Figure 7 Puccinia psidii. (a) Uredinia on abaxial surface (scale bar
= 500 lm), (b) uredinia and telia (arrowed; scale bar = 500 lm), (c) erumpent
uredinium (scale bar
= 125 lm), (d) erumpent uredinium (scale bar = 20 lm), (e) single urediniospore with tonsure (scale bar = 5 lm), (f)
teliospores (scale bar
= 10 lm).
Figure 8 Photographic sequence showing the impact of Puccinia psidii over time on Rhodamnia angustifolia, a rare and endangered Queensland
species. (a) Initial detection of rust on new shoots and expanding foliage, March 2011; (b) high level of P. psidii infection on new shoots and
expanding leaves, December 2011; (c) severe defoliation following repeated infection by P. psidii, January 2012; (d) foliage and branch dieback
15 months after initial infection was detected, June 2012. Photographs are of cultivated plants, Brisbane.
Plant Pathology (2013)
Puccinia psidii in Queensland, Australia
commonly reported from botanic gardens and nature
reserves, with disease impacts ranging from minor leaf
spots to severe dieback and infection, and premature
senescence of ﬂowers and fruits. In comparison, P. psidii
is rarely severe on native vegetation in Brazil, even
though it has been identiﬁed from a range of native
Myrtaceae and causes occasional epidemics in native
guava plantations (Ribeiro & Pommer, 2004).
The spread of P. psidii via movement of infected
nursery stock, and other human assisted mechanisms,
played a signiﬁcant role in the initial distribution and
establishment of the disease in different regions of Qld.
Now that the disease is established and widespread in
Qld, further spread of P. psidii into new regions is
likely to result from wind and rain dispersal of spores.
Short distance dispersal is facilitated by animals and
insects (Coutinho et al., 1998). Dominant southeasterly
winds and the presence of susceptible species, e.g.
Melaleuca quinquenervia and Melaleuca leucadendra,
that provide a near-contiguous corridor along the east
coast of Australia (Carnegie & Lidbetter, 2012), are
Figure 9 Branch dieback and infection of
shoots on a mature Rhodomyrtus psidioides
tree (a, b) and infection and dieback of
regenerating seedlings under adult trees (c,
d). Photographs are of cultivated plants in
the Brisbane Botanic Gardens, Mt Coot-tha.
Figure 10 Puccinia psidii infection on inﬂorescences of Melaleuca leucadendra (a, b), inﬂorescences and ﬂowers of Chamelaucium uncinatum
(c, d), and immature fruit of Rhodamnia sessiliﬂora (e), and mature fruit of Rhodamnia rubescens (f).
G. S. Pegg et al.
reported detections of P. psidii in Qld, report numbers
have ﬂuctuated. Peaks in reporting were often followed
by declines, a pattern repeated several times over the
duration of this study. Factors inﬂuencing these patterns
have not yet been studied in detail in Australia. How-
ever, Tessmann et al. (2001) identiﬁed disease outbreaks
of P. psidii on Syzygium jambos in Brazil as being clo-
sely linked to duration of leaf wetness and relative
humidity (RH), combined with nocturnal temperatures
ranging from 18 to 22
°C. A high correlation between
progression of P. psidii on Eucalyptus grandis and days
with 90% RH or higher for 8 h, combined with temper-
atures between 18 and 25
°C has been demonstrated
(Glen et al., 2007). Data collected as part of the current
study indicate that temperature is not the main factor
inﬂuencing disease development, with reports of new
infections throughout the year. The inﬂuence of host
physiology and changes under different climatic condi-
tions is also likely to inﬂuence disease development. This
requires further study.
Climatic conditions since P. psidii was ﬁrst detected in
Qld have favoured spread and disease development with
above average rainfall and associated periods of high rel-
ative humidity occurring across most of coastal Qld
(www.bom.gov.au). This has undoubtedly led to optimal
plant growth conditions, providing repeated growth
ﬂushes and high numbers of new shoots and young
leaves, which are most susceptible to infection (Coutinho
et al., 1998). Interestingly, a decline in reporting of
P. psidii coincided with consecutive days of heavy rain-
fall. Previous studies (Lana et al., 2012) have also
observed lower levels of P. psidii with increased rainfall
levels in areas of Brazil. A reduction in spore levels due
to high rainfall over a short period of time is a possible
explanation. Reduced human activity outdoors during
rainfall periods may also have reduced rust observations
The host range of P. psidii in Qld has expanded rap-
idly from the ﬁve species initially detected in January
2011 to more than 160 species in July 2012. As reported
by Carnegie & Lidbetter (2012), the host range recorded
in Australia is signiﬁcantly greater than the known host
range for this disease internationally. This study alone
has identiﬁed a further 56 host species and two genera
not previously reported in Australia or internationally
(Carnegie & Lidbetter, 2012). The ﬁrst new genus and
species was Mitrantia bilocularis, a rare rainforest species
endemic to north Qld, which appears moderately suscep-
tible to P. psidii and is considered a vulnerable species
(Atlas of Living Australia; www.ala.org.au). The second
was Sphaerantia discolor, also endemic to north Qld
rainforest ecosystems and also listed as vulnerable (Atlas
of Living Australia; www.ala.org.au). The host range of
P. psidii is likely to continue expanding as the fungus
becomes established in new geographic regions and
where new host species exist.
