that two products based on two vascular system exposed. Although P. Efficacy of different species of Streptomyces, ultimum var. ultimum seldom pro- Various Mycostop and Actino-Iron, were as duces zoospores, the motile propagules effective as metalaxyl at reducing the produced by such as symptoms associated with Pythium, the fungus has been isolated Biological root rot when artificially inoculated with Pythium ultimum var. ultimum from reservoirs where the fertilizer so- Control Agents compared to the control plants. Many lutions are stored (J.A. Gracia-Garza, roots remained functional throughout unpublished) and can easily be dis- and Biorationals the duration of the experiments and seminated throughout a greenhouse the overall appearance and number of operation that uses a recirculating subir- against Pythium bracts of commercial quality of the rigation system. Root Rot in plants were similar for the three Several chemical products are rec- treatments mentioned above. In an ommended for use against this patho- Poinsettia additional experiment, Mycostop was gen. In Ontario, metalaxyl (Subdue, tested in combination with a single Syngenta Crop Protection Canada Inc., application of metalaxyl either at 3, 7, or 11 weeks after transplanting. Guelph, Ont., Canada) and fosetyl- J.A. Gracia-Garza,1,5 Plants inoculated with P. ultimum aluminum (Aliette, Rhone-Poulenc var. ultimum and treated with Canada, Mississauga, Ont., Canada) 2 3 M. Little, W. Brown, metalaxyl either on week 3 or 7 after are two chemicals registered for the 4 1 transplanting in combination with control of root rot caused by Pythium T.J. Blom, K. Schneider, two applications of Mycostop, had in ornamental crops. However, recent W. Allen,1 and J. Potter1 greater fresh root weight than those studies have indicated that some iso- only treated with metalaxyl at week 11 lates of Pythium are becoming less or the chemical control (three applica- sensitive to metalaxyl (Daughtrey, tions of metalaxyl). However, there 1998). Thus, alternative strategies must ADDITIONAL INDEX WORDS. Euphorbia was no significant difference in the pulcherrima, Gliocladium, metalaxyl, number of bracts or the bract diameter be found before resistance to these Pseudomonas, Streptomyces, Tricho- between plants treated with metalaxyl pesticides is fully developed. Many dif- derma at weeks 3 or 7 followed by Mycostop ferent organisms, including actino- and those plants treated with the mycetes, have been reported as poten- SUMMARY. Pythium root rot (Pythium fungicide alone. A reduction in the tial biocontrol agents (BCA) against spp.) is a common disease of green- amount of fungicide used to control Pythium (Liang et al., 1996; house-grown poinsettias (Euphorbia pythium root rot can be achieved when Mahadevan and Crawford, 1997; pulcherrima) that can cause serious used in combination with a biocontrol McCullagh et al., 1996; Rankin and plant loss or reduction in plant agent without compromising the Paulitz, 1994). Streptomyces are aero- quality. Application of effective health of poinsettias. bic, gram-positive actinomycetes with chemical fungicides to poinsettia plants has reduced losses due to reported activity against several plant Pythium; however, development of pathogens, including Pythium resistance to these fungicides is a oot rots caused by Pythium (Mahadevan and Crawford, 1997). legitimate concern, as well as the species are of great con- The mechanisms by which Streptomy- environmental implications of using R cern to growers in the floricul- ces are able to reduce losses due to chemical pesticides. In this study, a tural industry particularly since the soilborne pathogens include competi- group of products of biological origin adoption of new irrigation technolo- tion for nutrients, and production of and known biocontrol agents were gies that prevent the run off of chemi- antimicrobial products and lytic en- evaluated for their efficacy to control cals into the environment. At present, zymes (Kortemaa et al., 1994; pythium root rot of