BIOLOGICAL CONTROL OF CAMELLIA FLOWER BLIGHT

Alison Stewart (Supervisor) and Ron van Toor (PhD student)
Soil, Plant and Ecological Sciences Division, PO Box 84, Lincoln University, Canterbury, New Zealand

This research project, supported by the Brian Mason Scientific and Technical Trust and NZ Camellia Society, investigates the potential for biological control of camellia flower blight, caused by the soil-borne pathogen Ciborinia camelliae (Fig 1). Flowers are infected by wind-borne spores that are ejected from cup shaped fruiting bodies produced from survival structures called sclerotia, which are present in the soil (Fig 2).

Fungicides applied to soil beneath camellia bushes in spring give limited control of fruiting bodies. Cultural control options include burning of fallen camellia flowers that may contain developing sclerotia, and covering the ground with either polythene or pine needles. Restricting the spread of the disease to other locations can be achieved by transferring only bare-rooted camellia cuttings or scions that are free of flowers. However, these options have not been adopted readily by camellia growers, and the disease is now established in New Zealand.

Fig 1: Camellia flower blight		Fig 2: C. camelliae fruiting body

In this project, which commenced 1 August 1999, we are investigating the use of beneficial microorganisms for parasitism of the soil-borne sclerotia, and the use of specific bark mulches to prevent germination of sclerotia and subsequent release of spores. The use of beneficial microorganisms and elicitor compounds to prevent infection of camellia petals is also being investigated. DNA fingerprinting is being used to determine the level of genetic variability of C. camelliae populations in New Zealand, to indicate the level of specificity required for potential biocontrol agents to be effective.

Key results to date:

• Fig 3: Camellia petals untreated (left), pathogen treated control (middle), and treated with Pseudomonas marginalis GA8/Ps4 (right).

  Novel methods were developed to determine viability and level of parasitism of C. camelliae sclerotia.
• Effective mycoparasites of sclerotia of a closely related pathogen Sclerotinia sclerotiorum did not control soil-borne sclerotia of C. camelliae.
• In laboratory assays, several bacterial and fungal isolates (Bacillus, Pseudomonas and Cladosporium species) have provided almost complete protection against ascospore infection of flowers (Fig 3). These isolates are currently being cultured and formulated for assessment of their ability to protect flowers on camellia bushes under field conditions.

Photos on this page are courtesy of Lincoln University

- Photos may be viewed full-size by clicking on thumbnail graphics -

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