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Factors influencing the susceptibility of apple trees to Trametes (Polystictus) versicolor


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Darbyshire, B 1968 , 'Factors influencing the susceptibility of apple trees to Trametes (Polystictus) versicolor', PhD thesis, University of Tasmania.

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"Polystictus dieback" of apple trees is a serious problem in Australian orchards and the literature suggests that the disease is only extensive and causes severe injury to trees in orcharding areas of this country. The disease is associated with a wood rotting Basidiomycete, Trametes versicolor, and as a result of attack by this fungus limbs or whole trees may be destroyed. By growing apple trees in sand culture a quantitative relationship was established between a phosphorus deficiency and an increased susceptibility of limbs to destruction by the fungus (Wade, unpubl.).
The results reported here are directed towards an attempt to explain the parasitic nature of T. versicolor on apple trees in Australia. A field survey failed on confirm any relationship between phosphorus status and the incidence of dieback in trees.
The effects of reserve nutrients accumulated by trees on the development of the fungus were then examined using in vitro methods. The fungus was grown on blocks of apple wood in culture jars containing different nutrient sources incorporated in a medium. When a carbon source was absent from the media, decay of wood was high. With a high carbon or nitrogen deficient media wood decay was comparatively low. Solution culture experiments indicated that production of extracellular polyphenol oxidase is an important factor in this effect. With increasing glucose content of media, decay of wood was increasingly suppressed. Polyphenol oxidase production was suppressed with increasing media sugar levels.
By extracting wood blocks before subjecting them to attack by the fungus the presence in the wood of an inhibitor to the growth of the fungus, was demonstrated. It was postulated that such an inhibitor may be associated with soluble sugar levels in trees.
Inoculation trials demonstrated a varietal variation in susceptibility of trees to the disease, an increased amount of dieback resulting from winter inoculations and an inability of the fungus to grow in one year old wood. The trials also indicated a relation between high soluble sugar levels and a lower rate of establishment of the fungus. This result although not entirely conclusive, confirmed the results of the in vitro experiments.
It is concluded that environmental and managerial conditions to which trees are subjected in Australia, result in an increased susceptibility of limbs to attack and ultimate destruction by T. versicolor. The increased susceptibility of branches may be explained in terms of a lowered soluble sugar content and an associated lower level of the suggested inhibitory factor to the growth of the fungus.

Item Type: Thesis - PhD
Authors/Creators:Darbyshire, B
Keywords: Trametes versicolor, Apples
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Copyright 1967 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

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Thesis (PhD) - University of Tasmania, 1967. On spine : "Polystictus" dieback of apple trees.

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