Evaluation of commercial arbuscular mycorrhizal inoculants

Transcription

1 Evlution of commercil rbusculr mycorrhizl inoculnts A. Fye 1,2,3, Y. Dlpé 4,7, K. Ndung u-mgiroi 5, J. Jefw 2, I. Ndoye 3, M. Diouf 1, nd D. Lesueur 6 Cn. J. Plnt Sci. Downloded from by on 04/06/18 1 Institut Sénéglis de Recherches Agricoles, Centre d étude Régionl pour l Améliortion de l Adpttion à l Sécheresse, BP 3320, Thiès, Sénégl; 2 Tropicl Soil Biology nd Fertility, c/o ICIPE Duduville Cmpus, Off Ksrni Rod, PO Box , Nirobi, Keny; 3 Université Cheikh Ant Diop de Dkr, Fculté des Sciences et Techniques, Déprtement de biologie végétle, BP 5005 Dkr, Sénégl; 4 Estern Cerel nd Oilseed Reserch Centre, Agriculture nd Agri-Food Cnd, 960 Crling Ave., Ottw, Ontrio, Cnd K1A 0C6; 5 Kenyn Agriculturl Reserch Institute, PO Box 107, Kitle, Keny; nd 6 Centre Interntionl de Recherches Agronomiques pour le Développement, UMR Eco&Sols (CIRAD-IRD-INRA-SupAgro), Lnd Development Deprtment, 2003/61 Pholyothin Rod, Lrdyo Chtuchk, Bngkok 10900, Thilnd. Received 18 December 2012, ccepted 15 July Published on the web 1 October Fye, A., Dlpe, Y., Ndung u-mgiroi, K., Jefw, J., Ndoye, I., Diouf, M. nd Lesueur, D Evlution of commercil rbusculr mycorrhizl inoculnts. Cn. J. Plnt Sci. 93: In order to improve the use of commercil inoculnts, 12 rbusculr mycorrhizl fungi (AMF) inoculnts were evluted in two-step experiment under greenhouse conditions using mize. First, commercil mycorrhizl inoculnts were propgted in trp pot culture experiment under sterilized snd to evlute their potentil for mize (Ze my L.) root coloniztion s compred with n indigenous soil inoculum nd to survey the AMF species present in the products. Three inoculnts significntly incresed root coloniztion levels compred with soil inoculum. Insted of 12 declred AMF species, 13 fungl strins were extrcted from the pot culture survey, including five undeclred species, while four declred species did not produce spores. In second experiment, commercil products were inoculted into soil to ssess their impct on mize growth nd yield. Six weeks fter plnting, seven inoculnts incresed root coloniztion levels compred with control soil, while only three inoculnts incresed slightly the shoot biomss of mize plnts. These experiments highlight the need to pre-evlute commercil mycorrhizl inoculnts on selected crop nd regionl soil before lunching lrge-scle field use. Key words: Commercil inoculnts, mize, spore popultion, Keny Fye, A., Dlpe, Y., Ndung u-mgiroi, K., Jefw, J., Ndoye, I., Diouf, M. et Lesueur, D Evlution of commercil rbusculr mycorrhizl inoculnts. Cn. J. Plnt Sci. 93: Afin d optimiser l usge des mycorhizes en griculture, douze inoculnts commerciux de chmpignon mycorhizien rbusculire (CMA) furent e vlue s en serres sur le mïs. Dns un premier temps, les inoculnts furent propgés en pots sur sble stérilise fin d e vluer leur potentiel sur l colonistion rcinire du mı s pr rpport ` celui d un sol gricole du Keny et d inventorier les espe` ces CMA contenues dns les inoculnts. Trois inoculnts ugmente` rent le tux de colonistion rcinire compré u sol gricole. Treize espe` ces AMF furent isole es des inoculnts dont 5 non de clrées. Qutre des 12 espe` ces nnonce es n ont ps sporule. Dns une seconde expe rience, les inoculnts furent utilise s en combinison vec le sol gricole fin d e vluer leur impct sur le rendement du mı s. Six semines pre` s le semis, 7 inoculnts ugmentèrent le tux de colonistion rcinire