Potential for the use of exogenous chemical elicitors in disease and insect pest management of conifer seedling production

The Open Fo es Science Jou nal, 2009, 2, 17-24 17 1874-3986/09 2009 Ben ham Open Open Access Po en ial o he Use o Exogenous Chemical Elici o s in Disease and Insec Pes Managemen o Coni e Seedling P oduc ion J.K. Holopainen*,1, J. Heija i1, A.-M. Ne g1, M. Vuo inen2 and P. Kainulainen1 1Depa men o En i onmen al Science, Uni e si y o Kuopio, P.O. Box 1627, FI-70211 Kuopio, Finland 2The Finnish Fo es Resea ch Ins i u e, Suonenjoki Resea ch S a ion, FI-77600 Suonenjoki, Finland Abs ac : Elici o s a e compounds, which ac i a e chemical de ences in plan s. Va ious biosyn he ic pa hways a e ac i- a ed in ea ed plan s depending on he compound used. The mos in ensi ely s udied elici o o manipula ing de ence pa hways in plan s is me hyl jasmona e, which modi ies e.g. he p oduc ion o e penoids, he main cons i uen s o coni e oleo esin. O he commonly es ed chemical elici o s a e salicylic acid, me hyl salicyla e and benzo hiadiazole, which a - ec p oduc ion o phenolic compounds in plan s. Bo h jasmona e-based and salicyla e-based elici o s ha e been shown o ha e supp essi e e ec s on ungal diseases and insec pes s o plan s. So a , knowledge ega ding he e iciency o elici- o ea men s o enhancing pes and ungal disease esis ance o coni e seedlings is e y limi ed. We e iew cu en knowledge o he e ec o hese elici o compounds on pes and disease esis ance in plan s, and we analyze he po en ial p os and cons o using elici o s o u u e pes managemen s a egies in o es nu se ies. Keywo ds: Induced de ence, indi ec de ence, plan ola iles, e penoids, p iming, MeJA, MeSA, BTH. INTRODUCTION Bo eal coni e o es s o m he la ges biome on Ea h. When g owing ac i ely hese o es s a e conside ed o be one o he mos signi ican global sinks o a mosphe ic CO2 [1]. Regene a ion o coni e o es s wi h good quali y seedling ma e ial is essen ial o main aining he la ge o es ed a eas as an ac i e CO2 sink a e o es logging. Along wi h global wa ming he p essu e by pes insec s and mi es and a ious plan pa hogens will be an inc easing h ea o o es y in bo eal o es a eas in he u u e [2]. Feeding inju ies caused by insec s and mi es, o a ack by ungal hyphae and pa hogenic bac e ia, will elici na u al de ence mechanisms in plan s [3]. Chemical de ences agains he bi o ous o ganisms can be di ec , a ec ing eeding o ep oduc ion o an he bi o e, o indi ec , supp essing he impac o ha ming o ganisms by a ac ing o main aining he na u al enemies o he bi o es [3, 4]. This will include ac i a ion o genes in ol ed in ce ain biochemical pa hways in plan s o p oduce enzymes, which a e esponsible o p o- duc ion o seconda y me aboli es. These seconda y plan me aboli es a e ac i e chemical compounds ha a e no no - mally essen ial o basic plan physiology, bu ha e e.g. a de ensi e ole agains he bi o es and pa hogens. In coni e s, e pene-based chemical de ence is dominan , while in he whole plan kingdom e penoids a e he mos di e se g oup o plan seconda y me aboli es wi h o e 40,000 known compounds, when all de i a es o he uni e sal p ecu so s isopen enyl diphospha e (IPP) and i s isome , dime hylallyl diphospha e (DMAPP) a e conside ed [5]. Majo e penoids in oleo esin a e he en-ca bon mono e penes, 15-ca bon *Add ess co espondence o his au ho a he Depa men o En i onmen al Science, Uni e si y o Kuopio, P.O. Box 1627, FI-70211 Kuopio, Finland; E-mail: ja mo.holopainen@uku. i sesqui e penes and 20-ca bon di e penes [6]. P oduc ion o gene ically modi ied coni e ees wi h inc eased esin-based de ence capabili y has been p oposed ea lie [7]. Recen ly, coni e s ea ed wi h exogenous elici o s e.g. me hyl jas- mona e (MeJA) ha e shown inc eased esin p oduc ion and esis ance agains he bi o es [8]. The e pene-de i ed