Puccinia horiana P. Hennings
A destructive fungal disease of chrysanthemums
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Name: Puccinia horiana P. Hennings
Fungi: Basidiomycetes: Uredinales: Pucciniaceae
Common Names: chrysanthemum white rust; rouille blanche (French); Roya blanca (Spanish)
Until the early 1960's, P. horiana was confined to Far East countries; however, it has since spread rapidly on infected imported cuttings throughout Europe and has reached parts of Africa, South America, Australia, and New Zealand. Localized introductions have occurred in North America. At present, however, the fungus is only considered established in parts of Mexico, and not in the United States or Canada. In Europe, this fungus is a serious nursery disease, frequently causing complete loss of greenhouse chrysanthemum crops.
Issues of Concern:
This fungal disease has been intercepted in the United States on chrysanthemums over 3,000 times since the mid-1980's and is still being intercepted. In particular, there has been a recent increase in infested cut flowers coming from the Netherlands. Therefore, there is the continual risk of this organism becoming established in the United States. The introduction and spread of this disease has the potential to be extremely damaging to the commercial horticulture and florist industries. Once established, it is very difficult and costly to eradicate.
Hosts: The Florist's Chrysanthemum, Dendranthema x grandiflora, is the only commonly cultivated species that is susceptible to the disease, although a number of less common chrysanthemum species are also known as hosts.
Asia (Brunei Darussalam, China, Israel, Japan, Korea, Malaysia, Taiwan, Thailand); Africa (South Africa, Tunisia); Oceania (Australia and New Zealand); Europe (Austria, Belgium, Denmark, Finland, France, Italy, Netherlands, Sweden, Switzerland, Germany, Yugoslavia, Hungary, Russia, UK, Ukraine, Bulgaria, Croatia, Greece, Slovakia, Slovenia); South America (Argentina, Brazil, Chile, Uruguay, Colombia, Venezuela, Peru), North America (Mexico)
Quarantines: P. horiana is of quarantine significance to NAPPO countries. Host materials such as Chrysanthemum spp. and Dendranthema spp. are subject to various regulations to prevent the entry of the pathogen from infested countries.
The fungus has been found on chrysanthemum plants or plant parts, imported as cut flowers, propagative material, houseplants, and corsages. The first symptoms on chrysanthemum leaves infected with this pathogen are small yellow to tan patches on the upper surface, up to 5 mm in diameter. Centers of the patches become necrotic with age. On the corresponding under surface, raised, buff or pinkish, waxy pustules are found. Under humid conditions, the pustules turn whitish when basidiospores are produced. Severely infected leaves wilt, hang down the stem, and gradually dry completely. Symptoms most commonly occur on younger leaves and flower bracts, but can occur on other green tissue and on petals.
The disease is spread by infected host materials, in which the disease can remain systemic but not visible.
National Agricultural Pest Information System datasheet
CFIA/CIA Policy Directives
A pest data sheet is available in Quarantine Pests for Europe, Second Edition, 1997, pp.905-909, CAB International, Wallingford UK.