pr rpport u sol témoin lors que 3 inoculnts entrıˆne` rent une légère ugmenttion de l biomsse e rienne. Ces e vlutions démontrent l ne cessite d effectuer une pre -évlution des inoculnts commerciux sur une culture et un sol donne s vnt de les implnter ` grnde échelle. Mots clés: Inoculnts commerciux, mı s, popultion sporle, Keny 7 Corresponding uthor (e-mil: yolnde.dlpe@ gr.gc.c). Competing interests: The uthors declre tht they hve no competing interests. The mention of commercil products in this publiction does not imply ny endorsement by the uthors. Other products of similr qulity exist in world mrkets. The products mentioned in this publiction re for illustrtive use only. No finncil support from commercil compnies hs been received by the uthors. Arbusculr mycorrhizl symbiosis is mutulistic ssocition between the mjority of terrestril plnts nd microscopic fungi of the phylum Glomeromycot. As obligte symbionts, the rbusculr mycorrhizl fungi (AMF) rely on their host plnt to obtin crbon nd to complete their life cycles. In return, functionl mycorrhizl symbiosis cn improve plnt growth, helth nd tolernce to biotic nd biotic stressors (St-Arnud nd Abbrevitions: AMF, rbusculr mycorrhizl fungi; PGPR, plnt growth promoting rhizobcteri Cn. J. Plnt Sci. (2013) 93: doi: /cjps

2 Cn. J. Plnt Sci. Downloded from by on 04/06/ CANADIAN JOURNAL OF PLANT SCIENCE Elsen 2005; Subrmnin nd Chrest 2009) by fcilitting plnt ccess to more soil minerl nutrients (Smith nd Red 1997; Ghooni et l. 2005). It is ssumed therefore, tht the judicious use of these nturl inoculnts cn reduce the need to mend soil with chemicl fertilizers, thus incresing the vibility of sustinble griculture (Gemm et l. 1997). Over the pst few decdes, compnies throughout the world hve mnufctured nd commercilized AMF inoculnt using either single AMF species or mixtures of AMF species tht my include plnt growth promoting rhizobcteri (PGPR) or other symbiotic nd/or biocontrol fungi (Gininzzi nd Vos tk 2004). Industril mnufcturing of AMF s crop inoculnts is reltively new nd, despite the prcticl demonstrtions of their efficiency, their doption by crop producers hs been slow, most likely due to the qulity nd efficiency of mrketed products. One of the min issues with the use of commercil AMF inoculnts in griculture is relted to their performnce under specific locl conditions. Ntive AMF species re often considered more mutulistic thn non-ntive ones (Lmbert et l. 1980; Henkel et l. 1989; Clvente et l. 2004; Oliveir et l. 2005; Querejet et l. 2006). Gur et l. (1998) nd Rowe et l. (2007) compred locl field-collected strins nd foreign commercil inoculnts nd found gret vribility of commercil inoculnt performnces. Corkidi et l. (2004) showed tht hlf of 10 commercil inoculnts filed to form mycorrhizl ssocitions. Such negtive results hve been thought to be cused by low dpttion of exotic AMF inoculnts to locl edphic conditions such s soil nutrient concentrtions nd other biotic fctors (Schreiner 2007). In ddition, soil inocultion with exotic AMF strins hs been suspected to be potentilly dngerous by influencing the soil microbil composition nd structure (Mummey et l. 2009) nd disturbing the indigenous microbil community (Fye et l. 2009). Since AMF inoculnts re expected to be n importnt component of the upcoming new green revolution (Frzer et l. 2009), whether ntive AMF re more effective symbionts thn non-ntive ones must be evluted on cse-by-cse bsis (Trbell nd Koske 