YELLOW L:%MHNA'I'ED ROOT ROT OF DOUGLAS FIR1

Abstract Yellu~s~ laminated ror~t rot occ:urs in 111ost tlalive cc~riifcrs throlnghoirt the range

(if LPougla,5 iir in Rritisk Coliitnbia. 'I'hv c~itlsc of this disease has txen ascribecf to 3 vltriety of iJortn weir i i ABurr., or a spctc:ies of Z'oria distinct from 13. weirii . r . 1 hct f~in!:us grow:+ from infected to he:llthy roots throug11 p11ysioIogir;illy weal;- c.~~etP c:ont.acting ;)uints or f~~sioils, ar~rl thc tiisease is inost prevalent i l l I)i)11g9'1as fir 1iec:a:lse of thc common occurrcs~cv: of root fusion in this species. Hlouglas fir is suxxptit)lc a t a n y age over six ycars brnt intii\.:idual trees show marl& differ-

r . cnc:es in their resistancr 10 1iiilir:g by the tli+easc. H hc symptom picture xrai-ies g!-c;ltly I~i t%s~t :n infected trees xncl is tlircctly rclatvcl to the resistance shown 1-~y the intlivid~ial host. T n o c u l ~ ~ i ~ ~ u-aay I-cnnnin viable for over 50 years in sttamps and soots. 'rhe lungus tlocs not appcar t o spread through the soil iior docs i t :I j~pcar to I)e alilc' t ( J peeuclr;ltc healtl~y ~~~~~1; ti*suc. L l ! t houi2;li the c-ontrnl of this tIisc::se Is (:i~rr~:ntly important in Illany 1or.alizetl areas, sevc.ral characteristic:^ ir) t lle beha:-ior of the causal f ilelgus indicatc that it sviil t)ecorne mcsre inlyort;\nt a5 i'~~.:!ri;~ge:i1~11t of secoud groivtla llouglas tir forests t)ecornes more inteilsive.

Introduction

Yellow 11;lt~linar~ted root rot was first ol~servecl a t the Forest Experiment S ta~ion , I,;~ke ('owit-lln11, Vancouver Isl,~n(l (Fig. I : I * ) in 1929, a n d has since heen found to be prevalent throughout ihc cornnlercial range of Dougl,ss fir (F'se7idofszegc~ taxQoJia tPois.) Hriti.) in 8-Sritisl-a C:ol~rnil~in. hlounce, Bier, and Not~Ies (7) clcscriB,cd the cliseasc aard the causal fungus in 1940, Bier ancl Hi~ckl;~~-td (1) dcscrit~td ct:xmctge caused by the disease in 1947, asad I3rr~h;en;tn ( 5 ) reported on its o ~ c ~ i a - r ~ a ~ ~ ~ in 1948. ,. B he distril)~ltio14 of' the tliscxse and the nature of its spread through estalilishecl plots were studied between 1939 dnd 1950. ?'his paper sunmrnarizes the results of' thcsc studies and other Gcltl ol~scrvations.

Cause s f the Tlisease

P>escrit,ing the Iirngus carrsing j.cllrnv Bnnlina-tcd root- rot of I>ouglns fir, hlIouncc., Uicr, ;tntl Nobles (7) stated: '':IIthougifa differing sotnewhat l r o ~ n PoP~c~: weirl'i J'lrrrr. :IS it is I o u ~ ~ i f on n-(:stern retP cedar (Il'hujn pl~zeata 11. Dora.) , fungus w-o11Itl s:.rbrn to be tll.lt species or a forrrl of i t occurring oam lIoilg1,ts fir." r , C lie ~ ) r t ' s c ~ ~ t i n v ( ~ s t i ~ ' ~ t i o ~ ~ s inclicntc: tll,st the. f~ t l lg i l s causing ycllow lnrni~aated root rot of I.>o~tg-l:~s fir is ;L v;~riety of P. wetrii or a species of Porin distinct: from 13, weir?,%.

,ldilti2!~;.rtpi ~ S C P ~ C I C ~ I bSe$tenzher lil, I'P-$2. I,'ont~,ii',:~f:iol;: No. 66, Din,.ision of Forest Biolnpy, St.ience Service, Department r l f ,Agrz'-

cubi!:re, Otr'a7iy~. 7'he .si?~dy 701:s ccrvried ou! .i~ili? tile suflflnrt (if t72e R,h?..szon (1.f Forest Bzology, LI.;cl;ent:c Sr:rn.i(.,,, !?r,fi,r r t f i~en t :;/ rlgricrllture, (?tt/~7;ji~ ; the U n , i ; ~ ~ ~ s i t y (tf British. Ghlumhit~ Resetrre:h Clo~ntpt!itfe~, 17:!ncori;!er, B. C. ; //LC: N(L/ ionc1.2 Rr.ce:rrclz, C,'c~zirrcil, Ottcr wn; nnrt the I 'u~~lel l diizer (I,70mk~: ~ 3 7 L'L'li! ited, L,7c!rr~o IIZYJY.

\lssqcic~ie 19ro.fess!~r 1,f Forest I'u!l?(dngy, I+il:lersi!y (;f Br i t i sh C,'oizimbia; formerly A~riczalt ,~rnl; Resecirch ( ) f i c t ~ , I~i~~is.io.ri. (I!! Liotcr-7iy ilttd I'ltlnt I'nthology, ,Sciertce Service, Depart- ? i ~ ~ n ! oJ A2vicirlf ilrp. I'ictoriu, B . C:.

\,.lnrdc;r,lti~r/if Rcseirrch r!$(:er, P)ln~z's.L'o?z ( ! f Forest Biology, Science Service, T.,7ictorlrc, ulzd iiesenrcli 13 ssi.\'intrt. r:'ni~4rrsil:y o-f Eriti.s/? I k , l :~n? fG~.

Q,yric~!lizirtrl liese(rrc:h O j i c ~ r , I1i.iisioi.l 1 4 Forest Biology, Science Serz~ice, I,'ic:toricr., I3.C:. " N1~7a~hi:rs i-,! i tc~l ics r f jer to loca l i t i~ s mizrked ( 1 1 2 the dds!ributio~z mop, Fig. I .

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70 C A N A D I A N JOURNAL OF H07' r lNY. V O L . 32

A comparison was 111ade between 75 isolates fro111 yellow laminated root rot of Douglas fir ( A ) and 35 from yellow ring rot of western red cedar (B), groaa-n for two urccks a t room temperature on 2';f, Difco ~ n a l t agar. Cultures from A varied noticeably in shades of Isro\vrira, com~nonly with cream to cinnamora toncs, while cultures from 23 werc tanifornlly Izrown, with yellow or tawny toncs. The margin of the advancirlg zone of cultures from A was raised, and the mat felty with white aerial hy~pllac, aa~llilc the margin of the advancing zone of culturcs fro111 B was ;tpprcssed, and the mat cottony with yellow t o tan aerial hyphae.

When iso1;ltes from A ;ind B were grown separately in paired cultures thtly showed no signs of antagonism, but when grown together they developed :en ant;rgonistic zone line.

