PREFACE TO CHAPTER 3. Biotic and abiotic interactions are important components of any biocontrol system. Host

Transcription

1 PREFACE TO CHAPTER 3 Biotic nd biotic interctions re importnt components of ny biocontrol system. Host plnt ge, within popultion genetic vribility of the host, nd turfgrss competition re interconnected nd determine the efficcy nd performnce of biologicl control gent. Trxcum officinle inter-popultion vrition is well documented in the literture nd in Chpter 3, 14 ccessions of Trxcum officinle collected from different regions in Cnd, USA nd Europe were evluted for their susceptibility to S. minor. In ddition, the effect of plnt ge (growth stge) in the presence nd bsence of grss competition on susceptibility of dndelion to S. minor ws lso studied. The results of this chpter hve been submitted to Weed Reserch (submitted 29 Nov 2005) nd the mnuscript is presently in the peer review process. The mnuscript is co-uthored with my supervisor, Professor Aln K. Wtson. I designed the experimentl set-up, performed the experiments nd the sttisticl nlysis, nd wrote the mnuscript. Professor Wtson supervised the work, provided finncil nd technicl resources, nd corrected the mnuscript. 39

2 CHAPTER 3 Efficcy of Sclerotini minor for dndelion control: Effect of dndelion ccession, ge, nd grss competition MOHAMMED H. ABU-DIEYEH nd ALAN K. WATSON Deprtment of Plnt Science, McGill University, 21,111 Lkeshore Rod, Ste.-Anne-de-Bellevue, Quebec, Cnd, H9X 3V9 40

3 3.1. Abstrct Control of Trxcum officinle (common dndelion) nd other brodlef weeds in temperte turfgrss hs been redily chieved with phenoxy nd like herbicides. The herbicide option hs been revoked through municipl nd provincil legisltion in mny regions of Cnd, necessitting the need for lterntive pproches. We exmined the effects of dndelion ccessions, ge, nd grss competition on the performnce of Sclerotini minor (IMI ) s biologicl control for dndelion in turfgrss. The fungus showed identicl symptoms on 14 different ccessions of dndelion nd reduced bove ground nd below ground biomss by 94% nd 96%, respectively with no difference mong ccessions. Folir dmge nd dndelion mortlity cused by S. minor ws ffected by plnt ge nd the presence of grss competition. Dndelions of ll ges were more severely ffected by S. minor tretment in the presence of grss competition. Grss competition hd greter impct on folir biomss, wheres the fungus hd greter impct on root biomss of newly estblished dndelions. In ddition to competition for resources, we hypothesized tht the grss swrd provides microenvironment fvouring the success of S. minor s biologicl control gent of dndelion. This suggests tht proper mngement of the turfgrss environment improves the efficcy of S. minor s biocontrol for dndelions. Keywords: ge, biocontrol, bioherbicide, ccessions, competition, dndelion, Sclerotini minor, synergy, Trxcum officinle, turfgrss. 41

4 3.2. Introduction The fungus Sclerotini minor Jgger (IMI ) is being studied s biologicl control for dndelion nd other brodlef weeds in turfgrss environments (Ciotol et l. 1991; Riddle et l. 1991; Brière et l. 1992; Schnick et l. 2002; Stewrt-Wde et l. 2002). Recent greenhouse nd long-term field studies hve demonstrted effective control even in low-mintined turf with very high weed infesttion levels dominted by common dndelion (Abu-Dieyeh et l. 2005; Abu-Dieyeh & Wtson 2006: Chpter 5). S. minor is n sporogenic scomycete nd when pplied to turfgrss, rrely produces scleroti (melnized survivl structures), nd these scleroti do not survive over winter (Stewrt-Wde et l. 2002). Field nd greenhouse studies confirmed tht turfgrss species re not susceptible to S. minor IMI (Chpter 8). Independent humn nd environmentl toxicologicl studies hve estblished tht S. minor IMI is neither toxic nor pthogenic to non-trget orgnisms. A biocontrol pthosystem involves severl biotic nd biotic interctions. Understnding the components of plnt-pthogen system is required to mximize the biocontrol success rte (Cousens & Croft 2000). A mjor limiting fctor cn be the host plnt ge, s weed popultions re often mixture of individuls in vrious functionl stges intercting in reltionships with ech other, with other popultions nd with the environment (Rdosevich et l. 1997). Within popultion, genetic diversity of the host is importnt in biocontrol situtions nd should be mtched with pthogen specificity (Cousens & Croft 2000). Generlly, crop interspecific competition fvours biocontrol success by incresing competitive stresses on weed growth nd infesttion (Kennedy & Kremer 1996; Cousens & Croft 2000) 42

