EFFECTS OF THE SYSTEMIC FLOWER INFECTING-SMUT USTILAGO-BULLATA ON THEGROWTH AND COMPETITIVE ABILITY OF THE GRASS BROMUS-CATHARTICUS

1 The effects of the flower infecting-smut fungus Ustilago bullata on the performance of its host Bromus catharticus were investigated throu gh a series of glasshouse-based experiments. 2 Smut infection resulted in the complete sterility of Bromus catharticus; reduced the overall size of infected individuals regardless of plant density or the relati ve frequency of healthy and infected individuals; changed the allocati on of resources between roots and shoots; and reduced the rate of seed ling emergence but not final emergence percentages. 3 Despite these ef fects, infection did not affect the relative competitive ability of in fected plants growing at high nutrient levels as reflected by dry weig ht accumulation. Here healthy and infected individuals competed equall y for the same limiting resources (k(hd) = 1 = 1/k(dh)) Under low nutr ient conditions, however, healthy plants showed an increased competiti ve ability relative to infected plants (k(hd) = 1.52; k(dh) = 0.66). 4 These results are considered in light of the evolutionarily interesti ng position systemic smut diseases occupy relative to other fungal pat hogens and endophytes.