Cailt~~rcs from A rarely attack blocks of western red cedar i~loc~aldted in zitro, but cover Ilo~aglas fir I~locks cluite rapicily with mycelium, advancing with an even, raised white margin. The mat producctl is creamy brou-n, thick, , ~ n d feltg-, arltl will often clevelop large chocolate-brown crusts upon its s~xrfnce. These resemble initial sporophore formation, but do not develop to the fruiting stage. Jnoculation of similar blocks with cultures from B rcsults in growth on both species of \vc:e,od, although rather Inore luxuriarltly upon tlae L)ougl:-ts fir. Each block is rapidly covered with long feathery extensions of the thin, cc~ttcsny, yellow-Ijrown rnat.

,A m:xcroscopic connparison was made be1 ween 85 sporophores associated wit11 A and 42 sporo~)hores associated with B. Thc sporopl-nores of A (Fig. 2) were S u d ~ brown (10) with tones of cinnamon, pink, and p u r ~ ~ l e , ;anti, a t maturity, frcqueratly had a rough coarse surface. These fruit-bodies are annu:~l, occ;ssionally with a second layer of tubes arising irom the substrate and forming on the surface of small sectiotls of the old sporophore. The sporophores of B (Fig. 3), on the otllcr hat-td, :ere more ~111iformIy coIored, being Suda~i brown (20) with ~ ~ c l l o w lo tawny toncs. The mature sporoyllore has a finely textured smooth surface. In particular v;lrirmce with the sporo- phores of A , those of B arc pcre~lnial. con~monly iornlirlg urlifornl t~abe %:tyers for six or more years. Because of this the other nlacroscopic ~Iifferences, the fungus c;~using yellow 1;~11linaled root rot of Do~aglas fir will be referred to as "annual" P. zueir?'i, ;mtI that C ~ L U S ~ I ~ ~ yellow ring rut of \vestern red cetfar as "perennial" P. weira'i throughout this paper.

Distribution and Hosts s f the Disease

In Rriiish Colurnbia "ann~aal" P. weirii has been isoIatec1 iron1 Doug-Bas fir thro~aghout the range of that species in and west of the Coast liangc (Fig. I ) . Although isolates have been obtained from many areas in the Interior of the I'rovince, insufficient data I'rorn this region arc available to establish the extreme eastern and northern ranges of the disease.

66~\nnual" P. weirii has been isolated from Douglas fir, western red cedar, nrestei-11 heanloclc (7l~uga heierophylla (Raf.) (Sarg.), grand fir (Abies gra~zdis (Dougl.) Lincll.), nrna1)ilis fir (Abies amubilis (Dougl.) Forb.), Sitka spruce

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BC:CKLA,VD E T Ad,.: ROO?' K07' OF DOUGLAS F I R

FIG. 1. 'I'he occurrence o f yellom- Ianlii~ated root rot in Douglas fir in southern British Colunabia, Each blaclc dot represents one or moru collections o f the disease.

(Picea sitchensis (IZong.) C'arr.) western larch (Lnrix occide?ztalis h-eatt.), n-esttbr~a white pine (Pinats rrzonficola Ylougl.), and ponderosa pine (Pinus po~zderosa I,;Lu~s.). Apparently, if inoculum were present, "annual" 8. weiriz' coultl attack ;any species of conifer under suitable conditions. On the other hanti, "~serenni:tl" P. zcjeirii has not been isolated from any coniferous host other than \vester~~ retl cedar.

"lAnnua19' P. wet'rii has rarely bccrl isolated from hosts beyond the rsatur~~B tlistribaation of Douglas fir. 'The fungus was not recorded in studies of decay in hemlock, spruce, ant1 true fir in the ITpper Columbia Basin, the Queen ('hnrlotte Isl~tnds, or the Prince Gcorge District. Isolates from western hemlock on the west coast of Vancouver fslant-f (4) and thc Upper I<itimat (2) have been ol)t;aia~ed, but in the former case stands of Douglas fir were found on ;~dj:~ccnt sites.

Relation of the Most to the Disease Sprei~d

'I'o ascertain the degree sf spread of "aalnur~l" P. weir;?: through the soil, 24 Tlo~aglas fir k>locks, heavily infected with the fungus, were enlbedded in hammus and mineral soil horizons. Excavation four months later yielded no cuiturcs from tfic adjacent humus, soil, and wood debris. In fact, no isolations ctiuld bc made of ' 6a~nua199 P. weivii from the inoculation bIocks as they had been invaded by secondary soil organisms. In glass tubes containing sterilized

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forest duff or ~ninerrel soil, however, the fungus grew rapidly, extending 23.4 cm. i ~ i t o the tfuff 21ntl 17.3 crn. into the mineral soil by the end of eiglit weeks. In the forest (luff the myceliunn completely perrrmeated the soil, while in the nminer,ll soil the rnjrceliurra was sparse. 'These data , while qualified bj- differ- ences iri environnient, indicate t11,lt soil organisms have an arit,~gonist ic or suppressive :~ction upon "annual" P. weirii, and prevelzt or greatly irrlpeclc its spredtl i hrough the soil under nntaar;~l c-onditions.

Incbcul:~tio~as with woort chips or agar perrnented with ";lr-snu:tlW P. z e i ~ i i failed to produce iilfcctiori ira living trees. Garrett ( 6 ) ;trtd ICishbeth (9) indic,~te t%le s,lrne la(-k of success using a simi1,~r type of inoculun~ with otkcr root distb,~ses. In only two cascs of 36 was inft~ctio~i induced ill mechanically inj~arcd Dor~glns fir roots bjr direct tralismissio~l from lar-gc., k~~~vily-ps.ri l~s.atcd wood bloclis.

Hec;tuse of the failr~re oi i~rtifi(*i;~I Inocil1;~tions anct bec:lust. of tlnc strongly suppra:ssive iecticsn of soil org,rnisnis upon "nnnu,~l" P. yveirii, strldies nT\lc:re rn:tctc sf natural infect ion through root l~rsioils :~nct ; ~ i root cont;~cts ur161cr chronic pla>,siological daaress. Thew c-ont:~cts niay act a s initial infec'tion courts w11eri the root c-onnes into contac-t with another root cither l i~~i r ig (Fig. 4 9 ) , or clead (Fig. 14), 11-hit-11 contains via blc i~loculurn. As evidcnccd bj- a largik nunil)er of t'x(:dv;ltcd roots (Figs. 16, 19, 19, ;md 20), the ~)i-iinci~~;~l nlode of tr,lnsmission is through root fusio~z which fornls a direct pnss:L,gr:

for the hurigus. 0 1 a c . cxc,~vation in ;L 35-year-olcl plot- disclosctl 15 Dougl;ts fir trees f u s d rant% disr.;:scd in a single seric.s.

