Puccinia psidii in Queensland, Australia: disease symptoms,
distribution and impact
G. S. Pegg
ab
*, F. R. Giblin
b
, A. R. McTaggart
c
, G. P. Guymer
d
, H. Taylor
e
,
K. B. Ireland
e
, R. G. Shivas
f
and S. Perry
e
a
Department of Agriculture, Fisheries and Forestry, Horticulture and Forestry Science, Agri-Science Queensland, GPO Box 267, Brisbane,
Qld 4001;
b
Forest Industries Research Centre, University of the Sunshine Coast, Locked Bag 4, Maroochydore DC, Qld 4558;
c
Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Ecosciences Precinct, GPO Box 267, Brisbane,
Qld 4001;
d
Department of Science, Information Technology, Innovation and the Arts, Queensland Herbarium, Brisbane Botanic Gardens
Mt Coot-tha, Mt Coot-tha Road, Toowong, Qld 4066;
e
Department of Agriculture, Fisheries and Forestry, Plant Biosecurity and Product
Integrity, Biosecurity Queensland, GPO Box 267, Brisbane, Qld 4001; and
f
Department of Agriculture, Fisheries and Forestry, Plant
Pathology Herbarium, Biosecurity Queensland, GPO Box 267, Brisbane, Qld 4001, Australia
Puccinia psidii has long been considered a significant threat to Australian plant industries and ecosystems. In April
2010, P. psidii was detected for the first time in Australia on the central coast of New South Wales (NSW). The
fungus spread rapidly along the east coast and in December 2010 was found in Queensland (Qld) followed by Victo-
ria a year later. Puccinia psidii was initially restricted to the southeastern part of Qld but spread as far north as
Mossman. In Qld, 48 species of Myrtaceae are considered highly or extremely susceptible to the disease. The impact
of P. psidii on individual trees and shrubs has ranged from minor leaf spots, foliage, stem and branch dieback to
reduced fecundity. Tree death, as a result of repeated infection, has been recorded for Rhodomyrtus psidioides. Rust
infection has also been recorded on flower buds, flowers and fruits of 28 host species. Morphological and molecular
characteristics were used to confirm the identification of P. psidii from a range of Myrtaceae in Qld and compared
with isolates from NSW and overseas. A reconstructed phylogeny based on the LSU and SSU regions of rDNA did
not resolve the familial placement of P. psidii, but indicated that it does not belong to the Pucciniaceae. Uredo
rangelii was found to be con-specific with all isolates of P. psidii in morphology, ITS and LSU sequence data, and
host range.
Keywords: eucalyptus rust, guava rust, Myrtaceae, myrtle rust, Puccinia psidii, systematics
Introduction
Puccinia psidii was first described from Psidium guajava
(guava) in Brazil in 1884 (Coutinho et al., 1998), from
which its common name guava rust was derived. The
disease has since been reported from a range of plant
species in the Myrtaceae in South and Central America
as well as the United States (Florida and California;
Coutinho et al., 1998). More recently, P. psidii has been
reported outside of the Americas, with detections in
Hawaii (Uchida et al., 2006), Japan (Kawanishi et al.,
2009), China (Zhuang & Wei, 2011) and South Africa
(Roux et al., 2013).
Historically, P. psidii has had a significant impact on
industries reliant on Myrtaceae, including the all-spice
(Pimenta dioica) industry in Jamaica (MacLachlan,
1938) and the eucalypt plantation industry in Brazil
(Ferreira, 1983; Glen et al., 2007). In the 1970s, the
disease earned a new common name of eucalyptus
rust, because of the severe damage caused to eucalypt
plantations grown for paper and pulp production in
Brazil (Coutinho et al., 1998).
For many years, P. psidii has been considered a signifi-
cant threat to Australian plant industries and ecosystems
(Grgurinovic et al., 2006; Glen et al., 2007), and strict
biosecurity measures were implemented to prevent its
introduction. In April 2010, P. psidii was identified for the
first time in Australia on the central coast of New South
Wales (NSW) (Carnegie et al., 2010). Originally detected
on Agonis flexuosa, Melaleuca viminalis (Callistemon vim-
inalis) and Syncarpia glomulifera (Carnegie et al., 2010),
the host range rapidly increased as the rust fungus spread
within Australia. Carnegie & Lidbetter (2012) reported
the host range of P. psidii, from natural infections in
Australia, as 107 species from 30 genera of Myrtaceae.
The geographic distribution of P. psidii has expanded
rapidly since it was first detected in December 2010 at a
retail nursery in Brisbane, Queensland (Qld). This paper
discusses the spread and the impact of P. psidii on host
species in Qld and implications for natural ecosystems and
commercial operations. In addition, new host records are
identified and the systematics of P. psidii is discussed in
the light of morphological and molecular data.