alco- hol pacli axel ( axol) is also used as a pha maceu ical agen agains cance . P oduc ion o his compound in Taxus sp. cell cul u es can be e icien ly up- egula ed by speci ic ex- e nal s imuli such as MeJA elici o [9]. Thus, elici o com- pounds a ec he syn hesis o chemical compounds in plan s, bu his will esul in cons ain s in ca bon alloca ion and ul ima ely educe plan g ow h o e en s op he shoo elon- ga ion a e he elici o ea men [8]. The e o e, de ailed in es iga ions o he whole plan physiological and g ow h esponses a e manipula ion o induced de ences a e needed. MECHANISM OF INDUCED DEFENCES IN PLANTS Plan de ence, including physical de ence based on e.g. cu icle s uc u e, a ious ho ns and hai s, and chemical de- ence based on chemical compounds can be di ided in o cons i u i e and inducible de ence componen [3]. Cons i u- i e de ence can be ound in heal hy plan s ha a e no ha med by bio ic o abio ic s esso s. In many ci cums ances, cons i u i e de ence is no enough o p o ec agains a ack by mic obes o he bi o es. When an insec akes a bi e, o he app esso ium o ungal hyphae a acks he plan cells causing lysis and disin eg a ion o cell memb anes, he de- ence esponses o he plan a e ac i a ed. Biological o abi- o ic induc ion will lead o o ma ion o new p o ec i e plan s uc u es o p oduc ion o new chemical compounds in plan issues and i ola ile, hey may be emi ed. A e ungal pa hogen and insec he bi o e a ack he e is also an inc ease in chemical compounds ha a e al eady ound cons i u i ely in heal hy plan s. Tissue concen a ions and ola ile emis- sions o o ganic compounds may bo h be ele a ed, bu e- 18 The Open Fo es Science Jou nal, 2009, Volume 2 Holopainen e al. sponsi eness o di e en compounds depends on he ype o a acking o ganism e.g. [10]. INDUCIBLE BIOSYNTHETIC PATHWAYS IN PLANTS In his sec ion, he h ee majo biochemical pa hways, leading o he o ma ion o plan seconda y me aboli es, i.e. e penoids, phenolics and alkaloids, will be b ie ly desc ibed. Many plan amilies ha e speci ic pa hways p oducing com- pounds, which a e e y esponsi e o elici o s like glucosi- nola es in c uci e s [11], bu hese compounds a e no ound in coni e s. Plan e penoids a e o med ia wo sepa a e pa hways, which a e ac i e in di e en sub-cellula compa men s. The me hyle y h i ol phospha e pa hway (MEP) is ac i e in plas- ids including chlo oplas s. MEP pa hway is mos ly espon- sible o he p oduc ion o isop ene and mono e penes, bu ecen obse a ions by Phillips e al. [7] ha e sugges ed ha he MEP pa hway is p ima ily esponsible o p o iding p e- cu so s o induced oleo esin biosyn hesis and hei majo compounds, di e penes. Ace a e-me alona e pa hway (MVA) is ac i e in he cy- osol whe e sesqui e penes a e p oduced [12]. Bo h pa hways p oduce isopen enyl diphospha e (IPP), which is ans o med o o m e pene p ecu so s. Some plan s ess- ela ed induc- ible e penes like he homo e pene 4,8-dime hyl-1,3,7- nona iene (DMNT) a e p oduced ia bo h o he wo e pene pa hways [12] gi ing e idence o c oss- alk be ween he pa hways. This is an indica ion ha he e is a dynamic pa h- way alloca ion, when plan s a e unde s ess and e penes a e u gen ly needed o plan de ence. Plan phenolics a e syn hesized by se e al di e en bio- syn he ic pa hways, bu mainly ia he shikimic acid and malonic acid pa hways. Plan phenolics a e a e y di e se g oup o plan seconda y compounds om six ca bon simple phenolics o polyme ic annins, which ha e monome uni s o phenolics [13]. Plan alkaloids a e a la ge g oup o ni ogen-con aining plan seconda y compounds o med om common amino acids, lysine, y osine, yp ophan and o ni hine. Alkaloids a e oxic o many he bi o es and ha e medicinal p ope ies [14]. Keinänen e al. [15] ha e demons a ed ha alkaloids espond o exogenous elici o s among he o he majo g oups o plan chemicals. EXOGENOUS ELICITORS