Estimativa de parâmetros genéticos de caracteres da planta e da qualidade do grão em uma população de milho opaco (Zea mays)

A single population with a broading genetic variability having an opaque kernel phenotype was used in this study in order to estimate genetic parameters associated with yielding, plant and ear height, %protein, % tryptophan and % tryptophan in the protein. A total of 364 half-sib progenies were evaluated using a lattice square design with two replications. The additive genetic variances found for yielding (σ2A = 333.44 g/pl), plant height (σ2A = 187.85) and ear height (Σ2A = 122,08) indicated that there are enough genetic variability among progenies. For those characteristics associated with protein quality the genetic additive variance detected among progenies are showing that genetic progress with selection can be achieved within those characters. Estimates of genetic correlations between yielding and plant or ear height had a low value suggesting that if one select for yielding, the plant and ear height will not be affected. The genetic correlation between yielding and protein quality was positive for % protein (rA = 0.303), negative for % tryptophan (rA = -0,178) and negative for % tryptophan in the protein (rA = -0,568). It was also found a negative genetic correlation for % protein and % tryptophan in the protein (rA = -0,591). The data in this stud has been shown that if one select for yielding ability the protein quality will decay, but because of the enough genetic variability present in the population it will be possible to select for quality without changing the yielding.Uma população de milho denominada ESALQ-VD-opaco foi utilizada no presente trabalho para se estimar parâmetros genéticos e fenotípicos associados a caracteres de produtividade, altura da planta e da espiga, % triptofano e % triptofano na proteína. Um total de 364 progenies de meios irmãos foram avaliadas em látices com duas repetições. As estimativas das variâncias genéticas aditivas para produção de grãos (s²A= 333,44 g/pl), altura da planta (s²A= 187,85) e altura da espiga (s²A = 122,08) indicam a existência de suficiente variabilidade genética no material. Para os caracteres de qualidade do grão, detectou-se também suficiente variabilidade aditiva, permitindo obter progressos genéticos com a seleção. Estimativas de correlações genéticas entre produção de grãos e altura de planta e da espiga, foram de baixa magnitude favorecendo a seleção para produtividade sem alterar significativamente altura da planta e da espiga. As correlações genéticas entre produção de grãos e caracteres para qualidade protéica foram positiva para proteína (rA = 0,303), negativa para triptofano (rA = -0,178) e negativa para triptofano na proteína (rA = -0,568). Verificou-se também uma correlação negativa entre % proteína e % triptofano na proteína (rA = -0,591). A população mostra que selecionando-se para produtividade haverá uma redução na qualidade da proteína, contudo existe suficiente variabilidade genética presente que permite melhorar o valor nutricional da semente sem prejuízo para a produtividade de grãos

Evaluation of two cycles of selection among and within half-sib families in two populations of maize in the Northeast of Brazil

