Natural infection of new hosts by hemlock dwarf mistletoe

8 Pages·1994·0.48 MB·English

by  Mathiasen, Robert L

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Rocky Great
Mountai—ns Southwest Plains
Research Note
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RM-RN-530
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December 1994
USDA
Forest Service
Rocky Mountain Forest and
Range Experiment Station
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New Om on
Natural Infection of Hosts
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by Hemlock Dwarf Mistletoe
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Robert L. Mathiasen 2:0
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New and additional host/parasite combinations for hemlock dwarf
mistletoe based on natural infection are reported from Oregon,
Washington, and Alaska. A summary of the host range of hemlock
dwarf mistletoe based on natural infection and artificial inoculations
is included.
Keywords: Arceuthobium tsugense, hemlockdwarfmistletoe, hosts
Introduction mertensiana (Bong.) Carr.) but also commonly para-
sitizesPacificsilverfir(Abiesarjiabilis(Dougl.)Forbes),
Hemlock dwarf mistletoe (Arceuthobium tsugense noble fir (Abies procera Rehd.), subalpine fir (Abies
(Rosendahl)G.N.Jones)parasitizesseveralcommer- lasiocarpa(Hook.)Nutt.var. lasiocarpa)andwhitebark
cially important conifers in the Pacific Northwest pine (Pinus albicaulis Engelm.) (Hawksworth et al.
(Hawksworth and Wiens 1972, Smith 1969). This 1992) (Table 1). Mountain hemlock dwarf mistletoe
dwarfmistletoeisdistributedfromthecentralSierra occasionally parasitizes western white pine (Pinus
Nevada inCalifornia throughOregon, Washington, 772ontzco/flDougl.)(Hawksworthetal.1992,Mathiasen
and British Columbia into southeast Alaska. Its and Hawksworth 1988) and is rarely found on
known elevational range is from near sea level in Brewer's spruce (Picea breweriana S. Wats.)
m
BritishColumbia and Alaska to about2,500 inthe (Hawksworth 1987).
central Sierra Nevada. Westernhemlockdwarfmistletoe(subsp. tsugense)
The presenttaxonomic treatmentofthis mistletoe consists of two morphologically indistinguishable
consistsoftwo subspecies (Hawksworthetal. 1992): host races: the western hemlock race and the shore
subspeciestsugense-westernhemlockdwarfmistle- pine race (Hawksworth et al. 1992).
toe and subspeciesmertensianae- mountainhemlock The western hemlock race frequently infects
dwarfmistletoe.Themountainhemlockdwarfmistle- westernhemlock (Tsuga heterophylla (Raf.) Sarg.) but
toe primarily parasitizes mountain hemlock (Tsuga alsocommonlyparasitizesPacificsilverfirandnoble
Wolunteer, Rocky Mountain Forest and Range Experiment fir when these hosts occur near infected western
Station. Headquarters is in Fort Collins, in cooperation with hemlock (Hawksworth et al. 1992) (Table 1). It has
Colorado State University. been found parasitizing grand fir (Abies grandis
1
^
—
Table 1. Summary of host susceptibility to mountain hemlock dwarf mistletoe and western hemlock dwarf mistletoe
based on observations of natural infection.
Host susceptibility class
Dwarf mistletoe Principal Secondary Occasional Rare
A.tsugensesubsp.mertensianae Abiesamabilis Pinusalbicaulis Pinusmonticola Piceabreweriana
Abieslasiocarpa Pinuscontorta
var.lasiocarpa subsp.latifolia^
Abiesprocera Tsugaheterophylla^
Tsugamertensiana
A. tsugensesubsp. tsugense Abiesamabilis Abiesgrandis^ Larixoccidentalis
(westernhemlockrace)
Abieslasiocarpa Pinuscontorta Piceaengelmannii^
var.lasiocarpa subsp.latifolia^
Piceasitchensis^
Abiesprocera
Pinusmonticola
Tsugaheterophylla
Pseudotsugamenziesii
Tsugamertensiana
A. tsugensesubsp. tsugense Pinuscontorta Pinusmonticola
(shorepinerace) subsp.contorta
Tsaugaheterophylla
'Susceptibility classes are explained in text.
^Reportedfor the first time in this note based on natural infection.
^Classification ofgrand firas an occasionalhost of western hemlock dwarfmistletoe (western hemlock race) is basedon
Hawksworth and Wiens (1972) (Table 5 andAppendix - Specimens Examined), but this classification needs furtherstudy.
''Reportedas a principal host for the first time in this note.