Elici o s es ed o pes managemen pu poses a e usually syn he ically p oduced molecules o he chemical com- pounds, which no mally ha e an endogenous ho mone ole in con olling plan de ence. Fu he mo e, ungal cell wall componen s like alame hicin pep ide [16] and chemical compounds in insec sali a o egu gi an can ac as na u al elici o s (Fig. 1). E hylene, C2H4 is a na u al plan ho mone. An e hylene- eleasing subs ance 2-chlo oe hylphosphonic acid (E hephon) ac i a es s ilbene p oduc ion and inc eases he numbe o pa hogenesis- ela ed p o eins in g ape ine leading o he p o ec ion agains ungal pa hogens [17]. Me hyl jasmona e (MeJA), (Z,E)-me hyl 3-oxo-2-(2- pen yl) cyclopen ane ace a e is a plan ho mone o med ia he oc adecanoid pa hway oge he wi h jasmonic acid (JA) [18]. JA and MeJA a e o med in plan s unde a ious bio ic s esses. Biosyn hesis is belie ed o s a wi h he oxygena- ion o ee linolenic acid (LA), wi h u he eac ions ca a- lysed by a lipoxygenase (LOX) enzyme. MeJA is a ca abo- li e o JA and bo h ac i a e genes con olling he seconda y me abolic pa hways. Syn he ic oc a-decanoid phy oho mone mimic compounds like co onalon (6-e hyl indanoyl iso- leucine conjuga e) a e highly ac i e elici o compounds in- ducing simila esponses in se e al plan species [18]. Me hyl salicyla e (MeSA), me hyl-2-hyd oxybenzoa e is an o ganic es e and na u al p oduc o many plan species. MeSA can be p oduced by es e i ying salicylic acid (SA), which as a na u al plan ho mone, a ec s e.g. plan g ow h and de elopmen and ac s as a signal in plan de ence. The compound was egis e ed as a pes icide o he i s ime in 1972, when i was classi ied as an insec epellen [19]. BTH, benzo-(1,2,3)- hiadiazole-7-ca bo hioic acid S- me hyl es e is a unc ional analogue o salicylic acid and ma ke ed wi h he ade names Bion and Ac iga d. I has been shown o induce esis ance o a wide a ie y o plan pa hogens and o ha e e iciency compa able o ha o adi- ional ungicides in con olling e.g. Pe onospo a species [20]. Chi osan is a non- oxic and biodeg adable polyme o be a-1,4-glucosamine. I is a deace yla ed o m o chi in de- i ed om c us aceous shells such as hose o c abs and sh imps. Chi osan has a di ec e ec on ea ed mic oo gan- isms e lec ing i s ungicidal po en ial, bu i also induces a se ies o de ence eac ions in ea ed plan s [21]. ELICITOR IMPACTS ON CONIFER XYLEM CEL- LULAR STRUCTURE AND CHEMISTRY MeJA is one o he mos commonly s udied elici o s on coni e ous ees. MeJA ea men a ec s he syn hesis o e penoids. The e o e, i in luences he cellula s uc u es whe e syn hesis and s o age o coni e oleo esin akes place [22], [23]. Hudgins e al., [24] ound ha in se e al Pinaceae species MeJA induced a esponse pa ly simila o wound- ing, including polyphenolic pa enchyma (PP) cell ac i a ion and xylem auma ic esin duc (TD) o ma ion. MeJA ea men induces xylem TD o ma ion and su ace esinosis in membe s o he Taxodiaceae amily, o ma ion o axial phloem esin duc s bu no xylem duc s in he A auca iaceae and Cup essaceae amilies, whe eas Podoca paceae species showed no induc ion o esin-p oducing s uc u es. In Sco s pine (Pinus syl es is) seedlings MeJA ea men induced he o ma ion o esin duc s in a con inuous band in newly de- eloping s em xylem [8]. Resin duc densi y was signi i- can ly inc eased in xylem c oss-sec ions o Sco s pine seed- lings (Fig. 2). Fu he mo e, MeJA ea men in concen a ion o 100 mM educed annual diame e g ow h and acheid cell lumen a ea, bu no e ec s we e seen in hickness o ba k and phloem [8]. In ano he MeJA expe imen wi h saplings o ou Sco s pine p o enances, only one p o enance showed MeJA induced educ ion in s em diame e [25]. All Pinaceae species ea ed wi h MeJA showed phenolic deposi ion in polyphenolic pa enchyma cells, and ea ly ligni ica ion o phloem ib es was obse ed in mos o he s udied non- Pinaceae