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Wright, E., and Wells, H. R. Tests on the adaptability of trees 

 and shrubs to shelterbelt planting on certain Phymatotrichivm. 

 root rot infested soils of Oklahoma and Texas. Jour. Forestry 

 46: 256-262. 1948. 



Poria Root Rot of Douglas-Fir 



G. W. Wallis 



Forest Entomology and Pathology Branch, Canada Department 

 of Forestry, Victoria, British Columbia 



Poria tveirii Murr. is a root rot of coniferous species common in 

 Northwestern United States and southern British Columbia, Canada. 

 The disease occurs in patches or centers of infection. Aboveground 

 symptoms become apparent only after the disease has reached an ad- 

 vanced state. Shortening of the leader growth, sometimes accom- 

 panied by a distress crop of small cones on Douglas-fir, is followed 

 by a thinning and yellowing or reddening of the foliage, and finally 

 by death of the tree. Windthrow of living trees is common, the 

 major decayed roots breaking close to the root collar. 



Sporophores, forming on the underside of decayed logs and up- 

 rooted stumps, are found only periodically during the summer and 

 early autumn. The resupinate fruit bodies are cinnamon buff to 

 brown, usually with a broad to narrow white to cream sterile margin. 

 On species other than western red cedar the sporophores usually 

 form only a single tube layer; on cedar a perennial fruit body is 

 formed. Setal hyphae and setae are abundant. Basidiospores are 

 globose to subglobose becoming oblong-ellipsoid with a small apiculus, 

 4-4.9 X 2.8-3. 2/x. No conidiospores are formed either in nature or 

 in culture. Hyphae have simple septa, branching frequently immedi- 

 ately below the septum, but with no clamp connections. 



The incipient stage of the decay is usually characterized by a cres- 

 cent-shaped to spherical pattern of reddish-brown stain in the cross 

 section of the stump. In the advanced state of decay, the wood breaks 

 down to a yellow, laminated, pitted rot. Setae and setal hyphae are 

 abundant in the laminated wood and a brown crustlike sheet often 

 forms over mycelial masses on exposed wood surfaces. 



This fungus, although capable of causing death to the majority of 

 coniferous species in the Douglas-fir region, is most important as a 

 root rot causing extensive losses in 25- to 125-year-old Douglas-fir and 

 as a butt rot of cedar. The infection arises when roots contact the 

 fungus present in roots and stumps of the previous crop. Spread to 

 adjacent trees occurs when a healthy and diseased root are in contact. 

 The role of basidiospores in the spread of infection is as yet unkown. 

 It has been estimated that the productivity of second-growth 

 Douglas-fir stands in western Washington and Oregon is, on the 

 average, reduced by about 5 percent as a result of the activity of 

 this fungus. A method for the economic control of Poria root rot 

 is, as yet, unknown. 



Intercontinental spread is possible through shipment of infected 

 logs. Infection of seedlings below 6 years of age is not known. 



