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


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Darbyshire, Benjamin 1967 , '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 vitroexperiments.
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, Benjamin
Keywords: Trametes versicolor, Apples
Copyright Holders: The Author
Additional Information:

Thesis (Ph.D.) - University of Tasmania, 1967. On spine : "Polystictus" dieback of apple trees. Includes bibliography

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