Susceptibility of Plant Species in Eucalyptus marginata Forest to Infection by Phytophthora cinnamomi

Abstract

Estimates of the susceptibility of plant species of Eucalyptus marginata forest to Phytophthora cinnamomi were obtained by determining the frequency of plant death and isolation of the pathogen from plants occurring in disease centres in the forest. Plant species were assessed and sampled in 63 active disease centres and 17 old centres infested with P. cinnamomi in E. marginata forest north of the Preston River, south-westem Australia. Impact of P. cinnamomi was intermediate (scattered deaths) in 46% of active disease centres and high (most susceptible plants dead) in 29% of active centres. Impact in 65% of old disease centres was high. Dicotyledons (Magnoliidae) out-numbered monocotyledons (Liliidae). Just over half of the species were from six Magnoliidae families with the largest number of species from the Papilionaceae and Proteaceae. The greatest number of species within the Liliidae were consistently 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 the 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 Epacridaceae; and the Liliidae family Xanthorrhoeaceae, as well as the only species 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 species in active disease centres, the frequency of isolation of P. cinnamomi from plants was much less than the frequency of recently dead plants sampled. Isolation from plants was less frequent than from adjacent soil. The pathogen was isolated from plant or soil mainly for species of the Papilionaceae, Proteaceae, Epacridaceae and Dilleniaceae of the Magnoliideae and the Iridaceae and Xanthorrhoeaceae of the Liliidae. 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. cinnamorni.