English names: Chrysanthemum white rust
Nordic names: Hvid Krysantemumrust (DK), Krysanteemin valkoruoste (FI), Vit krysantemumrost (SE), Hvit krysantemumrust (NO)
Major host plants
Chrysanthemums are the only hosts, especially the florists' cultivars (Dendranthema morifolium). Some cultivars appear to be more susceptible than others.
Pale green to yellow spots appear on the upper surface of leaves. These spots are up to 5 mm in diameter and may become sunken with brown and necrotic centers. Prominent pustules develop subsequently on the corresponding areas on the lower surface of leaves. At first, the pustules are buff or pinkish coloured. Later, they become waxy white when basidiospores are produced. If the attack is severe, leaves can wilt and flowers and stem may exhibit symptoms with pustules.
P. horiana originates in Japan and has spread via Africa to Europe.
A map can be downloaded from EPPO's website. See instructions here.
P. horiana spends all its life on a single host. Teliospores are produced in the pustules. When the teliospores germinate they produce basidiospores that are released and carried by wind to new hosts. High humidity and a film of moisture seem to be necessary for the germination of both types of spores. Only 5 hours of wetness is sufficient for a new infection to become established when temperatures are between 17-24°C. Then basidiospores are able to germinate and penetrate the plant surface. The incubation period is normally 7-10 days after which symptoms appear.
P. horiana is spread on infected cuttings and plants, including cut flowers of glasshouse chrysanthemums.
Detection and inspection
The fungus can be detected on the basis of visual symptoms: waxy, light coloured pustules opposite other rust fungi with brown coloured pustules. The identification is verified on the morphological features of the teliospores.
Pest status and importance
Puccinia horiana is a serious fungal disease of chrysanthemums. Once established, it frequently causes severe losses of glasshouse chrysanthemum crops. In addition, it is difficult and expensive to eradicate.
Source of information
See further information here:
Author: Jorma Räutapaa
Editor: Elise T. Yamamoto Buch