whole_KileGA1971.pdf (58.53 MB)
The host-pathogen relationship between apple and trametes versicolor and factors affecting host susceptibility
thesisposted on 2023-05-26, 21:55 authored by Kile, G. A
Examination of a large number of apple trees infected with Trametes versicolor, indicated that the fungus was a facultative parasite which caused a white rot of the sapwood. Papery bark was a distinctive but non-specific external symptom of the disease. The development of papery bark was influenced by seasonal and nutritional conditions and was not a reliable indicator of susceptibility of trees to T, versicolor. Discoloration of the sapwood always occurred in advance of fungal colonisation and decay. The formation of discolored wood involved the loss of starch and nuclei from ray and xylem parenchyma and the eventual necrosis of these cells. Necrotic cells were filled with a brown amorphous material which appeared to be oxidised phenolics. In young wood, ray and xylem parenchyma formed polysaccharide wound gum which was deposited in the vessels of the sapwood-discolored wood transition zone. The levels of K, Ca, Mg, moisture, pH, neutral solvent extractable materials and phenolics in discolored wood, differed from those in the adjacent sapwood. Bacteria were present in discolored wood in advance of the fungus. Discoloration was a non-specific response of the sapwood to mechanical or pethological stimuli. In vitro decay tests indicated that discolored wood was more resistant to decay than normal sapwood. Discoloration of the wood and gum formation therefore appeared to be an active host resistance mechanism to fungal penetration and decay. The host reaction to wounding was related to the physiological cycle of the tree and with age cells lost the ability to synthesise wound gum and reduced amounts of extraneous material were formed in the ray and xylem parenchyma. Evidence indicated that the resistance of young apple sapwood to colonisation and decay by T. versicolor was due to its vital nature and ability to elaborate an effective fungal inhibitory barrier. The susceptibility of living wood to fungal decay increased with age, due to a natural decline in host resistance.
Rights statementCopyright 1971 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). Thesis (Ph.D.) - University of Tasmania, 1971. Bibliography: l. 214-229