2007). On the other hnd, rguments used by inoculnt producers to promote their products, del with (i) the potentil of inside microbil isoltes nd mycorrhizl growth helpers to increse plnt yield nd protection, (ii) the microbil propgule density within the inoculnt nd, (iii) the diversity of species used (Trbell nd Koske 2007; Wisemn et l. 2009). Arbusculr Mycorrhizl inoculnt efficiency, though in conformity with the previous cited criteri, remins lrgely dependent upon locl environmentl fctors such s soil minerl content, inoculnt mycorrhizl efficiency with the cultivted crop, nd niche competition with indigenous strins (Jefw et l. 2009). Thus, evlution of the bio-fertilizing potentil of exotic strins must tke into ccount their dptbility to locl soil nd cultivted crops. This study focuses on (i) ssessing AMF commercil inoculnts infectivity nd surveying AMF species effectively present in tested inoculnts in sterile substrte nd, (ii) evluting mycorrhizl inoculnts performnces in soil from monocrop cultivted field of mize (hybrid 513). MATERIALS AND METHODS Evlution of Commercil AMF Inoculnts in Sterile Snd Pot Culture Experimentl Design A trp culture experiment ws estblished in greenhouse t the Tropicl Soil Biology nd Fertility, Interntionl Center for Tropicl Agriculture (TSBF- CIAT) locted t the World Agroforestry Centre in Nirobi, Keny, to test 12 commercil AMF inoculnts. According to the mnufcturer s specifictions, microbil composition nd species concentrtion vried between inoculnts, but included t lest one AMF species, with or without plnt growth stimultors such s phosphorus solubilizing bcteri, N 2 fixers nd PGPR (Tble 1). A Kenyn soil from the Chuk Region clssified s Humic Nitisol (Food nd Agriculture Orgniztion 2006) ws collected t depth of 020 cm during cultivtion of mize with no recent fertilizer or orgnic mtter inputs. Soil ws sieved, homogenized nd chrcterized (Tble 2). Snd ws thoroughly wshed, sterilized nd filled in 3-L pots. Thirty-six pots were inoculted with commercil AMF products nd mnufcturer s recommendtion were duplicted. To ensure enough propgules for plnt root coloniztion, respective doses were supplied twice. Three control pots were inoculted with the soil t the rte of 100 g per pot nd three non-inoculted pots were dded s control tretment. Mize (Ze mys L.) (Hybrid 513) seeds from Kenyn seed compny ( co.ke) were used s the test crop. Seeds were surfcesterilized in 3.3% C(ClO) 2 for 5 min nd five helthy seeds were sown in ech pot before sprying pproximtely 1 cm of sterile snd over nd plcing in Sunbgs (Sigm-Aldrich # B7026). Pots were rrnged in rndomized block design over greenhouse bench nd snd moisture ws kept t 80% of field cpcity. After 1 wk of growth, plnt pots were thinned to 2 nd substrte moisture ws incresed to 90% of field cpcity for the remining 17-wk growth period. Modified Hewitt nutrient solution (Jizme-Veg et l. 1991) ws divided into five stocks of solution: Stock 1: KNO 3 (40.44 g L 1 ), Stock 2: CNO 3 4H 2 O (47.23 g L 1 ), Stock 3: MgSO 4 7H 2 O (36.97 g L 1 ) : KH 2 OPO 4 (0.027 g L 1 ); b: KH 2 OPO 4 (0.272 g L 1 ); Stock 4: NEDTA- Fe (4.21 g L 1 ), Stock 5: MnSO 4 4H 2 O (2.23 g L 1 ); H 3 BO 3 (3.09 g L 1 ); ZnSO 4 2H 2 O (0.268 g L 1 )nd CuSO 4 5H 2 O (0.375 kg L 1 ) nd pplied weekly t the rte of 10 ml per plnt to ensure nutrient vilbility for norml plnt growth. Low P stock solution 3 for the first 2 wk nd higher P stock solution b strting

