Correlation between the heterosis of maize hybrids and genetic divergence among lines

The objective of this work was to evaluate grain yield of maize single cross hybrids obtained from diallel crosses among contrasting lines, to estimate the combining ability of the lines, and finally to confirm if the genetic diversity among those lines assessed by molecular markers is correlated with single cross hybrids heterosis. The 36 single cross hybrids resulting from partial diallel and 12 parental lines were evaluated in Campinas in randomized block design, with three replicates and two control lines checks. General combining ability of the lines was estimated according to Griffing model 4. Correlations among matrices were estimated through Mantel statistics, considering heterosis, yield and specific combining ability with genetic divergence assessed by AFLP and SSR. The hybrids PM518 x L111 exhibited an outstanding yield and the lines PM518, IP4035 and L111 showed positive general combining ability. The estimate heterosis ranged from 927 to 6,698 kg ha(-1). A positive and significant correlation was observed in parental lines between heterosis and genetic diversity assessed by AFLP and SSR. The genetic divergence, however, was not enough to determine the specific combining ability and the hybrids yield.42681181

Empirical Comparison of Simple Sequence Repeats and Single Nucleotide Polymorphisms in Assessment of Maize Diversity and Relatedness

While Simple Sequence Repeats (SSRs) are extremely useful genetic markers, recent advances in technology have produced a shift toward use of single nucleotide polymorphisms (SNPs). The different mutational properties of these two classes of markers result in differences in heterozygosities and allele frequencies that may have implications for their use in assessing relatedness and evaluation of genetic diversity. We compared analyses based on 89 SSRs (primarily dinucleotide repeats) to analyses based on 847 SNPs in individuals from the same 259 inbred maize lines, which had been chosen to represent the diversity available among current and historic lines used in breeding. The SSRs performed better at clustering germplasm into populations than did a set of 847 SNPs or 554 SNP haplotypes, and SSRs provided more resolution in measuring genetic distance based on allele-sharing. Except for closely related pairs of individuals, measures of distance based on SSRs were only weakly correlated with measures of distance based on SNPs. Our results suggest that 1) large numbers of SNP loci will be required to replace highly polymorphic SSRs in studies of diversity and relatedness and 2) relatedness among highly-diverged maize lines is difficult to measure accurately regardless of the marker system

Genetic divergence of rubber tree estimated by multivariate techniques and microsatellite markers

Genetic diversity of 60 Hevea genotypes, consisting of Asiatic, Amazonian, African and IAC clones, and pertaining to the genetic breeding program of the Agronomic Institute (IAC), Brazil, was estimated. Analyses were based on phenotypic multivariate parameters and microsatellites. Five agronomic descriptors were employed in multivariate procedures, such as Standard Euclidian Distance, Tocher clustering and principal component analysis. Genetic variability among the genotypes was estimated with 68 selected polymorphic SSRs, by way of Modified Rogers Genetic Distance and UPGMA clustering. Structure software in a Bayesian approach was used in discriminating among groups. Genetic diversity was estimated through Nei's statistics. The genotypes were clustered into 12 groups according to the Tocher method, while the molecular analysis identified six groups. In the phenotypic and microsatellite analyses, the Amazonian and IAC genotypes were distributed in several groups, whereas the Asiatic were in only a few. Observed heterozygosity ranged from 0.05 to 0.96. Both high total diversity (HT' = 0.58) and high gene differentiation (G st' = 0.61) were observed, and indicated high genetic variation among the 60 genotypes, which may be useful for breeding programs. The analyzed agronomic parameters and SSRs markers were effective in assessing genetic diversity among Hevea genotypes, besides proving to be useful for characterizing genetic variability

Drosophila mediopunctata microsatellites II: cross-species amplification in the tripunctata group and other Drosophila species