5 Turf is mintined s vegettion cover nd cts s cover crop ffecting weed survivl nd exerts more below nd boveground competition thn mny other crops. Dense helthy turfgrss stnds re the best defence ginst weed coloniztion (McCrty et l. 2001; Busey 2003), but quntittive dt re not vilble to discern the reltive contribution exerted by grss competition towrds the performnce of biologicl control gent. Trxcum officinle G.H. Weber ex Wiggers (common dndelion) is perennil weed tht overwinters in the soil s seeds or s perennil roots which cn resprout the following spring (Cyr et l. 1990). My nd September re the pek months of nerly yer-round emergence of dndelion (Chepil 1946) nd the plnt my perennite up to yers (Roberts 1936). Therefore, n estblished dndelion infesttion in turf is popultion of mixed ges. The susceptibility of trget weed to bioherbicide my chnge with plnt ge. For exmple, younger stges were more susceptible to biologicl control gent (Boyette & Wlker 1985; Léger et l. 2001) while in others, the seedling stge ws less susceptible (Mkowski 1993; Hoke & Drger 2004). The detrimentl effect of plnt ge could be overcome by incresing inoculum concentrtion (Msngky et l. 1999) or by modifying the biotic nd biotic environments (Kennedy & Kremer 1996). Interspecific competition by plnting cover crop, improved the effectiveness of biocontrol gent on hedge bindweed (Guntli et l. 1999). Moreover, grss vegettion cover hs been shown to reduce mny growth fetures of certin weeds (Müller-Schärer 1991; Story et l. 2000) nd could be combined with biologicl control gent s complement for control (Dhileepn et l. 2000). 43

6 Biotic interctions between grss competition nd dndelion ge nd biotypes re expected in turfgrss environments. But it is importnt to hve cler understnding of the mgnitude of the contribution of ech fctor nd the combintions of fctors on dndelion control efficcy s influenced by S. minor. The objectives of this reserch were to ssess the susceptibility of different dndelion ccessions nd different ges of dndelion to S. minor (IMI ) nd to quntify the reltive importnce of turfgrss competition nd the biologicl stress of S. minor on dndelion survivl nd biomss reduction Mterils nd methods Phenotypic vritions of dndelion ccessions During the summer of 2004, fruiting heds of individul dndelion plnts were collected from university cmpuses or botnicl grden lwns from different loctions in the USA, Cnd, nd Europe. Seeds of ech ccession were sown onto potting soil (2/3 blck psteurized soil nd 1/3 Pro-mix (Premier Promix, Premier Horticulture Ltee, Rivieredu-Loup, QC) in 40 x 30 x 8 cm trys in the greenhouse (24 ± 2 o C with 15 hr of light/dy t photon flux density minimum of 350 ± 50 µmol m -2 s -1 ). Ten 2-wk-old seedlings with uniform vigour from ech ccession were individully trnsplnted to 15-cm-dimeter pot contining mixed potting soil (s described bove). These potted seedlings were rrnged in completely rndomized design on greenhouse bench nd mintined under conditions described bove, with progrmmed drip irrigtion of 20 ml/pot three times dy. Eight weeks fter trnsplnting (10-wk-old plnts) morphologicl study ws ccomplished to ssess the vritions mong ccessions (Appendix-3). 44

7 Efficcy of the grnulr S. minor bioherbicide on 14 dndelion ccessions Sclerotini minor (IMI ) ws isolted from disesed lettuce plnts (Lctuc stiv L.) from southwestern Quebec nd the stock culture ws mintined s scleroti t 4 o C. The myceli of the germinted scleroti were used to inoculte utoclved brley grits ( mm dimeter) s described in chpter 5 (Abu-Dieyeh nd Wtson 2006). The S. minor grnulr formultion ws freshly prepred two weeks prior to tretment pplictions. Vibility nd virulence of the fungl inoculum were ssessed prior to use on PDA pltes nd excised dndelion leves (see chpter 5). Seven 2-wk-old seedlings with uniform vigour from ech of the 14 ccessions were individully trnsplnted into 15 cm dimeter pots contining mixed potting soil (s bove). Pots were plced rndomly on greenhouse bench nd mintined under conditions described bove. Eight weeks fter trnsplnting, plnts were misted with wter nd five plnts of ech ccession were selected t rndom nd ech ws inoculted with 0.2 g of the S. minor grnulr formultion. Two plnts of ech ccession remined s untreted controls. Two min. durtion of mist ws pplied dily over ll the pots for one week. Symptoms of dmge to dndelions were recorded weekly for two weeks fter ppliction using 0 to 10 visul scle, where 0 = no or less thn 10% dmge in boveground biomss compred to the control of the sme ccession, 1 = 11-20%.9 = 91-99% nd 10 = 100% collpse of the boveground biomss. Dt were converted bck to percentge (fter Schnick et l. 2002). The experiment ws repeted. 45