3 FAYE ET AL. * EVALUATION OF COMMERCIAL INOCULANT 1203 Tble 1. List nd chrcteristics of tested commercil AMF inoculnts Inoculnts AMF speciesnumber No. AMF propgules Other orgnisms Added fertilizer NPK Cn. J. Plnt Sci. Downloded from by on 04/06/18 1 NA 100 g 1 2 NA 100 g g 1 502, Kelp cc 1 312, Kelp cc 1 7 Ectomycorrhize Trichoderm 4 bcteri g 1 Humic cid, kelp, vitmins cc cc 1 11 Ectomycorrhize 412 kelp 2 Trichoderm 15 bcteri g cc NA 12 6 NA t 3 wk fter plnting were pplied t the rte of 2 ml per plnt. Mycorrhizl Root Coloniztion nd AMF Spore Assessment At hrvest, two rndom test plnts were uprooted crefully from ech pot tretment. Roots were wshed nd preserved in 70% ethnol. The root mycorrhizl coloniztion ws ssessed by stining with Trypn Blue (Phillips nd Hymn 1970) nd root coloniztion levels were ssessed using the technique developed by McGonigle et l. (1990) trgeting 50 root intersections. AMF spores were extrcted from 100-g smple of snd by wet-sieving nd sucrose grdient (Dlpe nd Hmel 2007). Snd ws thoroughly mixed with 0.5 L of wter nd two drops of Tween 80 nd, pssed through superposed 38-, 150- nd 500-mm sieves; sievings were distributed into 100-mL tubes contining 25 ml of wter filled from the bottom with 50% sucrose solution (vol/vol) before centrifuging the mixture t 2500g for 4 min. Superntnts were recovered, wshed through 38-mm sieve to dilute the sucrose solution nd condensed to pproximtely 20 ml volume. Spores were isolted mnully from concentrted superntnts under dissecting microscope (Olympus SZ-STS), trnsferred to microscopic slides with micro-pipette nd mounted in polyvinyl lcohol, lctic cid, glycerol (Omr et l. 1979) nd polyvinyl lcohol, lctic cid, glycerol Melzer s regent (1:1). Identifiction of spores ws performed under light microscope (Nikon Eclipse 800) using originl descriptions, synoptic keys nd specilized websites ( invm.cf.wvu.edu). Identified species recovered were compred with strins listed in the corresponding commercil inoculnts. Evlution of Commercil AMF Inoculnts into n Indigenous Soil Experimentl Design nd Inocultion This experiment ws estblished in rndomized block design with three replictes in the sme greenhouse. PVC tubes with volume of 8 L (15.6-cm dimeter) closed t the bottom with double nylon 1-mm mesh were filled with the sme soil described in the previous experiment. Inocultion of mycorrhizl products ws performed s in the first experiment nd control tretment (not inoculted) ws dded. To ensure norml plnt growth, nutritive solutions were supplied with KNO 3 (0.562 g kg 1 of dry soil), NH 4 NO 3 (0.385 g kg 1 ), MgSO 4 (0.133 g kg 1 ) nd CCl 2 (0.287 g kg 1 ) nd MgCl 2 (0.290 g kg 1 ) thoroughly mixed with soil before plnting. Phosphorus ws pplied t 60 kg h 1 of springly soluble Mijungu phosphte rock (30% of P 2 O 5 ) mixed seprtely for ech tube. Plnts were wtered dily ( ml) during the experiment by dding distilled wter (6 wk). Twice per week, soil moisture content ws djusted to 90% of the field cpcity (29.5%). Tble 2. Chrcteristics of the Kenyn soil used in the study Clss Texture ph (H 2 O) Olsen P (ppm) ExN ExC ExMg ExK ExN Orgnic C (%) AMF spores number Humic Nitisol cly