*E-mail: geoff.pegg@daff.qld.gov.au
ª 2013 Crown copyright.
Plant Pathology
ª 2013 British Society for Plant Pathology
1
Plant Pathology (2013)
Doi: 10.1111/ppa.12173
Materials and methods
Distribution and spread
To determine the distribution and spread of P. psidii following
its initial detection in Qld, surveillance was conducted in nurser-
ies (retail, production and wholesale), parks, gardens and natu-
ral bushland areas. Initial surveys focused in and around
infected premises but were extended as the number of detections
and host records increased. During the initial stages of the incur-
sion, samples were collected for all suspect reports for disease
confirmation in the laboratory. As the disease became more
widespread, samples were only collected from new host species
and/or new geographical locations.
To track disease spread and identify new hosts, a public
reporting system for P. psidii was implemented. Samples from
reports of new hosts or locations were collected for botanical
confirmation before infected specimens were deposited in the
Qld Plant Pathology Herbarium (BRIP). The location of infected
plants in native vegetation and home gardens was recorded using
a Global Positioning System (GPS; Garmen 76 Series). All data
were mapped by GIS mapping systems (
ARCGIS
v. 10.0; ESRI).
Maps were generated monthly to show changes in disease distri-
bution. The database system BioSIRT (Biosecurity Surveillance,
Incident Response and Tracing) was used as the primary reposi-
tory for data relating to P. psidii detections in Qld. Surveys and
public reports were recorded and located spatially in BioSIRT.
Host range and diagnostics
To determine the host range of P. psidii following the initial
detection of the disease in Qld, inspections of retail, wholesale
and production nurseries were conducted in addition to surveil-
lance in parks, gardens and natural bushland areas. Samples
were pressed and dried prior to examination by a botanist to
confirm the host species. Host range data were also captured
through the public reporting system, including information on
the host species, as well as severity of rust symptoms, assessed
from digital photographs. Samples were deposited in BRIP after
P. psidii was confirmed. Reports without photographs of disease
symptoms and host were recorded as suspect but were not
included as a confirmed report.
Identification of P. psidii was through a combined morphologi-
cal and molecular barcoding approach with the internal tran-
scribed spacer (ITS) region of ribosomal DNA (rDNA; Schoch
et al., 2012). Specimens of P. psidii in Qld were compared to
those collected in NSW and from overseas. All samples were
examined under the light microscope for sori and characteristic
spores. Slides of sori and spores were examined at
9400 for the
presence of urediniospores, teliospores and basidiospores. Uredin-
iospores were examined under oil immersion at
91000 and by
scanning electron microscopy as described by Pegg et al. (2008).
Uredinia and telia were selectively removed from fresh leaf
material with a vacuum pump and stored in DNA extraction
buffer. DNA was extracted according to the protocol outlined
by Aime (2006) using the UltraClean Plant DNA Isolation kit
(MoBio Laboratories). The ITS region was amplified with
ITS1F/ITS4B (Gardes & Bruns, 1993). The ITS2-large subunit
(LSU) region was amplified with Rust2inv (Aime, 2006)/LR7
(Vilgalys & Hester, 1990) and nested with LROR/LR6 (Vilgalys
& Hester, 1990) according to the protocol by Aime (2006). The
small subunit (SSU) region was amplified with NS1 (White
et al., 1990)/Rust 18S-R (Aime, 2006). Amplification of the LSU
by nested PCR required an initial denaturation of 3 min at
94
°C; 42 cycles of 30 s at 94°C, 1 min at 58°C and 1Á5 min at
72
°C; with a final extension for 7 min at 72°C. The nested SSU
protocol was identical, except for annealing at 63
°C for 1 min.
The LSU and SSU sequences for specimens of P. psidii were
added to the data set of Minnis et al. (2012). Prospodium tuber-
culatum was included in the data set to increase sampling of the
Uropyxidaceae. Maximum likelihood was implemented as a
search criterion in RA
X
ML (Stamatakis, 2006) and P
HY
ML v. 3.0
(Guindon et al., 2010). GTRGAMMA was specified as the model
of evolution in both programs. The RA
X
ML analyses were run
with a rapid bootstrap analysis (command -f a) using a random
starting tree and 1000 maximum likelihood bootstrap replicates.
The P
HY
ML analyses were implemented using the ATGC bioinfor-
matics platform (available at: http://www.atgcmontpellier.fr/
phyml/), with SPR tree improvement, and support obtained from
an approximate likelihood ratio test (Anisimova et al., 2011).
