No abstract

Fusarium circinatum Nirenberg & O'Donnell, the fungus responsible for pitch canker disease, is a destructive pathogen of Pinus spp. Pitch canker was first described in 1946 in the southeastern United States, and since 1987 has been reported in numerous other locations including California, Mexico, Japan, and South Africa. To make a preliminary assessment of relationships between populations of F. circinatum in these different locations, we compared allele and genotype frequencies based on eight polymorphic regions of DNA from 76 isolates of the fungus. Patterns of relatedness indicate that the California and Japanese populations of the fungus share lineages with the southeastern U.S.A. population. Genetic diversity is highest in Mexico, implicating it as the center of origin for the fungus. The association of multiple vegetative compatibility groups with a common multilocus genotype suggests that vegetative compatible group diversity may be generated by mutation, rather than through recombination resulting from sexual reproduction.Key words: genomic subtraction, tree disease, genetic distance.

No abstract

Tidal flooding is widely believed to be an important determinant of marsh plant distributions but has rarely been tested in the field. In New England the marsh elder Iva frutescens often dominates the terrestrial border of salt marshes and we examined its flood tolerance and distribution patterns. Marsh elders only occur at elevations where their roots are not subject to prolonged water table flooding. Consequently they are found on the terrestrial border of marshes and at lower elevations associated with drainage ditches and locally elevated surfaces. Marsh elders transplanted to elevations lower than they normally occur died within a year with or without neighbors and greenhouse tests revealed that I. frutescens is much less tolerant of flooded soil conditions than plants found at lower marsh elevations. We also manipulated the water table level of field plots and found that increasing or decreasing water table drainage led to enhanced and diminished I. frutescens performance, respectively. Our results demonstrate the importance of water table dynamics in generating spatial patterns in marsh plant communities and provide further evidence that supports the hypothesis that the seaward distributional limits of marsh plant populations are generally dictated by physical processes.