4 Cn. J. Plnt Sci. Downloded from by on 04/06/ CANADIAN JOURNAL OF PLANT SCIENCE Dt Collection nd Anlysis Plnt shoot height ws mesured twice per week. Chlorophyll concentrtion percentges in the two youngest fully developed leves were determined t 6 wk fter plnting using chlorophyll meter (Model SPAD 502; Konic Minolt Sensitive, Inc; 101 Willims Drive Rmsey, NJ). At hrvest, plnts were cut 1 cm bove the soil surfce, soil debris ws wshed from the roots, nd fresh subsmple ws collected in 70% ethnol for mycorrhiz coloniztion ssessment s in the first experiment. Shoots nd roots were oven dried for 72 h t 658C nd dry biomsses ws recorded. For both experiments, nlysis of vrince on fctors (biomss, chlorophyll content or root coloniztion) ws crried out using Generl Liner Model procedures of SAS softwre (SAS Institute, Inc. 2006) with the LSD option for the test of mens seprtion. Significnce ws evluted t P RESULTS Effects of Commercil AMF Inoculnts on Mize Root Coloniztion nd AMF Spore Survey in Snd Culture Among the 12 mycorrhizl inoculnts tested, three (2, 10 nd 12) significntly (P B0.001) incresed mize root coloniztion by mycorrhiz compred with the soil (19%). Seven inoculnts (1, 3, 6, 7, 8, 9 nd 11) induced root coloniztion t much lower levels (from 0.7 to 3%) thn the soil inocultion, while two inoculnts (4 nd 5) did not colonize roots (0%) s in control (snd only) (Fig. 1). Overll, 11 AMF species (9 Glomus, 1Prglomus nd 1 Gigspor) were declred to be present in the commercil inoculnts studied (Tble 3). A totl of 13 AMF spore species were extrcted nd identified from the 18-wk-old snd trp cultures. Among them, five species were not listed in the commercil inoculnts. Gigspor gignte, Aculospor scrobicult, Glomus fscicultum nd G. pllidum were extrcted from unique commercil inoculnt trp culture, while spores of A. tubercult, species not listed in ny inoculnts, were found in bundnce within seven of tested inoculnts. Except for G. clrum, G. irregulre, G. etunictum, G. mossee nd Prglomus brsilinum, there were few mtches between climed nd trpped species. In the non-inoculted pot tretment, no AMF spores were detected. Mycorrhizl Potentil of Commercil Mycorrhizl Inoculnts in Soil Effects of commercil mycorrhizl inocultion on mize plnt growth nd yield in the Kenyn soil re summrized in Tble 4. After 21 nd 24 d of growth, shoot heights of mize plnts inoculted with inoculnts 2 nd 10 were found significntly higher (P B0.05) thn the control. However, t the end of the 6-wk growth period, plnt heights, shoot nd root dry weight, nd shoot:root rtio were not significntly different from the control. Significnt negtive effects obtined with inoculnt 12 lso totlly disppered s well s negtive effect on chlorophyll lef content induced by inoculnt 7. Inocultion of commercil mycorrhizl products did not llow significnt totl dry biomss increses of mize plnt compred to control tretment. In ll tretments (inoculted or not), high level of P deficiency hs been observed. In terms of mycorrhizl potentil, inoculnts 2, 4, 7, inoculnts 6, 9, 12 nd inoculnt 10 significntly incresed root coloniztion percentge t PB0.05, PB0.01 nd P B0.001, respectively, compred with soil lone (Fig. 2). The highest root coloniztion levels were obtined with inoculnts 9 (46.83%), 10 (56.67%) nd 12 (47.67%). The effects of inoculnts 1, 3, 5, 8 nd 11 were similr to the control tretment. DISCUSSION Root Coloniztion Potentil of Commercil Inoculnts in Sterile Snd Culture Ten of the twelve mycorrhizl inoculnts tested succeeded in colonizing mize roots in sterile snd pot cultures (Fig. 1). These results re different from those reported by Corkidi et l. (2004) nd Trbell nd Koske (2007), who found tht most commercil inoculnts were unble to colonize roots. However, only three