species [22]. Exogenous Chemical Elici o s in Disease and Insec Pes Managemen The Open Fo es Science Jou nal, 2009, Volume 2 19 Applica ion o 0.01% MeJA o he soil o po ed Doug- las- i seedlings (Pseudo suga menziesii (Mi b.) F anco) caused nume ous ana omical and chemical changes in he oo s, s em and oliage. These changes we e, o he mos pa , simila o bo h s udied ull-sibling amilies. One o he mos dis inc i e changes was induced auma ic esin duc o ma ion in oo s and s ems [26]. Simila o ma ion o auma ic esin duc s was epo ed by Al a o e al. [27] o occu in he de eloping xylem o ees ollowing insec a - ack. De elopmen o auma ic esin duc s is expec ed o allow ees o mo e induced esin o he si e o damage as a apid and a ge ed de ence agains he bi o es o in ading pa hogens. Chemical di e ences be ween MeJA- ea ed and con ol Douglas- i seedlings we e mainly limi ed o he oo s and s em, hough some changes also occu ed in he oliage [26]. In s ems some di e penes we e inc eased 25- old in concen a ion, which was p obably possible because o inc eased numbe s o auma ic esin duc s. IMPACTS OF ELICITORS ON PLANT DEFENCE CHEMISTRY The elici o s a e compounds ha ha e a na u al unc ion in plan signalling. Gene exp ession analysis by Phillips e al. [28] o No way sp uce (P. abies) demons a ed ha genes encoding 1-deoxy-D-xylulose 5-phospha e syn hase (DXS), which ca alyzes he i s s ep o he MEP pa hway, a e dis- inc ly induced by he a ious elici o s. In cell cul u es, he gene PaDXS2A was induced by ea men wi h chi osan, me hyl salicyla e, and Ce a ocys is polonica (a ba k bee le- associa ed, blue-s aining ungal pa hogen). Howe e , ano he Fig. (2). Xylem c oss-sec ions om s ems o Sco s pine (Pinus syl es is) seedlings ea ed wi h (A) 0 mM (con ol) o (B) wi h 100 mM MeJA, showing MeJA e ec on esin duc densi y (2 esin duc s in con ol and 9 in MeJA ea men ). Red a ea is xylem and blue a ea on he igh is cambium and phloem. Sec ions we e s ained wi h a mix u e o sa anin and alcian blue. Ba = 0.5 mm. Fig. (1). S uc u es o he elici o compounds. 20 The Open Fo es Science Jou nal, 2009, Volume 2 Holopainen e al. gene PaDXS2B was induced by ea men wi h MeJA and chi osan, bu was no a ec ed by MeSA o C. polonica. Mono e pene syn hase was ac i a ed a e applica ion o MeJA o he g ow h medium and se e al mono e penes ac- cumula ed in No way sp uce cell suspension cul u e. Chi o- san and MeJA bo h ac i a ed genes encoding he pa hogene- sis- ela ed 14-3-3 p o ein in seedlings and cell suspension cul u es o Whi e sp uce Picea glauca [29]. Heija i e al. [8] obse ed ha in Sco s pine seedlings he o al mono e pene concen a ion in he cu en -yea xylem was signi ican ly inc eased by 100mM MeJA ea men . O he indi idual mono e penes only he concen a ion o - pinene inc eased signi ican ly. No changes in he o al mono e pene concen a ion we e obse ed in he cu en and p e ious-yea ba k o needles. The o al esin acid concen a- ion in he cu en -yea needles and s em xylem was signi i- can ly highe in he 100 mM ea ed han con ol seedlings. In needles o MeJA ea ed seedlings he concen a ions o mos indi idual esin acid compounds inc eased, whe eas in s em xylem, only he concen a ion o abio ic acid inc eased. This was an indica ion o di e en ial esponses by a ious plan pa s o coni e seedlings o sp aying seedling oliage wi h MeJA. Ano he long- e m MeJA ea men expe imen [25] wi h Sco s pine saplings demons a ed ha olia MeJA applica ion a ec s needle seconda y chemis y wi h signi i- can ly ele a ed concen a ions o wo mono e penes, - pinene and limonene. In wo o he s udied pine p o enances MeJA inc eased he concen a ions o esin acids in he nee- dle oleo esin as well. Soil ea men o Douglas i seedlings wi h MeJA sig- ni ican ly inc eased he concen a ions o mos mono e penes in oo s and s ems, whe eas (E)--ocimene dec eased