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Defences against Predation and Disease
Very little work has been done on mechanical and chemical defences of protea species against herbivory and disease.
| The low carbon to nitrogen ratio in leaves might prevent herbivory and disease. To date there are few records of rusts, smuts, or mildews affecting proteas, and very few accounts of bacterial infection. This may, however, be due to lack of research. Extrafloral nectaries, hairs, glandular rims and divided leaves, may help in reducing herbivory and infection. |  |
Proteoid roots are prone to infection by Phytophthora Dieback fungus, but different species vary in degree of susceptability. This is a major problem with Pincushions and Conebushes. The Phytophthora fungus spreads in surface water and attacks the plants roots. Normally this is not a problem, but in hot weather the weakened root system may not be able to support the leaves and the plant may die (due to drying out!) within a few hours.
Avoiding running water and planting resistant species are the best options in ones garden. Alternatively, if you want to grow susceptible species, grow them on a resistant rootstock (pincushion rootstocks work best and a cultivar "Spike" has been bred for this purpose).
An antifungal substance, p-hydroxybenzoylcalleryanin is secreted by Protea cynaroides roots and may confer resistance to Phytophthora. However recent research suggests that Phytophthora seldom attacks Sugarbushes, and the cause may be a stem canker disease.
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