White rust of chrysanthemum

Puccinia horiana P. Hennings


Puccinia horiana, the causal agent of white chrysanthemum rust, is a rust fungus. It often attacks the garden chrysanthemum and is noticeable by light mottling of the leaves. Plants intended for planting must be free of Puccinia hor iana.


Puccinia horiana, the causal agent of white chrysanthemum rust, is a non-host-changing rust fungus. The spores can penetrate the leaf within two hours at favorable temperatures (optimum 17 °C) and at least five hours of leaf wetness. The incubation period is usually seven to ten days, but at temperatures above 30 °C (short-term) it can be up to eight weeks.

Damage symptoms

The first signs of infection with white chrysanthemum rust are small pale green to yellow spots visible on both sides of the leaf. As the disease progresses, creamy-white, sometimes waxy-looking pustules develop on the undersides of the leaves in these spots. These rust pustules are most commonly found on young leaves and flower bracts, but they can be found on any part of the foliage including flowers. These symptoms occur primarily during cooler and wetter weather.

Infected plants may also be asymptomatic during hot and dry weather. Under these conditions, it can take up to eight weeks for infected plants to show symptoms.

Host plants

The main host is the garden chrysanthemum Dendranthema x grandiflorum, as well as the naturally occurring chrysanthemums: Chrysanthemum japonense, Chryanthemum makinoi var. wakasaense, Chrysanthemum shiwogiku, Dendranthema boreale, Dendranthema japonicum.


The disease occurs worldwide. White rust of the chrysanthemum has been widespread in large parts of Europe (including Austria) since the mid-1960s. Furthermore, the pathogen occurs in many countries in Asia, South America and Africa.

Propagation and transmission

Spread occurs mainly through trade in latently infested chrysanthemum cuttings. Since the spores of white chrysanthemum rust are very sensitive to drought, spread by wind over longer distances can only occur during very wet weather periods. Within a stand, infections usually happen through water droplets, contaminated soil, dead leaves, tools, clothing, shoes, or cultivation work.

Economic importance

White chrysanthemum rust has been occurring in Europe since about 1963. Early infestation can lead to total loss of production.

Prevention and control

Preventive measures

  • Use of healthy cuttings
  • Immediate inspection of purchased plants for symptoms on arrival at the farm
  • Regular infestation checks during cultivation
  • Avoid leaf wetness: do not irrigate from above, observe dew point in greenhouse
  • Avoid excessive nitrogen fertilization

Measures in case of disease occurrence

Phytosanitary status

All plants intended for planting must be free of Puccinia horiana.

Specialized information

Puccinia horiana is a non-host-changing rust fungus with a shortened development cycle. Only teleuto- and basidiospores are formed. The teleutospores are on no stalks, which are about 45 µm long. The two-celled, thin-walled teleutospores themselves are pale yellow in color and elongated to oblong-cusped in shape. They are slightly constricted at the septa. The spore dimensions are 30-45 x 13-17 µm. The teleutospores germinate with delicate-walled small basidiospores that spread the disease in the stand. These are hyaline, slightly curved, broadly ellipsoidal to spindle-shaped, and measure 7-14 x 5-9 µm. Germination of teliospores can be observed in situ .

Last updated: 15.12.2021

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