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Reduced flower pigmentation in the legume 'Swainsona formosa' is associated with increased susceptibility to 'Phytophthora cinnamomi' and other soil-borne pathogens. This study aimed to identify the mechanism for these differences in susceptibility. Chemical analyses of stem tissues that had been previously inoculated with 'P. cinnamomi' revealed that neither anthocyanin nor total phenolic content increased with infection. Such results suggested that observed differences in susceptibility, as indicated by flower colour, were related to preformed rather than induced stem chemistry. Acetone extracts from healthy, uninfected stem tissues of a red-flowered line were highly toxic to the fungus, while extracts from a white-flowered line were non-toxic and those from a pink-flowered line were intermediate in toxicity and this was correlated with the total phenolic and proanthocyanidin concentration of the extracts. Precipitation of proanthocyanidins with bovine serum albumen removed the toxicity of the extracts. It was concluded that differences in the proanthocyanidin content of tissues contributed to the differences in disease susceptibility of plants with different flower colours. |
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