8 Effect of the S. minor bioherbicide on bove nd below ground biomss of dndelion Fifty 2-wk-old seedlings for ech of seven ccessions (two from Cnd, three from USA, nd two from Europe) were trnsplnted equidistntly into drined, plstic continers (40 x 32 x 20 cm, 19 L cpcity) (Sterilite Inc., Montrel QC) contining mixed potting soil. There were 10 continers with five seedlings for ech of the seven ccessions. The continers were plced in rndomized complete block design in the greenhouse nd mintined under conditions described bove. The plnt continers received progrmmed drip irrigtion of 50 ml five times dy. Two weeks fter trnsplnting, 2.5 g of commercil grss seed mixture [30% Kentucky bluegrss (Po prtensis L), 40% creeping red fescue (Festuc rubr L. vr. rubr) nd 30% turf type perennil ryegrss (Lolium perenne L.), C.I.L. Golfgreen, Brntford, ON] ws scttered uniformly over the soil surfce in ech continer. Just prior to weed control tretment ppliction (8 weeks fter trnsplnting), the plnts were misted with wter. Three out of five plnts in ech pot were selected t rndom nd treted with 0.2 g of the S. minor grnulr formultion. The other two plnts were left untreted s controls. Symptoms of dmge to dndelions were recorded weekly for four weeks fter ppliction using the 0 to 10 visul scle. Plnt survivl ws recorded weekly for six weeks. Plnt regrowth ws mesured s reduction in % dmge by estimting the biomss of new leves produced post inocultion compred to the control within the sme continer. Dmge estimtes of the three treted plnts in ech continer were verged nd nlyzed s one experimentl mesure. Six weeks fter ppliction, ll dndelion plnts were crefully removed from the soil, the roots were 46

9 thoroughly wshed nd dissected bove the crown, seprting bove ground nd below ground biomss. Treted nd control plnt mterils (leves or roots) from ech continer were seprtely bulked, plced in pper bgs, oven dried t 80 o C for 72 h, nd then weighed Interctions mong the S. minor bioherbicide, dndelion ge, nd grss competition Dndelion seeds collected in spring 2002 from lwns on the Mcdonld cmpus, McGill University, Ste-Anne-de-Bellevue, QC nd stored t 4 o C were sown onto mixed potting soil (s described bove) in plstic continers (40 x 32 x 20 cm, 19 L cpcity). Dndelion seeds were sown t timed intervls to ttin plnt mteril of desired plnt ge sttes (4, 6, 8, 10 nd 13 weeks) t the time of tretment. Extr seeds were sown for ech plnt ge to hve replcement plnts if required. One week fter germintion, seedlings were thinned to four equidistnt seedlings per continer. Two weeks fter germintion of dndelion seeds, 2.5 g of commercil grss seed mixture (C.I.L. Golfgreen, Brntford, ON) ws scttered over the entire surfce of one-hlf of the continers designted for certin plnt ge group. The remining continers of ech plnt ge were not sown with grss. Once estblished, the grss ws clipped with hedge shers (PlntSmrt, Wl*Mrt, Montrel, QC), ech week to mintin pproximtely n 8 cm grss height, but clipping of dndelion leves ws voided. The experiment ws split-split-plot design with four replictions of ech plnt ge nd conducted twice through time, in Mrch 2003 nd Min plots were weed control tretments, untreted or treted with spot ppliction of 0.2 g plnt -1 grnulr 47