^Previously reportedhostbased on artificialinoculations by Smith (1965) and Smith and Wass (1979). Reported for the first
time in this note basedon natural infection.
^Classification ofEngelmann spruce as a rare host ofwestern hemlock dwarfmistletoe (western hemlockrace) is based on
Hawksworth and Wiens (1972) (Table 5 andAppendix - Specimens Examined) and on fieldobservations near Trinity, WA,
reported in this note.
^Reportedfrom newlocations in Alaska in this note.
(Dougl.) Lindl.) (Hawksworth and Wiens 1972), but mistletoe, butin 1972 the two races ofmistletoe had
populations of this host/parasite combination need notbeendesignated.Basedonthelistingofspecimens
further study (Mathiasen, unpubHshed). Thisraceis they examined (Appendix - Specimens Examined),
rare on mountain hemlock (Fiddick and van Sickle the western hemlock race is the taxon Hawksworth
1979, Hawksworth et al. 1992, Shaw 1982), western and Wiens reported on Engelmann spruce.
whitepine (Gill 1935, Hawksworthetal. 1992), Sitka The shore pine race primarily parasitizes shore
spruce (Picea sitchensis (Bong.) Carr.) (Hawksworth pine (Pinus contorta Dougl. ex Loud, subsp. contorta)
1987, Laurent 1966, Molnar et al. 1968) and coastal (Hawksworthetal. 1992,SmithandWass1976,Wass
Douglas-fir(Pseudotsugamenziesii(Mirb.)Francovar. 1976). It rarely occurs on western white pine
menziesii) (Hunt and Smith 1978). Hawksworth and (Hawksworthetal. 1992,HuntandSmith1978,Kuijt
Wiens (1972) reported Engelmann spruce (Picea 1956)andwesternhemlock(Hawksworthetal. 1992,
engelmannii Parry) as a rare host for hemlock dwarf Smith and Wass 1979, Wass 1976) (Table 1).
2
Inoculationstudies have demonstrated thatsev- %vas based on shoot morphologv (primarilv shoot
eral other trees are susceptible to hemlock dwarf size and color), host infection and elevation
mistletoe (western hemlock race). By artificially (Hawksworth and Wiens 1972, Hawksworth et al.
inoculating seedlings and trees in greenhouses, 1992).
plantations, or in the field the following trees have
been shown to be susceptible to ^vestern hemlock Western Hemlock Dwarf Mistletoe
dwarfmistletoe: easternhemlock(TsHgti canadensis
(L.) Carr.) (Wier 1918), western hemlock from the Western hemlock dwarf mistletoe (western hem-
interior of British Columbia (Smith 1965, Smith lock race) was found parasitizing lodgepole pine
and Wass 1979), lodgepole pine {Pmiis contorta {Pinus contorta subsp. latifolia) near Trinitv, Chelan
WA
Dougl. ex Loud, subsp. latifolia (Engelm. ex Wats.) Countv, (near the confluence of Phelps Creek
Critchf.) (Smith 1965, 1974^ Smith and Wass 1979), and the Chiwawa River approximateh' 26 km north
white spruce {Picea glaiica (Moench) Voss) (Smith ofLakeWenatchee,48', 04' X., 120^ 51' W.). Several
1965, 1974), Xorway spruce {Picea abies (L.) Karst.) infected lodgepole pine were growing near hea\'ilv
(Smith1965),westernlarch{LarixoccidentalisNutt.) infectedPacificsilverfir. Shootproduction^vascom-
(Smith 1970, 1974), ponderosa pine {Pinus ponde- mon and prolific on all infected lodgepole pine. Xo
rosa Laws.) (Smith 1974, Smith and Craig 1968), infected lodgepole pine ^vere observed near infected
Monterev pine {Pinus radiata D. Don) (Smith 1974, ^vestern hemlock.
Smith and Craig 1968), Scots pine {Pinus sylvestris To estimate natural susceptibilitv of lodgepole
L.) (Smith 1974, Smithand Craig 1968) and^interior pine to \vestern hemlock dwarf mistletoe
Douglas-fir {Pseudotsuga menziesii (Mirb.) Franco (Ha^vksworth and ^Viens 1972), temporary- circular
var. glauca (Beissn.) Franco) (Smith 1974, Smith plots(radius6m)wereestablishedaround10heavily
and Wass 1972). Smith (1974) successfully infected infectedPacificsilverfirgroovingnearinfectedlodge-
western white pine and grand fir with the shore polepine. Eachtreegreaterthan 10 cmindiameterat
m
pine race ofwestern hemlock dwarf mistletoe, but breast height (1.4 above the ground) in each plot
not with the western hemlock race. In addition, wasexamined fordwarfmistletoe infectionsand the
Smith (1974) was unable to artificially infect Sitka following data recorded: species, diameter (nearest
spruce even though the western hemlock race 2.5 cm), and dwarf mistletoe rating (Hawksworth
does rarelv infectthis hostinnature (Hawksworth 1977). Almost 10'~c of the lodgepole pine g^o^ving
1987, Laurent 1966, Molnar et al. 1968). Artificial nearinfected Pacific silverfirwere infected (Table2).
