Graduate Thesis Or Dissertation
 

Map.JPG

Public Deposited

Downloadable Content

Download image
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hm50tx06n

Descriptions

Attribute NameValues
Creator
Abstract
  • The root pathogen, Phytophthora lateralis Tucker and Milbrath, continues its destructive spread among Port-Orford Cedars (Chamaecyparis lawsoniana (Murr.) Parl.) of southwestern Oregon. This thesis concerns spread of the fungus between root systems of individual trees in a 49-year-old stand predominantly of Port-Orford- Cedar. The contribution of root grafts to spread is given special attention. Root systems of five groups of trees, 36 in all, were hydraulically excavated and examined for the frequency and character of root grafting and for the part played by the grafts in disease spread. Eighty three percent of the trees studied had at least one root graft and frequently trees were grafted into complexes of as many as nine trees, functionally uniting widely spaced (39 feet) individuals. The frequency of root grafting was found to be a linear function of both horizontal and vertical distances between trees of a pair. If either distance is increased the frequency of root grafting decreases. Root grafting is therefore most prevalent in dense stands on level ground and least prevalent in sparse stands on slopes. Disease may spread between trees by fungus sporulation on infected roots followed by reinfection (discontinuous spread) and/or by vegetative spread between root grafted trees (continuous spread). The two forms were compared with respect to rate of spread. Approximately 91 percent of the disease spread in the study trees resulted from discontinuous spread, while only 9 percent resulted from continuous spread through root grafts. An elementary simulation model was formulated to determine the degree of association of roots of trees separated by given distances. The model is used to explain disease spread between trees in the absence of root grafts. Here, an hypothesis, "wash back," is introduced to explain disease spread upslope by the overlap of infected and healthy roots. The following conclusions concerning disease spread emerge from examination of root systems: (1) disease spread through root grafts is of minor importance over time as compared with spread by sporulation and reinfection; (2) root grafts are important in disease spread in the absence of sporulation and reinfection (vegetative fungus spread through grafted complexes will result in continued tree mortality), and (3) disease spread upslope through root grafted trees becomes less likely as slope steepens. Disease spread between overlapping root systems of healthy and infected trees can account for disease spread upslope in the absence of root grafts.
Rights Statement

Relationships

Parents:

Items

Thumbnail Title Date Uploaded Visibility Actions
file details Map.JPG 2017-10-25 Public Download