Since the site and age of ;L s t a r~d deter-~rline tkze anlournt of root fusicsrz 1vliich n-ill occur, thesc two factors arc of pririw im l~o r t , e~ i~e in the spre<ltl of i l ~ e <Bise,~s~. The most r,ipid spread and h~;lvithst c l :~m~~ge ~vill LI.ISII;LIIY he c ~ b s ~ r v t ~ d in stantls 20- to 60-J-c;~rs-oltl irz good, 11-ell-stocked, sites, wllerc t lae numhcr of rn;~jor root coamt;tct s are nt a 1 n-rsixirn~lm. In younger st;incis, root co~at;~cts ;we

11ot SO Iialinerous, since the root systems are not extensive. St;~n(ls cst:el)lished on sites with clecj~ dry st~ils also show little spread, since t l ~ e roots are small : ~ n d fibrous ant1 grow downward, nanini~llizirlg- the ~ilanalber of contac-ts made with ; L ~ . ~ ~ L C C I ~ ~ trees. In older- siands, natural thinnirsg has reduced the nuanher of root conlt,~c t s and the fungus must travel f:ertlla~r betwetbn trees.

01)scrv;ltioizs in L1ougl:~s fir forests indicate tha t 2% site or soil c:rp.a%>lc of salpport ing satisfactory growth in young st :tncis rri:~y support on1~- poor growth , ~ s tlac stand ages. 'This naay be caalsctf by tlae sh:illowness of tlac organic layer in tlae soil, the close proxi~riit j~ of irlzpervioaes 1;lyers or stone rlaasses, or changes or flact uations in the water table (5). illthough the ~-esult;tnt e'rrly declilie in vigor is reportccily :~ssoci;itetl with high iracidcb~lcc of root t-fiscascs (5), it is not alsklally associated wit12 j~ellow laminated root rot. Sites severely :I ffected wi t%a this disease are those which neccbssitiltc or s t i~nul~ l te the proc_luc- tiona of sh:ellow, r ,~di ;~t ing, frequently cont;~c-ting, root systenis. l 'his is dernonstr:itcd 114. studies on the follomring four areas.

In two of these areas (Fig. I : 1 and 6 ) , the t1ise:we w:ls very scaraArc.. A study of unaffectecl trees i~icIic,~ted contiiluous and rapid growth, somewhi~t:

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A l i C K L A N D RT AL.: ROOT ROT Of; DOU(r1,A.Y F I R 73

stimulated hy ikie effects of the thinning causecl by the dise;tse. In a third area (Fig. 1 : Z ) , early growtli of the st:tnd 11xd been good to :z~sproximntely age GO. Beyoaatl this age, grow111 had rxtssed a pecrk and the trees wcrc re;b~%Bi~~g earl)- m;tturity. :I11 exarnin;~taon in(lic;~lccI I hclt the soil was shallow, overlj-ink' lieavy gravel n-itla the root systerris of the trees spre;xd close to the surface. Beyoritf age 60 the site w,ls un;thlc to s~lpport vigorous growtll anel definite clcclirlc in vigor ealsuect. 'f he soot rot fursgl~s h;ad spreatl over approxi- rn;~tcl~' three acres, xncl a t agt: 80, 34(!/; sf thc. s t c d haci %:~11~rm following atti~c-k by the l i a ~ l g ~ s and 4OC% of t%pc st;xn(h~g trclchs urcre i1afccI6-cl ( I 1). :t~iothe~- area (i'ig;. 1 : 8 and 0 ) the soil was S~B;L%%OW ;111d ga-owth mTas never r:!]i~id. At nri c;aril- age ;~clj :ecent roots of thc tPe~lsc reprodt~c-tion were frec~u~~rmtl y in cont:tct and 1;~rg~: ct'tltcrs o f ii~lec t ion ere pres<.nt. I,if t IC 01- 110 stiil-i~e%at ion of gron-tll occtlrred in urinfccted trrhes follo~l-i~ig thirsning of the stanel k q - t hc

r .

disetisc. T he estc~rzsiare sy~i-e;~tl of 11ie disease in the two 1,ttte.p. cdlses ;LI~I)C;LP-CC~

to I~cl inilucncctl by the tiealse g r o ~ v ~ i l r ~ f sh,tlloui roots ; L I I ~ H B I ~ E I ~ ~ * ~ O I I S root cormt.lcts, arld not by the dying Ex~c:k of soots due to '~dverse site conclitionls.

Cil:ir,tcteristic;il1~7, the alisens:. sprcdtfs r;kciially froill the source of irioculum. Ce11ter-3 oh the tlisa::tse 111;~y, tli~1-(lF~)1-(:, I)(: orily ;L I'ew scluaa-e heet when thacrw ar-o few root c o n t ~ ~ r ~ t s , or SIVCB-~L% ;I(-L-~"S iri size TV!ICI~ roots re in freciur.nt contact. Fluut~~~ltioris in the r-,~tc o f sl)rc:,lri of [lie disr.:~sc c,~11 Ipe attrihutc(l ao the vciri;~-tion in thy a-~urraber of root c'oi~t~~c'ts. 'l'liis is a~scn~plifii~ct b ~ r ;L stel(l\' ,ia-c1;1

(Fig. 1 : I j -vvlls.re, in 1035 :it age 381, thc.1-c. wci-cl 43 liviri:; trees ;irmcH 2 clcacl fa-0111

yellow 1anii1a:ktc.d 1-o:)t rot ; in 1990. 31 livillg, 8 clciitl from root rot, :trrc% 4 n ind- tlaroi~11: in 104.5, 26 living. ;tnd 5 di"ta1 from I-oot rot; arid, ilia 1950, 15 living, an(l 1 I dc1,tcI from root rot. 111 very )Tc>alrig st Lands root coi1tnc.t s :lrch ivn- ; L H I Q ~

tlic centers of irifc:ctio~a appe;" to c.~ml,~rge sIowly. Froram approxirnnrcb1y 2 0 t o 60 >-ears of agr1 the roots tlavc hec*ornc closely intc~r\vovc~a ;LI~CI the e ~ ~ i ~ ~ ( ~ r s eri!,~rg:-d. rapidly. Srlbst.cluelr?t t 0 this, the sy~reacl :ippe;~i-s to slcsn~ doi~rl as ;l,~tur<ll thilirning in the stiu~cl h,ls rc~(lucccl I he ii~lmlser oh root corlt,~cts and thc. fun;zus is cht>ckcaf or must ti-;tt'el grts;ttchr slistclncchs t~eforcb lurthcr infthct ion orc~li-s. ,Iusili;~ry conditions 11-llich will give rise to fluctuations in the sprcatI -vvill be high rc~sist:ericc to Iiiliirig 1 1 3 1 tlith clisease i r a inciivitlual trees, chain terrni11,~tic)n d ~ c to l,tctc of root conit:zcts, and scc*o~ldarj- sources of inor.~lla~nil.

1 Iilticl- ri'~t!ar~d conc~itior~s, I)ougl;~s fir over the age of six yti;~rs ;tppear to be c.b~u;tlly susccl~tit)l~ to at B ; L ~ I C 1))' this lairigus. AS ' l ( ~ n n ~ ; ~ l " J p e weir i i had rjcst I)ccar isc18:itcri from any tree uncjit~ SIX yecLrs oi ;tg(> i11 t 1le f i a k l t i , 50 t11rc.t.-ye;er-ol(i srxt.dIiitgs n-itln d.irs?agcd roots in contact wit11 111ocl;s of inict.tec% woocI were grown in aniricral or highly tsrg,triic soil. Thc fungt~s cctlltl ~ o t E,c isol,~tc(l from ,i111~ o f thtx bc.ecllinps ,~fte:.a- ,I itli~iirl~urn expos11i-e of six ~non t l~s .

