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UC Agriculture & Natural Resources Agriculture

Title Non- native plants are main hosts for sudden oak death in California

Permalink https://escholarship.org/uc/item/3zw0s0df

Journal California Agriculture, 57(1)

ISSN 0008-0845

Authors Garbelotto, Matteo Davidson, Jennifer M. Ivors, Kelly et al.

Publication Date 2003

Peer reviewed

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RESEARCH ARTICLE ▲ Non-oak native plants are main hosts for sudden oak death pathogen in California

AB Matteo Garbelotto Jennifer M. Davidson Kelly Ivors Patricia E. Maloney Daniel Hüberli Steven T. Koike David M. Rizzo ▼ C D The finding of ramorum — the pathogen that causes sudden oak death in four California native trees — on in led us to hypothesize that its range in California’s natural was much greater than previously suspected. In addition to the affected oak species, we have now identified an additional 13 species from 10 plant families that EF act as hosts for P. ramorum in California. Our data indicates that nearly all of the state’s main tree species in mixed-evergreen and redwood-tanoak forests — including the coniferous timber species coast redwood and — may be hosts for P. ramorum. The broad host range of P. ramorum, the variability of symptoms among different hosts G H and the ability of the pathogen to disperse by air suggests that it may have the potential to cause long-term, landscape-level changes in California forests.

nown as “sudden oak death” in Kthe popular press, Phytophthora ramorum (Phylum Oomycota) is a re- cently described plant pathogen that causes a deadly canker disease of tanoak, coast live oak, California Symptoms of by Phytophthora ramorum on various hosts in California forests black oak and Shreve’s oak in Califor- include: (A) tanoak with phloem canker on main trunk, (B) stem canker on tanoak stops nia and (Rizzo et al. 2002b; at the soil line, (C) madrone with foliar and stem lesions, (D) bay laurel/Oregon myrtle with -tip necrosis, (E) coast redwood with needle necrosis on understory sapling, Goheen et al. 2002). This disease has (F) Douglas fir with tip wilting due to branch cankers, (G) big leaf maple with marginal reached epidemic proportions in oak leaf scorch, and (H) rhododendron showing foliar lesions.

