Heterobasidion Annosum (Fr.] Few Years Preceding Tree Death

History Annosus Root Disease in Europe and the Southeastern United States: Occurrence, Research, and Historical Perspective' William J. Stambaugh2 Abstract.--The history of annosus root In the eastern United States and Canada, disease in Europe and the southeastern United where H. annosum has been known mycologically States is reviewed in prefacing the focus of this since the 1980's (Ross 1975), disease occurrence symposium on the disease as it occurs in the was not recognized until the late 1940's as western United States. The topic is developed plantations reached thinning age at an increasing mostly from world literature on the disease number of locations (Kuhlman and others 1976). A published since mid-1970. The occurrence of major research effort, spearheaded by the USDA annosus root disease in both plantations and Forest Service, soon followed, especially in the natural stands of conifers is discussed, with southeastern United States, where vast mono- particular emphasis on disease range, host- cultures of fast-growing, densely planted pathogen variability, and environmental southern pines required frequent thinning and influences. Concluding attention is given to thus were considered vulnerable. As studies re-examination of the U.S.D.A. Forest Service evolved, it became evident that the mode of guidelines for management of annosus root disease spread in the principal southern hard pines in the southeastern United States in the light of conformed to that of Pinus spp. in Europe current understanding and the continuing need for (Kuhlman and others 1976), whereas butt rot and improved technology transfer. windthrow of live stems are more common in eastern white pine (P. strobus L.), western hemlock (Tsuga heterophylla [Raf.] Sarg.) (Edmonds and others 1984), and perhaps other less resinous species, much like that of spruce in Europe. The "death circle" in Hartig's (1894) Additional data on disease impact showed textbook description of annosus root disease significant reduction in height and trunk nearly a century ago has become an all too diameter growth in loblolly pine (P. taeda L.) familiar sight in conifer stands throughout the (Alexander and others 1975, Bradford and others north temperate region. Even then, he recognized 1978) and slash pine (P. elliottii Engelm. var. tree-to-tree spread of Trametes radiciperda elliottii) (Froelich and others 1977) during the Hartig (equals Heterobasidion annosum (Fr.] few years preceding tree death. Bref.) via root contacts, but it was not until more than 50 years later when Rishbeth (1951) In the last two decades in the United made the connection by showing the potential for States, the emphasis in research on H. annosum disease initiation through plantation thinning has shifted almost exclusively to the western and basidiospore colonization of fresh-cut states where the pathogen attacks a broad array stumps, thereby reaching adjacent trees. This of tree species in a variety of environments and mode of spread has accounted for a long history where its potential in second-growth forest of damage in Europe where losses occur as: (1) management is a mounting concern because of the mortality of residual stems in young conifer historical record of the disease elsewhere. Now, plantations, following and related to the extent after the passage of nearly 100 years, more than and number of thinnings (Greig 1984) and (2) wood cursory attention, and two bibliographies loss from butt and heart rot of old-growth (Koenigs 1960, Hodges and others 1971), the timber, particularly Norway spruce (Picea abies literature base on the disease is conservatively Karst.), on previously cut-over lands (Dimitri estimated at 1800 research papers and reports. 1973). The total loss from such impacts has been estimated for the countries of the European The focus of this paper is drawn primarily Economic Community alone at $35 million annually from the literature published since the mid- (Dimitri 1973). 1970's, as identified by the last IUFRO (International Union of Forest Research 1 Organizations) conference solely devoted to Presented at the Symposium on Research and annosus root rot (Kuhlman 1974), the eastern Management of Annosus Root Disease in Western states status report by Ross (1975), and the North America, April 18-21, 1989, Monterey, disease management recommendations of Kuhlman and California. others (1976). These accounts basically closed the ledger on USDA Forest Service research on the 2Professor of Forest Pathology, Duke disease in the eastern United States. With University, Durham, NC research continuing so actively in the west ever USDA Forest Service Gen. Tech. Rep. PSW-116 3 since, there is ample justification for naming Kuhlman and others 1976) been used to achieve, this