Kingdom: Fungi
Division: Ascomycota
Class: Ascomycetes
Order: Helotiales
Family: Sclerotiniaceae
Genus: Ciborinia
Species: C. camelliae
Scientific name: Ciborinia camelliae
Synonym: Sclerotinia camelliae
Common name: Camellia Flower Blight, Petal Blight
Camellia Flower Blight is caused by the fungus Ciborinia camelliae, one of the largest classes of fungi, containing about 30,000 species. This fungus that attacks only opened flower parts and is promoted by rainy or moist weather. Most of the 3,000 named Camellia species and cultivars are affected by this fungus.
At first, small brown necrotic spots appear on the petals, with centres discolouring first. Later these spots enlarge and eventually cover the whole petal. After a few days, the whole flower becomes brown and the flowers drop prematurely. These spots can be distinguished easily from weather injury, which is usually indicated by lighter coloured spots and is limited to the outer margin of camellia flowers. Closed flowers cannot be infected but infection can take place at any time after the tips of the petals are visible in opening buds.
If the infected flower heads are left on the ground they will decompose, becoming the fungi's passage into the soil. Once in the soil, the fungi can survive for three to four years. The fungi begin to emerge from dormancy when weather conditions are warm and moist. You can see mushroom-like structures arise from the over-wintering fungi. They release millions of microscopic spores which are carried by the wind to emerging and opening flowers. Spores are windblown and can travel up to 2 kilometres. The disease can also be spread from flower to flower by direct contact. The spores germinate if moisture is present and if conducive temperatures (15-21 degrees C) are provided. When these conditions are met, infection occurs, and the blighted flower symptoms begin to appear. As the fungi progress, the flowers fall to the ground only to start the cycle once again.
Examine the fallen flower heads for small, hard black bodies called sclerotia. These are hard brown or black fungus bodies which develop at the base of old infected flowers. Sclerotia later produce one or more mushroom-like growths (apothecia), which, in turn, produce spores to cause new petal infections. Sclerotia can survive in soil at least 4 years and serve as a source of apothecia each year. Sclerotia are active during the normal flowering period of camellia.
There is no satisfactory method for controlling camellia flower blight at present and there is no indication that a satisfactory control procedure will be developed in the foreseeable future.
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