18 CALIFORNIA AGRICULTURE, VOLUME 57, NUMBER 1 TABLE 1. Known hosts of Phytophthora ramorum in California, plant part infected and original detection method Overall, we found direct PCR am- Plant part Detection plification from symptomatic plant Host: common name, species infected method tissue to be more sensitive and reli- Bay laurel/Oregon myrtle, californica (Lauraceae) PCR Big leaf maple, (Aceraceae) Leaves PCR able than culturing for initial detec- California black oak, Quercus kellogii (Fagaceae) Main stem Culture tion of P. ramorum. Of the 13 non-oak California buckeye, (Hippocastanaceae) Branches, leaves PCR host species we have identified in Coast live oak, (Fagaceae) Main stem Culture California, 10 were first detected this Coast redwood, (Taxodiaceae) Branches, leaves PCR Coffeeberry, Rhamnus californica (Rhamnaceae) Branches, leaves PCR method (table 1). Although cultures of Douglas fir, Pseudotsuga menziesii (Pinaceae) Branches, leaves Culture P. ramorum have been obtained from all Evergreen huckleberry, Vaccinium ovatum (Ericaceae) Main stem, branches, leaves Culture but one host species, the time period nec- , Lonicera hispidula (Caprifoliaceae) Leaves PCR essary to identify its expanded host range Madrone, menziesii (Ericaceae) Branches, leaves PCR Manzanita, Arctostaphylos manzanita (Ericaceae) Branches, leaves PCR was considerably shortened by the use of Ornamental rhododendron, Rhododendron sp.1 (Ericaceae) Branches, leaves Culture species-specific molecular primers. Rhododendron, Rhododendron macrophyllum (Ericaceae) Branches, leaves PCR Shreve’s oak, var. shrevei (Fagaceae) Main stem Culture Pathogen evaluated in hosts Tanoak, Lithocarpus densiflorus (Fagaceae) Main stem, branches, leaves Culture Toyon, arbutifolia (Rosaeceae) Branches, leaves PCR Isolation of P. ramorum from symp- tomatic plants was the first step in de- termining the pathogenic role played forests along approximately 185 miles California forests (table 1). Our data by this microbe on new hosts. How- (300 kilometers) of the Central Coast of indicates that nearly all of the main ever, association between symptoms California during the past 7 years (Rizzo tree species, including the coniferous and the presence of P. ramorum does et al. 2002b; Garbelotto et al. 2001). timber species coast redwood not necessarily imply that this microbe Initial work on the disease in Cali- (Sequoia sempervirens) and Douglas fir plays a primary causal role. Rather, fornia concentrated on and oak (Pseudotsuga menziesii), in mixed- P. ramorum may simply be an opportu- mortality. However, in December 2000, evergreen and redwood-tanoak nistic colonizer of plants diseased by we learned of a possible connection types may be hosts for P. ramorum. other agents. We conducted controlled with an undescribed species of Oaks in the subgenus Quercus (such experiments to further test pathogenic- Phytophthora causing a stem and leaf as the white oaks) still appear to be ity between May 2001 and May 2002. blight on ornamental rhododendron unaffected by P. ramorum. Understory Healthy plants were challenged with and viburnium plants in and shrubs — such as manzanita (Arctosta- the pathogen, and the development of the Netherlands (Rizzo et al. 2002b; phylos manzanita), toyon (Heteromeles symptoms was described and quanti- Werres et al. 2001). A comparison of arbutifolia), coffeeberry (Rhamnus fied (Rizzo et al. 2002a). The process, morphological characters and DNA se- californica) and honeysuckle (Lonicera known as Koch’s postulate, ends with quences confirmed that the California hispidula) — are also hosts for P. ramorum. the successful reisolation of the micro- and European were the organism from artificially infected plant DNA aids in new-host discovery same species of Phytophthora (Rizzo et tissue. Because most hosts were tested in al. 2002b). The European Phytophthora Field diagnosis of P. ramorum was separate trials, a comparison of suscepti- was eventually described as P. ramorum initially attempted via direct isolation bility levels across hosts is not appropri- (Werres et al. 2001) and this name was from symptomatic plant tissue. ate, and trial results for each host were applied to the California oak pathogen Phytophthora species, however, are often analyzed independently. (Rizzo et al. 2002b). difficult to culture from plants, which For most experiments, three geneti- The finding of P. ramorum on rhodo- may lead to false-negative isolations cally different isolates of P. ramorum dendron in Europe led us to hypoth- and misdiagnoses. Our DNA-based were used: Pr-5 from tanoak, Pr-6 from esize that its host range in California’s diagnosis consisted of a process includ- coast live oak and Pr-52 from rhodo- natural forests was much greater than ing: 1) freeze-drying of samples, 2) dendron. Foliage inoculations of 2-to-3- previously suspected. Using the symp- grinding of infected plant tissue and year-old plants were conducted by toms described for three affected oak DNA extraction, and 3) amplification of misting leaves with sterile distilled wa- species (Quercus spp. [Q. kellogii, Q. P. ramorum DNA using the polymerase ter and then pinning inoculum plugs to agrifolia, Q. parvula var. shrevei]), tanoak chain reaction (PCR). Once amplified, the upper surface of leaves. Sterile agar (Lithocarpus densiflora) and rhododen- the DNA can be analyzed in a variety plugs were used as controls. A plastic dron as a guide, we examined and of ways to confirm that it belongs to the bag was then placed over the indi- sampled leaves and stems of tree and target species. Four specific PCR prim- vidual leaves and misted again with shrub species on numerous sites with ers were developed based on sequences sterile distilled water before sealing. oak mortality in California. In addition of the internal transcribed spacer (ITS) Each trial generally consisted of 10 to the original four host species in the of nuclear ribosomal DNA unique to leaves per host species per isolate, plus oak family (Fagaceae), we have now P. ramorum (Garbelotto et al. 2002). Two controls. In all trials, seedlings were in- identified an additional 13 species new protocols were also developed to cubated for 2 weeks in a greenhouse from 10 plant families as hosts for eliminate cross-reactivity with various that was maintained at 68°F to 75°F P. ramorum throughout its range in other species. (20°C to 24°C). For each trial, we re-

