Cattleya walkeriana, one of the most improved Brazilian Cattleyas, is a popular tropical orchid endemic from Brazil and currently endangered. In the present study, for the first time microsatellite markers were developed for C. walkeriana and their transferability was tested for the species C. loddigesii and C. nobilior. The markers were used for genotyping 26 C. walkeriana specimens from different growers and from different levels of improvement. The transferability was successful, with five polymorphic loci transferred to C. loddigesii and six polymorphic loci to C. nobilior. Eight loci were polymorphic, revealing a maximum of two to ten alleles per locus in C. walkeriana and two to four and two to five in C. loddigesii and C. nobilior, respectively. There was no significant linkage disequilibrium in the studied loci. For C. walkeriana, the observed and expected heterozygosities ranged from 0 to 0.963 and from 0.138 to 0.841, respectively. These markers identified polymorphisms and may be used to study the genetic diversity, gene flow or hybridization of these species.

ABSTRACT. The aim of this study was to evaluate the genetic diversity among native plants and some individuals obtained from crosses with unknown genealogy of C. walkeriana as well as C. loddigesii and C. nobilior and to advance towards solving the question of the genetic purity of the "Orchidglade" clone. Eight microsatellite loci were used to evaluate the genetic diversity between individuals of C. walkeriana. Microsatellites were not efficient in determining the genetic diversity between C. walkeriana groups (native and improved). The difficulty in determining the genetic distance between the different genotypes can be attributed to the complex mating system of the species and to a weak genetic barrier that facilitates the development of hybrids. Our analysis revealed smaller genetic distances between the "Orchidglade", "Equilab", "Kenny" and "Pedentive" clones and the species C. loddigesii and C. nobilior. Native C. walkeriana plants were genetically more distant from the C. loddigesii and C. nobilior species.Keywords: orchid improvement, genetic variation, genetic differentiation, Cattleya loddigesii, Cattleya nobilior.Diversidade genética entre clones famosos nativos e melhorados de Cattleya walkeriana Gardner RESUMO. O objetivo desta pesquisa foi o de avaliar a diversidade genética entre plantas nativas e indivíduos de genealogia desconhecida de C. walkeriana, bem como C. loddigesii e C. nobilior, e também avançar na solução do dilema da origem do clone "Orchidglade" de C. walkeriana. Oito locos microssatélites foram utilizados para avaliar a diversidade genética entre indivíduos de C. walkeriana. Os marcadores microssatélites não foram eficientes na determinação da diversidade genética entre os grupos C. walkeriana (nativas e melhoradas). A dificuldade em determinar a distância genética entre os genótipos diferentes pode ser devida a um sistema complexo de reprodução das espécies e devido a uma fraca barreira reprodutiva facilitando o desenvolvimento de híbridos. Nossa análise revelou menores distâncias genéticas entre os clones Orchidglade, "Equilab", "Kenny" e "Pedentive" e as espécies C. loddigesii e C. nobilior. As C. walkeriana nativas se mostraram geneticamente mais distantes das espécies de C. loddigesii e C. nobilior. Palavras-chave: melhoramento de orquídeas, variação genética, diferenciação genética, Cattleya loddigesii, Cattleya nobilior.