Puccinia kuehnii (W. Krűger) E. J. Butler 1914

California Pest Rating for
Puccinia rusts. Photo credit: Cesar Calderon, USDA APHIS PPQ. Bugwood.org
Puccinia rusts. Photo credit: Cesar Calderon, USDA APHIS PPQ. Bugwood.org
Puccinia kuehnii (W. Krűger) E. J. Butler 1914
Pest Rating:  C

Initiating Event:

On February 9, 2016, USDA’s Animal and Plant Health Inspection Service (APHIS) notified the CDFA that the rust pathogen, Puccinia kuehnii was added on February 2, 2016, to their ‘List of Pests no Longer Regulated at U.S. Ports of Entry’ under the Federally Recognized State Managed Phytosanitary (FRSMP) program (USDA APHIS 2016).  Consequently, USDA APHIS will no longer take regulatory action against this pathogen at ports of entry.  Therefore, and at the request of Stephen Brown, Assistant Director, CDFA, the risk of infestation for P. kuehnii is assessed here and a permanent rating is proposed.

History & Status:

Background:  Puccinia kuehnii is one of two major rust fungi on sugarcane and causes orange rust.  The other rust fungi known as P. melanocephala, causes brown rust and is relatively common.  The orange rust of sugarcane pathogen, P kuehnii, most likely originated in Asia-Oceania regions where Saccharum spp. are native.  In other countries where the pathogen occurs, such as Indonesia and the South Pacific, sugarcane has existed for several centuries and it is assumed that P. kuehnii was likewise introduced and also existed in those countries for the same period of time.  The pathogen is now wide spread in Asia and Australia and was recently discovered in West Africa and the Western Hemisphere and from sugarcane-growing regions in the southeastern United States, Central and South America, and the Caribbean Basin (Dixon & Castlebury, 2016). It is likely that the pathogen was introduced to Australia along with sugarcane that was introduced about 150 years ago as there are no known native hosts present in that region (CABI, 2016).  In the USA, P. kuehnii was first reported from Florida having been detected in infected, brown rust-resistant, sugarcane cultivars. The disease appears to be distributed widely in the South Florida sugarcane-growing region (Comstock et al., 2008).  In 2013, orange rust was also reported from the southern region of Louisiana’s sugarcane production area (Grisham, et al., 2013).  Puccinia kuehnii has not been reported from California nor is sugarcane a major production crop of the State.

Disease cycle:  Puccinia kuehnii completes its life cycle on the same host and has an incomplete lifecycle. Spermagonia and aecia spore states are unknown.    Urediniospores are produced abundantly under natural conditions, but the production of teliospores and basidiospores are comparatively less common.    Under favorable conditions of humidity and temperature, urediniospores present on host germinate to penetrate the tissue.  As the fungus grows, uredinia (fruiting structures) are formed and urediniospores are produced in abundance.   Urediniospores are produced between 10°C and 34°C and optimally at 15-25°C for urediniospores and 26°C for teliospores.  Relative humidity above 97% favors urediniospore germination (Hsieh & Fang, 1983; CABI, 2016).

Dispersal and spread: The main risk for natural dispersal of spores over long distances (over 2000 km) is by wind and wind-blown rain.  Other potential means for spread are the movement of infected leaves and spore-contaminated clothing (CABI, 2016).

Hosts:  Saccharum officinarum (sugarcane) is the main host.  Other hosts include few weeds and ornamental grasses belonging to Saccharum spp. within Poaceae: Saccharum arundinaceum, S. barberi, S. bengalense, S. edule, S. munja, S. narenga, S. rufipilum, S. sinense, S. spontaneum; S. ravennae (syn. Erianthus ravennae); Sclerostachya fusca (Afshan & Khalid, 2013; CABI, 2016; Dixon & Castlebury, 2013; EPPO, 2016; Farr & Rossman, 2016 )

Symptoms:  Orange rust disease is characterized by the development of lesion that initiate as small (0.5 mm diameter) spots on leaves and enlarge into elongated brown lesions (2-8 mm x 0.5-2 mm wide).  As the lesions enlarge, fungal mycelium protrudes through the leaf surface, usually on its underside, producing abundant urediniospores. These pustules usually occur in patches or groups, but cover entire leaf surfaces in severe infections. Severely infected leaf tissue becomes necrotic leading to early senescence. Affected crops appear brown with very little green tissue remaining at all. Symptom development may take 3-4 weeks from infection, depending on weather conditions (CABI, 2016).

Disease Potential:  Orange rust of sugarcane is considered a disease of low economic impact that has rarely caused significant economic losses.  The only severe economic loss was reported in Australia in 2000 on the introduced, highly susceptible Q124 sugarcane variety that was subsequently replaced (CABI, 2016).  The potential for establishment and spread of the pathogen in California is reasonably low as sugarcane, the main host, is grown in limited acreage in dry climates of the Imperial Valley.