http://danr.ucop.edu/calag • JANUARY-MARCH 2003 19 TABLE 2. Pathogenicity of Phytophthora ramorum on leaves of native California plant species; all have been found infected in the field corded symptoms, measured lesion P. ramorum Control length and width and plated pieces Lesion Lesion Percent size, mm* size, mm* of stems or leaves on the selective Host: common name (species) Nreisolation (range) N (range) Phytophthora growth medium PARP Bay laurel/Oregon myrtle 28 100 5 8 1.1 to verify presence or absence of (Umbellularia californica) (0–15) (0–2) P. ramorum. All leaf inoculations Big leaf maple 42 100 19.9 12 2.7 were conducted at least twice. (Acer macrophyllum) (1–45) (0–6) Methods for stem inoculations have California black oak 15 100 4.9 6 2.6 been previously described (Rizzo et al. (Quercus kellogii) (1–14) (1–3) 2002b). Seedlings (stem diameter ap- California buckeye 48 94 13.6 18 2.5 proximately 1 centimeter) of coast red- (Aesculus californica) (4.5–29) (0–9) wood and Douglas fir were inoculated Coast live oak 18 100 2.1 6 1.6 with isolate Pr-52 in two separate trials (Quercus agrifolia) (1–4) (1–2) started in January (five seedlings per Coast redwood† 56 43 4.9 19 1.6 treatments) and March 2002 (10 seed- (Sequoia sempervirens) (1–20) (1–3) lings per treatment). Both trials lasted Seedlings 20 100 13.7 20 6.2 (4–21) (0–11) 6 weeks. All data was analyzed by ANOVA Coffeeberry 30 30 4.4 10 2.1 (Rhamnus californica) (1–15) (1–3) using the software program JMP (SAS Institute Inc., Cary, NC, 1995). In all Douglas fir‡ 58 47 2.01 15 1 (Pseudotsuga menziesii) (1–12) (1) cases, there were no significant differ- Seedlings 20 75 38 20 9 ences between different isolates and the (12–64) (0–16) different trials, so data was combined Evergreen huckleberry§ 57 84 15.3 20 2.0 for final analysis. (Vaccinium ovatum) (3–22) (1–13) Symptoms and severity Madrone 18 100 26.9 6 3.5 () (15–47) (1–10) The symptoms of P. ramorum have Manzanita¶ 101 82 10.6 34 2.1 only been observed on aboveground (Arctostaphylos manzanita) (1–23) (1–6) plant parts such as leaves, branches and Tanoak 18 100 34.5 6 2.0 stems, regardless of the host (table 1). (Lithocarpus densiflorus) (25–48) (1–4)

In several instances, stem lesions end at Toyon 44 72 5.4 16 2.3 the soil line. Although P. ramorum is (Heteromeles arbutifolia) (1–10) (1–4) deadly on certain oaks (Quercus spp.) * The average of lesion length and width 14 days after inoculation, except for coast redwood and Douglas fir, where it and tanoak, disease progression and is only the length. Mean lesion lengths of P. ramorum were significantly greater on all hosts, with the exception of the extent of damage on individual coast live oak and Douglas fir, than those of control inoculations at P < 0.05 based on ANOVA with contrasts. † Fifteen inoculations of individual leaves led to discoloration of two or more adjacent leaves. On one inoculation, plants of most non-oak hosts is not well 60 mm of the adjacent stem was killed. characterized yet. ‡ Twenty-six of 58 single-leaf inoculations resulted in lesions of 17–85 mm long on adjacent branches (5 mm diameter) even though the lesion length on the inoculated needle was 1 mm and apparently not connected to the longer stem On several ericaceous plant species, lesions. P. ramorum was recovered from 13 of these branch lesions. P. ramorum causes significant foliar § Typical leaf lengths were 15–20 mm; entire leaves turned black on 72% of inoculations. On three inoculated leaves, blight and branch dieback (table 1). P. ramorum moved into the stems and caused lesions of 30–50 mm length. ¶ Typical leaf lengths were 15–20 mm; entire leaves turned black on 33% of inoculations. On six inoculations, Death of madrone (Arbutus menziesii) P. ramorum grew through petioles and caused branch cankers of 35–55 mm on the main stem. saplings in less than 4 months was ob- served in the field (P.E. Maloney, un- published data) and it is suspected that the pathogen can kill mature madrone Coast redwood. Symptoms on coast colored lesions were observed on trees. Death of mature redwood are associated with saplings sprouts in the field and apparently lead (Rhododendron macrophyllum) has also and basal sprouts on large trees. On to death of the . P. ramorum was been observed in Oregon (Goheen et al. saplings, P. ramorum causes discolora- detected using the PCR diagnostic test 2002). On other hosts, such as bay laurel tion of needles and cankers on small from 12 of 90 symptomatic basal (Umbellularia californica), California buck- branches, resulting in an overall decline sprouts collected at seven locations eye (Aesculus californica) and big leaf in tree vigor. The pathogen was iso- spanning the known geographic range maple (Acer macrophyllum), P. ramorum lated from the needles and small of P. ramorum in coastal California. appears to be primarily a leaf patho- branches of 11 coast redwood saplings While it appears that P. ramorum may gen with very limited stem infection. — about 1 to 6 inches (2 to 15 centime- be relatively abundant at these sites on Leaf inoculations of all suspected hosts ters) in diameter — at two locations coast redwood, the results also indicate resulted in the formation of lesions, and (Jack London State Park in Sonoma that other causes of sprout mortality P. ramorum was successfully reisolated County and Henry Cowell State Park in may be occurring. Greenhouse inocula- from all inoculated hosts (table 2). Santa Cruz County). Distinct purple- tions of coast redwood stems and

