selection and assignment to defined heterotic groups. So, the objectives of this study were to evaluate genetic variability and identify heterotic groups among Brazilian popcorn varieties. Thus, diallel crosses of advanced generations of the popcorn hybrids, IAC 112 and Zélia, and of three open-pollinated popcorn varieties, RS 20, Branco, and SAM were performed. Ten hybrid combinations, the five parents, and five check treatments were arranged in a block design with four replicates in two tropical-zone locations (CWb climate). Both additive and non-additive effects were important for grain yield, plant height, ear height, and husk cover. For popping expansion, only the additive effects were important. Hybrid combinations between the local variety (Branco) and F2 populations (IAC 112 and Zelia) resulted in the third and fourth highest values for popping expansion. The best grain yields were obtained with hybrid combinations involving SAM. Cultivars Zélia, IAC 112, and RS 20 increased popping expansion, whereas cultivar Branco increased grain yield of hybrid combinations. The following conclusions may be drawn: Brazilian popcorn populations have reduced heterosis and genetic variability to popping expansion in relation commercial cultivars; there is genetic variability among Brazilian popcorn populations that allows the exploitation of additive and non-additive effects for grain yield; it is possible to increase grain yield by using local varieties; but it would be difficult to obtain commercial hybrids from local varieties because they have poor performance for popping expansion.

Multivariate analyses of genotype x environment interaction of popcorn

The objectives of this work were to evaluate the genotype x environment (GxE) interaction for popcorn and to compare two multivariate analyses methods. Nine popcorn cultivars were sown on four dates one month apart during each of the agricultural years 1998/1999 and 1999/2000. The experiments were carried out using randomized block designs, with four replicates. The cv. Zelia contributed the least to the GxE interaction. The cv. Vicosa performed similarly to cv. Rosa-claro. Optimization of GxE was obtained for cv. CMS 42 for a favorable mega-environment, and for cv. CMS 43 for an unfavorable environment. Multivariate analysis supported the results from the method of Eberhart & Russell. The graphic analysis of the Additive Main effects and Multiplicative Interaction (AMMI) model was simple, allowing conclusions to be made about stability, genotypic performance, genetic divergence between cultivars, and the environments that optimize cultivar performance. The graphic analysis of the Genotype main effects and Genotype x Environment interaction (GGE) method added to AMMI information on environmental stratification, defining mega-environments and the cultivars that optimized performance in those mega-environments. Both methods are adequate to explain the genotype x environment interactions.

Predicting the genetic gain in the Brazilian white maize landrace

Os objetivos deste trabalho foram avaliar a variabilidade genetica e predizer os ganhos geneticos de uma populacao crioula de milho branco resgatada em Barbacena, Minas Gerais (MG), devido a importância social e economica do milho branco em determinadas localidades brasileiras, a manutencao e ao resgate de populacoes crioulas e aos poucos trabalhos sobre esse tipo de grao. Para tanto foram instalados tres experimentos, com 100 progenies de meios-irmaos, em Campos dos Goytacazes, Rio de Janeiro (RJ), Coimbra e Barbacena (MG), escolhidos pelas diferencas edafoclimaticas. Pela analise de variância foram verificadas diferencas significativas entre as progenies para todos os caracteres, o que indicou a presenca de variabilidade genetica na populacao para os tres locais. Em Campos dos Goytacazes e Coimbra, a variância genetica da populacao crioula de milho branco foi responsavel pela maioria da variância fenotipica para produtividade de graos, podendo ser explorada em ciclos de selecao. Em Barbacena, nao foi detectada variância genetica significativa para a produtividade de graos. Para a populacao crioula de milho branco Barbacena, conclui-se que caracteres do componente primario de produtividade como estande final e numero de plantas com graos podem apresentar ganhos geneticos direto e indireto com a produtividade e sao adequados para o melhoramento. No entanto, e necessario o pre-melhoramento da populacao antes desta ser utilizada diretamente em germoplasma elite. Alem disso, foi observado que a populacao apresenta variabilidade genetica e ganhos geneticos preditos altos; as medias das caracteristicas agronomicas sao adequadas somente para o sistema produtivo tradicional com poucos insumos e policultivo; e a diferenca entre os ambientes proporciona resposta especifica das progenies, ou seja, interacao progenie x ambiente.