Durante os anos agrícolas de 1974/75/76, foram realizados dois ciclos de seleção entre e dentro de famílias de meios-irmãos nas populações do milho (Zea mays L.) Dentado Composto e Flint Composto, em diferentes regiões do Nordeste brasileiro. Em cada ciclo, foram avaliadas 500 famílias de meios-irmãos, de cada população, em látice simples duplicado 10 x 10, com uma repetição por local. Em 1978, os materiais referentes aos ciclos original I e II de cada população foram multiplicados através do cruzamento planta a planta. Em 1979, esses seis tratamentos, juntamente com outras dez populações, foram avaliados em experimentos, no delineamento de blocos casualizados, cinco repetições e em dois locais, com o objetivo de se averiguar a eficiência da seleção. A análise estatística mostrou ocorrência de variação significativa para ciclos de seleção no Dentado Composto, mas não no Flint Composto. Não foi detectada significância para a interação Ciclos/Dentado x Locais nem para Ciclos/ Flint x Locais. Verificou-se significância para Restantes x Locais, confirmando a sensibilidade dos materiais do Centro-Sul quanto ao efeito de locais, o que não ocorreu com as populações que estão em processo de melhoramento no Nordeste. O progresso genético estimado por ciclo anual (coeficiente de regressão linear) foi de 475 kg/ha (15,47%) para o Dentado Compsoto, e de 157,5 kg/ha (5,20%) para o Flint Composto, sendo este último estatisticamente não significativo dentro do nível convencional de probabilidade. Os ganhos observados no presente estudo são indicativos de suficiente variabilidade genética nas duas populações, o que permitirá ganhos substanciais nos subsequentes ciclos de seleção. During the planting periods of 1974/75/76, two cycles of selection were carried out among and within half-sib families in populations of maize (Zea mays L.) Dentado Composite and Flint Composite at different regions of the Brazilian Northeast. ln each cycle 500 half-sib families of each population were evaluated with simple lattice duplicated 10 x 10 and one replication per local. ln 1978, seeds of original I and II Cycles of each population were multiplicated using controlled sib crosses. In 1979, these six treatments with the other ten populations were evaluated in experiments using a randomized block design, with five replications and at two different locations, in order to observe the selection efficiency. The statistical analysis showed significant variation to selection cycles in Dentado Composite, but not for the Flint Composite. No significative interaction was shown for Cycles Dentado x Locations and Cycles/Flint x Locals. The interaction of "Restantes x Locations" was significant, confirming the sensibility of Centro-Sul materials to locations effects, which did not occur with populations that are under selection at the Northeast region. The observed genetic progress by annual cycle (linear regression coefficient) was 475 kg/ha (15.47%) for Dentado Composite, and 157.5 kg/ha (5.20%) for Flint Composite, being the latter statistically not significant within conventional probability level. The estimated gains in this study are indicative of broad genetic variability in the two populations, thus permitting substantial gains in subsequent cycles of selection.

Comparison of RAPD, RFLP, AFLP and SSR markers for diversity studies in tropical maize inbred lines

In order to compare their relative efficiencies as markers and to find the most suitable marker for maize diversity studies we evaluated 18 inbred tropical maize lines using a number of different loci as markers. The loci used were: 774 amplified fragment length polymorphisms (AFLPs); 262 random amplified polymorphic DNAs (RAPDs); 185 restriction fragment length polymorphisms (RFLPs); and 68 simple sequence repeats (SSR). For estimating genetic distance the AFLP and RFLP markers gave the most correlated results, with a correlation coefficient of r = 0.87. Bootstrap analysis were used to evaluate the number of loci for the markers and the coefficients of variation (CV) revealed a skewed distribution. The dominant markers (AFLP and RAPD) had small CV values indicating a skewed distribution while the codominant markers gave high CV values. The use of maximum values of genetic distance CVs within each sample size was efficient in determining the number of loci needed to obtain a maximum CV of 10%. The number of RFLP and AFLP loci used was enough to give CV values of below 5%, while the SSRs and RAPD loci gave higher CV values. Except for the RAPD markers, all the markers correlated genetic distance with single cross performance and heterosis which showed that they could be useful in predicting single cross performance and heterosis in intrapopulation crosses for broad-based populations. Our results indicate that AFLP seemed to be the best-suited molecular assay for fingerprinting and assessing genetic relationships among tropical maize inbred lines with high accuracy.579588Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Genetic similarity among soybean (Glycine max (L) Merrill) cultivars released in Brazil using AFLP markers

Genetic similarity among soybean genotypes was studied by applying the amplified fragment length polymorphism (AFLP) technique to 317 soybean cultivars released in Brazil from 1962 to 1998. Genetic similarity (GS) coefficients were estimated using the coefficient of Nei and Li (Nei and Li 1979), and the cultivars were clustered using the unweighted pair-group method with averages (UPGMA). The parentage coefficients of 100 cultivars released between 1984 and 1998 were calculated and correlated with the genetic similarity obtained by the markers. The genetic similarity coefficients varied from 0.17 to 0.97 (x = 0.61), with 56.8% of the coefficients being above 0.60 and only 9.7% equal to or less than 0.50. The similarity coefficients have remained constant during the last three decades. Dendrogram interpretation was hindered by the large number of cultivars used, but it was possible to detect groups of cultivars formed as expected from their genealogy. Another dendrogram, composed of 63 cultivars, allowed a better interpretation of the groups. Parentage coefficients among the 100 cultivars varied from zero to one (x = 0.21). However, no significant correlation (r = 0.12) was detected among the parentage coefficients and the AFLP genetic similarity. The results show the efficiency of AFLP markers in large scale studies of genetic similarity and are discussed in relation to soybean breeding in Brazil