20 CALIFORNIA AGRICULTURE, VOLUME 57, NUMBER 1 The broad host range of P. ramorum, the variability of symptoms among different hosts and the ability of the pathogen to disperse by air suggests that it may have the potential to cause long-term, landscape level changes in California forests. leaves caused lesions similar to those oculations of individual Douglas fir of molecular genetic analyses of P. observed in the field (table 2). In addi- leaves resulted in discoloration of in- ramorum populations. Genetic finger- tion, extensive discoloration of the xy- oculated leaves and the subsequent die- printing on a number of California, Or- lem was noted in sapling inoculations back of adjacent leaves and twigs. egon and European isolates is under (data not shown). Inoculations of stems resulted in way using a technique called amplified The importance of P. ramorum in the resinosis from the bark, cambial necro- fragment length polymorphisms dieback and death of mature coast red- sis and dieback, and discoloration of fo- (AFLPs)(Vos et al. 1995). Recent studies wood trees is still uncertain. In January liage (table 2). Symptoms on Douglas (Garbelotto et al. 2001; unpublished 2002, the dieback of a mature coast red- fir do not appear to be common in the data) reveal that a single individual of wood in an urban setting in Marin field at this time and have not been ob- P. ramorum has been clonally reproduc- County was reported in the press and served on overstory trees. ing and is responsible for over 80% of attributed by a local arborist to infec- all in California and Oregon. P. ramorum in Calif. tion by P. ramorum. This diagnosis was The genetic analysis confirms that the conducted by a private laboratory and Across the range of known hosts, we same individual is capable of infect- based on detection of a Phytophthora can distinguish two different types of ing all hosts. This result is significant species using a nonspecific immunoas- diseases: nonlethal foliar and twig in- because identical-looking pathogens say (ELISA). We have confirmed that fections, and lethal branch or stem in- isolated from different hosts may rep- P. ramorum was present in the discol- fections. Foliar infections play a key resent undistinguishable but geneti- ored xylem of the stump of the tree us- role in the epidemiology of P. ramorum cally different microorganisms. In ing direct PCR amplification and DNA by serving as a source of inoculum, addition to the results stemming from sequencing. We were unable to directly which is then spread aerially through the genetic analyses, inoculation of all isolate the pathogen from the discol- splash (Davidson, Garbelotto et al. hosts with cultures isolated from oaks ored tissue, nor bait the pathogen from 2002). The most likely dispersal and rhododendron always resulted in bark or soil samples taken from the of P. ramorum, sporangia typical disease symptoms (table 2). base of the tree. This tree was affected and chlamydospores, are readily pro- Such data strongly suggests that the by a concrete patio and driveway and duced on foliage (particularly of bay pathogen moves from one host to an- had extensive root rot by two unidenti- laurel/Oregon myrtle and Rhododen- other with no evidence of host specific- fied wood-decay fungi and by a root dron spp.), but we have yet to find ity for different isolates. pathogen known as the oak root fungus them on infected oak bark. Therefore, The establishment and spread of or honey mushroom (Armillaria mellea). P. ramorum epidemics in California oak P. ramorum may be mediated by foliar The role of P. ramorum in the develop- forests may be driven by the presence infections on a variety of hosts. Fur- ment of dieback symptoms on this tree and susceptibility of associated plant thermore, both reproductive (such as is difficult to determine because of the hosts, not the oaks themselves. sporangia) and resting (such aschla- presence of these other pathogens and Two recent studies have reported a mydospores) structures have been abiotic factors. Three other large urban significant association between the pres- found to accumulate in soil and water redwood trees in Marin County re- ence of bay laurel/Oregon myrtle trees (Davidson, Rizzo et al. 2002). Prelimi- ported in the popular press to be asso- and P. ramorum infection on certain oaks nary results indicate that plant mate- ciated with P. ramorum were negative (Quercus spp.)(Swiecki and Bernhardt rial can become infected if placed in for the pathogen both by PCR analysis 2002; Kelly and Meentemeyer 2002). contact with infested soil or water, and culturing, although all of these Likewise, our preliminary studies indi- which are likely to play an important trees had extensive decay caused by an cate that foliar host infection may pre- role both in the natural and artificial unidentified canker rot fungus and cede infection of oaks (Quercus spp.) transmission of this pathogen. A. mellea. We have not observed un- and tanoak on a site. We hypothesize Temperature and moisture. The usual mortality or disease symptoms of that P. ramorum may need to produce presence of P. ramorum has been con- overstory coast redwood in natural for- inoculum on the leaves of these associ- firmed in 12 California counties: (from ests (Maloney et al. 2002). ated hosts to serve as a springboard to north to south) Humboldt, Mendocino, Douglas fir. The impact of P. ramorum oak species. Hosts with relatively small Sonoma, Napa, Solano, Marin, Contra infection on Douglas fir is also not yet lesions may be especially important in Costa, Alameda, San Mateo, Santa clear (Davidson, Garbelotto et al. 2002). the transmission biology of P. ramorum Clara, Santa Cruz and Monterey. The We recovered the pathogen from in- because such lesions do not kill leaves levels of infestation vary significantly fected branch tips of Douglas fir at a but can support abundant sporulation among counties. While large areas single location in Sonoma County. for extended periods of time. within Marin, Santa Cruz, Sonoma and Cankers on small branches 0.2 to 0.4 Multiple plant hosts and epidemics. Monterey counties are severely af- inches (0.5 to 1 centimeters) in diameter The hypothesis that P. ramorum may fected, the disease is still sporadically resulted in wilting and dieback of need multiple plant hosts to cause epi- present in all other counties. It has been branches and needles. Greenhouse in- demics is also supported by the results hypothesized that P. ramorum may

