©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 7 (4): 1233-1244 (2008) Heterotic groups in tropical maize germplasm by test crosses and simple sequence repeat markers C.G. Aguiar 1 , I. Schuster 1 , A.T. Amaral Júnior 2 , C.A. Scapim 3 and E.S.N. Vieira 1 1 Cooperativa Central de Pesquisa Agrícola, Setor de Biotecnologia, Cascavel, PR, Brasil 2 Laboratório de Melhoramento Genético Vegetal, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ, Brasil 3 Departamento de Agronomia, Universidade Estadual de Maringá, Maringá, PR, Brasil Corresponding author: A.T. Amaral Júnior E-mail: amaraljr@uenf.br Genet. Mol. Res. 7 (4): 1233-1244 (2008) Received August 15, 2008 Accepted September 4, 2008 Published November 11, 2008 ABSTRACT. The objectives of the present study were to determine heterotic groups of germplasm lines of tropical maize by test crosses and by simple sequence repeat (SSR) markers and to compare ive grouping methods of heterogeneous maize. Sixteen lines of nine populations in the S 5 generation were evaluated in test crosses with three testers. The results of four experimental trials over two years were used to group the lines by ive methods: evaluation based on the hybrid mean in top-cross tests, hybrid index, genetic diversity by the Mahalanobis distance, genetic diversity by the Euclidean distance, and genetic diversity by SSR markers. The concordance of grouping by the Mahalanobis and Euclidean distance amounted to 87.50%, and the concordance of these methods and grouping by SSR markers was 56.25%. Grouping by SSR markers was consistent with