Linkage analysis between dominant and co-dominant makers in full-sib families of out-breeding species

As high-throughput genomic tools, such as the DNA microarray platform, have lead to the development of novel genotyping procedures, such as Diversity Arrays Technology (DArT) and Single Nucleotide Polymorphisms (SNPs), it is likely that, in the future, high density linkage maps will be constructed from both dominant and co-dominant markers. Recently, a strictly genetic approach was described for estimating recombination frequency (r) between co-dominant markers in full-sib families. The complete set of maximum likelihood estimators for r in full-sib families was almost obtained, but unfortunately, one particular configuration involving dominant markers, segregating in a 3:1 ratio and co-dominant markers, was not considered. Here we add nine further estimators to the previously published set, thereby making it possible to cover all combinations of molecular markers with two to four alleles (without epistasis) in a full-sib family. This includes segregation in one or both parents, dominance and all linkage phase configurations

Variabilidade isoenzimática em uma coleção brasileira de urucum (Bixa orellana L.)

The objectives of this work were to optimize the isozyme electrophoresis technique for Bixa orellana, and use isozyme markers for a preliminary survey on the genetic variability in Brazilian annatto germplasm accessions. Collection consisted of seed samples from sixty open pollinated trees, representing two Northern and four Southern geographic provenances. The extraction, electrophoresis, and interpretation of annatto isozymes are described. Three out of the twenty-one identified isozyme loci were polymorphic in the collection. The percentage of polymorphic loci (P = 21.05) and the expected heterozygosity in annatto (HT = 0.064) were low, compared to other tropical woody species. A UPGMA phenogram, constructed with Nei's genetic distances, clearly separated the germplasm provenant from North and Central Brazil. Variability was significantly higher among the accessions from Maranhão. A sharp genetic differentiation was detected between accessions from Maranhão and Pará States, despite their geographical proximity. The distinctive isozyme polymorphism, observed in the accessions from Maranhão, together with reports on local morphological heterogeneity in annatto fruit shape, color, and pubescence, calls for more detailed genetic and taxonomic investigation.Os objetivos deste trabalho foram: otimizar a técnica de eletroforese de isoenzimas para Bixa orellana, e usar marcadores isoenzimáticos para um estudo preliminar da variabilidade genética, presente em uma coleção de germoplasma de urucum. Foi estudada uma coleção de amostras de sementes oriundas de 60 indivíduos de polinização aberta, que representam duas procedências do Norte e quatro do Sul do Brasil. São descritas a extração, a eletroforese e a interpretação de isoenzimas de urucum. Três, dos vinte e um locos isoenzimáticos identificados, foram polimórficos na coleção examinada. A porcentagem de locos polimórficos (P = 21,05) e a heterozigosidade esperada em urucum (HT = 0,064) foram baixas, em comparação com outras espécies arbóreas tropicais. O dendrograma UPGMA, construído com base nas distâncias genéticas de Nei, diferenciou claramente as procedências de urucum do Norte, daquelas oriundas do Brasil Central. A variabilidade foi significativamente superior na procedência Maranhão. Uma pequena diferenciação genética foi detectada entre os acessos do Maranhão e do Pará, apesar da proximidade geográfica. O polimorfismo isoenzimático diferenciado, observado no germoplasma procedente do Maranhão, somado a relatos de heterogeneidade morfológica local com relação à forma, à cor e à pubescência dos frutos de urucum, sugerem uma investigação genética e taxonômica mais detalhada dessa espécie

Regulação fenólica da resistência à infecção por Microcyclus ulei Henn v. Arx em progênie de Hevea.

Three progenies of Hevea, with different levels of resistance to isolation of M. ulei (UNA) were studied. The progenies were: Fx 25 (moderately susceptible), Fx 2804 (highly susceptible) and P10 (resistant). The inoculation was made at the fourth flushing, with six to eight day-old leaflets. The progenies were maintained in a growth chamber. After 24, 72 and 144 hours, inoculated and noninoculated leaflets were collected to determine phenol, anthocyanin and chlorophyll contents. Progenies Fx 25 and Fx 2804 showed low phenol levels, decreasing levels of chlorophyll and a great number of injuries and sporulation. Progenie P10 showed high levels of phenol and chlorophyll, compared to the control. It did not show any injury. The anthocyanin levels decreased in all progenies. Consequently, Hevea resistance to M. ulei infection seems to be related to variations of leaf phenol levels.Foram estudadas três progênies de seringueira, com diferentes níveis de resistência ao isolamento de M. ulei, denominado UNA: Fx 25 (moderadamente suscetível), Fx 2804 (altamente suscetível) e P10 (resistente). A inoculação foi realizada no quarto lançamento, com folfolos de seis a oito dias de idade. As progênies foram mantidas em câmara de crescimento. Após 24, 72 e 144 horas foram feitas coletas dos folíolos inoculados e não inoculados e realizou-se a quantificação do teor de fenóis, antocianina e clorofila. Observou-se que as progênies Fx 25 e Fx 2804 apresentaram baixos níveis de fenóis e decréscimo no nível de clorofila, grande número de lesões e esporulação. A progênie P10 apresentou alto teor de fenóis com relação à testemunha, bem como de clorofila, não apresentando lesões. O nível de antocianina decresceu em todas as progênies. Assim, a resistência da seringueira à infecção por M. ulei parece estar associada à variação do teor de fenóis em suas folhas

Genetic control of Eucalyptus urophylla and E. grandis resistance to canker caused by Chrysoporthe cubensis

Chrysophorte cubensis induced canker occurs in nearly all tropical and subtropical regions where eucalypts are planted, causing losses in both wood quality and volume productivity, especially so in the warmer and more humid regions of Brazil. The wide inter and intra-specific genetic variability of resistance to canker among Eucalyptus species facilitates the selection of resistant plants. In this study, we evaluated resistance to this pathogen in five Eucalyptus grandis (G) and 15 E. urophylla (U) trees, as well as in 495 individuals from 27 progenies derived from crosses between the trees. In the field, six-months-old test seedlings were inoculated with C. cubensis. Lesion length in the xylem and bark was measured eight months later. The results demonstrated that xylem lesions could preferentially be used for the selection of resistant clones. Eight trees (7 U and 1 G) were susceptible, and the remainder (8 U and 4 G) resistant. Individual narrow and broad sense heritability estimates were 17 and 81%, respectively, thereby suggesting that canker resistance is quantitative and highly dependent on dominance and epistasis