mycorrhizl inoculnts 2 (P B0.05), 10 (P B0.001) nd 12 (P B0.01) colonized mize plnt roots t higher rtes thn the Kenyn soil. Consequently, those inoculnts might be promising cndidtes for greenhouse plnt production. However, there is need to test inoculnts under field conditions to confirm their performnce s suggested by Sorensen et l. (2008). The remining AMF inoculnts, which gve root coloniztion levels lower thn the soil, re indeed inefficient under these specific soil nd crop environment conditions. However, it is not known if they would perform well under other growth conditions nd with other crops. Inoculnts AMF Spore Assessment in the Snd Trp Culture Some AMF species dvertised on the commercil inoculnt lbels were found sporulting in pot cultures, while some others were not detected. The 18-wk trp pot culture period might be not long enough to llow estblishment nd differentition of ll AMF species of n inoculnt even though Khliq et l. (2010) considered this period s sufficient to llow AMF propgules to revitlize, infect mize roots, nd sporulte. In fct, AMF species such s Aculospor nd Gigspor gener possess low sporultion potentil, mostly differentiting fewer thn dozen spores within 6-mo growing period (Dlpé nd Declerck 2002). Others, generlly smll-spore species, such s G. irregulre, cn produce hundreds of spores within 4-mo period in unique in vitro root culture (St-Arnud et l. 1996).

5 FAYE ET AL. * EVALUATION OF COMMERCIAL INOCULANT 1205 Cn. J. Plnt Sci. Downloded from by on 04/06/18 Root colonisztion (%) c c c c Control Bsed on these ssumptions, the presence in some pot cultures of species tht were neither dvertised by inoculnt producers nor found in the control pots remins unexplined. The use of Sunbgs minimized crosscontmintion between pots nd should considerbly reduce the risk of introducing outside AMF species. On the other hnd, industril production of mycorrhizl inoculnts is mostly performed under greenhouse pot culture conditions, with qulity control, propgule density nd AMF species identity verified through subsmple nlyses (Gininzzi nd Vos tk 2004; Fortin et l. 2008). Producers use diversity of biologicl inoculnts nd of formultions going from single ubiquity AMF species to rnge of strins nd species with or d Snd+AgriSoil Snd+1 e Snd+2 Snd+3 Snd+4 Snd+5 Snd+6 Tretments Snd+7 b b b Fig. 1. Percent root coloniztion of mize plnts grown in sterile snd inoculted with the 12 commercil inoculnts, soil nd without inocultion (Control). Brs represent the stndrd error of the difference (SED) for effects of product ppliction. Vlues with different letter re significntly different t PB0.05. Snd+8 Snd+9 e Snd+10 without dded fertilizers hoping by those strtegies to provide optiml inoculnts suitble for diversity of pplictions. The 12 commercil inoculnts tested were in vivo mss produced in continers with the dvntge of low-cost technology, but risky in term of potentil contmintion by outside AMF orgnisms. For commercil use, high root coloniztion nd sporultion potentils to ensure rpid propgtion nd mximise AMF strin vibility nd productivity over time re preferentil selection criteri of AMF strins (Fortin et l. 2002). Menwhile, inoculnt producers opt to dd non-microbil ingredients such s fertilizers, vitmins, nd other substrtes s stted by Schweinsberg- Mickn nd Mu ller (2009) nd confirmed in Tble 1. Tble 3. Arbusculr mycorrhizl fungi species composition of commercil inoculnts nd species detected from 