'Plant Breeding: Sustaining the Future' Abstracts of the XVIth EUCARPIA Congress, Edinburgh, Scotland, 10-14 September 2001 DEVELOPMENT OF CRITERIA FOR DEFINITION AND IDENTIFICATION OF ESSENTIALLY DERIVED VARIETIES A.E. MELCHINGER, M. BOHN University of Hohenheim, Institute of Plant Breeding, Seed Science, and Population Genetics, 70593 Stuttgart, Germany

The concept of "essentially derivation" (ED) was introduced to the 1991 Act of the UPOV Convention to prevent the abuse of the "breeder's exemption" principle.  A variety is essentially derived from an initial variety (IV), of if it is (1) predominantly developed from the IV, (2) clearly distinguishable from the IV, and (3) conforms to the IV in the expression of essential characteristics that result from the genotype or combination of genotypes of the IV.  In contrast to the concept of ED is based on the phenotypic differences between varieties.  Molecular markers can be employed to determine the genetic similarity between varieties.  Molecular markers can e employed to determine the genetic similarity between varieties.  If genetic similarity between an IV and a new variety exceeds a defined threshold, the new variety will be regarded as an essentially derived variety (EDV).  However, no crop specific EDV thresholds are yet available.  In this study, we determined the factors that influence the genetic similarity between varieties by detailed simulations and verified the results by using AFLP and SSR data obtained for a set of 160 maize tripletts.  On the basis of these findings, we developed a biometrical approach to determine crop specific EDV thresholds.