10 formultion of S. minor. The subplots were the presence or bsence of grss competition nd the sub-sub-plots were the different dndelion ges of 4, 6, 8, 10 nd 13 weeks of ge. Tble 3.1 provides the verge number of leves for ech group of plnt ges t the time of ppliction. Prior to fungl ppliction, ll plnts were misted lightly with wter to id grnule dhesion to dndelion leves. Plnts were grown in greenhouse t 20 ± 2 o C with 15 h of light per dy t photon flux density minimum of 350 ± 50 µ mol m -2 s - 1. Plnt continers received progrmmed drip irrigtion of 150 ml three times per dy. Tretment efficcy ws visully recorded weekly for six weeks fter ppliction using 0-10 scle (s described bove). Dmge estimtes of ll 4 plnts in ech continer were verged nd treted s one experimentl unit. Dndelion survivl nd regrowth fter 100% dmge of bove ground biomss were recorded weekly for six weeks. Six weeks fter ppliction, dndelion plnts were hrvested s described bove Determining the efficcy of the S. minor bioherbicide on dndelion t flowering stge Dndelion rrely flowered under greenhouse conditions nd the effect of S. minor on the flowering stge of dndelion ws delyed until sufficient number of plnts cme into flower. A seprte experiment ws conducted under similr greenhouse conditions s described bove with 10 plnts in the presence of grss [16- to 18-wk-old; 20 leves (18-24) leves/plnt] nd nother 10 plnts without grss [14- to 16-wk-old; 16 leves (14-20 leves/plnt] ll in the reproductive phse (t lest one flowering scpe). The S. minor grnulr formultion ws pplied (0.2 g/plnt) on five plnts of ech group; the other five remined s untreted controls. The plnts were misted with wter prior to inocultion 48

11 nd dily for week fter inocultion. One month fter ppliction, the boveground dmge, bove nd belowground biomss nd survivl rte were ssessed s mentioned bove Dt Anlysis Morphologicl phenotypic differences mong different ccessions were nlyzed with Kruskll-Wllis test for one wy nlysis of vrince nd the mens of ech chrcter were seprted using Tukey s test t P 0.05 (dt not presented). Dmge through time dt for ech time period, dry mtter biomss dt nd the number of survived plnts from the two experimentl repets on plnt ge were nlyzed seprtely showing similr results. The dt from both repets were pooled then subjected to Levene test of SAS (SAS Institute Inc., Cry, NC, 2002) to test for homogeneity of error vrinces. Dt from both repets were combined s error vrinces were homogeneous. SAS GLM procedure of repeted mesures ws used to determine effects on boveground dmge through time. Above ground dmge dt t 2-wk-post ppliction for the 14 ccessions study, % survivl of plnts nd the bove nd below ground biomss dt of ech experiment were subjected to ANOVA of SAS procedure nd the mens were seprted using Tukey s test t P 0.05 (SAS 2002). 49

12 3.4. Results Vegettive phenotypic vrition of dndelion ccessions Dndelion ccessions were differentited by severl chrcters, most of them relted to lef morphology (M.H. Abu-Dieyeh & A.K. Wtson, unpublished, see Appendix-3). Despite the intr-popultion vrition within ech ccession, within ech single chrcter there ws significnt vrition mong the ccessions. The rosettes of dndelion could be with erect, in between or hve flt leves. The tp root length rnged from 98 to mm. Lef nd root biomss vritions were lso recorded mong the different ccessions of dndelion Susceptibility of dndelion ccessions to S. minor There were no significnt (P = 0.731) differences in bove ground dmge mong the 14 ccessions two weeks fter S. minor ppliction in preliminry experiment (dt not shown). Dmge rnged from 82 to 96%. There were no significnt differences in boveground dmge (79.4% to 96%) mong seven ccessions four weeks fter ppliction. Biomss reduction of treted plnts ws highly significnt (P 0.01) compred to untreted plnts. The verge percentge reduction in lef nd root biomss ws 94% nd 96%, respectively (Figure 3.1). Some plnts were not completely defolited nd survived the tretment. Other plnts resprouted from the root crown even fter complete bove ground collpse (Figure 3.2). There ws no significnt differences mongst ccessions in either the percentge of plnts survived (P = 0.654) or the number of resprouted plnts (P = 0.967) fter S. minor tretment. The surviving folige nd regrowth ws very wek nd lcked vigour. 50