Worldwide Distribution: Africa: Cameroon, Cote d’Ivore; Asia: China, India, Indonesia, Japan, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, Vietnam; Central America and Caribbean:  Costa Rica, Cuba, Dominican Republic, Guatemala, Jamaica, Nicaragua, Panama; North America: USA, Mexico; South America: Brazil, Colombia, Ecuador; Oceania: American Samoa, Australia, Cook Islands, Fiji, French Polynesia, Guam, Micronesia, New Caledonia, Papua New Guinea, Samoa, Solomon Islands (CABI, 2015; Dixon & Castlebury, 2013; EPPO, 2016; Farr & Rossman).

In the USA it has been reported from Florida and Louisiana (Comstock et al., 2008; Grisham et al., 2013).

Official Control: Puccinia kuehnii is on the “Harmful Organisms Lists” for Brazil, Costa Rica, Egypt, Honduras, and Morocco (PCIT, 2016). Currently, the pathogen has not been rated for California.

California Distribution Puccinia kuehnii is not established in California.

California Interceptions: None reported.

The risk Orange Rust of Sugarcane would pose to California is evaluated below.

Consequences of Introduction: 

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

Low (1) Not likely to establish in California; or likely to establish in very limited areas. 

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

Risk is Low (1):   The potential for establishment and spread of the orange rust pathogen in California is likely to be low as sugarcane, the main host, is grown in limited acreage under dry climates of the Imperial Valley.  Spore germination and plant infection are not expected to be favored under climates of low relative humidity common to that region.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

Risk is Low (1):  Sugarcane is the main host of P. kuehnii.  The pathogen is largely limited to Saccharum spp. and the related species Sclerostachya fusca.    

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

High (3) has both high reproduction and dispersal potential.

Risk is High (3): Puccinia kuehnii has high reproduction and dispersal potential via its windblown spores that are primarily transmitted by strong winds over distances of several hundred kilometers.  Also, they may be spread over long distances via infected plant leaves and spore-contaminated human clothing. 

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

Risk is Low (1): The economic impact of Puccinia kuehnii to California is considered low as the potential for establishment and spread of the pathogen is reasonably minimal within a state where sugarcane is not a majorly cultivated crop and requires high relative humidity for pathogen infection.  Potential incidents of the disease occurring under conducive climates could lower crop yield.  

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.

Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Risk is Medium (2):  Puccinia kuehnii infections could affect production of ornamental grasses belonging to Saccharum spp. and grown in private and/or public commercial environments.    

Consequences of Introduction to California for Myrtle Rust:

Add up the total score and include it here. (Score)

-Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

Total points obtained on evaluation of consequences of introduction to California = 8 (Low).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

Not established (0) Pest never detected in California, or known only from incursions.

-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Not Established (0).  Puccinia kuehnii is not established in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score:  Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8 (Low).



Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Puccinia kuehnii is C.


Afshan, N.S., and A. N. Khalid.  2013.  Checklist of the rust fungi on Poaceae in Pakistan. Mycotaxon 125: 1-17.

Comstock, J. C., S. G. Sood, N.C. Glynn, J. M. Shine Jr., J. M. McKemy, and L. A. Castlebury.  2008.  First report of Puccinia kuehnii, causal agent of orange rust of sugarcane, in the United States and Western Hemisphere. Plant Disease, 92(1):175. http://www.apsnet.org.

Dixon, L. and L. Castlebury.  2016.  Systematic Mycology and Microbiology Laboratory, ARS, USDA. . Invasive Fungi. Orange rust of sugarcane – Puccinia kuehnii. Retrieved March 10, 2016, from /sbmlweb/fungi/index.cfm.

EPPO.   2016.  Puccinia kuehnii (PUCCKU).  PQR database.  Paris, France: European and Mediterranean Plant Protection Organization.  http://www.newpqr.eppo.int.

Farr, D. F. and A. Y. Rossman.  2016.   Fungal databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA.  Retrieved August 24, 2016 from http://nt.ars-grin.gov/fungaldatabases/.

Grisham, M. P., J. W. Hoy, J. S. Haudenshield, and G. L. Hartman.  2013.  First report of orange rust caused by Puccinia kuehnii in sugarcane in Louisiana. Plant Disease, 97(3):426-427. http://apsjournals.apsnet.org/loi/pdis.

Hsieh, W. H., and F. G. Fang.  1983.  The uredospore production of Puccinia melanocephala and Puccinia kuehnii in sugarcanes. Plant Protection Bulletin, Taiwan, 25(4):239-244.

USDA-PCIT.  2016.  United States Department of Agriculture, Phytosanitary Certificate Issuance & Tracking System (PCIT). https://pcit.aphis.usda.gov/PExD/faces/ViewPExD.jsp .

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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Pest Rating:  C

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