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terms of the average number of nucleotide per motif (14 nucleotides in average) followed by compound
motifs (12 nucleotides in average) which were represented by perfect and imperfect repeats.
BLASTN and BLASTX were used to align the 123 microssatellite sequences to Genbank database.
From these, 33 unigenes presented similarity to protein domains with possible multiple functions. The
most frequent category was the nucleic acid binding proteins (19% of the sequences similar) and it was
followed by protein kinase related proteins and conserved genes of unknown function.
Ultimately, a total of 123 microsatellites were characterized. The microsatellites had their
annealing temperatures optimized and were evaluated in 6% acrylamide gels (Figure 1). A total of 93
microsatellites were polymorphic (75.6%), 27 monomorphic (22.0%), and 3 (2.4%) did not amplify at
all. All amplified products obtained for common bean accessions were of the expected range size.
The allele number ranged from 2 to 9 alleles per locus with a 2.9 average value. PIC values varied
from 0.04 to 0.83, 0.46 average value. The lowest PIC (0.04) was shown for microsatellite SSR-
IAC60, which detained a core motif of five repetitive units, (TG) 5 . Middle American genetic distances
ranged from 0.37 to 0.71, with 0.57 average value; Andean genetic distances varied from 0.50 to 0.80
with 0.62 average value. Genetic distances among pairs of cultivars obtained from different gene
pools ranged from 0.51 to 0.81 with 0.74 of average value. Cluster analysis allocated genotypes in
two distinct groups according to their domestication centers (Figure 2). The three principal coordinate
analyses (Figure 3) divided common bean materials in two main groups according to their Andean and
Middle American origin reflecting the same group-association observed in the final dendrogram. Three
materials, Tu (11, Middle American) Jabola (18, Andean) and Kaboon (12, Andean), and Fradinho Cruzeiro
(19, Vigna spp.) were clearly depicted from the others. Essentially the same tendency represented by
the dendrogram was observed by DUARTE et al. (1999) using RAPD markers: a clear separation among
cultivars from Middle American and Andean South American domestication centers.
So far, the more microsatellites available for common bean, the better the genome mapping,
as marker density of linkage maps can be increased. YU et al. (2000) reported that SSR sequences
are fairly abundant in bean genome and widespread distributed. Once developed, microsatellites are
ideal markers, stable and easy to assay by polymerase chain reaction. Several important genes such
as the resistance genes may be linked to microsatellite motifs, which make them relevant for several
genetically applied studies of germplasm characterization, mapping and marker assisted-selection.
Documentos, IAC, Campinas, 79, 2007
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