Kishl~cth (81, disc-ussirig the behavior of Fomes cI;nr,o.ws Fr. on pi11t.s~ points out that t lacy fungils c,ln infcc. t a living roof clirect ly through aloi-ma1 henItliy tissuc>s. In no si~mglc ccis:\ 1 ~ 1 s "',~nnur~l" Y. w e i ~ i i i i c h e ~ n of~served groi~-ing lreihly 011 I lic rc)ot surface or pcnetratirig lle,~lt hy l1a1-1; tissues.

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7 4 C A S A D I A M JOt'KNrtL OF RC)?'A2\T Y . VOL. 32

As isolates which differed markedly in macroscopic appearance were obtained from different individual Douglas fir hosts, there sccnictf t o be :L

possibility that- strains varyirig in virulence might exist in this fungus. Three root excavation studies dc~norlstrated that the rext ion of a tree to attack by the fungus is rel,~ted to resistance to killing by tlie disease rather than t o str'lins in the fungus. After the roots were uncovered, the progress of the fungus wits traced from a source of inoeul~inl tha-ongh a series of fusetl and contacting roots. The form of attack. the symptoms produced, anti the length of time from initial infection to death varied with each intlividual tree without relationship to the proximity of the original infection court (Fig. 19) .

Signs and Sympfsms Sporophores of "annual" P. weirl?; on Douglas fir, western hemlor-k, ancl

grand fir are tgq~ically crustlike, 1 to 2 ft. in1 length, occasio~ially up to 8 f t ., and form 011 the underside of severely tlecayed logs on moist sites (Fig. 2) . 0cc:~sion;~lly snnall irregular sporophores, u p to six inches long. rnay form in root crotches of dead ancl down trees. In shaded moist locations large crusts are also occ;ksionally ]~)roduced oaa the side of S ~ U B T ~ ~ S with the surfare rnised in small mounds or riclgcs for the productio~i of vertical tubes. Sporophores on s t a n ~ l i ~ ~ g livi~lg trees have only bee11 observeci in one regiori where they were produced on dead nrens a t ilme bases of severely deci~j-ed, over-mature Douglas fir (Fig. 1 : 4) .

hlounce, Bier, and Nobles (7) describe the symptoms of yellow latninxted root rot in Douglas fir as follows:

""The first inciic:ition of the presenc-e o f the tliseasc is a I-vtartlation of growth. . . . . 'This is usually accornpa~lieeI by a 'distress' croI) of cones, which are srllaller than norrnal. An infPi-ted tree may show these signs, accom~)anied k~y ;L gradual thinning of the folixgc, for a year or t ~ 7 o before there is browning of all the needles, signifying that the tree is de,l(l. Bec,luse o f the decaj ctl roots these trees are subject to wind and snow d a ~ n i ~ g e nnci they are conlnlonly fourid uprooted with the large roots broke11 oTf a short distance from the crown."

Detailed studies of 32 centers of irifectio~~ and sevabral hun~lred field ol~serva- tlons revealecl, however, that these visih~le symptoms may be partiaIIy or en1 ire1 y absent, directly dependent on the resistltnce of the individual 10 killing by the disease.

On(-e the fung~ls is established in a, host, varying sj~mptoms are evident when the main roots are reachecl. The fungus appears to grow rapidly through the outer portion of the woody core in trees 1:tcking rcsistnnce 1-0 killing by the tlisense (Fig. 17j, ancl centrally in tlae woody core in trees sliowing resistancc..

T'rccs lacking resistance to killing t)y the clisease may die within three years of initial infectio~a an(1 shuw defiriite synlptorns of distress l~efoi-e the fungus reaches the root collar. Thin, yellowish loIiage, less than one-quarter of normal terrmi11a1 growth, ar1t1 a hcavy crop off sni:~ll cones in the upper crown are usually followed tlae succeetling year t ~ y redtlcning of the needles and

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Signs and synptoms of yell0117 In~ninated voot rot in I>oitgIas lip

Frc. 2. .I young sporophore o f the yellow larninntecl root rot fung~ns o n tlac nndcrsitIc1 of thc l ~ ~ t t t ol ,I fd1lt.n K)UIIL$L~ tlr. X

!;I(. 3. ,i sporophcirc oi P'oritr i~ t '7r i i on \~t~stc.i-rl rccl c.ctl,lr -cc-tioneci to show the p ~ r t , ~ r r ~ i : ~ l t r~lle I,~yers. X 4

I:I(,. 1. .\ "diztrcb7" crol) of cone- , ~ l ~ t l rc.t,~~-tlecl tcrruirldl gronth on a 14-year-olcl I)ougla:, lir signifying I:~cli ill ri.-i\tanc.c. tts kiliirlg 1 1 ~ the root rot fi~ngils.

FIO. 5. "'ICoot balls" of 30-year-old I)oi~glrt,-, fir. 'J'hcbe treca, when living, dlvwcd rc.;istance lo liilling by the root rot fu~lgus.

FIC~. 6. :Idvanc-ed yi>Ilow ldnlinatecf root rot in the but t an(! roots of a ~ S - J ' ~ ; L P - O ~ C ~ 1)ouglas fir. B'dlle~sing of ! Rc (zip :rnd I,steral roots and some advetntitic~us root develop- ment I~n\c . st,lrtcc\. ICc-in i~~ll)r.c.gii,ltio~i oi thc \vood ,l(ljC~cent t u the clccay colnlnn is intlic.<~tc.tl in I hi. l onqi l t1clin.11 scc-l i o r ~ ~ .

I.T(;. 7. -\ l o ~ t ~ i t ~ t ( \ i ~ ~ 11 wt.fion or 1 1 1 ~ louc*r- 1)oIc o r ' I k s 5 - > t ~ e ~ ~ - c ~ l ~ l l j o i ~ g l : ~ \ I L ~ ~ 'I'IIP 1~itRogmi elcsiroyvti wtnic. root\ , I I I ~ ~ ! I ( ~ ~ I I - ~ W O O ~ I , then, ~lirough ,I chnnge iit I w b t ~ . ~ ~ i ~ t ; l ~ i ( ' ~ , , ~ t t acketi t he sapwood :and irnmr<liately kil1t.c.i the tree.

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Damage to Dougla:, Gr T ~ z I E : , ~ ~ 1157 y~11uw k~11~i1l;lted mo t rot

Flc; 8 , l,Vt!steril hcnllocl; a n d western re(l cctdar rcprotlucing in an opening cuust:tl 1)y the clisease at Poavelt River. b~Iuc11 of 1 tiis reprotlt~ction is infected.

Fic;. 9. 1,'arying c.ro$vn syrnptonis in n ceriter of infertion in a 35-year-old si;lncl at. E;ll;c Cocs-ichan. 'fhc trees are ruot-fusecl as indicated in Figs. 19 anti 28.

FIG, loe 11 large center ol infection in a 45-yenr-old stanti a t Sproat T,r*ktt. "llistress" cropscof cories may Ile seen 017 tlie cleat1 trees, thinriing of the foliage, and other synipton~s o n thc living trees. Few t.rces ira this area rn:~nifested appreciat)le resistku~ce to the disease.

