Puccinia psidii
Ohi'a Rust - Puccinia psidii Winter
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Ohi'a rust
Puccinia psidii is a rust apparently native to parts of the American tropics. It was first described on Psidium pomiferum in Brazil in 1884. Puccinia psidii is unusual among rusts in having a wide host range, so far, believed to be all the species in the family Myrtaceae. The full host range of P. psidii is unknown.
Puccinia psidii was discovered in Hawaii during spring 2005, when authorities were alerted to an infected native ohi'a (Metrosideros polymorpha) tree. Additional detections on several non-native species and on two native species of Eugenia (E. koolauensis and E. reinwardtiana) occurred during the months after the first detection. Eugenia koolauensis is listed as an endangered species (1). So far the pathogen has only been found on Oahu.
Ohi`a trees constitute approximately 75% of native Hawaiian forests and are an important habitat for Hawaii's endemic birds. Any threat to the forest poses a major threat to Hawaiian biodiversity. While it appears to be too late to prevent establishment of this strain of P. psidii, conservationists are developing a strategy aimed at preventing the introduction of other strains that might be either more virulent or more cold-tolerant and thus able to damage forests at higher elevations.
The introductory pathway of Puccinia psidii is unknown; it might have been through barked wood products (considered by Australia to be a pathway) or live plants. The source material probably originated from South America, Central America, or Florida.
Puccinia psidii was introduced into Florida sometime before 2001. The presence of the pathogen in Florida greatly complicates the regulatory situation, since an organism that is already in the country cannot be treated as a "quarantine pest" unless there is an "official control program" targeting the pest. At present, there is no such program with USDA APHIS involvement.
Imports of wood packaging, logs, and lumber involving tropical hardwood species (including Eucalyptus) into Hawaii must be debarked or fumigated (Code of Federal Regulations - 7CFR319.40-5). Imports of most living plants are subject only to inspection (Code of Federal Regulations - 7CFR319.37). The tiny size of the rust spores makes detection during inspection unlikely.
In a pest risk assessment for Eucalyptus logs and lumber originating from South America, the USDA concluded that P. psidii posed a moderate risk to the nation as a whole. Factors cited in justifying that ranking included the impossibility of detecting microscopic spores, the rust's ability to spread under favorable climatic conditions, its wide host range, and the great vulnerability of Hawaii, which is home to numerous native and introduced species in the Myrtaceae family.
The Hawaii Department of Agriculture has initiated surveys to determine the distribution of the rust and is developing interim rules to prevent the movement of plant and plant parts in the family Myrtaceae within the state.
Australia considers P. psidii to be a high-priority quarantine pest; it would threaten Eucalyptus in natural populations and plantations as well as bottlebrushes (Callistemon and Melaleuca spp.) and lilly-pillies (Syzygium and Eugenia spp.) (2,3).
Sources
Information, unless otherwise noted, is cited as a personal communication with Lloyd Loope, USGS-PIERC, Makawao, Maui, Hawaii on August 17, 2005.
Code of Federal Regulations. January 1, 2005 (Title 7, Volume 5). 7CFR319.40-5: Logs, lumber, and other unmanufactured wood articles - importation and entry requirements for specified articles. (available by using search engines/retrieval services at http://www.gpoaccess.gov/fr/index.html).
Code of Federal Regulations. January 1, 2005 (Title 7, Volume 5). 7CFR319.37: Nursery stock, plants, roots, bulbs, seeds, and other plant products - prohibitions and restrictions on importation: disposal of articles refused importation. (available by using search engines/retrieval services at http://www.gpoaccess.gov/fr/index.html).
