ABSTRACT:The objectives of this study were to identify the genetic variability and estimate the level of homozygosity in a castor bean F4 population using microsatellite markers (SSR).To this end, it was performed the genotyping of the population through 53 pairs of SSR primers. Allele frequencies were estimated by number of alleles per locus, expected heterozygosity (H e ), observed heterozygosity (H o ) and polymorphic information content (PIC). An array of genetic dissimilarity was generated by Nei and Li index, and hierarchical cluster analysis was performed using the Unweighted Pair-Group Method Averages (UPGMA) method.
O objetivo deste trabalho foi avaliar os parâmetros genéticos de caracteres agronômicos, em populações fixas e segregantes de mamoneira (Ricinus communis). Os experimentos foram conduzidos entre 2006 e 2009, com populações fixas e segregantes obtidas de cruzamentos entre as cultivares BRS 149 Nordestina, BRS 188 Paraguaçu, EBDA MPA 17, Mirante 10 e Sipeal 28. Os caracteres avaliados foram: estatura de planta (EST), número de dias do plantio ao florescimento (FLO), número de frutos de três racemos (NFR), número de sementes de três racemos (NSR) e peso de sementes de três racemos (PSR). No cruzamento 'BRS 149 Nordestina' x 'Sipeal 28', as variâncias mostraram maior participação dos efeitos de ambiente e os coeficientes de herdabilidade apresentaram valores abaixo de 50%. No cruzamento 'BRS 149 Nordestina' x 'Mirante 10', os valores de herdabilidade variaram de 24,6 (NFR) a 86% (FLO). No cruzamento 'BRS 188 Paraguaçu' x 'EBDA MPA 17', os valores de herdabilidade foram baixos para a todos os caracteres, exceto para o florescimento. Progressos genéticos podem ser alcançados por seleção quanto à precocidade de florescimento na maioria dos cruzamentos analisados. A seleção artificial deve ser aplicada a gerações avançadas, pois o ambiente exerce forte influência nos caracteres fenotípicos. Devem ser adotados métodos de melhoramento mais rigorosos para a condução da população segregante, a fim de se obter maior ganho genético.
Cacao is a crop of global relevance that faces constant demands for improved bean yield. However, little is known about the genomic regions controlling the crop yield and genes involved in cacao bean filling. Hence, to identify the quantitative trait loci (QTL) associated with cacao yield and bean filling, we performed a QTL mapping in a segregating mapping population comprising 459 trees of a cross between 'TSH 1188' and 'CCN 51'. All variables showed considerable phenotypic variation and had moderate to high heritability values. We identified 24 QTLs using a genetic linkage map that contains 3526 single nucleotide polymorphism (SNP) markers. Haplotype analysis at the significant QTL region on chromosome IV pointed to the alleles from the maternal parent, 'TSH 1188', as the ones that affect the cacao yield components the most. The recombination events identified within these QTL regions allowed us to identify candidate genes that may take part in the different steps of pod growth and bean filling. Such candidate genes seem to play a significant role in the source-to-sink transport of sugars and amino acids, and lipid metabolism, such as fatty acid production. The SNP markers mapped in our study are now being used to select potential highyielding cacao varieties through marker-assisted selection in our existing cacao-breeding experiments.
Cacao is an important crop, its beans are key raw materials for the chocolate and cosmetic industries. Ceratocystis wilt of cacao (CWC) caused by Ceratocystis cacaofunesta is a lethal disease for the crop. Therefore, the selection of resistant cacao varieties is one of the viable ways to minimize losses in cacao production. In this paper, we described the identification of a major QTL associated with CWC in an F1 mapping population from a cross between a resistant, “TSH 1188,” and a susceptible genotype, “CCN 51.” A set of 266 trees were genotyped using 3,526 single nucleotide polymorphic markers and then multiple QTL mapping analyses were performed. Two QTLs were identified on chromosomes IV and VI. The major QTL was located at 20 cM from the top position of chromosome VI, accounting for more than 60% of the phenotypic variation. The favorable allele T1, with haplotype GTT, came from the “TSH 1188” parent. It was evident that the haplotype combination T1C2 on chromosome VI was the most significant for resistance, since 93% of resistant trees had this haplotype. The major QTL converged to a genomic region of 739.4 kb that harbored nine candidate genes, including two major classes of resistance genes, which would make them the primary candidates involved in the resistance to CWC. The haplotypes detected are now used to improve the efficiency and precision of the selection of resistant trees in cacao breeding.
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