Patterns of isozyme diversity and vegetative reproduction of willows in Israel

Isozyme tests were used to examine the genetic structure of six populations (n = 206 individuals) of the two willow species in Israel, Salix alba and Salix acmophylla. The 14 enzymes revealed 23 putative loci, of which 15 were polymorphic. Sexually dimorphic populations (females and males) and monomorphic ones (all female) were tested in these two species, with the following results: (1) The two sexually dimorphic S. alba populations were the most variable in isozymes. (2) The all-female population of this species had lower genetic diversity. The three tested S. alba populations are part of S. alba's continuous geographical distribution in the Upper Jordan Valley in Israel. Apparently, genetic variability is maintained in this area and, to some degree, also in the all-female stand. (3) However, the sexually dimorphic S. acmophylla population showed lower isozyme diversity than the S. alba populations, probably because S. acmophylla populations in Israel tend to be smaller and more isolated than those of S. alba. (4) The two all-female populations of S. acmophylla showed no variability at all; i.e., all 23 loci were monomorphic, indicating that each of these two populations are a single clone. The biased sex ratios, together with the relatively low values of genetic diversity and heterozygosity indicate a possible genetic drift, strong sib-mating, and vegetative propagation in these willow populations.