The rapid emergence of Acacia mangium as the key industrial plantation species in Indonesia has been followed by the equally rapid emergence of red root rot (Ganoderma philippii) as its potential nemesis. As a consequence, and on severely affected mineral soils in equatorial tropical environments in particular, A. mangium may no longer be capable of producing commercial yields after three rotations. In this experiment, 100-tree plots were established in commercial plantings of A. mangium at five sites which represented the range of growing conditions used for plantation establishment in Indonesia. Repeated monitoring at approximately 6-month intervals of above-and below-ground variables was used to explore relationships between measures of tree health and root rot. Crown colour and density were poor predictors of either the presence or severity of infections. Tree mortality increased more or less linearly with time and led to the progressive coalescence of initially discrete disease gaps. The average rate of disease development was about 0.3% per month, and average time from infection to tree death was conservatively estimated at around 1 year. Trees with more than four dead/missing neighbours had a >50% chance of being dead by the following monitoring. By the end of the monitoring period >40% of trees were classified as dead/missing, although this value varied from 20 to 70% depending on site, tree age and rotation. Canonical discriminant analysis correctly allocated >90% trees into their correct group on the first monitoring and similarly classified whether trees would be dead or missing in the following monitoring.

An investigation of root rot in Acacia mangium plantations in Indonesia generated over 1000 fungal isolates from field surveys at six locations. The majority of isolates were identified as Ganoderma philippii or Ganoderma mastoporum by species-specific PCR, but this still left 274 isolates to be identified. As barcoding initiatives for fungi are still in the early stages, to assist identification of these isolates in this way we developed a database of sequences based on identified sporocarps and also searched public DNA sequence databases for sequences with high similarity. The database of sequences from sporocarp collections is more limited than public DNA databases. This resulted in more reliance on public DNA databases for a high proportion of taxa. Several pathogenic species were identified, with Phellinus noxius occurring at several locations and on both A. mangium and Eucalyptus pellita. Ganoderma steyaertanum was isolated from A. mangium roots and Rigidoporus microporus from E. pellita roots, each at a single location only. Potential pitfalls of using public DNA databases for fungal identification are discussed and methods to avoid these and increase confidence in the identification are presented.

DNA sequence variation in the rDNA internal transcribed spacers (ITS) was exploited to design species-specific primers for Ganoderma philippii and Ganoderma mastoporum, two fungi associated with red root rot in Acacia mangium and other perennial crops. Specificity was verified against five other Ganoderma species, 34 other basidiomycete species and two ascomycete species. The PCR tests assisted in the identification of 822 fungal isolates obtained from A. mangium and Eucalyptus pellita plantations in Indonesia. These tests have provided a high level of confidence in the identification of the major root rot pathogens, information that can be used to support the development of management options for their control in A. mangium plantations.

No abstract

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.