IMPACT OF THE FLOWER SMUT USTILAGO-CYNODONTIS (USTILAGINACEAE) ON THEPERFORMANCE OF THE CLONAL GRASS CYNODON-DACTYLON (GRAMINEAE)

Effects of the flower-infecting smut fungus Ustilago cynodontis on the growth, survival, and competitiveness of the clonal rhizomatous peren nial grass Cynodon dactylon were explored through a series of glasshou se experiments. Ustilago cynodontis sterilized C. dactylon by replacin g floral structures with a teliospore-producing fungal stroma. Infecti on caused a reduction in overall dry matter production and the growth rate of stolons, changed the allocation of resources between roots and shoots, and affected the survival of C. dactylon plants growing in po ts under crowded conditions in a naturally lit glasshouse. In mixtures of healthy and infected plants, the growth of infected ones was dispr oportionally affected. Infection had no effect on the germination or e mergency of seedlings. Transmission of the pathogen along stolons was incomplete, especially as the length of the stolen increased. The nutr ient status of the soil had no significant effect on stolen growth. Re sults are discussed in terms of the differential effect of systemic fl oral smut diseases on tiller-forming and clonal rhizomatous perennial grasses.