Cakile maritima and C. edentula are naturalised hosts of the necrotroph Alternaria brassicicola that occur along the coast of New South Wales, Australia. The effect of infection on the growth and reproduction of both host species was investigated. Plant height, leaf number and pod number of C. maritima were reduced by up to 69, 50 and 30% of the control, respectively, and similar responses were observed for plant, pod and seed weight. Regression analysis showed that A. brassicicola infection reduced various measures of host fitness and fecundity (plant weight, pod number and weight). Negative correlations existed between disease severity and measures of plant growth and reproductive ability, but a positive correlation existed with incidence of infected seed during pod maturation. The responses of C. edentula to infection were generally similar to those of C. maritima. These data show that infection with A. brassicicola can reduce the growth and reproductive potential of C. maritima and C. edentula.