The Effect of the Systemic Smut Urocystis carcinodes on the Long-Lived Herb Actaea spicata

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Abstract
The interaction between the herb Actaea spicata and the perennial systemic smut fungus Urocystis carcinodes was studied by marking and following 100 plants in an eight-year field study and in a four-year experiment where plants from the diseased population and from a healthy population were transplanted to three different localities. In the field study 11 plants died during the eight years. The results also show that only seven plants remained healthy throughout the study and that seven showed disease symptoms every year. In total, 67 different combinations of disease expression were observed during the study. There was a significant correlation between size of the plant and berry production. Plants with disease symptoms were overall larger than plants without symptoms within particular years, and plants showing disease symptoms every year were also significantly larger than plants healthy all eight years. Sectioning and staining of live plants revealed that the disease can be present in basal parts of the leaves and adjoining rhizome even in plants with no disease symptoms. In the transplantation experiment the transmission was low and the number of plants showing disease symptoms among the diseased plants varied between the years with highest levels the second year after transplantation. The results also show that plants with disease symptoms the first two years were larger than plants healthy the first two years after transplantation. We hypothesise that the observed pattern of disease history within individual plants depends on the latency of the fungus which may be caused by the level of host resources available to the fungus.

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