Teliospores were identiﬁed from a range of host spe-
cies with different levels of susceptibility to P. psidii. The
detection of teliospores did not appear to be limited to
season, with detections made during warmer wetter
months of summer and the drier winter months. Ruiz
(1988) reported that teliospores occur under natural con-
ditions in Brazil on Eucalyptus cloeziana during the war-
mer months of the year (December to March). Other
studies indicate that temperature plays a role in spore
development, with the ideal temperature for germination
of urediniospores being 20
°C and subsequent mainte-
nance of infected plants at 25
°C or above likely to pro-
duce telia rather than uredinia (Coutinho et al., 1998).
Urediniospores have been detected on a range of host
plants in Qld at all times of the year.
Symptoms of infection by P. psidii range from minor
leaf spots to severe foliage and stem blight, as well as
infection of ﬂowers and fruit of some species. Of the
highly or extremely susceptible species, several have
importance economically, e.g. Backhousia citriodora and
Chamelaucium uncinatum, and environmentally, e.g.
Melaleuca quinquenervia. The level of natural resistance
within species populations in Australia is unknown. Field
observations indicate variability in susceptibility to the
disease within some species. It is unclear at this point in
time if this is a true reﬂection of resistance or variation
in host phenology and/or localized microclimatic and
edaphic conditions. Variations in inoculum levels may
also be important.
The impacts that P. psidii will have on fragile and threa-
tened ecosystems in Australia, e.g. Melaleuca wetlands,
are unknown and difﬁcult to predict. The disease has been
recorded on 15 species of Melaleuca with half considered
highly or extremely susceptible based on survey data from
this study, including Melaleuca viridiﬂora, which occurs
predominantly in higher rainfall areas of northern
Australia (Boland et al., 1992). This species is an integral
component of diverse tropical lowland environments in
northern Qld (Skull & Congdon, 2008) and is regarded as
an endangered ecological community (EPBC, 2012).
Melaleuca quinquenervia is considered highly suscepti-
ble to P. psidii, with infection causing seedling and tree
dieback, reduced ﬂower production and ﬂower death. Sim-
ilar observations were made in Florida (Rayamajhi et al.,
2006), where M. quinquenervia is a weed and P. psidii has
been used as a biocontrol agent. Melaleuca quinquenervia
habitats are threatened in Australia, with large areas
cleared for housing, road development and agriculture
(Catterall & Kingston, 1994). Impact on growth and
regeneration of M. quinquenervia by P. psidii may impact
on ecosystems crucial to maintaining biodiversity as well
as the quality of coastal waterways.
The known impact of P. psidii on eucalypts in Austra-
lia is limited and restricted to seedlings, apart from
Eucalyptus curtisii where infection has been identiﬁed on
new shoots of mature trees and coppice. In Brazil, heavy
infection of juvenile leaves and meristems of eucalypts
causes plants to become stunted and multibranched, with
highly susceptible individuals grossly malformed, and
Plant Pathology (2013)
Puccinia psidii in Queensland, Australia
levels have been reported as 20
–30% of trees, impacting
signiﬁcantly enough to affect growth rates and subse-
quent proﬁtability (Booth et al., 2000). Many eucalypt
plantations in Qld are subcoastal and located in areas
where P. psidii has not been detected outside of nurser-
ies. The majority of plantations are also more than
2 years old and less likely to be affected by P. psidii
based on observations in Brazil (Glen et al., 2007).
Some plant species are at risk of disappearing alto-
gether from their natural ecosystems because of infection
by P. psidii, especially species that are already rare and
endangered, e.g. Rhodamnia angustifolia, Rhodamnia
maideniana, Gossia gonoclada and Backhousia oligan-
tha. Only 11 R. angustifolia trees remain in their natural
habitat in central Qld (Snow & Guymer, 1999). Given
this restricted gene pool, the likelihood of identifying any
resistance in this population is limited. Similarly, only
12 G. gonoclada trees exist naturally and indications are
that this species is highly susceptible to P. psidii.
Some host range studies had investigated the suscepti-
bility of Australian native Myrtaceae to P. psidii, before
it entered Australia. Zauza et al. (2010) identiﬁed 60
of Rhodamnia rubescens seedlings as being resistant.
wardtiana. Both species are considered extremely suscep-
tible in Australia with no evidence of resistance, and
often the ﬁrst host to be recorded as the disease extended
its geographic range in Qld. This raises the important
issue of pathogen variability within P. psidii and the
need to maintain strict border controls, preventing addi-
tional strains entering Australia. In addition, the require-
ment for more investigation into potential resistance
within host populations should be considered.
Loss or signiﬁcant impact on common, dominant and
keystone species such as Melaleuca quinquenervia,
M. viridiﬂora and M. leucadendra are likely to have far
more devastating effects on ecosystem health than the
loss of minor ecosystem species, even species that are
listed as threatened. Loss of biodiversity through impact
on a wide range of species will occur as P. psidii spreads.
This is particularly salient given that Qld’s terrestrial
ecosystems are dominated by native Myrtaceae (REDD,
2012). Booth et al. (2000) highlight the potential impact
the disease may have on ecosystems and tourism, focus-
ing on the environmental attractions of coastal Qld. The
full impact of this disease in Qld and Australia may not
be realized for some years.
The authors acknowledge the facilities, and the scientiﬁc
and technical assistance, of the Australian Microscopy &
Microanalysis Research Facility at the Centre for Micros-
copy and Microanalysis, The University of Queensland.
Funding for the work provided by the Queensland govern-
ment and The CRC for Plant Biosecurity is greatly appre-
ciated. A. R. M. acknowledges the Australian Biological
Resources Study for funding (grant number RFL212-33).
The authors also wish to thank Tony Bean and Stephen
McKenna for assistance in the identiﬁcation and collection
of plant species as well as staff from Botanical Gardens in
Queensland. They would also like to thank Charlie Booth
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