Incidence and Evaluation of a New Rust Disease on Myrtaceae in Hawaii

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Incidence and Evaluation of a New Rust Disease on Myrtaceae in Hawaii:  

Puccinia psidii 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


Distribution: 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 in Hawaii   

Eucalyptus dunnii*


Eucalyptus grandis*

rose gum

Eucalyptus microcorys*


Eucalyptus smithii*


Eucalyptus torelliana*


Eugenia koolauensis


Eugenia paniculatum

brush cherry

Eugenia reinwardtiana


Eugenia  uniflora

surinam cherry

Melaleuca quinquenervia


Metrosideros polymorpha


Myriciaria cauliflora


Myrtus communis


Psidium guajava


Rhodomyrtus tomentosa

downy rosemyrtle

Syzigium cumini

java plum

Syzigium jambos

rose apple

Syzygium malaccense*

mountain apple

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, 

Syzigium spp.).  

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

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