Abstract
The objective of this work was to estimate the coefficient of parentage and to understand the genetic structure of 90 elite soybean cultivars, which are adapted to different Brazilian environments. A total of 4,005 coefficients of parentage (f) were obtained and used to group the cultivars by UPGMA method. The constructed dendrogram showed several related cultivar groups which shared similar ancestors and clearly showed the genetic structure of the main Brazilian cultivars. Effective population sizes (Ne) were also estimated for cultivars in different generations. The average f = 0.2124 value, obtained from cultivars classified into four decades according to the release year, suggested effective soybean population sizes of 11 and 13 calculated using arithmetic and weighted means, respectively. The relatively small Ne and the high parentage coefficient support the conclusion that there is a high similarity degree among the main soybean cultivars in Brazil.
Highlights
Soybean genetic breeding started recently in Brazil compared to other species of economic importance, but its contribution to the Brazilian agriculture has been very significant
The objective of this work was to evaluate the available genetic variability among parents for crossing, using estimatives of the coefficient of parentage, and to understand the genetic structure of 90 cultivars adapted to different Brazilian environments
The genealogies were obtained from diverse sources including technical documents, folders on released cultivars, and publications on the subject, as well as commom knowledge. Their genetic similarity was obtained by the coefficient of parentage (f) of each pair of cultivars calculated by the PROC INBREED of the SAS
Summary
Soybean genetic breeding started recently in Brazil compared to other species of economic importance, but its contribution to the Brazilian agriculture has been very significant. The increase in yield in the traditional cropping regions, the expansion of the agricultural frontier, incorporating areas of the “Cerrados” as productive lands, and the increase of crop rotation are unquestionable results of the benefit obtained by creating new cultivars that are higher yielding and better adapted to these regions (Hiromoto, 1996). The breeder has two choices when selecting parents for hybridization. The first is to maximize recombination, choosing genetically distant parents that have traits of interest, to obtain a recombinant population with wide genetic variability, increasing the chances to find genotypes that favorably combine these traits. The second choice is to minimize recombination using backcrossing for hybridization, selecting the donor parent among cultivars which are similar to the recurrent parent and carriers of the desirable trait for transfer.
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