Abstract

Subterranean clover burrs were collected during summer from 28 sites, 10 of which were in the <500 mm annual rainfall zone. All sites had been sown to the Dwalganup strain, 30-50 years ago. Spaced plants were grown from seed from burr subsamples of each population. Several morphological characters, flowering dates, and oestrogenic isoflavones in late spring leaf samples were determined. At maturity, burr samples were collected from each plant, and the isozyme patterns in seeds were determined for eight enzyme systems using starch gel electrophoresis. Populations from the lower rainfall (< 500 mm) sites usually consisted of one or two strains - Dwalganup with or without Geraldton - and variant (or 'unknown') genotypes were very rare or absent. Populations from the higher rainfall (> 500 mm) sites, on the other hand, comprised about 50% of a few known strains - mostly Dwalganup and/or Dinninup - the remaining 50% consisting of numerous variant genotypes. Infrequent outcrossing between the Dwalganup and Mt Barker strains is the likely major source of this variation. Possible explanations for the lack of variant genotypes in the lower rainfall zone are discussed.