Tropical maize germplasm: what can we say about its genetic diversity in the light of molecular markers?

Abstract

Knowledge about genetic variability of a crop allows for more efficient and effective use of resources in plant improvement programs. The genetic variation within temperate maize has been studied extensively, but the levels and patterns of diversity in tropical maize are still not well understood. Brazilian maize germplasm represents a very important pool of genetic diversity due to many past introductions of exotic material. To improve our knowledge of the genetic diversity in tropical maize inbred lines, we fingerprinted 85 lines with 569 AFLP bands and 50 microsatellite loci. These markers revealed substantial variability among lines, with high rates of polymorphism. Cluster analysis was used to identify groups of related lines. Well-defined groups were not observed, indicating that the tropical maize studied is not as well organized as temperate maize. Three types of genetic distance measurements were applied (Jaccard's coefficient, Modified Rogers' distance and molecular coefficient of coancestry), and the values obtained with all of them indicated that the genetic similarities were small among the lines. The different coefficients did not substantially affect the results of cluster analysis, but marker types had a large effect on genetic similarity estimates. Regardless of genetic similarity coefficient used, estimates based on AFLPs were poorly correlated with those based on SSRs. Analyses using AFLP and SSR data together do not seem to be the most efficient manner of assessing variability in highly diverse materials because the result was similar to using AFLPs alone. It was seen that molecular markers can help to organize the genetic variability and expose useful diversity for breeding purposes.

Genetic diversity in elite inbred lines of maize and its association with heterosis

“…However, molecular markers have allowed significant insights into the research of genetic divergence of maize (Smith et al, 1990;Lanza et al, 1997;Benchimol et al, 2000;Barbosa et al, 2003;Oliveira et al, 2004;Laborda et al, 2005;Bruel, 2006;Aguiar, 2008). The divergence of lines evaluated by molecular markers may reduce significantly the labor involved in pollination and make possible to obtain heterotic groups with further allotting of new lines in these groups and guiding the crosses to obtain the most productive hybrids.…”

“…Clustering relates the heterotic groups selecting the most promising crosses, thereby reducing both the number of crosses and the number of hybrids under evaluation (Guimarães et al, 2007). Laborda et al (2005) stated that the estimates of genetic divergence between the lines evaluated by molecular markers have reduced the manual labor involved in pollination, have clustered heterotic groups, and have directed breeding to obtain the most productive and vigorous hybrids. Several maize breeders have researched the correlation between the genetic diversity quantified by molecular markers of DNA and the performance of hybrids, but the results have been incongruous.…”

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

“…The high level of polymorphism detected increases the resolution of the study of genealogy and genetic diversity and reduces the number of markers required to distinguish genotypes. SSR markers have been used to analyze genetic diversity in several species, including maize (Laborda et al, 2005), wheat (Huang et al, 2007) and soybean (Yamanaka et al, 2007;Mulato et al, 2010;Singh et al, 2010).…”

Inference of genetic diversity in popcorn S3 progenies

“…Based on this correlation, estimation of genetic diversity between strains using molecular markers would help reduce the number of studies using pollination, as well as allowing identification of heterotic groups and direct crosses for the generation of superior hybrids in terms of productivity and vigor (Laborda et al, 2005). The use of molecular markers is of great relevance to studies on genetic diversity between strains developed in breeding programs.…”