sig- ni ican ly in he oliage. Fou o he i e de ec ed sesqui e - penes inc eased signi ican ly, mainly in he oo and s em, and ou o he eigh de ec ed di e penes inc eased in e- sponse o MeJA ea men , bu only in oo and s em issues [26]. Mille e al. [30] compa ed he e ec s o a ack by whi e pine wee ils (Pissodes s obi) o applica ion o MeJA -induced e penoid esponses in Si ka sp uce (Picea si chen- sis). Bo h insec s and MeJA caused auma ic esin accumu- la ion in s ems, wi h mo e accumula ion induced by he wee- ils. ELICITOR IMPACTS ON PLANT PATHOGENS ON CONIFERS K okene e al. [31] in es iga ed he e ec o chemical p e- ea men wi h MeJA o oxalic acid (OxA) on pa hogen esis ance o 13-yea -old No way sp uce ees. The ou e ba k o es ees was i s ea ed wi h chemical and hen 4 weeks la e inocula ed wi h he pa hogenic blue-s ain ungus Ce a ocys is polonica. Bo h chemicals signi ican ly educed symp oms o ungal in ec ion, bu MeJA was mo e e ec i e han OxA (51 e sus 18% educ ion in leng h o nec o ic lesions in he phloem ela i e o un ea ed con ol ees). The au ho s concluded ha MeJA ea men o No way sp uce appea s o ha e p ac ical po en ial as a ool o inc easing plan esis ance o ungal in ec ion, bu wi h a modes educ- ion in sapwood g ow h. Kozlowski e al. [32] ound ha umiga ion o P. abies seedlings wi h MeJA (3 days,25 μl 100 l-1 ai ) p o ec ed seedlings om Py hium ul imum in ec ion by up o 75%. The e was no a di ec ungi oxic e ec o MeJA, bu he accumula ion o ee salicylic acid (SA) in all pa s o he seedlings was ound, whe eas bound SA inc eased only in hypoco yls and co yledons. The only epo o BTH e ec s on pa hogen esis ance in coni e s indica ed ha olia sp ays o BTH, sepa a ely and in combina ion wi h po assium phosphona e, educed inci- dence o Phy oph ho a oo o on Pinus adia a and on o he cul i a ed plan s [33]. ELICITOR IMPACTS ON PEST ARTHROPODS Insec s and mi es, bo h a h opods, a e he mos impo - an in e eb a e he bi o es, which damage coni e seed- lings. Heija i e al. [8] es ed he eeding beha iou o he la ge pine wee il (Hylobus abie is L., Coleop e a: Cu culi- onidae) on he MeJA- ea ed seedlings o Sco s pine. The adul wee ils gnawed a signi ican ly smalle a ea o s em ba k in he 100 mM MeJA- ea ed plan s han in he con ol o 10 mM MeJA- ea ed plan s. In e es ingly, he 100 mM MeJA- ea men inc eased he esin acid concen a ion in he needles and xylem, bu no in he ba k. Bo h MeJA ea - men s inc eased he numbe o esin duc s in newly de elop- ing xylem. Howe e , he esin acid concen a ion inc eased in he ba k and dec eased in he xylem o he H. abie is gnawed seedlings compa ed o non-gnawed seedlings. This obse a ion sugges s ha he esin migh ha e lowed om su ounding issues o he ba k, and ha his possibly c ea ed a chemical and physical ba ie o he insec s. I is also pos- sible ha ba k issues migh ha e simul aneously unde gone de no o syn hesis o esin e penoids [34] as a esponse o eeding damage. Folia MeJA applica ion o Sco s pine saplings ep esen - ing ou seed o igins in h ee successi e yea s a ec ed nee- dle seconda y chemis y and signi ican ly inc eased concen- a ions o some mono e penes [25]. The g ow h a es o pine saw ly la ae o he species Neodip ion se i e and Dip ion pini we e educed on needles o MeJA- ea ed plan s wi h ei he high o al e pene o esin acid concen a ion [25]. CROSS PROTECTION WITH ELICITOR TREAT- MENTS So a he e a e no epo s on coni e s whe e impac s o elici o ea men on he bi o es concu en wi h o he he bi- o es o pa hogens we e s udied. Ome e al. [35] in es i- ga ed on g ape ines he e ec s o exogenous applica ions o he na u al plan induce , jasmonic acid (JA) on induced e- sis ance o he oli o ous Paci ic spide mi e, Te anychus paci icus, as well as he oo - eeding g ape phylloxe a, Dak- ulosphai a i i oliae. Folia jasmonic acid applica ion a concen a ions ha caused no