13 Combined effects of grss competition nd plnt ge on biocontrol efficcy Highly significnt effects (P 0.01) were obtined from grss competition, plnt ge, nd interctions of the two fctors on bove ground dmge of dndelion cused by S. minor. In the presence of grss competition, 4- nd 6-wk-old-treted plnts completely collpsed without ny recovery, wheres older plnts, fter lmost 100% dmge two weeks fter ppliction, showed some degree of recovery, positively correlted to plnt ge (Figure 3.3). For ll ges up to 10-wk-old-treted plnts, the fungus cused severe cumultive dmge of pproximtely 90% nd only the 13-wk-old-treted plnts were ble to recover prtilly with 50% dmge six weeks fter ppliction. When grown in grss free environment culture, 4-wk-old-treted dndelions were highly susceptible with 100% collpse of ll tested plnts (Figure 3.3). Older plnts were lso hevily dmged (80-95% bove ground dmge) two weeks fter ppliction. The level of dmge decresed with corresponding less dmge with older plnts. Incomplete dmge of plnt leves nd/or vegettive regrowth ws the cuse of decresing dmge vlues. There ws significntly less dmge to the 13-wk-old-treted plnts thn to younger plnts one week fter ppliction. The 6-wk-old-treted plnts responded similrly to the 8- nd 10-wk-old-treted plnts from the first to the fifth week fter ppliction. In the presence or bsence of grss competition, there ws no significnt difference in biocontrol efficcy on 4-wk-old-treted plnts. However, differences were significnt (P 0.01) on the 6- nd 13-wk-old-treted plnts. For the 8- nd 10-wk-oldtreted plnts there ws no significnt difference between the two grss tretments up to two weeks fter ppliction, but fterwrds the differences were significnt (Figure 3.3). 51

14 Except for the well estblished roots of the 13-wk- old dndelion, competition due to grss significntly reduced the survivl rte in ll plnt ges. Survivl ws due to regrowth fter prtil or complete (100%) folir dmge of the treted plnts. The boveground dmge ws lwys 100% whenever the grss ws present nd the regrowth, if ny, ws very fril tiny sprouts from dmged crowns of some plnts. The survivl rte ws correlted with plnt ge in the presence or bsence of grss competition. Survivl ws significntly lower in the presence of grss competition thn in the bsence of grss competition in ll ged plnts except for the 4- nd 13-wk-oldtreted plnts. In the presence of grss, no regrowth occurred for the 4- nd 6-wk-oldtreted plnts. Menwhile in the bsence of grss, only the youngest ge did not regrow (Figure 3.4). The biomss of leves nd roots ws severely diminished by combining grss competition nd S. minor tretments. The men differences were significntly (P 0.01) less thn ny other tretment combintion for both boveground nd root biomss (Figure 3.5). The boveground biomss for untreted dndelions without grss competition were similr for the 8-, 10- nd 13-wk-old-treted plnts (Figure 3.5A) while the 6-wk-old-treted plnts hd the sme root biomss s ll older ges (Figure 3.5B). The fungus lone or the presence of grss lone hd similr effects on the lef dry mtter of the 4-, 6- nd 13-wk-old-treted plnts while the grss fctor lone cused significntly more reduction thn the fungus lone on the 8- nd 10-wk-old-treted plnts (Figure 3.5A). However, there ws no significnt difference in root dry mtter reduction between fungus or grss presence lone, except in the 6-wk-old-treted plnts where the 52

15 fungus without grss ws significntly more effective in reducing root biomss thn grss competition lone (Figure 3.5B). The gretest biomss gin in the presence or bsence of grss competition occurred when dndelions were from 4 to 6 wk of ge (Figure 3.5). The root biomss gin ws significntly higher thn the gins during ll other growth periods in the bsence of grss, while not higher thn the 10- to 13-wk growth period under the presence of grss. Except for the oldest plnt ge, the fungus cused greter reduction in root biomss thn grss competition did (68-100% compred with 56-89%), wheres grss competition cused greter reduction in lef biomss, except for the two youngest ges (38-72% compred with 34-44%). Wheres in the presence of grss competition, flowering dndelions were highly susceptible to S. minor showing significnt bove ground dmge nd biomss reduction (Tble 3.2). Grss competition resulted in biomss reductions similr to those cused by the fungus lone. One month fter ppliction, only one out of five S. minor treted flowering dndelions ws ble to survive in the presence of grss with very wek regrowth, s compred to three out of five with some regrowth in monoculture. 53

16 Tble 3.1. Averge (± stndred devition) number of dndelion leves of different ge groups t the time of ppliction of the S. minor grnulr formultion. Averge of 16 plnt replictes. Grss Dndelion Age (weeks) plnting present 4.8 ± ± ± ± ± 1.0 bsent 5.6 ± ± ± ± ± 1.7 Tble 3.2. Influence of grss competition on the efficcy of S. minor to cuse dmge nd biomss reduction fter one month of ppliction on dndelion t flowering stge. Averge of five plnt replictes. Biomss (g) S. minor Grss competition Aboveground Dmge % Lef Root Treted present 94 (1) 0.28 c 0.38 c bsent 62 b 1.55 b 1.76 b Untreted present 6.0 c 1.68 b 1.98 b bsent 4.0 c (1) Mens in column shring the sme letter re not significntly different ccording to Tukey s test t P =

