Abstract
The selection of superior genotypes based on the simultaneous response to several characteristics of agronomic importance is a key strategy to overcome the scarcity of available varieties of papaya. This study aimed to apply the combined selection by using distinct selection indexes based on both the genetic values obtained by the REML/BLUP methodology and the real measured values to select agronomically superior genotypes of papaya within backcross progenies. The combined selection was carried out based on genetic and phenotypic values, original and standardized, multiplied by the agronomic weights. The results of the analysis of genetic parameters indicate that the evaluated progenies have expressive genetic variability for the considered traits, and that there are real possibilities of genetic progress with the selection. Among the analyzed indexes, the one based on standardized genetic value presented greater consistency in the ranking of genetic material, demonstrating the advantage of data standardization. Five progenies belonging to the BC1 generation, and five to the BC3 generation were selected using this index. A total of 27 plants ag-ronomically superior were selected within the top five progenies and recommended for generation advance, 23 being selected by combined selection and 4 using the direct selection for the four mainly characters in papaya breeding program: production, pulp and fruit firmness and soluble solids. Beyond the selection of superior genotypes for the development of future inbred lines, this study also allowed defining the best strategy to apply the combined selection in papaya using pre-dicted breeding values obtained by BLUP. This strategy may allow higher accuracy in the selection process, thus increasing the chances of success of the breeding programs.
Highlights
Despite its major socioeconomic significance and the fact that it is one of the main fruits that are sources of income to Brazil, narrow genetic variability has been observed in commercial plantations of papaya in almost all producing regions, revealing the reduced number of choices of commercial varieties [1]-[4]
Since one of the primary objectives of breeding programs is the prediction of the genetic value of the evaluated individuals [13] [14], the methodologies for mixed models emerge as an important selection procedure, involving the estimation of the variance components by the restricted maximum likelihood method (REML), while the prediction of the genotypic values was estimated by the best linear unbiased prediction method (BLUP), which provided a more accurate selection process [13]
The main purpose of this backcross program was to convert the dioecious sex of parent Cariflora to gynoecious-andromonoecious with the transfer of the chromosomal region that determines hermaphroditism donated by elite genotype “SS783”
Summary
Despite its major socioeconomic significance and the fact that it is one of the main fruits that are sources of income to Brazil, narrow genetic variability has been observed in commercial plantations of papaya in almost all producing regions, revealing the reduced number of choices of commercial varieties [1]-[4]. Part of this problem would be solved if more studies were carried out to identify and select agronomically superior genotypes from segregating populations. Since one of the primary objectives of breeding programs is the prediction of the genetic value of the evaluated individuals [13] [14], the methodologies for mixed models emerge as an important selection procedure, involving the estimation of the variance components by the restricted maximum likelihood method (REML), while the prediction of the genotypic values was estimated by the best linear unbiased prediction method (BLUP), which provided a more accurate selection process [13]
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