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Heterologous amplification of 134 recently developed Drosophila mediopunctata microsatellites is here reported. Cross-species amplification was analyzed in 30 species of the Drosophila and Sophophora subgenera, and emphasis was given to the tripunctata group. The overall microsatellite transfer rate was 48%. The highest cross-species amplifications were observed in D. unipunctata (n = 94) and D. roehrae (n = 82). The phylogenetic proximity to D. mediopunctata did not correspond to greater numbers of successfully amplified microsatellites. Of the 134 microsatellite loci, 21 failed to amplify in all species and 18 were detected in all of them. A UPGMA dendrogram, based on Jaccard's similarities in the tripunctata group, recovered few expected phylogenetic relationships. The data demonstrated that many D. mediopunctata microsatellites are now available as potentially useful markers for genetic investigation and conservation of other Drosophila species.11281296Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)APS [2004/03203-0]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2004/03385-1]APS [2004/03203-0

Drosophila mediopunctata microsatellites I: more than a hundred polymorphic loci available for genetic studies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We describe the first 134 polymorphic microsatellites loci developed for the fly Drosophila mediopunctata. A genomic DNA library double-enriched for dinucleotides was constructed and approximately 600 unambiguous microsatellites were identified. The DNA library consisted of 60% positive clones, short-sized dinucleotides (mean = 8.7 repeats) and 73% of AC/GT combinations. A total of 177 primer pairs were designed and thirteen strains were used to achieve optimal PCR amplification conditions and allelic variability of the isolated loci. The average number of alleles per locus was 4.6 and means of observed and expected heterozygosities were 0.23 and 0.62, respectively. The discriminating power average was 0.72. These new developed markers will be applied in the study of natural population dynamics and for the construction of a molecular linkage map for the species.11297307Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)GMM [2006/61184-8]APS [2004/03203-0]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2004/03385-1]GMM [2006/61184-8]APS [2004/03203-0

Tropical maize germplasm: what can we say about its genetic diversity in the light of molecular markers?

Knowledge about genetic variability of a crop allows for more efficient and effective use of resources in plant improvement programs. The genetic variation within temperate maize has been studied extensively, but the levels and patterns of diversity in tropical maize are still not well understood. Brazilian maize germplasm represents a very important pool of genetic diversity due to many past introductions of exotic material. To improve our knowledge of the genetic diversity in tropical maize inbred lines, we fingerprinted 85 lines with 569 AFLP bands and 50 microsatellite loci. These markers revealed substantial variability among lines, with high rates of polymorphism. Cluster analysis was used to identify groups of related lines. Well-defined groups were not observed, indicating that the tropical maize studied is not as well organized as temperate maize. Three types of genetic distance measurements were applied (Jaccard's coefficient, Modified Rogers' distance and molecular coefficient of coancestry), and the values obtained with all of them indicated that the genetic similarities were small among the lines. The different coefficients did not substantially affect the results of cluster analysis, but marker types had a large effect on genetic similarity estimates. Regardless of genetic similarity coefficient used, estimates based on AFLPs were poorly correlated with those based on SSRs. Analyses using AFLP and SSR data together do not seem to be the most efficient manner of assessing variability in highly diverse materials because the result was similar to using AFLPs alone. It was seen that molecular markers can help to organize the genetic variability and expose useful diversity for breeding purposes.11171288129

Evaluating genetic relationships between tropical maize inbred lines by means of AFLP profiling

Diversity among tropical maize inbred lines that compose breeding programs, is not well known. The lack of this information has made the arrangement of heterotic groups to be used for breeding purposes difficult. Methods of molecular analysis have been used as efficient alternatives for evaluating genetic diversity, aiming at heterotic group arrangement and acquisition of new hybrids. In this study, AFLP (amplified fragment length polymorphism) was used to investigate the genetic relationships among 96 tropical maize inbred lines from two different origins. The polymorphism level among the genotypes and the possibility of their allocation in heterotic groups were evaluated. Besides, correlations among genetic diversity and flowering time were analyzed. Nine primer combinations were used to obtain AFLP markers, producing 638 bands, 569 of which were polymorphic. Genetic similarities (GS), determined by Jaccard's similarity coefficient, varied from 0.345 to 0.891, with an average of 0.543. The dendrogram based on the GS and on the UPGMA cluster method did not separate the inbred lines in well-defined groups. Aiming at separating the lines into more accurate groups, Tocher's optimization procedure was carried out, 17 groups being identified. Association between flowering time and germplasm pools was detected. AFLP showed itself to be a robust assay, revealing a great power of detection of genetic variability in the tropical germplasm, and also demonstrated to be very useful for guiding breeding programs.1401243