inoculations using seeds of mountain hemlock This level indicates that lodgepole pine should be
dwarf mistletoe (subsp. mertensianae) have not classified as an occasional host of western hemlock
been attempted. dwarf mistletoe based on the host susceptibilitv
This note reports ne'w hosts for hemlock dwarf classificationsvstemusedbvHawks^vorthandWiens
mistletoe based on field observations made in Or- (1972). Their svstem ranks susceptibilitv according
egon and Washington in 1993. Some of these host/ to the percentage of infected trees within 6 m of
parasitecombinationshavebeenpreviouslyreported, heavilyinfectedprincipalhosts.Susceptibilit}'classes
based on artificial inoculations as mentioned above, are as follo^vs: principal host - 91-lOO^c infection;
but this is the first report of these host/parasite secondary- - 51-90% infection; occasional - 5-50%
combinationsoccurringnaturally. Additionaloccur- infection; rare - 1-4% infection; immune - no infec-
rencesofhemlockdwarfmistletoeonrarehostsfrom tion.
new locations in Oregon, Washington, and Alaska Heavyinfection ofsubalpine fir and Pacific silver
are reported also. Table 1 summarizes the host sus- fir by western hemlock dwarf mistletoe was ob-
ceptibilit}^ for the western hemlock and mountain ser\'edattheTrinit\'location.Tentemporary'circular
hemlock dwarf mistletoes based on obser\'ations of plots (radius 6 m) wereplaced around infectedwest-
natural infection. Specimensrepresenting the differ- ern hemlock to estimate natural susceptibilit\' of
ent host/parasite combinations are deposited at the subalpinefirandPacificsilverfirtowesternhemlock
USDA Forest Service Forest Pathology Herbarium dwarf mistletoe in this area. Data were collected as
(FPF) at Fort Collins, CO. Identification of the hem- described above. Infection was greater than 90% for
lock dwarf mistletoe populations described below both subalpine fir and Pacific silver fir, indicating
3
—
Table 2. Percentage of trees greater than 10 cm in diameter Infected by the
western hemlock dwarf mistletoe that were growing within 6 m of
severely infected western hemlock or Pacific silver fir near Trinity, WA
(20 plots).
Tree Number Mean Percent Mean dwarf
species sampled diameter (cm) infected mistletoe rating
Pacific silver fir 196 26 96 3.9
Subalpine fir 118 24 91 3.1
Western hemlock 21 14 57^ 1.3
Lodgepole pine 64 17 9 0.3
Engelmann spruce 36 22 3 1.0
Douglas-fir 16 38 0 0
Western white pine 12 20 0^ 0
Grand fir 9 14 0 0
Mountain hemlock 7 18 02 0
Western hemlock was not wellrepresentedin the understory and trees were small and
lightly infected.
^Infected trees ofthis species were observed elsewhere in the area.
that both species are principal hosts (Table 2). In developed and allowed foridentificationofwestern
addition, mean dwarf mistletoe ratings for these hemlock dwarf mistletoe. This is the first report of
species (greater than 3.0) indicates that they are western hemlock dwarf mistletoe on mountain
highlysusceptibletowesternhemlockdwarfmistle- hemlock in Oregon. All other reports of parasitism
toe (Table 2). This is the first report of infection of by hemlock dwarf mistletoe on mountain hemlock
subalpine fir by western hemlock dwarf mistletoe. from Oregon are based on infection by mountain
Other reports of hemlock dwarf mistletoe on subal- hemlock dwarf mistletoe (Hawksworth et al. 1992).
pine fir are based on parasitism by mountain hem- Another collection of western hemlock dwarf
lockdwarfmistletoe (Hawksworthetal. 1992). Why mistletoe parasitizing Sitka spruce was located near
infectionofwesternhemlockinthesestandswasless Halleck Harbor in Saginaw Bay, Kuiu Island, AK
thanthatonPacificsilverfiroronsubalpinefirisnot (56°, 28' N., 134°, 13' W.). One infected tree was
clear (Table 2), but may relate to the lower density growing among several heavily infected western
andsmallsizeofwesternhemlockinsampledstands. hemlock. Several branches on the spruce had large
Other trees were observed to be infrequently in- swellings, but no shoots. Dr. Frank Hawksworth,
fected by western hemlock dwarf mistletoe in the Rocky Mountain Forest and Range Experiment Sta-
Trinity area as follows (Table 2): Engelmann tion, examined these specimens and confirmed that
spruce - six trees; western white pine - two trees; they contained dwarf mistletoe tissues (cortical
mountain hemlock - two trees. Considerable shoot strands and sinkers).