FIG. 1 1 . .-In XO-year-oltl starld at S l c ~ ~ t z Falls hc;a\.ily t1:lm;igetl by wind-throw foliowing attack by t h e disc-ase.

ITI~;. I. Uc~llo\\- lalninatc~(1 ~-oof rot in the I)trtt of a 280-year-oEtl T)orrglas lir. 'I'ht. t-:i11+i11 ~ L I I I ~ L I S is J n ~ i i11g OII t h c . lo~vci- rig111 of the (lc!cay c.;~\:ity-

Fat;. 13. Co;~rsc, nie<liun~, at~tl linc: I~yphac ol the f~ rng r~s in in(-ipient yilllow lanaiuntctl root rot. in Ilouglas tir. X 4OO

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61e;stll of the tree (Figs. 4, 0 , ancl 10). 'There is no forarlation of calIhas tissrrc or ad\-erntitious roots, as the sfisc:~sc syre'tds too rapidly for heialirmg or corn- ~wnsa tion t o occur. Srr~;tll o v a 1s o f incipient dec-izy , wa ter-sc):tked irn appear- anrc, are cornnlc~rlPj- ot,served in the sapwood on the surf,lce of tlle stump six inchcs aE~ove the g~-OUWCI, altlaough death m;ay orcear l~eiorc this symptom is c.uhil,itcd. Exa111in;~tion of the lower bole and excavated roots a t the time of tlr1:tth rc~.e,tls thdt the trcc was ltilled by the growth of the fungus throrrgh the s,zyn.ood (Fig. 71, tllc f~ lng i~s occasionitlly having entered through only onc. root.

(111 the ot1ac.r exti-<:mc, however, trees S I I O \ \ ~ ~ H P ~ resistance to killing by the clise,~se usti;d/y cxlli\)it 110 visil~le distress s ~ I ' I I ~ ~ c ~ ~ s , ;is the clestructis~n o f the rn,~in roots is c.cmpcns:ltcd for- by prc~duction of calleas tissue and siafisicnt

, . a(1vc1ltit ~CPIIS 1-oats (l;igs. 6 ~ I ~ c I 1 5) f o n ~ ~ ~ i ~ ~ t i l i r ~ 110rn1;tI vigor. I h e w rf ecs v&-ill III ii~lti~i11 norm<el growth throuyl~out the lile of the stand \vhcal they arth givet~ sufficiclnt prolec.tio11 fro111 ~vintf anti snow. If the surroundin;g qtarld is rernc~vid, howevcr, the. tree will fall, exposillg x "ball" of roots, winicI11 have heen tl~c-~1yed to \vitlaixn a slaori distnncc fro111 the root collar (Fig. 5).

'1-hc rra,ljom-iiy of trees inierted with yel%ow I;irnin:zterI root rot exhitjit s\.nlpionls tlirectly ill rclatiorl tr) tile degree of crirroachxllerlt by the B'urlgus upon t lze s.~ptvood. 11 Iiglat crop of CBI~CS (Fig. 01, not fol~ncB acij:ecent, ul~~lfrec t ('(1 ti-CCS, is j~rocIu(~ec1 when only st11;zIl ;L~c ;~s of sapwoo~l are i~ffected. L\Yacn the fris~gtis 1 1 ; ~ ~ encroaclned on the s:~pwood and irlfcrferccl with the lornl,~tio;l of c,lllus sissuc :and adventitiorms roots by we; lke~~i~lg tile tree, deacl c,tllas tissue rn,~>. c.ommo~mly he found on ,i root 11,ritl-a new (:allus growtll closcr to the root ca~ll,ir-. or tBe,ztJ rxllrrs tissuc ma57 be found on one or more of the n1,tjor roots with no c.;lllus growth on the rcrxlninirig roots. $111 ex;zrni~lration of the s t t~r i l l~ (1% :I fr-esllfy f~I1c:tl tree in the early stages of the disc<~se shows iri-c.guI<ir ;trms of inci~~ient clceay (Fig,.. 20). These areas are cotn~nonly cresccn t-sh:tg)cd nn(l usuLtBB!- directly above the i~~fer-tecl roots. They appear i r ~ the lilchartn-oocl close to the sapwooil, with S P Z I : ~ ~ ~ r a d i a t i ~ ~ g tongues ea-acro:~ch- in,:* i r s t o the s;zpivooal.

In trees sIlowing resistance to l~illing bgr the clisease, the decay volume increases nlorc. slowBjr tllan a h tree volume. 'These trecs provide an important source o f isloc.ulurrl for the next rotation as the fungus has been fi~und v i ;~bk i11 stunlps, large roots, ;zslcl lclrge blocks of ni-ood for periods exceeding 50 years (%;ig. 13). :in ex,~iari~l,ltior~ of tllc lower isole and major roots ol t11cse frees reveals tlmat the hc.arts~-ood is resinous, ~v i t h pronounred ha11(1s of rcsin- ir-~~pregn~tt ed tvor ~l frcclueal t ly t~ncircling the decay (Fig. 6). This waterproof, resin-soakt.it wood prevcnts the fungus fro111 being drowned, greatly irnpcc$cs its growt h , protects the \votrcB frc~m further s:s yrophytic invrtsicsn, and prc~vities a habitat that en,~E>l{.s the pLztlloge11 to survivc over extended perioets of time. I . 1 he resin is ;ipp;~r(~litlj ' r~eitlltr a barrier nor ;e toxicant, however, as resin- impregnated wooti is aften found within the decay cs111m11. Zn trees lacking resistramre to killing, the f~lrigus spreads rapidly through the entire bole after the death of the tree. 'Tllese trees may stand for 5 to 10 years and fall M-llen

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the bole breaks close to the grou~acl. These trees are of little importance in providing a source of inoculum for f~aturc gener;-ations of the host as a11 portions of the tree are tfecayed by the fungus aild other s~tpi-o~,h>~tes, and no vial~le inoculurn can be recovered witlli~i very few years.

Drought or clesicci~tion would appear ttr have l i~ t l e efTect 011 the survival of i~loculurn as isolatioals of ";tnnu;il" P. weirii were obtaiiletl from inlected wood l9locIts stored for 18 moalths in :L dry atrnospl-nere. Studies of the fungal mycelium in decaying \vood indicated that, iaa general, ijnc, n~ctliunl, and coxrse hyphae were prcsent (Fig. 13). Hn dried 19locks of infected wood, the fine hyphae had degeneraic.d, but most of the mediuin aimd all of the coarse layphae had retained their original form.

A stucly of the histories of severctl Douglas fir stands on the coast of Bri~.isla Col~mml.,ia lias reve2le.d two facts c:oncerninp past d;~rn,~gc c;eused by ye.110~ lanminaterl root rot. First, "~~n11ua1" P. weirii Icillcd pat clies of trees clanring the early st-ages of cfevelo~~ment of c11rrent1-y ovcrnl:eture stclnds. Second, fire ;lnd cle:lr-cut logging tended l o hold in check the spre;tcl of the disease and the amount of dal-nxge in succeeding genera.t.ions.

