Abstract

Subterranean clover burrs were collected during the summer period from 20 pastures, all of which had been sown to the Mt Barker strain before 1951. These population samples were surveyed for variation in morphological characters and isozyme diversity as in Part I. The old Mt Barker populations, on average, contained about 50% of a few known strains - mostly Mt Barker and/or Woogenellup - and 50% of numerous variant genotypes. The large amount of genetic diversity probably arose from infrequent outcrossing between Mt Barker and Woogenellnp or Mt Barker and Dwalganup. The population genetic structure in T. subterraneum populations is grouped into four types. Type 1 consists of a single commercial strain and type II of a few such strains. In type III about half of the population consists of very few known strains and the remaining half very many variant genotypes. In type IV the original strains have been completely (or almost completely) replaced by numerous variant genotypes. These findings are significant in defining procedures for seed certification in clover. We suggest that substantial genetic diversity may be important (if not essential) for long-term success of this species. This implies that potential cultivars should be evaluated in admixture with a number of already adapted genotypes.