poinsettia. These Mahadevan and Crawford, 1997). The products and organisms were com- 25% to 30% of commercial greenhouses pared to metalaxyl (Ridomil), a in the Niagara region of southern objectives of the study presented here fungicide commonly used to reduce Ontario, Canada, are using recirculat- were 1) to evaluate several commer- losses to Pythium. The results showed ing irrigation systems. In addition, cially available products of biological growers of potted floricultural crops origin for their ability to reduce or are replacing the traditional overhead eliminate root rot in poinsettia and 2) The support of Flowers Canada (Ontario) Inc., and all (drip) irrigation with subirrigation. to determine if a single application of the companies that provided samples and their repre- sentatives, is appreciated. These changes in irrigation practices the fungicide metalaxyl in combina- 1Agriculture and Agri-Food Canada, Southern Crop have increased the concerns about tion with a strain of Streptomyces Protection and Food Research Centre, 4902 Victoria pathogen contamination of fertilizer griseoviridis, will provide satisfactory Ave. N., P.O. Box 6000, Vineland Station, Ont., solutions and the reservoirs where these control of P. ultimum. Canada L0R 2E0. solutions are maintained. Poinsettia 2Brock University, St. Catharines, Ont., Canada L2S Materials and methods 3A1. plants are often infected by the patho- PLANT MATERIAL, PATHOGENS AND 3Ontario Ministry of Agriculture and Food. gen Pythium ultimum var. ultimum. Symptoms of plants infected with this SCREENED BCAS, AND BIORATIONALS. 4University of Guelph, Department of Plant Agricul- ture, 4890 Victoria Ave. N., Vineland Station, Ont., pathogen are stunting, chlorosis, and a Cuttings from stock ‘Freedom’ poin- Canada L0R 2E0. general wilting. Infected roots are settia plants, were collected and rooted 5Corresponding author; email Gracia- brown with rotted tips and the cortex in Oasis (Smithers-Oasis, Kent, Ohio) [email protected]. usually sloughs off easily, leaving the for 4 weeks. Rooted cuttings were

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then transplanted into 10-cm-diam- (Beckman Du 640, Beckman Instru- was inoculated (2 weeks after trans- eter (4-inch) plastic pots, using Sun- ments, Inc. Fullerton, Calif.), to ob- planting) with Po20 through shine Mix # 4, (SunGro Horticulture tain a final absorptivity reading of 0.14 subirrigation with an infested fertilizer Inc., Westerville, Ohio), a peat-based (wavelength of 650 µm). At this ab- solution, and the other set served as a soilless medium. sorptivity, the solution was estimated noninoculated control (i.e., Pythium- Plants were treated as follows to contain 6 × 107 cfu/mL (1.8 × 109 free). For those plants receiving a (Table 1): 1) control; 2) Actino-Iron cfu/fl oz). The bacterial solution was drench, each plant received 100 mL (Natural Industries, Inc., Houston, diluted to 106 cfu/mL (3.0 × 107 cfu/ (3.4 fl oz) of the appropriate solution. Texas) containing: Streptomyces lydicus fl oz) before inoculating the plants. Each treatment was placed in a sepa- WYEC 108, 18% to 20% iron, 30% to The strain TMCS 3 was grown on rate trough and each trough was con- 32% fulvic acid blended into the pot- Petri plates containing dex- nected to a separate tank. Recirculat- ting medium at 3 g·L–1 (label rate) trose agar (PDA) (Difco Laboratories, ing tanks were filled with a fertilizer before planting; 3) BTM (Earth Corp Detroit, Mich.) for 5 d before harvest- solution containing, in mmol·L–1 (ppm): – Environmental Ltd., Calgary, Alta., ing conidia. Conidia were scraped from 12.25 (760) nitrate (NO3 ), 2.25 (40.5) + Canada) containing several genera of the surface of the plate with a metal rod ammonium (NH4 ), 1.0 (97) – bacteria (Bacillus, Clostridium, after adding 15 mL (0.5 fl oz) of sterile dihydrogen phosphate (H2PO4 ), 3.5 Enterobacter, Pseudomonas, and Rhizo- water. The spore solution was diluted (136.5) potassium (K+), 3.75 (150) cal- bium) in a humic acid solution applied until a 106 