Groups or single ta-ces of hemlock, cechr, and grand fir, 60 to 100 years younger than the average age of the surroundi~ag old-growth Ilouglas fir stand, are frequently present in openirlgs caused lay "annu2~1" P. weirii tf~aring stand dcvelopnlerit. 'I'hcse trees a ~ i d the nearby Douglas fir are frequently infected with yellow laminatecl root rot. 'Thc Iosses causetf by tlae early and recent activities of the pathogcn may not be observed since the trees tha t filled in the openings have now grown to rrlercllarltable size. Little cull results where the tlcc~iy is present in a Haarvested tree bccc~use thc major loss is below stump height. Since young stands now under managenlent arc

Spreatl of yellow laminated root rot iri Ilouylarj fir FIG. 14. X root of ;i 10-year-old 1)ougl;rs fir on the left qrnwing into '3 split in an old

root of a 380-year-old 1)orlglas fir felled 50 ye,irs ago on the right. 'I'he young tree has been i~ifected tfmro~agh a pressure point on the root where i t enters the old root directly l ~ ~ l o w the axt.. Thc cut on the old root shows viable inoc~rliln~.

FIG. 15. Calluhing of tlccayetl roots and adr~entitiol~k root tfevelcrprnent in a igorous 55-year-olcl 1)ougBas fir following tla~nage t)y tht. clisease.

FIG. 16. LJcrtical section throilqh CI s~appn,ast~l Douglas fir fused to a dominant Douqlas fir root. 'I'he suppressetl tree was serni-par,lsitic a s i t retairieci onlv a tap root. I t was liilletl t)y the f t i n q ~ s entering frorrl the ho+t root.

I . 1 7 The Jise'nqe entering a 3.5-year-old I )or~glas hr through felaion with an adjacent heavily-irmfected tree.

Frc;. 18. Early stage in the contact and fusion of roots frunn adjacent 35-g1ear-old Ilouglas fir. The root5 arc one-quarter inch in diameter.

FIG. 19. A series of irlfcctctB root-fused 35-year-old 1)ouplas fir. 7'hc s j rnplonls of the disease show11 werc: tree in left hackqround, dead, with l igl~t cone crop, decay encroaching on sapwood a t stump lex t.1; tree in right hackgrou~ld, living, yellow needles and hea\-j? "~l i~t ress" crop of concs, sapwood inladed Imt not t o stlirz~p h e i ~ l i t ; tree in left foregroei~~tl, living and apparently healthy, decay entering two fusecl rootr; and tree in right tore- ground, living and apparently hcalthy, "watcrso,tked" stain in central core of four rc~ots.

FIG. 20. A lateral root fused to the root collar of a second 35-year-old 1)otiglns tlr. No syr~aptoms of distress were shown by either tree, although "'watersoaltcd" stain to advanced decay was preqent in 1)oth.

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BI;CKLAND E?' A L.: ROO?' ROT OF DOUGLAS PI12 7 7

nsrlnally Bl:irvesterl before the trecs are 100 years of age, the I-ien-alock, ccdiir, and grnntl fir filling in the openings c,lused by the ciisease mill be of unrncrchi~rntc~blc size (Fig. 8).

\Ifhen r>ougl:~s fir regetserates over extensive areas followirlg large clear- cuttirig operations or severe fires, yellow lxrninated root rot usra;~lly occurs in si.;~t tered locations. IVhen nl,lr~y old-growth trees are left, however, or regeneration f0110\vs the brealcdown of an overmature stand through wind- throw, 6 b t ~ ~ 1 ~ l ~ ~ ~ ~ l " P. zoeirii is oftera very destructive. 'L'he disease may, therefore. j~ersist from one gerler:ttion to the next wit11 irlcrensing irnport,~rice (Fig. 1 : I , 4, amd 5).

ildversc effects on stancl yields ciLn be obscrved on mimy of the best growing sites for DoengIi~s fir. Yellow laminated root rot was present, ireclueaatly c;tensirip; severe damage, in all of the Douglas fir mensuration plots cstirblished 114; the British (:olnmbia Yorest Service in the coastal region of the TJrovince. FOB- ex;~nmple, CL onc-termth-acre ~ ~ ~ e n s u r a t i o n plot, established in 21 30-year-old st~trid :lt Lake. Cowichnn (Fig. 1 : I ) , cont;tined a total of 1062. 7 cu. ft. of Do~mglas fir in 1035, 958.8 cu. ft. ill 1940, 1008.5 cu. ft. irm 1945, and 768.5 cu. ft. in 1950. (Id' tllc expected volumlc, 26>.8(;& \v;l-s lost fro111 1935 to 1940, 15. lC7i1 from 1940 to 1945, and 34. fro111 1945 to 1950, or a loss of 58.0% from 8935 to 1050. Since a 72.2%) increase in total cubic volume w,xs recortletl lor those trees whia.11 survived over the 15-year period, the losses rccortlecl c ~ l ) o ~ e are very scvcre.

On three plots estat)lished a t Yale (Fig. 1 : 7), in 60-year-old I_)ougl;~s fir, the basal area on each plot had been redrlced by 0.8, 7.3, and 23. Oy'c, in the six-j,e,tr period from 1035 to 1941 (1). 'l'hroughout the adjacent 20- to 35-year-old s tarids, many centers of irifectio11 were observed. In :e series of 14 one-te~ltlz-acre plots in 35-yeu-oltl 1)ouglas fir near Sproak Lake (Fig. 1 : 5j, the 11asi11 area W;LS rvciuced by 4.07{,, only tllree of the plots showing any net gain from 1946 to 1050. Only 82 .1 C/; of the expected t~asal area of the tlominant and codominant trees was produced during- this periotl, and 82.776 for thc 10 ye:aa-s previo1.1~.

i'i stand near Skertz Falls (Fig. 1 : 2) \\-as reported to be severely damaged b y wind-throw in 1949 (1 1) (Fig. I1 j. An cxanlination of 1225 80-year-old Douglas fir showed that 340% of the trees I-lad been n~itici-t11ro.cvn following ciarnitge by root rot and that 40%) of the standing trees were infected.

At Lake (:o\vichan in 1039. 13icr (7) established three sample plots in 35-ycar-old L)ouglas fir in centers of "annual" P. weirii infection. During the 10 years previous to 1039, 4 .8, 33.8, and 9.07/o of the donlirlant :xnd co- dorrsin,~r~t trees wcre killetl 1,y yellow larrlinated root rot on e;~ch of tlnese plots. Fronl 1039 to 1040, a further 1 .9 , 15.7, and 32.4y0 respectively had been killed. 'Tlmcse figures indicate that darnage from any one center of infection varies greatly fro111 orrc period to r~nothcr, even urscler slnlilar site contlitions.