symposium "... in Western North America." albeit limited, advantage in disease management. Citations to western work herein, however, will be selectively limited in deference to this being H. annosum fruits most consistently in the historical review topic of Smith (1989) that applanate form at duff level on infected trees immediately follows in this symposium. and 1- to 2-year-old stumps and, in resupinate form, dorsally on slash and root sprung/thrown roots. Basidiocarps, which initially appear as OCCURRENCE rubbery white pustules, are mostly annual in the south and tend to be perennial further north. Host-Pathogen Range Basidiospore inoculum is generally available throughout the year in the south (Ross 1973), in The incidence of H. annosum is greatest the northeast (Stambaugh and others 1962, where plantation culture and thinning of conifers Sinclair 1964), and in the northwest (Edmonds and are practiced and less so in natural stands, due others 1984), but it declines relative to rising in part to a diminished root-contact potential summer temperatures, and dwindles to only trace and the likelihood of intervening non-host amounts in southernmost latitudes (Ross 1973). species in mixed stands. Judging from the Just how uniform this inoculum is over the time comprehensive host list of Sinclair (1964) and and space of disease occurrence has been the subsequent updatings (Greig 1976, Webb and subject of much speculation and, until recently, Alexander 1985), there seem to be few coniferous little understanding. species that have not been reported as hosts. A number of hardwoods and woody shrubs are also Host-Pathogen Variability listed, but damage of any consequence is reported only from continental Europe on Alnus and Quercus World source isolates of H. annosum have spp. (Dimitri 1973) and from Great Britain on Q. shown some remarkable similarities in culture borealis Michx. and Nothofagus obliqua (Mirb.) (Rishbeth 1987) but also notable differences in Blume underplanted to Pinus spp. (Greig 1974). other physiological characteristics, including It remains to be seen whether the findings of H. virulence, as reported by Worrall and others annosum in several Central American countries (1983). The potential for linking virulence (Greig and Foster 1982) and in eastern Australia (that is, relative disease capacity) of the (Shain and Bolland, in Kuhlman 1974) pose any fungus with host origin became tenable with the threat for ultimate spread to extensive exotic discovery in Finland (Korhonen 1978) of two plantings of known hosts at various locations in intersterility groups: group S causes butt-rot the southern hemisphere, particularly Australia in Norway spruce and kills young pines in the and New Zealand. near vicinity; group P kills pines of all ages as well as young spruce, junipers, and even some Given its broad host range and its long hardwoods. Both groups have been identified in history of disease occurrence (Dimitri 1973, Ross the western United States but only P has been 1975), H. annosum must be considered present detected to date in the east (Harrington and throughout the north temperate region wherever others 1989). The host specificity implications local concentrations of host species exist. A of these findings were applied by Worrall and facultative parasite, the fungus utilizes many others (1983) in evaluating observed elevational substrates for its survival and reproduction. differences in the incidence of H. annosum in Basidiospores of H. annosum colonize freshly pine (P. ponderosa Dougl. ex Laws)-fir (A. exposed wood of conifers in newly cut stumps, concolor [Cord. & Glend.] Lindl. ex Hildebr.) which are the primary mode of stand access mixtures in California. Seedling inoculations of (Rishbeth 1951); in logging slash; in stem both species with isolates from their range wounds, as limited to western hemlock and true showed significant differential interaction firs, Abies spp. (Aho and others 1983); and in between isolate groups and host species; pine roots (Siepmann 1976). While root-contact isolates were most lethal on pine and least so on infection is the common pattern of spread fir, while the lethal effect of the isolates from (Rishbeth 1951, Hodges 1969), both the circum fir was intermediate between the pine extremes on stantial evidence of significant levels of root both. Alternative interpretations were explored infection in unthinned loblolly pine (Webb and and the need for further evaluation was others 1981) and the successful inoculation of indicated. roots with conidia in undisturbed natural soil (Kuhlman 1969) supports the view that The sexual cycle of H. annosum also was basidiospore percolation downward in soil resolved by Korhonen (1978) and later accounts for at least some direct root infection,

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