Incidence and Evaluation of a New Rust Disease on Myrtaceae in Hawaii:
Winter, Guava Rust
Anne Marie LaRosa
and Rob Hauff
USDA Forest Service, Institute of Pacific Islands Forestry
Hawaii State Department of Land and Natural Resources, Division of Forestry and Wildlife
The rust disease, Puccinia psidii
Winter, or guava rust, was originally
described in 1884 from infections on guava in Brazil. Until 2005 this pathogen was
unknown outside the Neotropics and the state of Florida. It was first detected in
Hawaii in the spring of 2005 on ohia-lehua (Metrosideros polymorpha Gaud) and
has since spread from Oahu to all major Hawaiian Islands (Killgore and Heu, 2005).
Host Range: Puccinia psidii has an unusually broad host range for a rust.
Worldwide, the host range currently includes 21 genera and 72 species of
Myrtaceae, including such common tropical species as Eucalyptus and guava
(Simpson and others, 2006). The host range of the pathogen in Hawaii includes 18
susceptible plant species in the family Myrtaceae, including common and
endangered native Hawaiian species and numerous introduced species, some of
which are invasive and widespread.
Biology: Puccinia psidii is generally thought to be a hemicyclic, autoecious rust
(Couthino and others 1998), but some authors think it may actually be a
heteroecious macrocyclic rust with an unknown alternative aecial host (Simpson
and others 2006). It affects leaves and meristems, inhibiting normal growth and
development, and is particularly severe on seedlings, cuttings, saplings, and
coppice (Ryachhetry and others 2001). The existence of numerous races/and or
clones of P. psidii differing in host pathogenicity (MacLachlan 1938; Tommerup
and others 2003) and a wide variation in susceptibility within host plants and
provenances have been reported (Simpson and others 2006).
Impacts: Spread of Puccinia psidii is a serious threat to forests and forestry in
Hawaii and the Asia-Pacific region. Its presence in Hawaii increases the chance of
spread to Asia and the Pacific region where host species are important biologically
and economically. The pathogen has been a problem in Eucalyptus plantations in
Brazil and is considered a serious threat to Eucalyptus plantations worldwide
(Coutinho and others 1998). The strong selection pressure by P. psidii on
Myrtaceae in its native range suggests a very significant threat to native species of
Myrtaceae in the Asia-Pacific region (Simpson and others 2006). Its presence in
Hawaii is particularly troubling because ohia-lehua is the dominant overstory tree in
over 80% of Hawaii’s native forests and is present over a broad environmental
gradient in early to late successional stages. Native plant community function,
particularly reproductive capacity, could be seriously affected by the spread of the
Figure 1. Ohia seedling with pustules.
Hosts of Puccinia psidii
Species in green are Hawaii native or indigenous species
* artificial innoculations in laboratory
Survey Objectives and Methods
Determine environmental range of the disease on the native and naturalized
Myrtaceous species in Hawaii.
● Survey within 1 m of the edge along trails and roads in representative natural
areas throughout the State for symptomatic plants.
● Compile information on disease presence, location and impacts from other
field researchers and managers throughout the state.
● Map and correlate disease incidence with environmental factors, including
elevation, temperature, rainfall, and prevailing wind direction
2. Determine host range of disease in Hawaii.
● Innoculate ohia and other species with urediniospores collected from infected
ohia. Confirm formation of uredia (rust pustules) for pathogenicity.
● Collect urediniospores collected from different hosts forest areas and multiply
in the laboratory for cross pathogenicity tests.
● Conduct cross pathogenicity tests between rust isolates collected from ohia-
lehua and other Myrtaceous species recorded as hosts in Hawaii (e.g., Eugenia
spp., Melaleuca quinquenervia, Psidium guajava, Rhodomyrtus tomentosa,
3. Develop a disease severity index.
● Develop a severity index for each host based on amount of leaf area infected.
● Produce descriptive photos.
● Publish a guide for natural resource and conservation organizations and nurseries.
4. Determine incidence of disease transmission in natural forest areas.
● Monitor infected rose apple (primary host in Hawaii) throughout the year to assess the occurrence
of rust epidemics.
● Assess spread by observing susceptible species adjacent to epidemic outbreaks for visible signs of
● Correlate incidence of epidemics and transmission with season, host phenology, weather, existing
sources of innoculum, and wind direction.
Related Surveys and Research
Complimenting the forest survey, the Hawaii Agricultural Research Center is carrying
out a nursery survey for P. psidii. Nurseries on all of the main islands that provide
seedlings to forestry and conservation are being targeted. Data such as host species,
disease severity, and host species growing in adjacent natural areas are being
Other related work on P. psidii includes molecular work conducted by the University of
Hawaii. Dr. Zhong is analyzing genetic material to characterize the disease in Hawaii
and comparing it to DNA samples from Brazil and Florida. Disease material from the
forest survey will be provided for Dr. Zhong’s molecular work to determine variation
within Hawaii. His work could support future quarantine rules for preventing further
races of P. psidii from entering the Hawaii and provide rapid identification capability
for detecting spores on imports.
Rob Anderson, a doctoral student at the University of Hawaii who is carrying out the
survey, is conducting additional research on disease transmission, pathogenicity
testing of Hawaiian Myrtaceae including different varieties of M. polymorpha, and
describing the life cycle of the disease.
Aerial detection surveys for impacts of P. psidii in native forests using a combination
of spectroscopy and LIDAR are being explored in collaboration with Stanford University
and the Carnegie Institute.
Coutinho, T. A., Wingfield, M. J., Alfenas, A.C., Crous, P. W. 1998. Eucalyptus rust: a disease with potential for serious
international implications. Plant disease 82: 819-825.
Killgore, E. M., and Heu, R. A. 2005. A Rust Disease on Ohia. New Pest Advisory. Department of Agriculture, State of Hawaii.
MacLachlan, J.D. 1938. A rust of the pimento tree in Jamaica. Phytopathology 28, 157-170.
Rayachhetry, M. B., Van, T. K., Cneter, T. D., and M. L. Elliott. 2001. Host range of Puccinia psidii, a potential biological control
agent of Melaleuca quiquenervia in Florida. Biological Control 22: 38-45.
Simpson, J.A., K. Thomas, and C.A. Grgurinovic. 2006. Uredinales species pathogenic on species of Myrtaceae. Australasian
Plant Pathology, 35: 549-562.
Tommerup, I.C., A.C. Alfenas, and K.M. Old. 2003. Guava rust in Brazil – a threat to Eucalyptus and other Myrtaceae. New
Zealand Journal of Forestry Science, 33: 420-428.
Figure 3. Disease damage on the endangered
nioi (Eugenia koolauensis).
Figure 2. Rose apple dieback caused by P. psidii.
Rob Anderson provided an outline of methods for the survey. Janice Uchida, Shaobin Zhong, Lloyd Loope,
and Pat Conant have contributed ideas for the survey. Ron Cannarella assisted with poster production.
Photo by D. Ogata
Photo by R. Hauff
Photo by J. Beachy