11 study of these stancls indicates that the disease usually remains highly active in an infected area for extended periods of tirne. 'I'he nur-rsl~er of trces affected each tleci-~de may decrease because of ille l~ick of root cont:tr.ts, hut ihc

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'i 8 CrlNABlk,\T JJOUKSAI, OF BOTANY. VOI-. 3&

ecc)nomic vi~luc of each tree has greatly increased. Examples of infection ce~zacrs continuing t-o develop over long periods of time C ; L ~ be found in 80-, 130-, and 280-year-old Douglas fir a t 1,;ike C'oex-ichan (Fig. 12j1 and in 300- j-c;tr-olcI anad older growth a t Cnmeron Lake, Stamp F;ills, xncl Sproat Ll i l i~ (Fig. 1 : I , 3, 4, and 5, respectively), although these centers do not occur frecluently (1 2).

Control of the Disease

'I'he practice of removing froan plant comnnunities individuals infected with v,asc.ular root disease gclnerally teamds to accelenste the spread of the disease. IT'ith recluccd cornpetition the roots of rneighl~oring plants grow aamore freely into the irlfectcd area ant1 therefore increase the nrlnl19cr oB root contacts with the ialorulurn. Further, where the infected plants are severed, the 1-e~ist~~arce of the host is immediately reduced and the I'eanglas will spre;ati rapidly thra>ugllout ;all tissues of the root system to bring it irl contart with nmore roots of ncljacent g18:~nts (6). From these general observations it c'an ljc c.sj)ectcd that Ilenvy losses rnay occur when trees are rear~ovecl from 3 stnnd of L)oragl;as fir which is Izeavily infected with yellow lnminatecl root rot. iYith t l - s e b high frequency of root fusions in B3ouglas Gr, stumps and roots of severed trccs rn,~y not die for several years. This precludes the entrance of soil oa-g,lnisnls wBaich u~ould rlonnally invade tlertd roots and prevent the spreaei of the disease. filIoreover, thilzning of Douglas fir stands infested with the tlistkase seeins inadvisable, as the infected trees showirlg resistance to hilling by the tlisrase lose the support of neighboring trees and soon fall frorn tlae chffec.ts of wirlal or srnon7 (Fig. 11).

-4 single center of infection a t T,ake Cowicharl was studied to cleicrr-pline wl~etller the felling of a11 affected trees would (lest roy the center or prc.\-c.rlt the sprec~d of the disease. 111 this center 29 trccs showcrl sever:rl s y ~ n ~ ~ t o r n s of tile. disease and three shoxx-ed a single syn~g~tom. 1\11 the roots of the trees 317 the ('enter were exposed, and the trees felled. "Xnnur-11" B, weiril was istsl.ttcd from 45 trees. Menloving all the infcctetl trees, those connec-ted by root contcicts, rancl an isolation strip one tree wicle around tlnenl, reqeliretl that 135 trees be rcrnovcd. Such a proced~arc is ~omrnerci~ally iimpracticablc, 11x1-tirellarly if there :ire several centers of infectiorn i11 a stand. Even after the removal of the irifected trees, the original source of iraoculurn will often rem:~in viable to form a new sourre of infection for trees s~ahsecluently estcahlisl~ed in the area.

In Douglas fir stands severely infested m~ith the d i s e ~ ~ s ~ , it has been suggested t h a t plmting of the area to anotlicr species of conifer for a rotation of crop woulcl reduce or cli1~1in;lte the disease. H P I most st,lncls where yellow laminated root rot occurs frequently, western hemlock is the only alternate speries that could be used, and i t is doubtful that this species wvulel provide a crop of staftirient ecouorrlic value to warrant such a rotation. Further, henllock itself is highlj, suscey~tible to yellow lrtminxtetl root rot. Although tllc disease

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BUCKLAND ET AL.: ROOT ROT OF D o L i ~ L A . s F I R a9

rrlrely spreads througlil a hemlock s t m d becctusc of the scarcity of root contacts, i t is probable tha t living infected trees would carry over many sotarces of inuc~alum to the nest rot a t' ion. :I study of the history o f heavily infected Doriglas fir stands indicates that

the most pr~ecticable method of checking the s p r e ~ ~ d anti reducing the incidence of the disease in the next crop is through clear-cutting and severe burning of the site followiilg h;na-vesting. illtlmough this drastic treatment woe~lci check the spread of the dise:tse to some degree in the ensuing crop, the advantages gaincd by such control Inay be outweighed by the 1l;u-nl done to the site.

I t is not as yet economically practicable to consider e rad ica t io~~ or immediate coiltrol of ycllow laminated root rot even in sevcscly damaged areas. Certain ch:nr;u-tcristics in thc: behavior of "annual" P. wei~i?: suggest practical metlloris of silvicuiturnl contrr~l which arc now being ccsnsideretl. Removal of infccted trees will only k)c feasible if current experiments show success in treating the stui.nps of freshly-felled infected trees with poisons or hormone-like herbicides to prevent the survival of the fungus in residual roots and stumps.

Discussion

IYith the constant lowerirag of old-growth Douglas fir reserves and the resialtant increasing dcpenderlce on young trees grown on short rotatio~ls, any agency adversely affecting the stocking of these young stands must be given careful consideration. As the young stand develops, natural thinning by competition rtnad disuase is desirable to maintain adr:q~aate growing space for good c~uality and yield of timber. In most young blouglas fir stands yellow 1anlin:~ted root rot is not seriously affecting the distribution and the amount of stocking at present. The disease is exterssivc in many areas, however, and by opening up the stands and subjecting the trees to wind and snow d:un;tge, poor and uneven-aged distribu~ ion results.

Signs and sy~m~ptorns of yellow lamin:ited root rot are not apparent until the disease is well estakslishcd ira the tree. Evcn thela, however, the sporophore of the fung~rs is r;irely produced, ;xnd the synlptoms may be partially or entirely ;~l)serit, dircctlj- dependtnt upon the rrsistance of the indivkltaal tree t o killing by the clise:tse. Altllougl~ the symptonas expressed hy any species are not solely di;~gi~ostic of this root disease, the centers of infection of L ' ; ~ n n u ~ ~ l " P. weivii are rrladily recognizccl in Do11gl:ts f i r - by the "root balls" of f:lllen trees and the ch;/rnc-icristic openings in llil otherwise well-stoc-lted stand.

.The exact ~iatur-61, of thc resistance of a host to killing bq- the disease h;ls not been stuelietl, but trees in which t l ~ c faa~lg~as grows through the s:kpivood mtrst cflffcr marlicclly in sonac chc1nic:il or physical property from trees in wBlic11 the fungus ga-ows through the hc;lrtwoocl. hro~ltoxic to the fu11gus. the hiall resin content of the I-oots ;ind hatts of trees shosving resistanr:c to killing by the disensc is hc!ieved to trc the most i~npor t~ ln t factor in the survivnl of "',lnnunl" P. w ~ i r i i fro111 one host generation to thc nest. When the f~angams grows through thc lieartwuocil there are solctom any o~ativard signs of loss oi vigor, Iaut when the fungus grows through the s:~.pwood mrirked syn~ptonas of loss

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of vigor are rapidly evident. 'The Litter trees arc. highly susceptible to ;at t,~cl; by bark bectles. In centers of ";~ranual" P. zueivii infection it is not uilcomrnori to find H:~rgc populatioals of 1~;1r1< beetles btr iltling u p ;and spreading oaat into t h e surrounding stand.

