SUSCEPTIBILITY OF PLANT-SPECIES IN EUCALYPTUS-MARGINATA FOREST TO INFECTION BY PHYTOPHTHORA-CINNAMOMI

Estimates of the susceptibility of plant species of Eucalyptus margina ta forest to Phytophthora cinnamomi were obtained by determining the f requency of plant death and isolation of the pathogen from plants occu rring in disease centres in the forest. Plant species were assessed an d sampled in 63 active disease centres and 17 old centres infested wit h P. cinnamomi in E. marginata forest north of the Preston River, sout h-western Australia. Impact of P. cinnamomi was intermediate (scattere d deaths) in 46% of active disease centres and high (most susceptible plants dead) in 29% of active centres. Impact in 65% of old disease ce ntres was high. Dicotyledons (Magnoliidae) out-numbered monocotyledons (Liliidae). Just over half of the species were from six Magnoliidae f amilies with the largest number of species from the Papilionaceae and Proteaceae. The greatest number of species within the Liliidae were co nsistently from Haemodoraceae. Families in which species tended not to die in disease centres were mainly from the Papilionaceae, Proteaceae , Mimosaceae, Myrtaceae, Dilleniaceae, Apiaceae and Goodeniaceae for t he Magnoliidae and Cyperaceae and Haemodoraceae for the Liliidae. The species which tended to die frequently in disease centres were mainly from the Magnoliidae families: Papilionaceae, Proteaceae and Epacridac eae; and the Liliidae family Xanthorrhoeaceae, as well as the only spe cies of the Zamiaceae. Phytophthora cinnamomi was isolated from 38 of the 105 species occurring in three or more active disease centres, but from only 17 of the 107 species occurring in old centres. For most sp ecies in active disease centres, the frequency of isolation of P. cinn amomi from plants was much less than the frequency of recently dead pl ants sampled. Isolation from plants was less frequent than from adjace nt soil. The pathogen was isolated from plant or soil mainly for speci es of the Papilionaceae, Proteaceae, Epacridaceae and Dilleniaceae of the Magnoliideae and the Iridaceae and Xanthorrhoeaceae of the Liliida e. Cross tabulation of species by frequency of death and isolation of P. cinnamomi from plant and soil provided the opportunity to classify the response of plant species to infection by P. cinnamomi.