18-wk-old trp cultures Inoculnts Climed species Species detected 1 G. spp. z A. tubercult z, G. mossee, G. constrictum, 2 G. spp. G. deserticol 3 G. ggregtum, G. etunictum, G. intrrdices G. mossee, G. deserticol, G. etunictum, G. mossee 4 G. ggregtum, G. etunictum, G. intrrdices, G. mossee A. tubercult, G. etunictum, G. mossee 5 G. ggregtum, G. etunictum, G. intrrdices, G. mossee G. mossee 6 Gi. mrgrit, G. ggregtum, G. clrum, G. deserticol, A. tubercult, G. mossee G. etunictum, G. intrrdices, G. monosporum, G. mossee, P. brsilinum y 7 G. ggregtum, G. etunictum, G. intrrdices, G. mossee A. tubercult, G. constrictum, G. etunictum, G. irregulre y 8 Gi. mrgrit, G. ggregtum, G. clrum, G. deserticol, G. clrum, G. deserticol, P. brsilinum G. etunictum, G. intrrdices, G. monosporum, G. mossee, P. brsilinum 9 G. intrrdices A. scrobicult, Gi. sp., G. fscicultum,g. irregulre, G. pllidum 10 G. clroideum, G. etunictum, G. geosporum, G.intrrdices, Gi. mrgrit, Gi. gignte, G. irregulre G. mossee 11 G. intrrdices A. tubercult 12 6 beneficil mycorrhiz from rid zones A. scrobicult, G. fscicultum, G. irregulre Snd+11 e Snd+12 z A, Aculospor; Gi, Gigspor; G,Glomus; P,Prglomus. y Previously identified s G. intrrdices (Sokolski et l. 2010).

6 1206 CANADIAN JOURNAL OF PLANT SCIENCE Tble 4. Effects of commercil rbusculr mycorrhizl fungi inoculnts on growth prmeters of 6-wk-old mize cultivted under the Kenyn soil Effects on plnt growth prmeters Tretments Shoot height 2124 DAP (cm) Shoot height t 6 WAP (cm) Chlorophyll (%) Totl dry biomss (g) Cn. J. Plnt Sci. Downloded from by on 04/06/18 Control: Soil without inoculnt A A A A SoilInoculnt A A A A SoilInoculnt B A A A SoilInoculnt A A N/A A SoilInoculnt A A A A SoilInoculnt A A A A SoilInoculnt A A N/A A SoilInoculnt A A B A SoilInoculnt A A A A SoilInoculnt A A N/A A SoilInoculnt B A A A SoilInoculnt A A N/A A SoilInoculnt C A C A AC Different letters cross columns indicte significnt (PB0.05) difference compred with the control. Inoculnts 4, 5, 6 nd 8, dvertised to contin Trichoderm, bcteri nd ectomycorrhizl fungi in combintion with N, P nd K fertilizers, gve mitigted results. When mixed inoculnts re developed, ech dded orgnism (bcteri, PGPR or ectomycorrhizl fungi, etc.) is expected to hve synergistic effect with other inoculnt components in order to optimize product efficcy. Potentil inhibitory effects between biotic growth promoters, microbil orgnisms nd ntive soil microorgnisms my lso progressively tke plce. It is then impertive to evlute commercil inoculnts loclly before lrge-scle use for crop production, Root coloniztion (%) b b especilly when multi-species nd ingredients re dded to the inoculnts. Mycorrhizl Potentil of Commercil Inoculnts in Soil The incresed shoot heights obtined with inoculnts 2 nd 10 t 21 nd 24 d fter plnting (Tble 4) my indicte their cpcity to rpidly estblish functionl symbiosis with mize plnts compred with other tested inoculnts. However, since ntive AMF isoltes re sometimes more mutulistic thn non-ntive ones (Lmbert et l. 1980), significnt growth effect from c b c d 0 Soil Only Soil+1 Soil +2 Soil+3 Soil+4 Soil+5 Soil+6 Soil+7 Soil+8 Soil+9 Soil+10 Soil+11 Soil+12 c Tretments Fig. 2. Percent root coloniztion of mize plnts grown in soil inoculted or not with commercil mycorrhizl inoculnts. Brs represent the stndrd error of the difference (SED) for effects of products ppliction. Vlues with different letter re significntly different t PB0.05.