productionwasobservedonallinfectedtrees.Thisis Few specimens ofwesternhemlockdwarfmistle-
the first report of western hemlock dwarf mistletoe toe have been collected from Sitka spruce
on these hosts in Washington (Hawksworth et al. (HawksworthandWiens1972,Laurent1966,Molnar
1992). et al. 1968). Specimens of this host/parasite combi-
Another population of western hemlock dwarf nation at FPF indicate that infections infrequently
mistletoeparasitizingmountainhemlockwasfoundat produce shoots (personal communicationwithC.G.
WapinitaPass,ClackamasCounty,OR,approximately Shaw III, 1994). Only two of five specimens ofhem-
17kmsouthofMountHood (45°, 14' N., 121°,42' W.). lock dwarf mistletoe on Sitka spruce at FPF have
Infectionofwesternhemlockand Pacific silverfirwas shoots. Only one of these, a collection made by M.
common in this area but rare on mountain hemlock McWilliams and R. Nathenson near Edna Bay,
(only two infected trees observed), although many Kosciusko Island, AK (55°, 57' N., 133°, 29' W.), has
mountainhemlockwereinthestand.Fewshootswere nearly mature fruits. This demonstrates that hem-
found on mountain hemlock, but they were well lockdwarfmistletoe canreproduce onSitka spruce.
4
Mountain Hemlock Dwarf Mistletoe Island, AK, is greatly appreciated. Dr. Charles G.
Shaw III, Rocky Mountain Forestand Range Experi-
Mountain hemlock dwarf mistletoe (subsp. ment Station, Fort Collins, CO, provided informa-
mertensianae) was rarely found parasitizing lodgepole tiononhemlockdwarfmistletoe/Sitka spruce speci-
pine{Pinuscontortasubsp.latifolia)nearMcKenziePass, mens at FPF and provided many useful suggestions
Lane Count}', OR (44°, 15' N., 121°, 48' W.). Hemlock for improving the manuscript.
dwarfmistletoe (undoubtedly the mountain hemlock
subspecies)haslongbeenknowntoseverelyparasitize
mountain hemlock, subalpine fir, and whitebark pine
atthislocalit}'(Gill1935,Hawksworthand\Viens1972);
however, this is the first report of mountain hemlock Literature Cited
dwarf mistletoe on lodgepole pine. Onlv one small
infectedlodgepolepinegrowingnearaheavilyinfected Fiddick, R.L.; van Sickle, G.A. 1979. Forest insect and
whitebarkpinewasobsen'ed. However,thelodgepole disease conditions, British Columbia and Yukon/
pine had several infections and each infection had 1979. Pacific Forest Research Centre Report BC-X-
producedseveralmistletoeshootsthatcouldbeidenti- 200. Canadian ForestService. 20p.
fied as mountain hemlock dwarf mistletoe. Although GUI, L.S. 1935. Arceuthohium in the United States. Con-
the principal dwarf mistletoe of lodgepole pine, necticutAcademv ofArts and Science Transactions.
ArceuthohiumamericanumNutt.exEngelm.,doesoccur 32: 111-245.
approximately 6 km west of McKenzie Pass Hawksworth, F.G. 1977. The 6-class dwarf mistletoe
(Hawksworth and Wiens 1972), it has not been ob- rating system. Gen. Tech. Rep. RM-48. Fort Collins,
ser\'edintheimmediatevicinit}'ofMcKenziePassand CO: U.S. DepartmentofAgriculture, Forest Ser\"ice,
is morphologically quite distinctfrom mountainhem- Rocky MountainForestand Range Experiment Sta-
lock dwarf mistletoe (Hawksworth et al. 1992, tion. 7 p.