phy o oxici y signi ican ly educed he p oduc ion o eggs by bo h he bi o es when hey we e eeding on ea ed plan s [35]. Nega i e c oss- alk be- ween he jasmona e and salicyla e esponse pa hways has been obse ed on oma o. The bac e ial pa hogen, Pseudo- monas sy ingae showed educed lesion de elopmen on o- ma o plan s ea ed wi h BTH and showing ac i a ed salicy- la e esponses, while esis ance o P. sy ingae was no e- duced o enhanced in dual-elici ed (BTH & JA) plan s [36]. In a wild oma o cul i a BTH did no in luence pe o mance o Spodop e a exigua ca e pilla s. In cul i a ed oma o, Exogenous Chemical Elici o s in Disease and Insec Pes Managemen The Open Fo es Science Jou nal, 2009, Volume 2 21 Fig. (3). Vola ile o ganic compound (VOC) emission om wo- yea -old Sco s pine (Pinus syl es is) seedlings sp ayed wi h 30 mM MeJA o 0 mM MeJA (con ol) 48 h be o e VOC sampling (Heija i e al. unpublished da a). educed ac i i y o a de ense p o ein (polyphenol oxidase) in dual-elici ed plan s esul ed in inc eased pe o mance o S. exigua, bu no h ips, spide mi es, ho nwo m ca e pilla s o P. sy ingae bac e ia [37]. The esul s indica e ha he nega- i e in e ac ions be ween elici o s a ec ing jasmona e and salicyla e signalling may ha e biological consequences on he e iciency agains some insec pes s. On he o he hand, Bough on e al. [38] epo ed ha a sp aying wi h a mix u e o BTH and MeJA on oma o has nea ly as good e iciency agains aphids as ha o MeJA alone. ELICITOR IMPACTS ON PLANT VOC EMISSIONS AND NATURAL ENEMIES OF PESTS Inducible plan ola iles emi ed a e he bi o e eeding ha e a signi ican ole in he o ien a ion beha iou o p eda- o s and pa asi oids o he bi o es [39-41]. Jasmonic acid and MeJA ea men a e known o induce simila emissions as he bi o e eeding and he e o e ha e some po en ial o making he ea ed plan s a ac i e o na u al enemies e en be o e he he bi o es a i e on cul i a ed plan s [42]. Ma in e al. [43] ound ha a 10 mM MeJA sp aying ea men igge ed a 5- old inc ease in o al e pene emission om Picea abies oliage, wi h a shi in composi ion o a blend domina ed by oxygena ed mono e penes (e.g. linalool) and sesqui e penes (SQT) e.g. (E)-- a nesene. 5.5 h a e he ea men , no SQT emissions we e de ec ed, bu a e 32.5 h emissions con ained i e SQT and six induced mono e pene compounds. MeJA ea men also induced MeSa emissions. The a e o linalool emission inc eased mo e han 100- old and ha o sesqui e penes inc eased mo e han 30- old. Kän- nas e e al. [44] ound ha he emissions om No way sp uce g a s, caused by E iophyidae mi e (Nalepella sp.) in es a ion had cha ac e is ic lowe -like ag ances con ain- ing la ge amoun s o sesqui e penes E-- a nesene, E,E-- a nesene, mono e pene (-)-linalool, MeSA, and minu e amoun s o some o he inducible e penes and alcohols. These emission p o iles, epo ed in wo di e en s udies, indica ed ha No way sp uce emissions a e MeJA ea - men ha e simila , bu no iden ical p o iles o inducible ola ile compounds. Ou own obse a ions using a Sco s pine (P. syl es is) p o enance (Fig. 3) indica ed ha MeJA ea men induces he ola ile emissions o he mono e penes linalool, limonene, my cene, -pinene and -pinene and ses- qui e penes E-- a nesene and -phelland ene 48h a e ea men . Emissions o hese compounds a e also induced a e eeding by pine wee ils (H. abie is), bu he quan i y is lowe and he a ios be ween he compounds a e di e en (Heija i e al., unpublished). Vola ile e penoid emission p o ile induced by whi e pine wee ils (P. s obi) om Si ka sp uce [30] was mo e complex han emission p o ile induced by MeJA ea men . Wee il eeding caused a apid elease o a blend o mono e pene ole ins, p esumably by passi e e apo a ion o esin com- pounds om eeding damage si es in he ba k s em. These apidly eleased compounds we e no ound in MeJA- induced emissions. This s udy showed