The genetic base of Brazilian soybean cultivars: evolution over time and breeding implications

Abstract

Genetic diversity is essential for crop breeding and one way to estimate it is through the concept of genetic base, which can be defined as the number of ancestors and their relative genetic contributions (RGC) to each cultivar. The RGC can be estimated through the coefficient of parentage between the ancestors and cultivars. Previous studies determined that the genetic base of Brazilian soybean was very narrow. The objective of this work was to evaluate the pedigree of 444 Brazilian soybean cultivars to estimate their genetic base. The cultivars were divided according to their release dates and according to their origin (public or private), and the genetic base for each group was also estimated. We found 60 ancestors, of which the top four (CNS, S-100, Roanoke and Tokyo, respectively) contribute 55.3% of the genetic base. Only 14 ancestors have an RGC over 1.0%, and they represent 92.4% of the genetic base. Analysis of the release dates indicated that there has been an increase in the number of ancestors over time, but the four main ancestors were the same over all periods, and their cumulative RGC increased from 46.6% to 57.6%, indicating a narrowing of the genetic base.

Genetic diversity in Brazilian soybean germplasm

“…In summary, the soybean genetic base used in the breeding program of Brazil was constructed from a small number of genotypes. Our data confirmed this pattern and reinforced the results described by Wysmierski and Vello (2013). In addition, the methods of soybean breeding contribute to aggravate the genetic bottleneck, since backcrossing is a routinely applied method to introduce qualitative traits into an elite cultivar, particularly in the case of transgenic lines.…”

“…If we consider the 14 soybean genotypes used in the breeding program, their contribution to the genetic base can reach up to 92.4% (Wysmierski and Vello 2013). This conclusion is supported by the result of this study, where 77 soybean cultivars clustered into only two groups, with a high fixation index in each cluster.…”

“…The genetic base of Brazilian soybean germplasm is known to be narrow (Wysmierski andVello 2013, Miranda et al 2001). The frequent use of a small set of genotypes in the breeding process could be considered a key factor for the loss of genetic diversity.…”

Molecular basis of a shattering resistance boosting global dissemination of soybean

“…In addition to the priority given in breeding programs to shattering resistance, the presence of pdh1 in most ancestral lines collected from East Asia likely facilitated its rapid North American distribution. Old North American cultivars with pdh1, such as S-100, Roanoke, and Tokyo (Table S2), also contributed in large part to the soybean's genetic base in Brazil (47), currently the world's other leading producer. We believe that the advent and extensive use of pdh1 in the breeding programs enabled soybean cultivation in semiarid areas and on large scales, leading to the current status of soybean as the most economically important legume.…”

Genetic divergence of roundup ready (RR) soybean cultivars estimated by phenotypic characteristics and molecular markers

“…Despite the high number, the Brazilian soybean cultivars are extremely uniforms because they originated from only a few ancestral lines, which resulted in a narrow genetic base of germplasm (Miranda et al, 2007;Priolli et al, 2010;Wysmierski and Vello, 2013). This fact, together with the lack of genetic variability, brings risks for cultivars productivity levels and susceptibility to pests, pathogens and environmental stresses.…”