17 Figure 3.1. Effect of S. minor (IMI ) on shoot (A) nd root (B) biomss of different dndelion ccessions six weeks fter spot ppliction with 0.2 g/plnt of S. minor grnules. Within ech grph, brs with common letter re not significntly (P = 0.05) different ccording to Tukey s test. Dndelion ccessions: 1. Ste-Anne-de- Bellevue, Québec, Cnd; 2. Cornwll, Ontrio, Cnd; 3. Tuscloos, Albm, USA; 4. Anchorge, Alsk, USA; 5. Sn Mrino, Cliforni, USA; 6. Cory Lodge, Cmbridge, UK; 7. Utrecht, The Netherlnds; 55

18 1.2 Aboveground dry mtter plnt -1 (g) b bc bc c bc b A 0.0 d d d d d d d b B Root dry mtter plnt -1 (g) bc bc bcd d cd Untreted e e e e e e e Treted with S. minor Dndelion ccession 56

19 Figure 3.2. Survivl nd regrowth of dndelion ccessions fter spot ppliction (0.2 g per plnt) of S. minor grnules. Error brs represent stndrd errors of totl survivl mens. Vlues re the mens of 30 replictes. Dndelion ccessions: 1. Ste-Anne-de- Bellevue, Québec, Cnd; 2. Cornwll, Ontrio, Cnd; 3. Tuscloos, Albm, USA; 4. Anchorge, Alsk, USA; 5. Sn Mrino, Cliforni, USA; 6. Cory Lodge, Cmbridge, UK; 7. Utrecht, The Netherlnds Prtilly killed plnts regrown plnts 35 Survivl (%) Dndelion ccession 57

20 Figure 3.3. Effects of plnt ge nd grss competition on the control of dndelion using S. minor. The mens were seprted using Tukey s test t P = 0.05, within ech grph, nd t ny time post ppliction, vlues with common letter re not significntly different. (A) grss bsent (B) grss present. 58

21 120 A b b b bc c b c b 60 c bc c b bc c b Above ground dmge (%) weeks old t ppliction 10 weeks old t ppliction 8 weeks old t ppliction 6 weeks old t ppliction 4 weeks old ppliction B b b b d c c b b b c Weeks post ppliction 59

22 Figure 3.4. The effect of plnt ge nd presence of grss on percentge survivl of dndelions, six weeks fter S. minor ppliction. Vlues with common letter re not significntly different ccording to Tukey s test t P = Survivl (%) 6 weeks fter ppliction With grss Without grss c c b b 0 d d d Dndelion ge t time of ppliction (weeks) 60

23 Figure 3.5. The effect of plnt ge nd grss competition on boveground (A) nd root biomss (B) of dndelions six weeks fter ppliction of S. minor grnules. Vlues in figure with common letter re not significntly different ccording to Tukey s test t P =

24 4.0 S. minor treted; with grss S. minor treted; without grss A Above ground dry mtter plnt -1 (g) 6 weeks fter ppliction Untreted; with grss Untreted; without grss i i hi de i fg fg b i cde gh hi cd ef h bc cde 4.0 B 3.5 b Root dry mtter plnt -1 (g ) 6 weeks fter ppliction bc c d d de de de ef ef fg g g g g g g Dndelion ge t time of ppliction (weeks) 62

25 3.5. Discussion Despite obligte pomixis, intrspecific vrition in T. officinle is well documented in the literture (s reviewed by Stewrt-Wde et l. 2002b) by isozyme nlysis (Solbrig 1970; Lymn & Ellstrnd 1984), microstellite DNA nlysis (Flque et l. 1998) nd meristic nd morphologic nlysis (Collier & Rogstd 2004). The high intrspecific morphologicl vrition within dndelion popultions hs lso been ttributed to phenotypic plsticity (Richrds 1973) Dndelion is highly dpted perennil (Stewrt- Wde et l. 2000b), with high phenotypic plsticity occurring in genotypiclly diversified popultions within the sme field (Solbrig 1970). Significnt morphologic nd meristic vritions were found in our 14 dndelion ccessions grown under constnt controlled environmentl conditions. Differences in florl stge timing nd reproductive efforts mong the ccessions were lso recorded (M.H. Abu-Dieyeh & A.K. Wtson, unpublished dt, see Appendix-3). Similr to the findings of Collier & Rogstd (2004), the vritions mong our dndelion ccessions were due to genotypic vritions rther thn phenotypic plsticity. In plnt: pthogen systems, phenotypic vritions cn be ssessed using virulence biossys rther thn isozymes or moleculr techniques (Cousens & Crft 2000). Sclerotini minor is necrotrophic, brod host rnge plnt pthogen tht cn cuse economic dmge to mny crops prticulrly lettuce nd penut (Abwi & Grogn 1979; Melzer et l. 1997). Newtown nd Sequeir (1972) identified lettuce lines tht were highly resistnt to S. sclerotiorum nd ttributed this to their upright growth hbit. However, subsequent evlution of these lines by Abwi et l. (1980) nd Subbro (1998) indicted tht there ws no ssocition between growth hbit nd resistnce nd 63

