Estratégias de análise da diversidade em germoplasma de cajueiro (Anacardium spp. L.) / Strategies for evaluating the diversity in germplasm of the cashew (Anacardium spp. L.)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The cashew (Anacardium occidentale) is a perennial arboreal fruit tree that is actually cropped in several tropical countries around the World. The Brazilian territory is probably the original and main diversity center of this tree fruit, as well as for most species of the genus Anacardium. On the other hand, studies concerning to the evaluation and characterization of the available germplasm are still incipient and restricted to accesses of A. occidentale. In this study, the genetic diversity in Anacardium spp. was evaluated from either the accesses kept by the Banco Ativo de Germoplasma do Cajueiro (BAG - Embrapa Agroindústria Tropical) located in Pacajus - CE and individuals sampled in a subspontaneous population of Anacardium occidentale L. located in Rio de Janeiro State. The characterization involved the analysis of the data for both morphometric and discrete phenotypic descriptors and the DNA molecular markers of the ISSR type. Forty five individuals of the Rio de Janeiro population and 91 accesses of BAG from different provenances, belonging to the species A. occidentale (common and precocious dwarf types), A. othonianum, A. humile and A. microcarpum were analyzed. The morphometric data were subjected to multivariate techniques consisting of discriminant analysis by Andersons and principal components methods, and cluster analysis by hierarchical UPGMA method and optimizing Tochers approach. Both molecular and discrete phenotypic data were investigated, by using discriminant analyses based on nonparametric k-nearest neighbor method, graphic projection of the distances in space and cluster analysis by UPGMA. Molecular variance analysis (AMOVA) was applied to the molecular data, as well as the comparative analyses of the results supplied by either three data classes and their combinations were also accomplished. The discriminant analysis techniques applied to the morphometric variables were appropriate for characterization of the Anacardium groups under evaluation. However, the method based on Andersons discriminant functions provided better discrimination of the groups, besides making possible the classification of unknown accesses or whose information were considered as doubtful. The cluster pattern UPGMA, based on morphometric data, exhibited by the populations under analysis rather appropriately reflected the level of the expected relationship among them, as considering both biological and historical evidences available. Relative to the discriminant analysis based on molecular data, it was only adequate for classification of the accesses from different A. occidentale populations. AMOVA showed that 27.5% of the accessed variation were due to the differences among the populations under investigation, whereas the remainder occurred because the differences among accesses within populations. On the other hand, the estimated values of 0ST between the population pairs showed that all populations were statistically different from each others, except for the pair othonianum x humile . Most discrete phenotypic descriptors presented wide variability, making possible to discriminate without ambiguities all Anacardium accesses under evaluation. However, the distribution patterns of this variability were "inadequate" to characterizing access groups from common origin. The comparative analysis of the different data classes showed that only the morphometric descriptors and molecular markers were correlated, whereas the discrete phenotypic descriptors presented null correlations with the others data classes. The Nordeste region was confirmed to be an important diversity center of A. occidentale, but Norte Fluminense and the Roraima State show natural populations differing from those found on the Northeast States. Therefore, there is a need for a more accurate investigation and material collections of these populations. Relative to A. othonianum and A. humile, it was concluded that there is a need for additional studies involving accesses and natural populations of these species either for getting a better elucidation of the taxonomic status of each one and the use and conservation of these genetic resources.

ASSUNTO(S)

genetic diversity anacardium genetica quantitativa anacardium diversidade genética cashew cajueiro

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