| dc.description.abstract | This study examined ecology, colonisation, biological control and detection of sapstain fungi in New Zealand.
A nationwide survey of New Zealand sapstain fungi was undertaken between 1996 and1998. In total, 1035 sites were sampled in the North and South Islands. From these collections, 1755 potential sapstain fungi were isolated and seventeen individual species were identified. The predominant sapstain fungi identified were Sphaeropsis sapinea,
Ophiostoma ips, O. floccosum, O. piliferum, O. querci and Leptographium procerum. This data was subsequently evaluated according to ecological criteria, including geographical and temporal distribution of sapstain fungi. A greater diversity of sapstain fungi was found in areas of New Zealand that were primarily plantation forestry. S. sapinea was isolated during more generalised forest sampling, and from both native and plantation forests. Ophiostoma species were isolated more frequently from Pinus radiata plantations, processing plants including mills and ports and were mainly isolated from harvested forest material such as logs, wood chips, and other wood products. S. sapinea was isolated more frequently in spring and summer while Ophiostoma species predominated during autumn and winter periods, probably linked with insect vectoring. This was the first attempt to link the sapstain organisms identified in New Zealand with their overall distribution within sectors of the forest industry, in different wood species, and in different types of wood samples.
New Zealand is one of the world's largest exporters of softwood logs. Exports of forest products provide 4% of New Zealand’s gross domestic product (GDP) with Japan, Korea, United States and the Philippines as major export markets for P. radiata logs. Conditions found within the holds of ships were thought likely to be ideal for the rapid colonisation of the sapstain fungi that results in dark penetrating stains. Log export research was designed to determine the extent of sapstain colonisation at specific points in the processing of logs from harvesting to the export destination. Two trials were established, in New Zealand summer and in winter, where mature P. radiata logs were harvested in New Zealand and shipped to export ports in Japan. Microclimatic conditions (temperature and relative humidity) on board the ships were recorded using data loggers both above deck and below deck. Nine species of sapstain fungi were isolated from logs during the summer trial. The most common species isolated were O. floccosum, O. querci and O. setosum. In contrast, a different combination of nine species was detected during the winter trial. S. sapinea, O. querci, O. floccosum, O. setosum and Ophiostoma piceae were most commonly isolated. The results of this study showed that the New Zealand sapstain fungi were being exported on logs. However, many of these fungi were previously recorded in Japan. In addition, no serious pathogens were detected.
It was recognised during the sapstain fungal survey and export trials that a more thorough fundamental understanding of sapstain colonisation was required to properly determine the impacts of sapstain fungi to the New Zealand forest industry. In vitro and field studies were established to measure the relative colonisation of different species of sapstain fungi using synthetic media and P. radiata wood. These studies were undertaken to determine which sapstain species colonised, and how species interacted with each other following inoculation. In addition, the impacts of environmental conditions on the establishment and development of fungi and the resulting associated stains were determined. Temperature was found to affect the growth of various species of sapstain fungi on synthetic media and on P. radiata wood and logs. In the field studies O. floccosum was found to be the most successful coloniser of P. radiata logs in both winter and summer. Environmental factors such as temperature and moisture content were found to affect stain development. All fungal treatments developed sapstain discolouration from 15 days following inoculation in the summer field trial. In contrast, no stain was evident on any treatment in the winter field trial 60 days following inoculation. The colonisation of P. radiata by sapstain fungi was determined using microscopic techniques. Sapstain fungal hyphae were abundantly present in the ray parenchyma cells, tracheid lumen and resin canals of P. radiata wood. No differences in hyphal penetration were observed between the different sapstain fungal species at the cellular level. From these results a better understanding of the biology of sapstain species emerged. This new knowledge of the mechanisms and environmental triggers of fungal colonisation and stain development will aid in the more advanced technologies and management strategies to successfully control sapstain.
The many negative environmental impacts associated with traditional anti-sapstain chemical treatments led to increased interest in the more benign treatments of logs and wood using biological control technologies. The potential biological treatment of sapstain fungi using albino strains of O. floccosum, O. piceae and O. pluriannulatum was evaluated. These albino fungi demonstrated varied growth characteristics at different temperatures on both synthetic media and on P. radiata wood specimens. Comparable growth was found when evaluating wild type and albino sapstain strains in synthetic media and P. radiata wood in laboratory and field studies. Four field trials showed considerable variation in the biological control potential of the albino strains against wild type sapstain fungi. The mode of action of the albino strains was found to be competitive, through the use of primary resource capture of wood nutrients. However, albino O. floccosum strains were shown to produce zonal barriers when challenged with S. sapinea.
Proteomic analysis of cell wall proteins was undertaken to differentiate sapstain fungi from other wood inhabiting fungi and in an attempt to develop a method of determining the presence of sapstain fungi in wood prior to the development of stain. Proteins were extracted from the cell walls of various sapstain fungi (L. procerum, O. ips, O. Querci and S. sapinea) and wood inhabiting fungi (Alternaria alternata, Epicoccum nigrum, Trichoderma koningi) grown in liquid culture. Two dimensional (2D) protein profiles were made and compared. A total of 93 proteins were analysed using mass spectroscopy and the profiles compared to protein databases. This is the first investigation using proteomics of the cell wall proteins of Ophiostoma species and S. sapinea.
This study addressed the importance of sapstain fungi in New Zealand on P. radiata and increased our understanding of ecological requirements of the different sapstain species. Differences between these species with respect to colonisation and the development of associated stains were identified and investigated, enabling a critical evaluation of those species that were found to be most significant to the New Zealand forest industry. The future of sapstain management depends on a thorough ecological understanding of key sapstain fungal species involved in the cosmetic degradation of wood and an ability to manage the impacts of these species on the New Zealand forest industry using a combination of forest management practises and biological and chemical control techniques. | |
