Genetic diversity of superior Salix clones selected for intensive forestry plantations F. A. Aravanopoulos a, *, K. H. Kim b, 1 , L. Zsua b a Laboratory of Forest Genetics and Plant Breeding, Department of Forestry and Natural Environment, Aristotle University of Thessaloniki, Thessaloniki, 54006, Greece b Laboratory of Forest Genetics, Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Canada, M5S 3B3 Abstract A number of willow clones are today in use in short rotation intensive culture plantations. The clonal nature of this crop makes it an easy target for pests and pathogens when grown in monocultures. This is a major concern as plantations of coppice must remain viable for up to 20 years to be profitable. In this paper the genetic diversity of 114 selected willow clones was examined and the possible solution of growing willows in multiclonal plantations is discussed. Forty five Salix eriocephala clones, 53 S. exigua clones and 16 clones of their inter-specific hybrid (12 S. eriocephala  exigua clones and 4 S. exigua  eriocephala clones), were evaluated. Starch gel electrophoresis was employed and 12 enzyme systems were used for the assessment of the genetic variation in the clonal material. A total of 29 loci and 57 alleles were revealed. Three measures of genetic diversity were used in order to evaluate the genetic base of the clonal set: average number of alleles per locus, percentage of polymorphic loci and mean heterozygosity. Results indicated that the genetic diversity within a species, is generally lower than the genetic diversity observed in natural populations or full-sib families of the same species. These results, however, are within the limits obtained from natural populations of the Salicaceae family. Heterozygosity values were found to be greater than similar values from poplar clonal material. In contrast to the results within species, inter-specific hybrid clones presented relatively high amounts of genetic diversity. The significance of these results in the management of clonal plantations is discussed from both the operational and conservation points of view. # 1999 Published by Elsevier Science Ltd. All rights reserved. Keywords: Salix, clones, genetic diversity, isoenzymes, multiclonal plantations, biomass 1. Introduction The potential utilization of willows (Salix spp.) in short rotation intensive culture (SRIC) planta- tions for energy, chemicals and fibre has recently come under close scrutiny. They are ideal candi- dates for this purpose because of their fast growth, high productivity, coppice ability and ease of vegetative propagation. [1, 2] The interest in willow SRIC plantations is being reinforced by: the evolution of pulp and paper technology which now allows the extensive utilization of fast growing hardwoods, the success of newly Biomass and Bioenergy 16 (1999) 249–255 0961-9534/99/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S0961-9534(98)00013-0 PERGAMON * Author to whom correspondence should be addressed. 1 Permanent address: Faculty of Forest Science, Chonbuk National University, Chonju, Chonbuk, 560-756, Korea