The study of some inbred lines of maize and hybrids F1 resulted from their crossing.

The genetic diversity is an important source of heterosis, which is more intense when extremes types participate. Also the information on the genetic diversity of inbred lines is fundamental for the germplasm multiplication and conservation. In this paper, the characterization and establishment of the phylogenetic relationships between the Romanian and foreign inbred lines were performed by using the phenotypic differentiation index (PDI total) calculated for 13 characters and the heterosis. The results show that the phenotypic differentiation index (PDI) can be an effective tool in forecasting maize hybrids, but not always the greatest PDI means also the greatest heterosis. F1 hybrids resulting from Romanian crossed inbred lines extracted from the II nd selection cycle from the national germplasm collection, present both a good specific combining ability and a good productivity for the parental forms, being the best from an economic point of view in the given conditions.