The root rot fungus Armillaria mellea introduced into South Africa by early Dutch settlers

Dead and dying oak (Quercus) and numerous other woody ornamental trees and shrubs showing signs and symptoms of Armillaria root rot were identified in the Company Gardens, Cape Town, South Africa, which were established in th e mid-1600s by the Dutch East Indies Trading Company. Nineteen isolates fro m dying trees or from mushrooms were collected and analysed to identify and characterize the Armillaria sp. responsible for the disease. The AluI dige stion of the amplified product of the first intergenic spacer region (IGS-1 ) of the rRNA operon of 19 isolates from the Company Gardens was identical to that of some of the European isolates of A. mellea s. s. The IGS-1 regio n and the internal transcribed spacers (ITS) were sequenced for some of the Cape Town isolates. Phylogenetic analyses placed the Cape Town isolates in the European clade of A. mellea, which is distinct from the Asian and Nort h American clades of this species. Identification based on sexual compatibi lity was conducted using A. mellea tester strains in diploid-haploid pairin gs, which showed some compatibility between the Cape Town isolates and test ers from Europe. Somatic compatibility tests (diploid-diploid pairings) and DNA fingerprinting with multilocus, microsatellite probes indicated that t he Cape Town isolates were genetically identical and may have resulted from vegetative (clonal) spread from a single focus in the centre of the origin al Company Gardens (c. 1652). The colonized area is at least 345 m in diame ter. Assuming a linear spread rate underground of 0.3 m/year to 1.6 m/year, the genet (clone) was estimated to be between 108 and 575 years old. These data suggest that A. mellea was introduced into Cape Town from Europe, per haps on potted plants, such as grapes or citrus, planted in the Company Gar dens more than 300 years ago.