Acacia mangium is a fast-growing tree species. It is mainly planted in large monocultures for pulpwood in South-East Asia. Root rot has become the most economically damaging disease of this species with high tree mortality rates observed during second and third rotations. Two main types of root rots have been found in A. mangium, viz. brown root-rot and red-root disease caused by Phellinus spp. and Ganoderma spp., respectively. To assess the future management options for root rot of A. mangium, we review past and current disease-management strategies for root rot in different temperate and tropical industrial tree crops. The efficacies of a wide range of silvicultural, chemical and biological options are detailed, and their potential utilization in managing root rot of A. mangium is discussed. We conclude that the current gaps in knowledge regarding identification, biology and disease epidemiology of the root-rot pathogens will need to be addressed so that effective management options can be developed.

This study describes and identifies the fungi associated with root-rot disease in Eucalyptus pellita, associated anecdotally with a species of Phellinus. Macro-and microscopic morphological observations and DNA analysis were used to identify sporocarps and fungal cultures growing from symptomatic root samples. Investigation of 12 sites in Central Sumatra revealed that red root-rot disease caused by species of Ganoderma (most commonly Ganoderma philippii) was as prevalent as root disease caused by Phellinus noxius. The study also detected the presence of several potential fungal agents of root rot at any one site. Fungal signs such as absence/presence of sporocarps were a poor indicator of root-rot incidence in stands. Instead, fungal isolation from infected roots was essential to obtain accurate identification of active pathogens.

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.