The objectives of the project were to develop an understanding of the disease dynamics caused
by Phytophthora citricola in native plant communities in the south of Western Australia. Prior
to 1983, the pathogen had only been reported twice from Australian forests. Since then,
P. citricola has been extensively recorded from plant communities north and south of Perth, and
is currently the second most frequently recovered Phytophthora species from the northern jarrah
forest and the northern sandplains.
The objectives were addressed by examining the biology, ecology and taxonomy of
isolates of P. citricola local to the southwest. Examination of the intraspecific variation of
P. citricola by isozyme analysis resolved three major electrophoretic subgroups (SG), and these
were aligned with morphological and cultural variation within the species. One electrophoretic
SG was confined to forested areas. This SG differed from other SGs in sporangial dimensions,
growth rate on two media and in vitro sensitivity to phosphonate. A redescription of the species
may be warranted.
P. citricola was positively associated with two roads in the northern jarrah forest. Road
surfaces were sampled, then soil overburden was removed and the surface of the concreted
lateritic layer beneath was sampled. Isolation of P. citricola declined away from the road into the
adjacent forest and was more frequently recovered from the caprock (up to 1 metre below soil
surface) than from the soil surface. The most probable source of introduction was from infested
soil on vehicles using the roads.
Oospores were shown to be produced in two soils, a lateritic gravelly loam and sand,
and in plants. In soil, the electrophoretic SG confined to the forest (loamy soil) produced only
limited numbers of oospores in the sandy soil of the northern sandplain. The restriction of this
SG to the forested areas is probably physiological, rather than limited dispersal, with the SG
currently occupying the full extent of its range. Estimation of the relative persistence of
oospores, zoospores and plant material colonised by P. citricola established that only oospores
(either free in soil or in colonised plant material) were important in long tern survival in soil.
Oospores were still viable after six months at two field sites, and after 18 months in soil in the
laboratory.
Phosphonate is currently the most promising method of control of Phytophthora induced
disease in native plant cornmunites of the southwest. The efficacy of phosphonate against
P. citricola was examined in vivo and in vitro against two SGs. Phosphonate successfully
inhibited lesion growth of both SGs in vivo, but of only one electrophoretic subgroup in vitro.
The ecological implications of infestation of native plant communities in the southwest
of Australia are discussed.
| Identifer | oai:union.ndltd.org:ADTP/221780 |
| Date | January 1996 |
| Creators | Felicity J Bunny |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Felicity J Bunny |
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