7 FAYE ET AL. * EVALUATION OF COMMERCIAL INOCULANT 1207 Cn. J. Plnt Sci. Downloded from by on 04/06/18 products 2 nd 10 before the 6-wk growth period might be due to performing ntive AMF ctivity. Combintion of exotic strins with ntive ones my llow significnt increses of plnt root coloniztion, but is not necessrily trnslted to higher plnt yields, s ppers with inoculnts 4, 6, 9 nd 12. As result, seedling growth prmeters mesured t 6 wk were not different between tretments. Interestingly, products such s inoculnt 2, 4, 6, 7, 9, 10 nd 12 induced mize root coloniztion t rte significntly higher thn the indigenous soil. These findings re in line with the results of Corkidi et l. (2004) who stted tht 6-wk growth period is sufficient to llow mycorrhizl development nd good AMF mize root coloniztion. On nother hnd, there ws slight increse of dry biomss observed with inoculnts 2, 10 nd 12 showing high root coloniztion rtes in sterile snd pot (Fig. 1) nd in the soil pot cultures (Fig. 2). These results suggest tht these inoculnts my hve good potentil nd, s such, cn be considered s performing mycorrhizl inoculnts. For inoculnts 6 nd 9, the 6-wk growth period my hve been long enough to llow good root coloniztion, but this is not reflected in plnt biomss increse (Tble 4). This result confirms tht root coloniztion efficiency might be used s n indictor of inoculnt vibility, but not of plnt growth efficiency, s is often expected in field studies (Billis nd Krmnos 2010). Similrly, no direct correltion ws estblished between inoculnt mycorrhizl potentil nd its AMF propgule density or species diversity. One convincing exmple is inoculnt 9, which ws climed to contin unique AMF strin t tremendously high propgule concentrtion ( propgules g 1 ), but colonized plnt roots t very low level in sterile snd with lmost 50% more root coloniztion thn when mixed with soil. The ddition to soil of lrge mount of spores from unique AMF species my stimulte the growth of ntive AMF popultion. Even so, the root coloniztion levels observed did not increse plnt biomss. Similr behvior ws recorded with inoculnt 6, which contined multiple AMF species in the rnge of 44 propgules per grm mixed with 11 ectomycorrhizl fungi plus kelp, humic cid nd vitmins. As demonstrted, the benefits expected from the use of commercil mycorrhizl inoculnts in mize production, up to 6 wk of growth, could not be clerly determined from the inoculnt formultion, lbels or plnt growth promotion dvertisements mde by producers. Results of the study indicted tht 6-wk growth period is not long enough to get significnt increses of mize shoot dry biomsses from ny of the commercil inoculnts tested. For complete evlution of the inoculnts potentil, it is importnt to pursue similr tests up to mize mturity in order to compre finl crop yields. The effectiveness of commercil inoculnts depends on environmentl nd soil conditions, such s minerl concentrtion, microbil composition nd crop type. To ensure successful use of inoculnts, preliminry trils must be crried out under locl growth conditions with the soil nd host-plnts expected to be used in the field. On the other hnd, good root coloniztion of commercil mycorrhizl inoculnts does not trnslte to plnt growth nd yield, nd my increse the necessity to investigte the functionlity of mycorrhizl symbiosis formed by commercil inoculnt. Moleculr tools could lso be used to elucidte the root occupncy cpcity of exotic strins within indigenous soils. ACKNOWLEDGMENTS The uthors re sincerely grteful to Sylvie Se guin nd Dr. Scott Redhed, Estern Cerel nd Oilseed Reserch Centre, Agriculture nd Agri-Food Cnd, Professor Christine Chrest, Deprtment of Biology, University of Ottw Cnd, Dr. Chntl Hmel, Semirid Pririe Agriculturl Reserch Centre, Agriculture nd Agri-Food Cnd, nd Nte Bogie, University of Cliforni, Merced, USA, for their scientific support nd revision of the mnuscript. 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