http://danr.ucop.edu/calag • JANUARY-MARCH 2003 21 Natural spread of the disease in California will be affected by weather patterns and by presence of genetic resistance in susceptible hosts. thrive in cool and moist environments; ing in a protected environment within tion of coast redwood and Douglas fir. if so, the extent and severity of diseases the plant tissue. However, the observation of P. ramorum that it causes may be correlated to tem- Based on the data currently avail- in the xylem of a large coast redwood, perature and moisture conditions. able, the intensity of the disease should the results of the inoculation studies P. ramorum growth is optimal at tem- be positively correlated with cool and for both conifers, and the detection peratures between 64.4°F and 71.6°F moist conditions. Further research, of P. ramorum in dying sprouts and (18°C and 22°C)(Werres et al. 2001). however, is under way to precisely branches suggest that the situation Laboratory trials recently showed that quantify the parameters associated requires more extensive research. the infection rate for bay leaves may with disease expression. The apparent limited gene pool of average 92% at 18°C, but only 50% and P. ramorum in , com- Landscape-level forest changes 37% at the less favorable temperatures bined with the extreme susceptibility of of 53.6°F and 86°F (12°C and 30°C), re- A broad host range and predomi- some hosts and the pathogen’s limited spectively (unpublished data). Besides nant clonal reproductive strategy are known area of distribution, suggest an cool temperatures, free water must be not unprecedented in the genus introduced organism, but its actual ori- present on plant surfaces for efficient Phytophthora (Erwin and Ribeiro 1996). gin and global genetic structure remain infection. P. ramorum produces infec- Phytophthora cinnamomi is known to re- unknown. Faced with uncertainty tious propagules called zoospores, produce mostly clonally and to attack about the origin, distribution and host which need to swim in a liquid envi- more than 2,000 plant species; it has range of P. ramorum, and because many ronment in order to reach a susceptible caused significant ecological damage to of the known hosts have ranges well host. Preliminary studies indicate that forest ecosystems in Australia, Europe beyond California, the , a minimum of 6 to 12 hours of free- and North America. The broad host Canada, and South standing water is required for infection range of P. ramorum, the variability of Korea have implemented quarantines of bay leaves. Rain, fog or dew accumula- symptoms among different hosts and against movement of certain plant ma- tion may result in the formation of a per- the ability of the pathogen to disperse terial and/or soil from California and sistent film of water on plant surfaces. by air, suggest that it may also have the Oregon. The United States has imple- Studies based on isolations of potential to cause similar, long-term, mented similar restrictions on the P. ramorum from infested soil indicate landscape-level changes in California movement of potentially affected that pathogen activity starts after re- forests. Hosts for P. ramorum include plant material from Europe. The dis- peated precipitation events and peaks canopy trees and understory shrubs. covery that even small foliar lesions during spring months (J.M. Davidson The long-term consequences regarding may potentially be epidemiologically and P.E. Maloney, unpublished data). mortality for non-oak hosts are un- important, combined with the difficul- Dry and warm weather in the summer known at this time. However, branch ties encountered in culturing the patho- and fall result in a sharp decrease and dieback on these non-oak hosts may af- gen, is proving to be challenging from a eventually complete arrest of P. ramorum fect leaf and seed production, nega- regulatory and monitoring perspective. activity in soil. Activity of the pathogen tively impact growth and regeneration, The use of the DNA-based diagnostic test on living plants can be inferred by the and predispose the plant to attacks by outlined here offers a reliable approach to isolation success of P. ramorum from other pathogens and insects. Sublethal detect P. ramorum, follow its movement and symptomatic plants in the field. Results infections of non-oak hosts may also al- ultimately understand its biology. from 2 years of collections indicated low P. ramorum to persist indefinitely in While regulatory actions may pre- that isolation success from living infested forests and affect the success of vent the spread of P. ramorum to new plants decreases sharply in the future regeneration and restoration ef- areas, California coastal forest ecosys- summer and fall without ever forts. It is unclear at this time what tems are currently witnessing an ex- reaching zero. This is probably the long-term consequences will be pansion of the infestation. Natural because P. ramorum is grow- for the harvesting and regenera- spread of the disease in California will

