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ERADICATION OF PHYTOPHTHORA CINNAMOMI FROM BLACK GRAVEL
GRAVEYARD SITES IN THE EUCALYPTUS MARGINATA (JARRAH) FOREST
M. Crone A , P.A. O’Brien A , J.A. McComb A , V. Stokes B , I. Colquhoun B and G.E.StJ. Hardy A
A Centre for Phytophthora Science and Management, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch,
Australia 6150.Email: m.crone@murdoch.edu.au
B Alcoa of Australia, Pinjarra, Australia 6208
ABSTRACT. Phytophthora cinnamomi can survive more than 50 years in the Eucalyptus marginata forest despite the death
of susceptible species. We investigated whether the eradication of vegetation from black gravel sites reduced pathogen
survival. After elimination of living plants pathogen recovery declined over 2 years compared to control sites. Annuals and
herbaceous perennials were shown to be predominantly asymptomatic hosts responsible for the persistence of the pathogen.
For the first time, a biotrophic or endophytic mode for this pathogen was shown by the presence of haustoria. Abundant
stromata were shown for the first time; these germinated to produce numerous selfed oospores (300-400 per mm 2 ) and thickwalled
chlamydospores. This is the first report of viable oospores capable of germination and colony development being
formed in a natural environment. The significance of these observations for P. cinnamomi control will be explored.
INTRODUCTION
Phytophthora cinnamomi is difficult to eradicate from
natural and managed ecosystems. However, since it is a poor
saprophyte and depends on living host material one
successful approach to eradicate it has involved the
temporary removal of all living plant material (1). The
current study aimed to eradicate P. cinnamomi from infested
graveyard sites in the jarrah forest. However, this method
can only be fully utilised once the life cycle of the pathogen
under adverse conditions is known. Previous studies focused
on susceptible woody species, but these were unimportant in
the current study as they have long disappeared from these
sites. Despite this P. cinnamomi persists on graveyard sites.
Consequently an emphasis was placed annuals and
herbaceous perennials.
cinnamomi. These stromata germinated to produce oospores
and chlamydospores, in turn facilitating the survival of the
pathogen under adverse conditions. For the first time the
identity and viability of these two spore types has been
shown within naturally infected root material.
Findings are likely to be applicable for pathogen
management in other natural environments or in
horticultural settings where build-up of inoculum may occur
in asymptomatic hosts. These findings will also be relevant
to extractive industries, such as the gravel industry where
soils are infested with P. cinnamomi.
MATERIALS AND METHODS
Two black gravels sites with adjacent controls were treated
with herbicide to kill all vegetation. Soil samples were
regularly collected and baited for P. cinnamomi to monitor
survival. In addition, annual and herbaceous perennials were
harvested weekly over winter to spring 2011 to determine
whether they were hosts of P. cinnamomi. Histological
studies of three species across the sampling period were
conducted to observe pathogen growth and survival
structures.
RESULTS AND DISCUSSION
Eradication Two years after removal of vegetation, P.
cinnamomi recoveries had declined by 60 % (Table 1).
Table 1. Number of Phytophthora cinnamomi recoveries
prior to treatment and post treatment on control (C) and
eradicated sites (E).
Site 1 recoveries Site 2 recoveries
Prior to treatment C: 10 ; E: 11 C: 10 ; E: 15
1yr post treatment C: 7 ; E: 5 C: 10 ; E: 6
2yrs post treatment C: 15 ; E: 3 C: 13 ; E: 3
Totals after treatm. C: 22 ; E: 8 C: 23 ; E: 9
Hosts P. cinnamomi was isolated from 15 out of 19 annuals
and herbaceous perennials, of these 10 species were
asymptomatic. The pathogen was constantly isolated from
the three histologically examined species during the period.
Mode of survival P. cinnamomi extensively colonised
asymptomatically the newly identified host species in a
biotrophic mode through haustorial (Figure 1A) production.
This is a new observation for a pathogen only known as a
necrotroph or hemibiotroph in susceptible woody species. It
is postulated that this biotrophic mode enabled the formation
of stromata (Figure 1B) not previously reported for P.
Figure 1. A Haustorium of P. cinnamomi in asymptomatic
annual and B germinating stroma in herbaceous perennial.
Scale: A = 500nm; B = 40µm.
ACKNOWLEDGEMENTS
APAI scholarship Australian Research Council
(LP0776740) and research funding from Alcoa Alumina
Australia were gratefully received
REFERENCES
1. Dunstan W.A., Rudman T., Shearer B.L., Moore N.A.,
Paap T., Calver M.C., Dell B., Hardy G.E.StJ. (2010).
Containment and spot eradication of a highly
destructive, invasive plant pathogen (Phytophthora
cinnamomi) in natural ecosystems. Biological Invasions
12: 913-25.
7th Australasian Soilborne Diseases Symposium 12