26 none of the screened ccessions possessed resistnce to S. minor. Despite the significnt morphologic nd meristic differences mong the 14 ccessions collected from different loctions in North Americ nd Europe, ll the ccessions were similrly susceptible to the S. minor grnulr formultion. The regrowth from the root crown of S. minor treted plnts could be n expression of tolernce. However, this regrowth ws very wek nd my mke dndelions more vulnerble to interspecific competition, seson long mowing, or winter injury. Severl studies hve indicted tht the regrowth fter biotic stress my be more constitutively resistnt to some pthogens nd insects thn older leves (Krbn & Bldwin 1997; Green & Biley 2000; Htcher & Melnder 2003), but this is not the cse in our pthosystem s the regrown dndelion leves hve shown high degree of susceptibility to second S. minor ppliction (M.H. Abu-Dieyeh & A.K. Wtson, unpublished dt). Although, there were no significnt differences in survivl nd regrowth mong the 14 ccessions, the highest percentge regrowth occurred in ccessions no. 3 (Albm) nd no. 4 (Alsk) (Figure 3.2). Interestingly, these ccessions hd the longer tproots, but not the highest root biomss. It is known tht competitive, well-estblished dndelions possess deep tp roots tht cn extend below the level of competition of grss roots (Loomis et l. 1938: cited in Stewrt-Wde et l. 2002b). In this study, dndelions of ll ges were susceptible to S. minor in the presence or bsence of grss competition. However, grss competition significntly incresed the boveground dmge, incresed root nd lef biomss reduction, nd reduced the survivl rte of treted dndelions. Grss competition my promote S. minor to exert 64

27 fster nd greter disese development nd consequentil less chnce for the plnt to cpture resources nd regenerte from the roots. The susceptibility of dndelions to S. minor decresed with plnt ge s hs been shown for other pthosystems including those studied for biocontrol (Boyette & Wlker 1985; Lèger et l. 2001; Riddle et l. 1991; Neumn & Bolnd 2002), lthough some plnts re less susceptible t the seedling stge (Mkowski 1993; Hoke & Drger 2004). Decresing susceptibility with ge is common even with herbicides, nd dndelion seedlings re susceptible to 2,4-D, while estblished dndelions re intermedite in susceptibility due to the sorption cpcity of the cuticulr membrne (Bker & Bukovc 1971). The effect of grss competition on dndelion estblishment nd development ws determined by exmining the dry mtter dt (presented in Figure 3.5) for untreted plnts s they progressed in ge. During the 6 wk period from tretment to hrvest, dndelion plnts gined the gretest biomss during the 4-wk to 6-wk period under both environments, but 2-fold higher root biomss (1.96 vs 1.03 g plnt -1 ) in the bsence of grss compred with the presence of grss. In the bsence of grss competition, root biomss ws mximized in the 6-wk-old plnts nd shoot biomss mximized in the 8- wk-old plnts. These results my explin why the efficcy of S. minor on the 6-wk-oldtreted dndelion ws similr to the efficcy on older plnts in the grss free environment. In competitive environment we hypothesized tht, dndelions will llocte resource differently, this lloction could occur grdully nd should fvour root resources in lter growth stges, consequently resulting in root extension deeper thn 65

