Pruning quality affects infection of Acacia mangium and A. crassicarpa by Ceratocystis acaciivora and Lasiodiplodia theobromae

Abstract

Pruning (singling) is a common silvicultural practice in commercial Acacia plantations because these trees tend to have multiple stems. The wounds resulting from pruning are susceptible to infection by pathogens. Ceratocystis acaciivora and Lasiodiplodia theobromae have recently been shown to be important pathogens of A. mangium in Indonesia, where they are commonly associated with wounds on trees. The aim of this study was to determine the impact of different wound types on infection of A. mangium and A. crassicarpa by these two pathogens. Isolates of C. acaciivora and L. theobromae, found to be the most pathogenic in a prior study, were used to inoculate pruning wounds.Results showed that pruning conducted in a manner to reduce stem damage, resulted in lower levels of fungal infection. Where pruning resulted in tearing of the bark, there were greater levels of infection and disease occurred even without artificial inoculation.2 Inoculation of pruning wounds on A. mangium and A. crassicarpa showed that both fungi have the potential to cause disease. However, C. acaciivora was most pathogenic.Results of this study showed conclusively that careful pruning will result in lower levels of disease in young A. mangium and A. crassicarpa plantations in Indonesia.Keywords: Botryosphaeriaceae, Ceratocystis, disease management, silviculture, woundinfecting pathogens. IntroductionPlantations of Acacia mangium and A. crassicarpa have expanded rapidly in Indonesia since the 1980's, specifically to provide raw material for Indonesian pulp and paper industries (Barr 2001, Anonymous 2004. These Acacia spp., however, tend to have poor stem form, with multiple stems and branches (Srivastava 1993, Lee andArentz 1997).Pruning (singling) is thus carried out to improve tree form and to increase tree strength, reducing stem or branch breakage, particularly after strong winds (Beadle et al. 2007).Furthermore, the capacity of A. mangium trees to self prune is low in areas with high rainfall (Lee and Arentz 1997) and pruning is consequently necessary. These practices also reduce the density of stands so that optimum tree growth can be achieved (Neilsen and Gerrand 1999).Wounds resulting from pruning activities provide infection sites for numerous pathogens (Glass and McKenzie 1989, Vartiamaki et al. 2009), including plantation grown Acacia spp. (Lee et al. 1988, Barry et al. 2005. For example, heart rot caused by a complex of Phellinus noxius and other unidentified basidiomycetes is common on Acacia spp. in Malaysia and Indonesia (Lee and Sikin 1999). A recent study to 3 determine the cause of death of young A. mangium trees in Indonesian plantations (Tarigan 2008, Tarigan et al. 2010 has shown an association between pruning wounds and disease caused by Ceratocystis acaciivora and Lasiodiplodia theobromae.In order to develop management guidelines for pruning Acacia spp. in Indonesia, a study was undertaken to consider the effect of the quality of pruning wounds on disease development. For this purpose, pathogenic isolates of C. acaciivor...

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