'The m ~ j o r cause f01- the severity of \rello~v 1;~miuated root rot in r)ougl:ss fir appears to be the cornniori hahit of root fusion in this species rather th,m host sansceptii)ility. Signs oE root fusion are frcclt~crlt in Dougl;ls fir st;kn(Bs where the healing or calIusi11g of tht. stumps of sc-lectivcly cut trees is conmaon.

r\ltBaoalgh "annual" P. xleiuii has hccn isolateell froan nn'lny con;fcrs in British ('olurnbia, root fusion is not cornnlon in specks other th:~n L)ougl,~s fir and centers of infection do not usu:slly clevelop.

Where yeBio\?r laminated root rot is prevalent it is evident that severe ecorao~nic loses can l)e e x p t ~ t c ~ l in ianmature streaids of Z)ougl,is fir. Such st;~lids may produce no incrense irn vol~rm:: Ero~lr as early as 30 to 40 years o f age uiltil the end of the rutation. '3'l~is d;~rn;~ge rcxprescnts ,L gre,~t econornic Boss in the c;t~i;~clty of the site for ~~oe,d-produc-lion, considera1)lc waste of growing space through ~xtcnsive opernings na;~de in the stand, r~lltl ;L ~ > o t ~ ' ~ l t i ; ~ l kixzarcl to future crops grown in the are,]. ,!Is l l ; ~ n ~ i ~ i i l l l Pa w ~ Z Y I . ~ may rern,~in vi:thle i11 deB~ris of tlie old stand for extended periods, the tendencj- will i)e for the irnr-idence of the disease to i t~crc~~sc .

To augnneilt siIvicr~ltura1 practices, economically sou~icl ~n~etllotls of dchstroy- ing c:eniers of infection 11akast Ijc consiclerecl ant1 cctrelul a t lerl t ion rsa ust necessarily he given to each ;Z~C;L of U011g1as fir rt'ge~nerdtior~ iniilsted with the clisc:isc. TO attain thrse: objectives, studies must he rnatfe of tllc manntr of intensification of the disease in the w e n , factors influc.nc:ing the survival of inocalHum B,t-tween stand rotations, ;inel site fx to r s iiaflrrealcirig tlie sprcad o f t h c k disease within the establishtd st,ln(B. As such i,autors arc usunlly cc)n-sg,lex t h y are too often ignored. They nltsst be considered hy the for~ster , how- ever, if maximum or even incre,~scd yields ;%!-e to be ~ b t ~ ~ i t i t d on sites w.\lere t-he disease is prevalent.

Dr. J. 1;. Bier, ,Associate Chief, 1)ivision of Forest I3iologj~, has given r~nuclm assistance and advice thro~aghout the course of his stucly. From the time Dr. Bier first startccl an investigation into the cause of yellow larnin,ltecl root rot o f Douglas fir in I938 until the present, Elis I;nowlcclge of tlne discasc. has been give11 freely to thc authors. Dr. R. E. I?oster, O&cer-in-Char,r:cf T/nit of Forest Pathology, Division of Forest Wiulogy, Victoria, and his staf'f 11;~ve assisted tEac work 111 every way possible sin(-e 1948.

(;r:tnts to aid the itawsttg,ttion, chiefly for winter reszarch, have been given by the Presitlent's Committee on Rcsearc-h, 1:nivcrsity of 13ritisIm Columbia, Vancouver, Bro~n 1949 to 1952, and by thc. National KewarcB-a Council, $tt:twa, for 1951 and 1952.

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hlat-~,lcs, Forester, have given contilsaaoaas support and advice thra,ugJ-nuut the

'%'o the rtforcmenkioriccl, iv\lo 1a;ivc. made the stncly possil~ic, and to many others nho have rt.ncte1-ed c.onsidtlr:tRBc assistarac-e, the authors are tlerp8y grateful.

References I . 1 1 , . . 1 T I , 1 . . Iicl,~tion of research i a l loreit pathology to thc nl,lnage-

l l l t ' t l i of -ei o!l~i qrowt h kr,rc.sth. I . I'oricr. wcirtz root sot , '111 ituportanlt riiw:~.,c 2~flct.t- iliq irnin,itul.c' -t,incls of I)ouplaa !~r. Brillsll Colr~rrrbia 1,tirlli ~er rnan , tTe11. 19 17.

2. I . . o r 1 , I. . I ' S O , . 1 . A ~ ) r ~ l i l n i t ~ i r y itir-e>tiq&tioin into t hc cie.c<~y lo,~c,, 511-t,iirac~<l in nes te rn IleiliIucl< atntl ainahili:3 fir in rhe [ T p p i ~ liitimat 1Seqi~)n. ('<in. flcpt . -2;r. 3lilneogra[)htd R c ~ ~ o l - t , Vict ori,i, H.C. 19501.

3. E ~ u c , F ~ . I s , \ N , T . S . P o r i t ~ utclrii: its 01-c:r~rrer~cc ant1 Ite!~;ia.io;~r on species c~ t l l c r tll:tn cedars. Noi-th~vest Sci. 2 2 : 7-11. 1948.

. 1 I , . . S I R , 1 . 1 . 1 I , . J. Sttldiea i : ~ f:,l.cst p:~thrlinq,. VII. IPcc,ay i:i v~ricstc:r:~ he1111o(:li and lir i r i thc Frarakiir! River ;lre:i, Y3ritish C;c.al(~~lak~ia. Can. J. I:t:sc,lrc.i~. 6:', 7 : 312-3.31. 1019.

5. I):\u, 1';'. Ti. I:orc.:~t Iiy!g,ric:i?c. TI. 'I'hc: i1111)erfttct ion o f t h e et~\-i:-on~llt.nt and its import- arv-e ~ I I tllc nzar?ng~~lnc~it OI ioresls. i<:rl!,ire Forestry lictv. 2") 307-,115. 1Cj50.

6 . C.\RILII*I..I., S. I). I<o(it ciis(;;lss f ~~ r rg i . C:hronic;z I3otianic.a. (:o., \Val th:im, Mass, f 0.1.4. 7 . XI:?u\ci.:, . . . I. , BJI ICK, J . E., an(I ;\\;orxi,tis, 311. IC. 11 root-rot of I1i;tlgi~ts fir caused by i ' o r ia

.i,.!rz/zt. 8:':,:n. J . i icsc:~n'l~, C , 18 : 522-535. 1940.

1 1. 131 )FK:, J . '11.. 'Fh(* o k < - L I I - ~ P ~ ~ ~ cb IT^ sprcacl of t11c rocji -1-1 ~t Pi)ria z ~ c i r i i ~ it1 SPC-OILI ! (;ro~vth I)cruqin\ fir a t 5 L u t ~ Fall-, I~,lric-o~~ver Isl'lnd, ' l3.Q'. 'i'llcsis. E.':lci~lty of I:orc.stry, i ; r ~ i ~ . c,f 1:~Eti-Il C'l~Iu!nl,ia, Vancor~ter, 13.C. 1948.

12. ' ~ ' F I o ? & I ~ , (;. 1'. ~ - ~ ~ ~ > i i b ! ~ - I l f ~ ( I { I P / C ~ ~~ote:,. &n. h?pt . i\gs., victoria, D.C. 19,jI.

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