15 research outputs found

    Root-infecting fungi associated with a decline of longleaf pine in the southeastern United States

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    symptoms A 35year-old longleaf pine stand exhibited trees in various stages of decline. A study was conducted to determine root-infecting fungi and other abnormalities associated with varying degrees of crown symptoms. A four-class crown symptom rating system was devised according to ascending symptom severity. Leptographium procerum and L. terebrantis were significantly associated with increasing crown symptom severity. Heterobasidion annosum was also isolated in higher frequency as crown symptoms increased. Also, evidence of insects on roots increased as did amount of resinosis observed. Edaphic and silvicultural factors may interact with these pathogens and insects to pose a pathological limitation on longer-term management objectives. Further research is needed to determine relationships among various edaphic, silvicultural, and biological factors associated with the decline syndrome on this site. t

    Biological and Management Implications of Fire-Pathogen Interactions in the Giant Sequoia Ecosystem

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    An overriding management goal for national parks is the maintenance or, where necessary, the restoration of natural ecological processes. In Sequoia-Kings Canyon and Yosemite National Parks, there is concern about the effects of fire suppression on the giant sequoia-mixed conifer forest ecosystem. The National Park Service is currently using prescribed fire management and prescribed burning as tools to reintroduce fire as a natural process. However, there are questions about the positive and negative effects of reintroducing fire in the giant sequoia-mixed conifer ecosystem. Reintroducing fire in the Sierra Nevada forests needs critical evaluation with respect to the pathogens that affect giant sequoias. We designed a 3-year study, funded by the U.S. Department of the Interior, National Park Service, to: (1) determine the effects of fire scars and their re-burning on the incidence, extent, and survival of fungi in giant sequoia; (2) identify pathogens, insects, location of decay, and other characteristics present in standing old-growth giant sequoia fire scars; (3) evaluate host specialization and cross infectivity of isolates of Heterobasidion annosum from white fir (Abies concolor), red fir (Abies magnipca), and giant sequoia (Sequoia gigantea); and (4) develop criteria and recommendations for monitoring the effects of fire on pathogens in giant sequoia stands. The total circumference of giant sequoia trees affected by fire scars ranged from 3.3% to 69.5%. Cross-sectional area affected by fire scars ranged from 3.2% to 53.7%. The season of year in which prescribed burning takes place could influence the effect fire has on giant sequoia. A survey of 90 fire scars for the presence of resin, MycocaIicium, carpenter ants, other insects, Arachnids, decay above and below groundline, and bird activity (i.e., cavities) yielded a high presence of each factor when all burn groups were combined. Statistically significant differences in bird cavity activity, decay above groundline, and carpenter ant activity were noted among the unburned group, 1-year burn group, and 5-year burn group. The Pilodyn wood tester was effective in determining the presence of decay above and below groundline. A variety of microfungi were found associated with giant sequoia fire scars. The fungi most frequently isolated were: Byssochlamys fulva from 34 out of 90 fire scars (38%), Acrodontium intermissum from 22 out of 90 fire scars (24%), and Tritirachium sp. from 14 out of 90 fire scars (16%). Several other microfungi and Basidiomycetes were also identified. H. annosum acts as both a saprophyte and a pathogen in the giant sequoia-mixed conifer ecosystem. The results of these experiments have demonstrated H. annosum can spread from true fir to giant sequoia and vice versa, given that they are of the same ”S” intersterility group

    Genetic Structure of Heterobasidion annosum in White Fir Mortality Centers in California

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    The structure of Heterobasidion annosum populations was studied in 1.5 mixed-conifer sites in central and northern California. Study sites displayed mortality of white fir trees in enlarging discrete patches (mortality centers). At each site, fungal genotypes were defined by somatic compatibility tests. In two sites, further genetic and molecular analyses were performed on field genotypes and on homokaryons obtained by dedikaryotization of field heterokaryons. Isolates were found to be colonizing mostly the roots and the bole sapwood of white fir trees, and no significant infections of other tree species were observed. Each mortality center was characterized by the presence of several fungal genotypes, all belonging to the S intersterility group. Both homokaryotic and heterokaryotic strains were present in all sites. Multiple genotypes were retrieved in individual trees or stumps. Out of 228 fungal genotypes, 86 % were found only within a single tree or stump, while 14 % had spread to adjacent trees. The two largest genotypes had diameters of 9 and 10 m, and had colonized fiv

    Detection and quantification of Leptographium wageneri, the cause of black-stain root disease, from bark beetles (Coleoptera: Scolytidae) in Northern California using regular and Real-time PCR

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    Black-stain root disease is a threat to conifer forests in western North America. The disease is caused by the ophiostomatoid fungus Leptographium wageneri (W.B. Kendr.) M.J. Wingf., which is associated with a number of bark beetle (Coleoptera: Scolytidae) and weevil species (Coleoptera: Curculionidae). We developed a polymerase chain reaction test to identify and quantify fungal DNA directly from insects. Leptographium wageneri DNA was detected on 142 of 384 bark beetle samples (37%) collected in Lassen National Forest, in northeastern California, during the years 2001 and 2002. Hylastes macer (LeConte) was the bark beetle species from which Leptographium DNA was amplified most regularly (2001: 63.4%, 2002: 75.0% of samples) . Lower insect?fungus association rates were found for Hylurgops porosus (LeConte), Hylurgops subcostulatus (Mannerheim), Hylastes gracilis (LeConte), Hylastes longicollis (Swaine), Dendroctonus valens (LeConte), and Ips pini (Say). The spore load per beetle ranged from 0 to over 1 × 105 spores, with only a few beetles carrying more than 1 × 103 spores. The technique permits the processing of a large number of samples synchronously, as required for epidemiological studies, to study infection rates in bark beetle populations and to identify potential insect vectors
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