California black oak Tanoak Coast live oak California buckeye

22 CALIFORNIA AGRICULTURE, VOLUME 57, NUMBER 1 In order to assist the natural recovery of the ecosystem it is essential to fully understand the pathogen’s biology and identify forest management approaches that can hinder its spread. be affected by weather patterns and by Davis. This research was supported by grants 2002. Sudden oak death caused by Phytoph- presence of genetic resistance in sus- from the USDA Forest Service and the thora ramorum in Oregon. Plant Dis 86:441. Hardy G, Barrett S, Shearer BL. 2001. The ceptible hosts. Preliminary studies Gordon and Betty Moore Foundation. We future of phosphite as a to control (Dodd and Garbelotto, unpublished greatly appreciate the technical assistance the soilborne plant pathogen Phytophthora data) indicate that individuals of both of A. Wickland, S. Murphy, S. Kane, cinnamomi in natural ecosystems. Austra- bay laurel and coast live oak display C. Jensen, G. Slaughter, D. Schmidt, lasian Plant Pathol 30(2):133–9. Kelly NM, Meentemeyer R. 2002. Land- different levels of disease resistance. J. Tse, T. Harnik, K. Hayden, A. Smith, scape dynamics of the spread of sudden oak In order to assist the natural recov- W. Van Sant and D. Henderson. The death. Photo Eng Rem Sens 68:1001–9. ery of California’s forest ecosystems, it European isolates were provided by Maloney PE, Rizzo DM, Koike ST, et al. 2002. First report of Phytophthora ramorum is essential to fully understand the S. Werres, with additional samples on coast redwood in California. Plant Dis pathogen’s biology and identify man- from E. Hansen, K. Bovero, R. Gross, 86:1274. agement approaches that can hinder its S. Tjosvold and P. Mordike. Comments Rizzo DM, Garbelotto M, Davidson JM, et spread. In Western Australia (Hardy et on the manuscript by T. Bruns and al. 2002a. Phytophthora ramorum and sud- den oak death in California: I. Host relation- al. 2001), targeted chemical treatments E. Hansen were greatly appreciated. ships. In: Standiford R, McCreary D, Purcell may have significantly slowed down KB (eds.). Proc 5th Oak Symposium: Oaks in References the spread of the disease. Results from California’s Changing Landscape. Oct. 22–5, a series of ongoing studies (Garbelotto, Davidson JM, Garbelotto M, Koike ST, 2001. San Diego, CA. USDA Forest Service, Rizzo DM. 2002. First report of Gen. Tech. PSW-GTR-184. p 733–40. Rizzo and Marais 2002) indicate that it Phytophthora ramorum on Douglas-fir in Rizzo DM, Garbelotto M, Davidson JM, et may be possible to employ chemical California. Plant Dis 86:1274. al. 2002b. Phytophthora ramorum as the treatments to prevent infection on indi- Davidson JM, Rizzo DM, Garbelotto M. cause of extensive mortality of Quercus spp. and Lithocarpus densiflorus in