Infection of Trientalis europaea by the systemic smut fungus Urocystis trientalis: disease incidence, transmission and effects on performance of host ramets

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Abstract
Summary: 1 The effects of fungus infection on a natural population of the pseudoannual plant Trientalis europaea were followed for 4 years. 2 The incidence of the disease was low, showed little temporal variation during the period of study and was not affected by ramet size. Disease reduced flowering, fruiting, stolon length and the number and size of daughter tubers, all of which were positively correlated with ramet size. The year–disease interaction was not significant, except for flowering, suggesting little variation in the aggressiveness of the pathogen. 3 Disease reduced survival of ramets to the end of the growing season, although the effect varied with ramet size, and decreased tuber survival both by reduction of tuber size and by reduction of the overwintering ability of tubers of a given size. 4 For two of the three annual transitions the size of the offspring ramets was affected negatively by infection in the previous year. 5 Disease transmission occurred along the stolons of only 31% of the diseased ramets. The probability of disease being shown in the following year decreased with stolon length. 6 Although disease had a detrimental effect on ramet fitness, the low level of incidence and the stability of the clone dynamics in simulation models suggest only a minor role of the disease in population regulation in this species.