Outcrossing rates and heterozygosity in natural populations of hordeum spontaneum koch in israel

The extent of cross-pollination was estimated quantitatively in 26 populations of wild barley (H. spontaneum) in Israel, using allozyme variation at 22 polymorphic loci. Individual population estimates varied from 0 to 9.6 per cent outcrossing. The overall average was 1.6 per cent, with a 95 per cent confidence range of 0.8-2.7 per cent. The evidence indicated that outcrossing was significantly higher in populations growing in the more mesic (2.1 percent), than in the xeric regions (0.4 per cent). The average frequency of multilocus homozygosity for the 22 loci was 0.963 which was in agreement with the level expected under the observed high rate of self-fertilisation, indicating no heterozygous excess. However, the heterozygotes encountered, displayed a very high degree of multiple heterozygosity which arises from extensive gametic phase (or linkage) disequilibrium. In general, these results do not support the contention that the bulk of the genetic polymorphism found in H. spontaneum in Israel has arisen in recent times by periodic introgression from cultivated barley (H. vulgare L.). Rather they indicate that extensive genetic polymorphisms probably predates the domestication of the crop, and is maintained independently of introgression.