A total of six hundred and sixteen fungal and two hundred and thirty two bacterial isolates were obtained either from the sapwood of Pinus radiata or from other sources, including UV mutagenesis. All isolates were screened on Pinus radiata wood chips for their survival and colonisation attributes. Of these isolates, two hundred and eighty two failed to grow or caused permanent deep seated discolourations or decay and were eliminated from the study. The remaining five hundred and sixty six isolates were assessed for their antagonistic ability against sapstain. In a dual screen on Pinus radiata wood chips, one hundred and twelve fungal and four bacterial isolates inhibited the growth of the known sapstain fungus, Ophiostoma piceae. In a second biological control screen, on Pinus radiata wood blocks, isolates of Gliocladium viride, Gliocladium roseum, Trichoderma hamatum, Trichoderma harzianum, Trichoderma sp., Trichothecium roseum and an isolate of the Thelephoraceae proved inhibitory to the sapstain isolates Ophiostoma piceae and Sphaeropsis sapinea providing between 94 and 100% control. These isolates were considered for further examination in the field. The remaining isolates provided poor or inconsistent inhibition or were mould fungi and, therefore, not suitable for direct application. All fungal and bacterial isolates that had shown inhibitory ability in the initial biological control screen and the remaining non-staining bacteria were examined for their ability to produce non-volatile metabolites that were inhibitory to sapstain. The bacterial isolates were examined in a preliminary dual plate screen in which 91 isolates were identified as producing inhibitory compounds. The best of these bacterial isolates were screened, with the fungal isolates, in a non-volatile metabolite trial utilising filter sterilised culture filtrates. Isolates of Bacillus sp., Fusarium solani, Gliocladium roseum, Gliocladium virens, Trichoderma harzianum, Trichoderma sp., Trichoderma viride and Trichothecium roseum were found to be significantly inhibitory to the growth of Ophiostoma piceae at concentrations of 50% or less. However, the filtrates did not provide adequate sapstain control, when tested on Pinus radiata wood block, to prompt consideration for further examination in the field. Studies are currently examining several of these isolates for the production of biologically active compounds. The six most promising isolates, from the wood chip and wood block trials, were tested in the field for their ability to control sapstain on unseasoned Pinus radiata sapwood and/or peeled logs. These were Gliocladium viride (FK75), Trichoderma hamantum (FK561), Trichoderma harzianum (FK228), Trichoderma sp. (FK247), Trichothecium roseum (FK238) and an isolate of the Thelephoraceae (FK33). The fungi were prepared as mycelial/spore homogenates. For application to the timber, the homogenates were mixed with 0.2% Alcosorb gel, producing 108 cfu/ml suspensions, these suspensions were applied by dipping. Diluted homogenates, 108 cfu/ml, were applied as spray treatments to the logs. All of the biological control agent treatments reduced the level of sapstain on either the logs or timber with Trichoderma harzianum (FK228), Trichoderma sp. (FK247) and Trichothecium roseum (FK238) providing control equivalent to that of the fungicides NP-1 and Diffusol for portions of the trial. Trichoderma sp. (FK247) and Trichothecium roseum (FK238) gave sapstain control in excess of 90% for the first 30 days of the timber trial equalling the control provided by NP-1 and Diffusol. In another trial, Trichoderma harzianum (FK228) was more effective than NP-1, providing 60% sapstain control, after six months, on the internal tissue of Pinus radiata logs. The six isolates selected for the field trials were examined in additional studies. In a dual inoculation study, Trichoderma sp. (FK247) exhibited localised antibiotic ability causing the lysis of mycelium of sapstain fungi. There was no evidence of mycoparasitic action by any of the six isolates. Trichoderma harzianum (FK228), Trichoderma sp. (FK247) and Trichothecium roseum (FK238) were observed to degrade cellulose. However, neither these nor the other isolates caused a significant change in the mechanical properties of Pinus radiata timber when compared to untreated controls. Decreasing pH or the addition of nitrate were identified as having potential for the promotion of biological control agent growth. The potential of mixed biological control agent inoculations was also examined. While these results are preliminary, they are extremely encouraging and provide a basis from which future studies can develop.
| Identifer | oai:union.ndltd.org:ADTP/276981 |
| Date | January 1995 |
| Creators | Kay, Stuart James |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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