28 grss roots. Although the finl lef or root biomss ccumultion (of the 4 wk- to 13-wkold plnts) ws proportionlly similr in the presence or bsence of grss competition, it ws ttined by the 8- nd 6-wk-old-treted plnts, respectively in grss-free environment, while both lef nd root mximl biomss occurred in the 13-wk-old plnts in the presence of grss. In the presence of grss, root biomss gin ws ~ 2-fold greter thn the lef biomss from the 8- to 13-wk-old plnts (1.29 nd 0.71 g plnt -1, respectively) Therefore the 13-wk-old-treted plnts were better estblished in the presence of grss, enbled them to regenerte fter S. minor ppliction s reflected in enhnced survivl compred with younger plnts. Except for the 4-wk-old-treted nd 13-wk-old-treted plnts, grss competition combined with S. minor reduced the survivl of dndelion significntly compred with no grss competition. In the cse of the grss free environment, the survivl ws more due to the incomplete dmge of the boveground biomss, while it ws due to root regrowth fter complete boveground dmge in the presence of grss competition. This regrowth ws very wek since the reduction in root biomss ws very severe, thus these plnts my hve likely soon succumb if the experiment ws extended longer. Our dt indicted decrese in survivl of regrown dndelions fter eight weeks compred to six weeks post ppliction of S. minor in greenhouse conditions (Chpter 5). Surprisingly, with the 8- nd 10-wk-old-treted plnts, the grss competition lone exerted more significnt reduction in boveground biomss thn the fungus with no grss competition while the fungus lone cused more significnt reduction on root biomss thn grss competition on the 6-wk-old-treted dndelions. Four-wk-old-treted dndelions were extremely susceptible to S. minor nd killed in both grss environments 66

29 nd importntly it ws the ge with the gretest gin of lef nd root biomss in both grss environments hence no significnt effect ws obtined from grss fctor on the efficcy of control. Erlier studies suggested tht the estblishment of dndelion seedlings ws strongly inhibited in res of dense grss cover due to insufficient open ground nd light penetrtion (Molgrd 1977). Chnces of seedling estblishment re decresed 23 times in res with lush grss vegettion compred with open res (Ford 1981). Grss competition significntly enhnced the efficcy of S. minor on flowering dndelion. Although the flowering plnts were older thn 13 weeks, there ws more boveground dmge, more biomss reduction, nd less survivl in the presence of grss competition. Similr results were obtined with Phom glomert on dndelion (Neumn nd Bolnd 2002). Survivl of dndelion treted in the spring (bout 90% in the flowering stge) with S. minor ws significntly lower thn tht in the fll tretment (Abu-Dieyeh & Wtson 2006: Chpters 5 & 7). In the bsence of control, the survivl of 2 cm long dndelion roots collected in My, t the time of mximum flowering, ws less thn tht for the roots obtined from June to September of the sme yer (Mnn & Cvers 1979). In the spring, dndelions re known to llocte more resources for flowering nd vegettive growth thn for root growth (Cyr et l. 1990), nd this my explin the reduced survivl nd regrowth of flowering dndelions fter S. minor infection. Our results ddress the importnce of grss competition to control dndelion with S. minor in turfgrss systems. From our field experiments, greter survivl of treted dndelions occurred in plots with low grss density nd/or bre ground thn in high 67

30 density grss plots (Chpter 7). Indeed, dndelion popultions in field environments re expected to be of mixed ges nd mixed genotypes nd consequently, survivl nd regrowth fter S. minor ppliction could be explined by severl fctors nd interctions rther thn grss competition lone. Additionl fctors, such s competition durtion, degree of grss estblishment, intrspecific competition within dndelion popultion, nd interspecific competition with other weeds, my ll ffect the competitiveness between dndelion nd turfgrss, nd consequently the performnce of S. minor Acknowledgments The uthors thnk Philippe Sèguin for his vluble help in sttisticl nlysis, Miron Teshler for his ssistnce in field nd lbortory ctivities, nd Inm Shheen for reviewing the mnuscript. The uthors thnk the following for providing the dndelion seeds used in this study: Hns Persoon (University Botnic Grdens, Utrecht, The Netherlnds); Michel D. Wll (Rncho Snt An Botnic Grden, Clremont, Cliforni); Jn Hnscom (Georgeson Botnicl Grden, University of Alsk, Firbnks); Brbr Miller (Alsk Botnicl Grden, Anchorge). Frnzisk Zerglein (Sir Hrold Hiller Grdens; Ampfield, Hmpshire, UK); Chrles E. Tubesing (The Holden Arboretum, Kirtlnd, Ohio); Debr Folsom (Huntington Botnicl Grden, Sn Mrino, Cliforni); Wesm Abdel-Rzq (Queen s Medicl Center, Nottinghm, UK); Suhil Hbshneh (University of Albm, Tuscloos); Peter Atkinson (Cmbridge University Botnic Grden, Cmbridge, UK); Deborh A. Lewis (Iow Stte University, Ames); Thoms Rosburg (Drke University, Des Moines, Iow); nd Yousef Abu-Nd (Plnt Science Deprtment., McGill University, Montrel, Quebec). 68