Gene and genotypic diversity of Phytophthora cinnamomi in South Africa andAustralia revealed by DNA polymorphisms

Phytophthora cinnamomi isolates from South Africa and Australia were compar ed to assess genetic differentiation between the two populations. These two populations were analysed for levels of phenotypic diversity using random amplified polymorphic DNAs (RAPDs) and gene and genotypic diversity using r estriction fragment length polymorphisms (RFLPs). Sixteen RAPD markers from four decanucleotide Operon primers and 34 RFLP alleles from 15 putative lo ci were used. A few isolates from Papua New Guinea known to posses alleles different from Australian isolates were also included for comparative purpo ses. South African and Australian P. cinnamomi populations were almost iden tical with an extremely low level of genetic distance between them (D-m = 0 .003). Common features for the two populations include shared alleles, low levels of phenotypic/genotypic diversity, high clonality, and low observed and expected levels of heterozygosity. Furthermore, relatively high levels of genetic differentiation between mating type populations (D-m South Afric a = 0.020 and D-m Australia = 0.025 respectively), negative fixation indice s, and significant deviations from Hardy-Weinberg equilibrium, all provided evidence for the lack of frequent sexual reproduction in both populations. The data strongly suggest that both the South African and Australian P. ci nnamomi populations are introduced.