Flower colour is associated with susceptibility to disease in the legume 'Swainsona formosa'

The hypothesis that plants of the ornamental Australian native legume 'Swainsona formosa' (Sturt's desert pea) with reduced flower pigmentation are more susceptible to soilborne diseases was investigated using red, pink and white-flowered lines challenged with 'Phytophthora cinnamomi'. Inoculations of roots, hypocotyls and detached stems showed that the red line was completely resistant, the white line highly susceptible, and the pink line intermediate in reaction. Similar results were obtained for root and detached stem assays using 'Pythium' irregulare and 'Fusarium solani' isolated from diseased white-flowered plants, but all lines were equally susceptible to Botrytis 'cinerea' in detached stem assays. Crosses between the red and white lines showed that white flowers and susceptibility to 'P. cinnamomi' were each determined by recessive alleles at single loci, which segregated together.