Leo Duc Haa Carson Schwartzhaupt da Conceicao

Combining ability of twelve maize populations

Genetic progress depends on germplasm quality and breeding methods. Twelve maize popu- lations and their crosses were evaluated to estimate combining ability and potential to be included as source populations in breeding programs. Plant height, point of insertion of the first ear, number of ears per plant, number of grains per ear, root and stalk lodging and grain yield were studied in two locations in Brazil, during the 1997/98 season. Genotype sum of squares was divided into general (GCA) and specific (SCA) combining ability. Results indicated the existence of genetic divergence for all traits analyzed, where additive effects were predominant. The high heterosis levels observed, mainly in Xanxere, suggested the environmental influence on the manifestation of this genetic phenomenon. Populations revealed potential to be used in breeding programs; however, those more intensively sub- mitted to selection could provide larger genetic progress, showing the importance of population im- provement for the increment of the heterosis in maize.

Herança da resistência à mancha-foliar de feosféria em milho

Phaeosphaeria leaf spot (PLS) has caused an expressive reduction in the corn grain yield in Brazil. The increment in sowing date amplitude, conjugated with the use of irrigated areas and zero tillage, had major contribution in the increase of phaeosphaeria leaf spot (PLS) incidence and severity. For this reason, it is important to develop resistant genotypes to this disease; however, an efficient selection depends upon the understanding of the genetic variability and inheritance of the resistance. Aiming to determine combining ability and the mode of inheritance for PLS, seven corn inbreds were crossed for diallel and generation mean analysis. The experiments were conducted in Xanxere, SC. Percentage of foliar area affected by the disease was evaluated 30 days after flowering. The genotypes presented amplitude of 4.3% to 67.0% of foliar area affected by PLS. The LA06 and its hybrids showed high level of resistance. Results indicated that selection for PLS resistant genotypes could be success- fully accomplished in corn breeding programs. At least two major independent genes were identified with a preponderant participation of addictive effects in the inheritance of the trait.

Herança de caracteres do trigo relacionados à qualidade de panificação

A qualidade de panificacao possui grande importância para a industria e produtores de trigo, e possibilita a agregacao de valor de mercado ao produto. O melhoramento voltado para a qualidade, porem, tem sido dificultado pela complexidade do carater e pela necessidade de testes adequados para a selecao em geracoes segregantes. O objetivo deste trabalho foi analisar a heranca dos caracteres volume de sedimentacao, indice de sedimentacao e teor de proteina, em dez cruzamentos envolvendo cinco cultivares de trigo classificadas distintamente quanto a qualidade de panificacao. As medias dos genitores diferiram entre si em relacao a todos os caracteres. Atraves das variâncias e dos parâmetros geneticos estimados, foi detectada variabilidade nos cruzamentos, no tocante aos caracteres avaliados, o que sugere a existencia de genes complementares relativos a esses caracteres. A cultivar CEP 24-Industrial contribuiu com o maior numero de genes para o incremento da qualidade no conjunto de cruzamentos analisados, e possui alelos favoraveis tambem para o teor de proteina. Os caracteres volume e indice de sedimentacao foram fortemente associados e apresentaram herdabilidade semelhante. O teor de proteinas influenciou as medidas de qualidade obtidas pelo teste de sedimentacao.

Seleção para tolerância ao alumínio em milho com base em parâmetros genéticos e análise multivariada

SELECTION FOR TOLERANCE TO ALUMINUM IN CORN BASED ON GENETIC PARAMETERS AND MULTIVARIATE ANALYSIS The improvement of plants, in the last 40 years, has pledged efforts in the search of maize genotypes with aluminum tolerance. The understanding of the existing variability and the genetic distance between genotypes serves as basis for crossings in breeding programs. The objective of this work was to study aluminum tolerance in maize based on multivariate analysis and genetic parameters in early generations. There were 74 families F 3:2 originated from two contrasting crosses for aluminum tolerance. The estimation of genetic parameters based on the components of variance, indicated the influence of the environment for all measured traits, which imposes difficulties for selection in acid soils. The analysis of the dendogram on the basis of the genetic distances disclosed the existence of two main groups. Crossings between inbreds with superior performance and families from different groups are potential source for maize populations to increase aluminum tolerance.