ha he ola ile o - ganic compound (VOC) emissions induced by elici o s could be pa ly simila o ce ain he bi o e-induced emissions, as he e was a delayed emission o linalool om bo h ea - men s. Al hough he emission analysis indica ed induced de no o biosyn hesis o linalool he di e ences in emission p o- iles could be de ec ed e.g. by na u al pa asi oids o wee ils. The e o e MeJA ea men does no necessa ily make seed- lings as a ac i e o na u al enemies o his he bi o e as ac- ual damage by he wee ils. The e a e no epo s o he di ec e ec s o elici o s on he beha iou o na u al enemies o coni e pes s. Ib ahim e al. [45] ound ha in Y- ube ol ac ome e es s wi h Co esia es alis he pa asi oid o c uci e - eeding diamond back mo h p e e ed odou o MeJA o il e ed ai . When eleased om aps MeJA and MeSA a ac ed pa asi oids o he amilies Ency idae and Myma idae o g ape ines [46]. These obse a ions indi ec ly sugges ha MeJA ea men could ha e po en ial in a ac ing na u al enemies o coni e seedling pes s o in ac plan s i seedlings a e ea ed be o e a ack by pes insec s and mi es. Howe e , he isk o in- 22 The Open Fo es Science Jou nal, 2009, Volume 2 Holopainen e al. c eased p e e ence o pes insec species o elici o - ea ed plan s is possible. PROS AND CONS OF ELICITOR TREATMENTS Phillips and C o eau [7] lis ed he possibili ies o gene ic enginee ing o manipula e oleo esin o ma ion and coni e esis ance agains ba k bee le a ack. These included a) im- p o emen o he speed and he le el o esponse a he c i i- cal ea ly s ages o ba k bee le a ack, b) inc easing he con- cen a ions o na u al compounds ha a e pa icula ly oxic o in ade s and c) in oducing new de ence genes. Elici o s cu en ly p o ide an excellen ool o simula ing he e ec s o gene ic enginee ing o enhanced mono e pene and di e - pene p oduc ion in coni e s. Elici o - ea ed plan s ha e highe concen a ions o oleo esin, and concen a ions o some compounds in he oleo esin a e mo e dis inc ly in- c eased a e ea men han o he s. Fu he mo e, elici o - ea ed plan s con ain and emi some sesqui e penes, which a e no ound in heal hy un ea ed plan s. Many o hese elici o -induced compounds a e known o a ac na u al enemies o pes s, indica ing ha elici o ea men may allow he c ea ion o a "bu e " o he bi o e enemies be o e he expec ed a ack by pes species. The use o elici o s in c op p o ec ion and pes manage- men is s ill in he e y ea ly s ages o use as a new con ol me hod, and hus he cu en expe iences come om expe i- men al ials, and no ye om la ge scale ag icul u al use. In o es ee p oduc ion he use o elici o s is e en mo e lim- i ed. The e o e, he ollowing summa y o ad an ages and disad an ages o elici o echnique is based mos ly on small- scale ield ials o g ow h chambe and g eenhouse expe i- men s wi h coni e ees. In addi ion p ac ical expe ience o elici o s in c op plan p oduc ion is conside ed. A leas he ollowing ad an ages o using elici o ea men s ha e been epo ed o can be expec ed: • insec eeding damage is educed [8]. • educed symp oms o ungal in ec ion [31]. • educed g ow h a e o he bi o es on elici o - ea ed plan s [25] may inc ease he mo ali y o pes s. • p omo ion o na u al biological con ol by inducing plan ola iles ha a ac na u al enemies o pes in- sec s [45], [46]. • majo pes species do no p e e elici o - ea ed plan s o e un ea ed plan s [45]. • educed en i onmen al haza ds as elici o s a ec di- ec ly he c op plan and hei acu e oxici y o o he o ganisms is lowe han ha o pes icides. • as p o ec i e ag ochemicals, elici o s can be applied wi h he cu en sp aying echnology. • elici o ea men s could be an al e na i e o gene i- cally modi ied (GM) plan s [47] o be e a ac ion o na u al enemies o pes o ganisms on cul i a ed plan s. • elici o - ea ed plan s bea lowe ecological isks and ha e less esis ance om he public han GM ech- nology [48]. The ollowing disad an ages o elici o ea men s can be summa ized: • dec eased pho osyn hesis [8]. • educed plan g ow h [8]. • educed c op plan i ness [38]. • possible educed quali y o imbe wood due o an excess o oleo esin p oduc ion [8]. • pes insec could p e e smell o elici o compounds compa ed o clean ai [45] which a ec o ien a ion beha iou o pes and inc ease pes p essu e. • some o he elici o compounds a e e y expensi e p oduc s and hei use is no cos e ec i e a he mo- men . CONCLUSIONS The e is inc easing e idence ha elici o s could be used in he u u e as al e na i es o adi ional pes icides o man- aging pa hogens and pes s in ag icul u e and nu se y p oduc- ion o o es ees. Elici o ea men s will change he chemical composi ion o he ea ed plan ma e ial. The e- o e, wi h ag icul u al c ops he e a e isks o al e ed ood quali y by inc eased le el o some seconda y me aboli es e.g [11], which may a ec human heal h. A educ ion in lowe - ing and ui p oduc ion could also be a p oblem in annual ag icul u al c ops [38]. In nu se y p oduc ion o o es ee seedlings al e a ions in seedling chemis y does no a ec hei comme cial quali y, bu any ha m ul e ec on he seed- ling g ow h [8] could be dele e ious. T ee seedlings ha a e oo small and slow g owing will no su i e in compe i ion wi h o he ege a ion. In coni e ous ees sys emic-induced esis ance (SIR) ep esen s a common and impo an phe- nomenon [49] [50], allowing localised induc ion by pa ho- gen, he bi o e o elici o o ac i a e de ences also in o he pa s o he plan . Howe e , i o ces ees o balance be- ween alloca ion o esou ces o g ow h and de ence in g ow- ing seedlings. The e o e, dose and iming o elici o ea - men s a e impo an in o de o ob ain seedlings which will be compe i i e in size when plan ed in o es a ion si e. Hube e al. [26] discussed he po en ial p ac ical applica- ions o MeJA ea men o coni e oo s as a pes manage- men s a egy. They sugges ed ha MeJA could possibly be added o he i iga ion wa e in o es nu se ies o imp o e coni e seedling p o ec ion agains pes s and pa hogens. E i- ciency o i iga ion ea men s and seedling g ow h pe o m- ance in nu se ies possibly could be imp o ed wi h inocula- ions o hizobac e ia, which a e known o ac i a e SA pa h- way and inc ease pa hogen esis ance in a hos plan [51]. Applica ion wi h lanolin pas e [22], umiga ion [32] and sp aying [8] ea men s wi h MeJA ha e also been success ul o inc ease pa hogen and pes esis ance o small coni e seedlings (Fig. 4). Slow- elease pa a in wax pelle s ha e been used o elease MeSA in whea ields [52]. The po ed seedlings ea ed a nu se ies may also ha e be e p o ec ion agains a ious bio ic s esses in hei plan ing si es, pa icu- la ly i he elici o is s ill ac i e in he po soil su ace o in pas e applied on ba k su ace. Co onalon and o he syn he ic compounds mimicing cu en elici o s will p obably be cheape o p oduce han syn he ic e sions o o iginal elici o Exogenous Chemical Elici o s in Disease and Insec Pes Managemen The Open Fo es Science Jou nal, 2009, Volume 2 23 compounds and may e en ha e longe las ing e ec s on seedlings. The e o e, phy oho mone mimics migh become employed in u u e cul i a ion p ac ices o elici ing plan esis ance o pes s and diseases, bu hey will equi e simila ex ensi e sa e y es ing as equi ed o pes icides as hey a e no na u al p oduc s. The success ul use o comme cial BTH in plan pa hogen con ol has al eady shown ha elici o s ha e a po en ial o eplace mo e oxic ungicides in u u e. Howe e , in ensi e esea ch is needed o de elop p ac ical elici o -based applica ions in coni e pes and disease man- agemen . ACKNOWLEDGEMENTS We hank he G adua e School in Fo es Sciences and Academy o Finland (decision no. 202300) o he inancial suppo o ou esea ch. Anonymous e iewe s and D . 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