California. vidual trees (see p. 6). The availability 2002. Phytophthora ramorum and sudden oak death in California: II. Pathogen trans- Plant Dis 86:205–14. of such treatments, and their careful ap- mission and survival. In: Standiford R, Swiecki TJ, Bernhardt E. 2002. Evaluation plication, may add a useful tool to an McCreary D, Purcell KB (eds.). Proc 5th Oak of stem water potential and other tree and integrated control approach for this Symposium: Oaks in California’s Changing stand variables as risk factors for Phytoph- Landscape. Oct. 22–5, 2001. San Diego, CA. thora ramorum canker development in coast ecosystem-level disease. USDA Forest Service, Gen. Tech. PSW-GTR- live oak. In: Standiford R, McCreary D, 184. p 741–9. Purcell KB (eds.). Proc 5th Oak Symposium: Erwin DC, Ribeiro OK. 1996. Phytophthora Oaks in California’s Changing Landscape. Diseases Worldwide. St. Paul, MN: APS Press. Oct. 22–5, 2001. San Diego, CA. USDA Forest Garbelotto M, Rizzo DM, Hayden K, et al. Service, Gen. Tech. PSW-GTR-184. p 787–98. M. Garbelotto is Extension 2002. Phytophthora ramorum and sudden Vos P, Hogers R, Bleeker M, et al. 1995. Specialist and Adjunct Professor, Depart- oak death in California: III. Pathogen genet- AFLP: A new technique for DNA fingerprint- ment of Environmental Science, Policy and ics. In: Standiford R, McCreary D, Purcell KB ing. Nucleic Acids Res 23(21):4407–14. Werres S, Marwitz R, Man In’T Veld WA, Management (ESPM), UC Berkeley; J.M. (eds.). Proc 5th Oak Symposium: Oaks in California’s Changing Landscape. Oct. 22–5, et al. 2001. Phytophthora ramorum sp. nov., Davidson is Postdoctoral Researcher, Depart- 2001. San Diego, CA. USDA Forest Service, a new pathogen on Rhododendron and ment of , UC Davis and Re- Gen. Tech. PSW-GTR-184. p 765–74. . Mycol Res 105:1155. search Associate, Pacific Southwest Research Garbelotto M, Rizzo DM, Marais L. 2002. Station, USDA Forest Service, Berkeley; Phytophthora ramorum and sudden oak death in California: IV. Chemical control. In: K. Ivors is Postdoctoral Researcher, ESPM, Standiford R, McCreary D, Purcell KB (eds.). UC Berkeley; P.E. Maloney is Postdoctoral Proc 5th Oak Symposium: Oaks in Researcher, Department of Plant Pathology, California’s Changing Landscape. Oct. 22–5, UC Davis; D. Hüberli is Postdoctoral Re- 2001. San Diego, CA. USDA Forest Service, Gen. Tech. PSW-GTR-184. p 811–8. searcher, ESPM, UC Berkeley; S.T. Koike is Garbelotto M, Svihra P, Rizzo DM. 2001. Farm Advisor, UC Cooperative Extension, Sudden oak death syndrome fells three oak Salinas ; and D.M. Rizzo is Associate Profes- species. Cal Ag 55(1):9–19. sor, Department of Plant Pathology, UC Goheen EM, Hansen EM, Kanaskie A, et al.

Bay laurel Big leaf maple Madrone Coast redwood Douglas fir

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