Ceratocystis spp. and Botryosphaeriaceae on plantation Acacia species in Central Sumatra, Indonesia

Abstract

The use of Acacia spp. in plantation forestry increased dramatically in Indonesia since the 1980’s after the Indonesian Government initiated a plantation development program known as Hutan Tanaman Industri (HTI). The aim of this programme is to supply raw material to especially the pulp and paper industries. Currently, more than one million hectares of Acacia plantations have been established, mainly on the islands of Kalimantan and Sumatra. These Acacia plantations, with A. mangium and A. crassicarpa as the main species, display robust growth with mean annual increments (MAI) of 25-30 m3/ha/year and 40-46 m3/ha/year on the average and the best site respectively. However, diseases limit the success of forestry plantations in Indonesia.

During disease surveys in Acacia plantations in Indonesia, symptoms resembling those caused by Botryosphaeriaceae and Ceratocystis spp. were identified and representative samples were collected from wounded and diseased A. mangium trees. Studies in this dissertation described the causal agents of the disease and provided some practical solutions to reduce the incidence of the disease. Seven fungal species were discovered, five of them are new to science, one representing a first report for Acacia spp. and one other species is confirmed as the most common fungal species in Acacia plantations in Indonesia.

The first chapter of this dissertation provided a background to the forestry industry in Indonesia and details were given on the diseases affecting plantation Acacia spp. in Indonesia. The review clearly shows that diseases such as stem diseases and root diseases can have a severe impact resulting in retarded growth of trees, reduced timber quality, and in severe cases they result in tree death. The most common disease reported from Acacia plantations prior to this dissertation was heart rot and root rot.

The second chapter outlines the discovery of Ceratocystis acaciivora prov. nom., a new species, and C. manginecans, a recently described species that causes a serious disease of mango trees in Oman and Pakistan, associated with disease of A. mangium in Indonesia. Identification of these fungi was achieved using morphological characteristics and comparison of DNA sequence data for the ITS, β-tubulin and Elongation Factor 1- gene regions. From pathogenicity trials on A. mangium and A. crassicarpa, both in the greenhouse and the field, it was clear that these fungi are pathogens.

In chapter 3 of the dissertation, three previously undescribed Ceratocystis species in the C. monililiformis sensu lato complex are identified. These have been given the names C. inquinans prov. nom., C. sumatrana prov. nom. and C. microbasis prov. nom. and were obtained from wounded A. mangium trees. The virulence of these three new species was tested on A. mangium and A. crassicarpa in the greenhouse and in the field. The results indicate that all three species are mild pathogens but they have the potential to cause disease on A. mangium and A. crassicarpa.

The fourth chapter of this dissertation reports on the occurrence of three species in the Botryosphaeriaceae on plantation-grown Acacia spp. in Indonesia. Two of the species are shown to be new to science and were provided with the names Pseudofusicoccum sumatranum prov. nom. and P. acaciicola prov. nom. The third species was identified as the well-known tree pathogen, Lasiodiplodia theobromae. Pathogenicity results indicated that all three species have the potential to cause disease of A. mangium and A. crassicarpa. However, L. theobromae was the most pathogenic and was the most common species isolated.

In the fifth chapter, the impact of different wound and inoculum types on infection by C. acaciivora prov. nom. and L. theobromae, the two most pathogenic wound-infecting pathogens on A. mangium and A. crassicarpa, is evaluated. Clear differences were found between careful and rough pruning techniques. The results indicated that improved management practices will minimize disease risk in plantations.