M
R
B
AYES
was used for a Markov chain Monte Carlo (MCMC)
search in a Bayesian analysis (Ronquist & Huelsenbeck, 2003). A
user-defined tree obtained from the maximum likelihood analyses
was used as a starting point. Four runs, each consisting of four
chains, were implemented for 5 000 000 generations. The cold
chain was heated at a temperature of 0
Á25. Substitution model
parameters were sampled every 5000 generations and trees were
saved every 5000 generations. Convergence of the Bayesian analy-
sis was confirmed using AWTY (available at: ceb.csit.fsu.edu/
awty/; Nylander et al., 2008) and used to calculate a burn-in.
Symptoms and impact
Targeted surveys were conducted to determine susceptibility of
host species to P. psidii. These surveys were conducted in public
parks and surrounding bushland, private gardens and arboreta in
Tallebudgera Valley and Cooroy on the Sunshine Coast, natural
bushland in Brisbane, the Gold and Sunshine Coasts and sur-
rounding suburbs, and botanical gardens in Mackay, the Gold
and Sunshine Coasts and Brisbane (Mt Coot-tha). National parks
surveyed included Lamington (Green Mountain) and Spring-
brook in the Gold Coast hinterland, Kondalilla in the Sunshine
Coast hinterland and Kuranda, Herberton Range and Crater
Lakes (Lake Eacham) in the Wet Tropics of far north Qld.
A disease rating system was developed to record species sus-
ceptibility. Host plants, including seedlings, saplings and mature
trees, showing evidence of infection by P. psidii, were rated for
susceptibility with the following scale (Fig. 1):
Relatively tolerant: minor leaf spots with rust sori on <10%
of expanding leaves and shoots, limited sori per infected leaf;
Moderately susceptible: rust sori present on 10
–50% of
expanding leaves and shoots, limited
–multiple sori per
infected leaf;
Highly susceptible: rust sori present on 50
–80% of expand-
ing leaves and shoots, evidence of rust on juvenile stems and
older leaves, leaf and stem blighting and distortion, multiple
sori per leaf/stem;
Extremely susceptible: rust sori present on all expanding
leaves, shoots and juvenile stems; foliage dieback; evidence
of stem and shoot dieback.
Results
Distribution and spread
In December 2010, following the first detection of P. psi-
dii on Gossia inophloia in a retail nursery in southeast
Qld, three additional nurseries were found to have infected
Plant Pathology (2013)
2
G. S. Pegg et al.
plants. At that time there was no evidence of infection in
peri-urban landscapes or natural bushland. By the end of
January 2011, P. psidii had been found at a further 19
locations in southeast Qld, including urban landscapes
and natural bushland (Figs 2 & 3). The first detection of
P. psidii on the Gold Coast occurred in February 2011. By
June 2011, P. psidii had been found as far west as
Toowoomba (127 km west of Brisbane, 27
°58′S, 151°93′E)
and by September 2011, north to Maryborough (260 km
north of Brisbane, 25
°32′S, 152°42′E; Fig. 2). By January
2012, P. psidii was detected in Bundaberg and Rock-
hampton, 370 km (24
°51′S, 152°21′E) and 650 km
(23
°23′S, 150°30′E) north of Brisbane, respectively.
Surveys in far north Qld failed to detect the disease until
May 2012, when P. psidii was found in natural bushland
near Cairns. By August 2012, additional detections
extended from Townsville to Daintree National Park, c.
100 km north of Cairns (Fig. 3).
By the end of August 2012 there were more than 1000
public reports and detections of P. psidii in Qld. To
date, P. psidii has been detected in coastal areas as far
north as the Wet Tropics World Heritage Area (including
Daintree, Kuranda, Barron Gorge, Crater Lakes and
Hypipamee National Parks) as well as Herberton
Ranges. In far north Qld, P. psidii has also been detected
in the drier regions on the Atherton Tablelands (includ-
ing Tolga, Yungaburra and Mareeba). Apart from detec-
tions in plant nurseries, P. psidii has not been identified
in areas west of the Great Dividing Range.
Based on data collected from southeast Qld, the num-
ber of reports of P. psidii peaked during April, May and
June 2011 followed by a decline in July and August
2011. Reports began to increase again towards the end
of August, peaking in November 2011 (Fig. 4), followed
by another decline in December 2011. In January 2012,
a total of 157 reports of P. psidii were received followed
by a further 95 in February and a dramatic increase in
reports in March 2012 with 252 reports. Comparatively
fewer reports (43) were made in April 2012. Some of
these report peaks coincided with media releases (Dayton
& Higgins, 2011).