Establishing a soybean germplasm core collection

Core collections are of strategic importance as they allow the use of a small part of a germplasm collection that is representative of the total collection. The objective of this study was to develop a soybean core collection of the USDA Soybean Germplasm Collection by comparing the results of random, proportional, logarithmic, multivariate proportional and multivariate logarithmic sampling strategies. All but the random sampling strategy used stratification of the entire collection based on passport data and maturity group classification. The multivariate proportional and multivariate logarithmic strategies made further use of qualitative and quantitative trait data to select diverse accessions within each stratum. The 18 quantitative trait data distribution parameters were calculated for each core and for the entire collection for pairwise comparison to validate the sampling strategies. All strategies were adequate for assembling a core collection. The random core collection best represented the entire collection in statistical terms. Proportional and logarithmic strategies did not maximize statistical representation but were better in selecting maximum variability. Multivariate proportional and multivariate logarithmic strategies produced the best core collections as measured by maximum variability conservation. The soybean core collection was established using the multivariate proportional selection strategy. (C) 2010 Elsevier B.V. All rights reserved

Comparison of RAPD, RFLP, AFLP and SSR markers for diversity studies in tropical maize inbred lines

In order to compare their relative efficiencies as markers and to find the most suitable marker for maize diversity studies we evaluated 18 inbred tropical maize lines using a number of different loci as markers. The loci used were: 774 amplified fragment length polymorphisms (AFLPs); 262 random amplified polymorphic DNAs (RAPDs); 185 restriction fragment length polymorphisms (RFLPs); and 68 simple sequence repeats (SSR). For estimating genetic distance the AFLP and RFLP markers gave the most correlated results, with a correlation coefficient of r = 0.87. Bootstrap analysis were used to evaluate the number of loci for the markers and the coefficients of variation (CV) revealed a skewed distribution. The dominant markers (AFLP and RAPD) had small CV values indicating a skewed distribution while the codominant markers gave high CV values. The use of maximum values of genetic distance CVs within each sample size was efficient in determining the number of loci needed to obtain a maximum CV of 10%. The number of RFLP and AFLP loci used was enough to give CV values of below 5%, while the SSRs and RAPD loci gave higher CV values. Except for the RAPD markers, all the markers correlated genetic distance with single cross performance and heterosis which showed that they could be useful in predicting single cross performance and heterosis in intrapopulation crosses for broad-based populations. Our results indicate that AFLP seemed to be the best-suited molecular assay for fingerprinting and assessing genetic relationships among tropical maize inbred lines with high accuracy

Partial diallel analysis of agronomic characters in rice (Oryza sativa L.)

Rice (Oryza sativa L.) breeding seeking to combine high productivity and cold tolerance for the temperate Latin America region is an important challenge. We estimated some useful parameters which can be used to investigate the genetic control of agronomic characters in crosses combining cold tolerance and productivity. A partial diallel design was used in crosses between six tropical indica rice cold susceptible genotypes (group 1) and seven japonica or indica/japonica cold tolerant rice genotypes (group 2). Parents and crosses were evaluated for agronomic characters under field conditions in two different experiments in 2005. The results showed significant mid-parent heterosis for all characters (plant height, tiller number, days to 50% flowering, panicle length, grains per panicle, sterility, and one-hundred grain weight). The predominant direction of dominance effects was negative for days to 50% flowering, and positive for all the other characters. General combining ability (GCA) and specific combining ability (SCA) were significant for all characters, although the GCA effects of the two groups were more important than the SCA effects