Thanks to the Almighty God for His guidance, protection and provisions during the course of this study. I wish to express my unreserved appreciation to my supervisor, Professor F. A. Aravanopoulos, for his suggestion on the topic of my interest, constructive criticism, patience and careful supervision of this work. My sincere gratitude goes to the members of my supervising committee, Professor F. A.Aravanopoulos, Professor A. Scaltsoyiannes and Professor E. Barbas for all their assistance during the laboratory work and write-up. I am also very grateful to Prof.Stamatelos, to the lecturer Dr. P. Alizoti for contributing to my knowledge in forest genetics, tree breeding and statistics that l have acquired during the period, as well as the entire staff of the Laboratory of Forest Genetics and Tree Improvement. I also express my sincere thanks to the members of the examining committee, namely