Genetic divergence of different temporal cycles of selection

Abstract

Since the mid 1960's, when the Maize Research Institute "Zemun Polje" began its maize breeding activities, there have been five cycles of selection primarily referring to the period of introducing new, higher-yield hybrids into mass production. This paper provides genetic characterization Of 30 maize hybrids developed by the Maize Research Institute "ZenlUn Polje", by RAID markers, in order to determine genetic relatedness of hybrids of different breeding cycles. The Jaccard similarity coefficients have been Computed and used for Cluster analysis by UPGMA and by Wards' method, discriminant analysis and correspondence analysis. Cluster analysis clearly delineates groups of hybrids by time cycles, while the correspondence analysis indicates that a division into three cycles Could be more adequate. The territorial map of the discrimination area, reduced to two dimensions, is an indication of the proximity between the cycles III and IV. Also the proximity of group centroids, of different cycles, by delineation lines indicates that the discrimination among groups is not so strong. The results Of all three analysis indicate that in genetic terms there -,ire three different selection cycles. Introduction of novel germ plasma into existing breeding material implies, in genetic terms, a beginning of new selection cycle.