Fungal root pathogen interactions in a mixed conifer forest in the Blue Mountains of northeastern Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2f75r986m

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  • The coniferous forests of the Pacific Northwest are affected by a variety of endemic fungal root pathogens. Forest disease surveys have noted the presence of two or more of these root pathogens infecting the same stump or root, and it has been suggested that these fungi may be interacting synergistically. To test this hypothesis, three separate root disease centers were studied where the dominant pathogens appeared to be either Armillaria ostoyae (Rom.) Herink, Heterobasidion annosum (Fr.) Bref., or Phellinus weirii (Murr.) Gilb. The spruce-type intersterility group of i. annosum was found infecting trees and stumps within both the P. weirii and A. ostoyae centers, and was isolated from some of the same roots as A. ostoyae. Three experiments were designed to study pairwise interactions between A. ostoyae, P. weirii, the spruce (S) and pine (P) type intersterility groups of ff annosum, and Perenniporia subacida (Pk.) Donk. Hyphal and mycelial interactions were studied microscopically on agar-filled culture slides, macroscopically on 2% and enhanced malt agar, and within wood blocks of an Abies sp. (either A. qrandis (Dougl.) Lindl., or . concolor (Gord. and Glend.) Lindl.) and Pinus ponderosa Laws. Direct interspecific hyphal contact occurred between fungi on culture slides, resulting in sporadic hyphal vacuolation. However, no other discernible reactions such as anastomosis or parasitism were observed. Only one of the pairings, A. ostoyae vs. H. annosum P-type, formed a definite band of vacuolated hyphae along their zone of interaction. Other pairings may have had more vacuolated hyphae in the zone of interaction, but this was difficult to quantify. Pairwise interactions were also studied on 2% and enhanced malt agar. Reactions between fungi included the formation of zones of inhibition, walling-off, abutting growth, or overgrowth of one isolate by the other. The reactions of identical fungal pairings were inconsistent between the two types of media. Isolations from these plate pairings revealed that visual observations may not be adequate to classify the reactions which occur. Interactions within sterilized wood blocks showed the formation of either single or parallel barrier lines between opposing fungi, and isolations revealed that the colonizing fungi remained separated on their respective sides of the barrier lines. The conclusion from this study is that root pathogenic fungi grow in proximity to one another in nature in what can be termed associations. However, experimental results lead to the conclusion that these fungi do not form complexes, nor do they interact synergistically in causing decay. Pathogenic fungi appear together independently, as conditions favorable for their individual infection biologies coincide with the presence of an inoculum source and a suitable host.
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