Heterozygosity following half-sib recurrent selection in popcorn using isoenzyme markers

Isozyme biochemical marker may be useful tool for genomic analysis of maize populations undergoing recurrent selection. Thus, isozymes markers was utilized for assess the changes in the genetic variability and distance in a Brazilian composite population of popcorn following four cycles of recurrent selection for yield. One hundred and ninety-six half-sib families were evaluated from each cycle and the ten highest-yielding families (5.2 percent) were recombined to produce the next cycle. Isozyme analysis considered 80 seedlings per cycle. Simple linear regression equations were estimated among the allele frequencies in each locus in function of the selection cycles, the genetic distances among the cycles and the average heterozygosity per locus for each cycle. Regression analysis did not reveal any common trend for changes in allele frequencies presumably due to selection. The estimates of the number of polymorphic locus, of the mean of allele per locus and the mean heterozygosity did not reveal any reduction in variability. It was concluded that four selection cycles did not cause relevant changes in the variability or genetic distance among the selection cycles of CMS-43 popcorn population. Isozymes markers analysis showed that the number of recombined half-sib families in recurrent selection was suitable.

Potencial genético de um sintético de milho de grãos duros para formação de híbridos / Genetic potential of a flint maize synthetic for hybrid production

O objetivo deste estudo foi determinar através das estimativas de parâmetros genéticos o potencial de um sintético de milho de gräos duros e de ciclo semiprecoce, para a formaçäo de híbridos e/ou melhoramento intrapopulacional. Foram utilizadas 142 progênies endogâmicas S2 do Sin EEL Flint, em cruzamentos topcrosses com um Sintético heteroticamente contrastante. Essas progênies topcrosses foram avaliadas utilizando-se o delineamento em látice simples 12 x 12, e em dois locais de teste. Os maiores valores médios para PED foram observados para os topcrosses n.º 101 (12069kg ha-1) e nº 72 (11068Kg ha-1), tendo o primeiro apresentado comportamento específico para Londrina, e o segunda demonstrado comportamento superior nos dois ambientes. Os valores das estimativas dos parâmetros estudados foram semelhantes aos encontrados em alguns estudos conduzidos em condiçöes tropicais. O grupo de progênies S2 da Sin EEL Flint conduziu a valores médios de , CVg e h² similares aos encontrados na literatura para outros genótipos. Observa-se que esse Sintético possui suficiente variabilidade genética e potencial para extraçäo de linhagens para formaçäo de híbridos e como germoplasma em programas de melhoramento

Inbreeding depression of 28 maize elite open pollinated varieties

The study of inbreeding depression is important for breeding strategies such as use of inbred progenies or extraction of inbreed lines. A diallel of 28 maize open-pollinated varieties was evaluated in 10 environments in the early 1990s. At the same time, S1 populations for each of the 28 varieties were evaluated in the same 10 experiments (environments). Yield reductions of the populations from S0 to S1 (mean of the 10 environments), varied from 34.6 percent (CMS-01) to 59.2 percent (CMS-30), with an average of 49.1 percent. Inbreeding depression was greater in populations with a wider genetic base, which had never been exposed to inbreeding (CMS-30, BR-107, PH4, Cunha, Saracura, Nitrodent, and Nitroflint). Inbred lines with greater yield means should be obtained from the BR-105, BR-111, CMS-01, CMS-03, BR-106, CMS-14c, and CMS-28 populations. The use of parameter estimates generated by analysis of inbreeding depression, allow to make inferences about frequencies of deleterious alleles in the population. The frequencies of favorable alleles in the parents can be obtained by diallel analysis. The association of these two types of information, can provide a better interpretation of the genetic parameters and also can improve the process of selection of parents for either an intra- or an inter-populational breeding program

Características físicas e químicas dos principais cultivares de milho pipoca plantados no Brasil / Physical and chemical characteristics of the main popcorn cultivars grown in Brazil

Fifteen popcorn cultivars grown in Brazil were analysed for expansion power, percent composition, dietary fiber, minerals, vitamins and aminoacids. The mean Expansion Power was 23.1, low for the international standards. The second major component in popcorn is the dietary fiber, ranging from 21 to 29 per cent. Minerals and vitamins are presents in small amounts. Popcorn, like others cereals, is defficient in the limiting aminoacid lysine and triptophan. The popcorn consuption, without addition of other ingredients, can be used in sodium restricted diets, and is a good source for dietary fiber intake