Hawksworth and Wiens 1972). Ha^vksworth, F.G. 1987. Taxonom}' of hemlock dwarf
Hawksworth et al. (1992) reported that mountain mistletoe. Proceedings of the 34th Western Interna-
hemlockdwarfmistletoe(subsp. mertensianae)hadnot tional ForestDisease Work Conference, 45-46.
beenfound parasitizingwesternhemlock,evenwhere Hawksworth, E.G.; Wiens, D. 1972. Biologv and classi-
this tree is closely associated with infected mountain ficationofdwarfmistletoes {Arceuthohium). Agricul-
hemlock. A western hemlock infected by mountain ture Handbook No. 401. Washington DC: U.S. De-
hemlock dwarf mistletoe has now been located ap partment ofAgriculture, ForestSer\ice. 234 p.
proximately 4 km southeast of Shuksan, Whatcom Hawksworth,E.G.;Wiens,D.;Xickrent,D.L.1992.New
WA
Count}', neartheMountBakerHighwavatBaglev Western North America taxa of Arceuthohium
Creek(48°,52' N., 121°, 38' W.). Infection ofmountain (Viscaceae). Novon. 2: 204-211.
hemlockandPacificsilverfirwascommoninthisarea. Hunt, R.S.; Smith, R.B. 1978. Natural infection of two
Althoughtherewerese\'eralwesternhemlockgrowing new hosts by hemlock dwarf mistletoe in British
near severely infected mountain hemlock and Pacific Columbia.CanadianPlantDiseaseSur\'ey.58:31-32.
silverfirthroughoutthearea,onl\'oneinfectedwestern Kuijt, J. 1956. A new record of d^varf mistletoe on
hemlock was obser\'ed. Therefore, western hemlock lodgepole pine and western white pine. Madrono.
shouldbeclassifiedasararehostofmountainhemlock 13: 170-172.
dwarfmistletoe.Severalinfectionswereonthewestern Laurent,T.H. 1966. Dwarfmistletoe on Sitka spruce - a
hemlock,butonlyafewhadproducedshootsandnone new host record. Plant Disease Reporter. 50: 921.
ofthese had mature fruits. Mathiasen,R.L.;Hawksworth,F.G. 1988.Dwarfmistle-
toes on western white pine and whitebark pine in
northern California and southern Oregon. Forest
Acknowledgments
Science. 34: 429-440.
Molnar,A.C.; Harris,J.W.; Ross D.A.; Ginns,J.H. 1968.
The assistance of Dr. Paul Hennon, USDA Forest British Columbia region. Canadian Department of
AK
Ser\ice,Juneau, withthecollectionofspecimens Forestr}' and Rural Development Annual Report.
ofhemlockdwarfmistletoe onSitka spruce onKuiu Forest Insect and Disease Sun'ev. 1967. 108-124.
5
Shaw,C.G. 1982. MountainhenJockis [an] occasional Smith, R.B.; Wass, E.F. 1972. Douglas-fir, a new
host for hemlock dwarf mistletoe in Alaska. Plant host for hemlock dwarf mistletoe. Bimonthly
Disease. 66: 852-853. Research Notes. Environment Canada, Forest
Smith, R.B. 1965. Some results ofartificial inoculation Service. 28: 15.
with western hemlock dwarf mistletoe seed. Bi- Smith, R.B.; Wass, E.F. 1976. Field evaluation of
monthlyProgressReport. CanadianDepartmentof ecological differentiation of dwarf mistletoe on
Forestry. 21: 3-4. shore pine and western hemlock. Canadian
Smith,R.B.1969.Assessingdwarfmistletoeonwestern Journal of Forest Research. 6: 225-228.
hemlock. ForestScience. 15: 277-285. Smith, R.B.; Wass, E.F. 1979. Infection trials with
Smith,R.B.1970.Infectionofwesternlarchbyhemlock threedwarfmistletoespecieswithinandbeyond
dwarf mistletoe. Bimonthly Research Notes. Cana- their known ranges in British Columbia.
dianDepartmentofFisheriesand Forests. 26: 16-17. Canadian Journal of Plant Pathology. 1: 47-57.
Smith, R.B. 1974. Infectionand developmentofdwarf Wass, E.F. 1976. Ecological study of shore pine
mistletoes on plantation-grown trees in British Co- stands infested with dwarf mistletoe on
lumbia.PacificForestResearchCentreReportBC-X- southeastern Vancouver Island. Pacific Forest
97. Canadian Forest Service. 21 p. Research Centre Report BC-X-142. Canadian
Smith, R.B.; Craig, H.M. 1968. Infection of Scots, Forest Service. 33 p.
Monterey,andponderosapinesbywesternhemlock Weir,J.R. 1918. Experimental investigationsonthe
dwarf mistletoe. Bimonthly Research Notes. Cana- genusRazoumofskya. Botanical Gazette. 56: 1-31.
dian Department of Forestry and Rural Develop-
ment. 24: 10-11.
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