The number of host species reported each month
increased as the number of detections increased. The high-
est diversity of species reported occurred in April (35),
May (34) and November (32) of 2011 (Fig. 4). Syzygium
jambos was the most commonly reported species in all
months, with the highest number of reports for this species
(79) occurring in March 2012. There were 82 new hosts
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
Figure 1 Puccinia psidii severity levels Relatively tolerant (a, b): sori present on
<10% of expanding leaves and shoots; limited number sori per
infected leaf; Moderate susceptibility (c, d): sori present on 10
–50% of expanding leaves and shoots; limited–multiple number sori per infected leaf;
High susceptibility (e, f): sori present on 50
–80% expanding leaves and shoots; some evidence of disease on juvenile stems; evidence of disease
on older leaves and stems; multiple sori per leaf/stem causing blight and leaf/stem distortion; Extreme susceptibility (g, h): sori present on all
expanding leaves and shoots and juvenile stems; shoot, stem and foliage dieback; evidence of older stem/shoot dieback.
Plant Pathology (2013)
Puccinia psidii in Queensland, Australia
3
Figure 2 Map of southeast Queensland plotting the number of detections and public reports of Puccinia psidii within the first 12 months of initial
detection.
Plant Pathology (2013)
4
G. S. Pegg et al.
recorded within the first 6 months following the initial
detection of P. psidii in December 2010 (Fig. 5). Only six
new hosts were identified in the following 4-month period
of July to October 2011. From November 2011 to Febru-
ary 2012 there was an increase in the number of species
identified, with 37 new hosts recorded and a further 13
new hosts between March 2012 and July 2012. The
majority (77%) of host species rated as highly or extre-
mely susceptible were identified within 6 months of P. psi-
dii being first detected. Since then, only a further eight
species have been added to this category.
Host range
Since P. psidii was first detected in Qld, 165 species
from 38 different genera have been identified as hosts
based on natural infections, the majority from the tribes
Myrteae (31%) and Syzygieae (28%) (Table 1; Wilson
et al., 2005). New host records of P. psidii were found
for 61 species in 22 genera from 11 tribes (Table 1),
including Acmena (1 species), Austromyrtus (1), Back-
housia (4), Corymbia (1), Decaspermum (1), Eucalyptus
(3), Eugenia (2), Gossia (3), Homoranthus (3), Hypoc-
alymma (1), Leptospermum (3), Lophostemon (1), Mel-
aleuca
(5),
Metrosideros
(2),
Pilidiostigma
(1),
Rhodamnia
(3),
Rhodomyrtus
(5),
Syzygium
(17),
Thryptomene (1) and Waterhousea (1). These records
also included two previously unreported host genera,
Mitrantia (Mitrantia bilocularis) and Sphaerantia (Spha-
erantia discolor). Puccinia psidii has not been recorded
from common guava (Psidium spp.) in Qld despite its
wide distribution and weed status. Puccinia psidii was
Locality diagram
Toowoomba
Rockhampton
Mackay
Cairns
Brisbane
Bundaberg
Townsville
August 2012
Toowoomba
Rockhampton
Mackay
Cairns
Brisbane
Bundaberg
Townsville
January 2011
Datum : GDA94 Projection : Geographic
0
200
400
600
800
km
Legend
Town
Myrtle rust detection
Wet tropics boundary
NSW
QLD
SA
NT
WA
Figure 3 Changes in distribution of Puccinia psidii in Queensland from January 2011 to August 2012.
Plant Pathology (2013)
Puccinia psidii in Queensland, Australia
5
confirmed from a single sample of Psidium sp. collected
in northern NSW (P. Entwistle, NSW, Australia &
G. S. Pegg, unpublished). Several genera and species
were found free of disease symptoms at sites where
P. psidii was detected (Table 2).
Sequence data
The ITS region was identical for isolates collected on 12
host genera (Table 3). A high identity was returned in a
BLAST
search to other sequences of P. psidii on GenBank
from eight other genera within the Myrtaceae. Sequence
trace chromatograms had three sites with single nucleo-
tide polymorphisms.
These sites were variable in
sequences obtained from GenBank. The LSU and SSU
regions were identical for 16 and four isolates, respec-
tively. The specimen collected on Myrtus communis
(BRIP 58517), the type host of Uredo rangelii, was
molecularly identical to all other isolates of P. psidii in
the ITS and LSU regions.
Phylogenetic analysis
Puccinia psidii was recovered as a rogue taxon in three
separate phylogenetic analyses on the combined LSU-SSU
data set. It did not have a well-supported relationship
with any rust family. It was sister to the Pucciniaceae in
RA
X
ML and Bayesian inference, or in a clade with
members from the Pileolariaceae and Uropyxidaceae
reconstructed in P
HY
ML (Fig. 6).
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Puccinia psidii
reports
Puccinia psidii reports
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Species reported
Figure 4 Number of new reports of Puccinia psidii in Queensland and the number of host species per month in comparison to the number of
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