Acacia plantations in Indonesia facilitate clonal spread of the root pathogen Ganoderma philippii

Ganoderma philippii is a root pathogen of many woody plants in tropical regions and is particularly aggressive to Acacia mangium, which is grown on a 6-year rotation for pulpwood in Indonesia. The disease becomes progressively worse over each rotation and control measures have met with limited success. We studied the population genetics of G. philippii to evaluate the role of sexual and asexual reproduction in its mode of spread. Populations were genetically distinct with high levels of inbreeding, and clonal spread to adjacent trees increased after the first rotation. Despite the high levels of genetic diversity seen at all sampling scales, migration rates appear low. Measures to reduce the underground spread of the pathogen as well as methods to prevent the initiation of new infections from basidiospores will be needed to reduce the incidence of root rot in A. mangium plantations.