cfu/mL concentration was cium (Ca2+), 1.0 (24) magnesium –1 2+ 2– as a monthly drench at 5.5 mL·L obtained. (Mg ), 1.0 (96) sulphate (SO4 ), 0.025 (label rate); 4) Modicell (DeruNed Pythium ultimum var. ultimum (1.4) iron (Fe2+), 0.005 (0.28) manga- BV, Bergschenhoek, The Netherlands) isolate Po20 (Po20) was originally iso- nese (Mn2+), 0.0035 (0.23) zinc (Zn2+), 3– containing enzymes extracted from sev- lated from a diseased poinsettia plant 0.020 (1.2) borate (BO3 ), 0.0008 eral genera of fungi applied as a monthly in the Niagara region. The pathogen (0.05) copper (Cu2+), and 0.0005 –1 2– drench at 1.5 mL·L (label rate); 5) was grown in a V8 liquid medium (0.08) molybdate (MoO4 ). Irriga- Mycostop (Kemira Agro Oy, Helsinki, amended with calcium carbonate tion of all plants was changed to clear –1 Finland) containing S. griseoviridis (CaCO3) [10 g·L (1.34 oz/gal) of water when cyathia began to produce strain K61 applied as a monthly drench V8 juice]. The growing medium was pollen according to commercial prac- at 0.06 g·L–1 (label rate); 6) Pseudomo- similar to that described by Miller tices. Experimental plants were grown nas fluorescens strain 15 (T.C. Paulitz, (1955) without adding agar. The cul- in a greenhouse for 15 weeks with the collection) applied by dipping the Oasis tures were incubated on an orbital following equal day/night tempera- cube in a solution containing 106 cfu/ mechanical shaker (150 rpm) for 10 d ture regimes: 21 °C (70 °F) during mL at transplanting; 7) metalaxyl under constant incandescent light at vegetative growth and flower initia- (Ridomil 240. E.C.; Syngenta Crop 26 °C (79 °F). Cultures were then tion, 19 °C (66 °F) during flower Protection Canada Inc., Guelph, Ont., blended for 30 s to homogenize the development and 17 °C (63 °F) for Canada) applied as a monthly drench sporangia and oospores in the culture. final 2 weeks before harvest of the at 0.04 mL·L–1 (label rate); 8) Sufficient inoculum was added directly experiment. From transplanting to RootShield (Bioworks, Inc. Geneva, to 25 L (6.6 gal) tanks used for recir- blackout, plants were maintained un- N.Y.) containing culating fertilizer solution at a concen- der long-day photoperiod using in- harzianum Rifai strain KRL-AG2 ap- tration of 102 sporangia/mL (3.8 x105 candescent light from 2200 to 0200 plied once as a drench shortly after sporangia/gal). The concentration of HR daily. Plants were pinched (top of transplanting at 0.6 g·L–1 (label rate); the pathogen was an approximate to plant removed) 10 d before the begin- 9) SoilGard 12G (Termo-Trilogy levels found in tanks for recirculating ning of blackout. Blackout was pro- Corp. Columbia, Md.) containing subirrigation systems in commercial vided daily with black curtains for pho- Gliocladium virens GL-21 applied to greenhouses for this region. Tanks were toperiodic control for 13 h (1800 to the potting soil (1 d) before trans- infested twice with the sporangial so- 0700 HR) to induce flower initiation, planting at 0.9 g·L–1 of substrate (label lution namely, at 1 and 6 weeks after starting 4 weeks after transplanting rate); 10) T. hamatum strain TMCS 3 transplanting. until the end of experiment. (TMCS 3) (J.A. Gracia-Garza, per- To determine the dynamics of the At the end of the experiment (15- sonal collection) applied as a drench pathogen population in the recirculat- week duration), the following mea- once shortly after transplanting at 106 ing tanks, samples [500 µL (17 × 10–6 surements or ratings were taken on 10 cfu/mL. All drenches were applied at fl oz)] of the fertilizer solution were randomly selected plants per experi- 100 mL (3.4 fl oz) per pot. Incorpora- taken on a weekly basis during the mental unit: number of bracts of com- tion of Actino-Iron and SoilGard into experiments. Samples (500 µL) were mercially acceptable quality, diameter the growing substrate took place 1 d plated on 90 mm (3.5 in) Petri plates of bracts (bract diameter was deter- before transplanting to allow incuba- of a selective medium for Pythium spp. mined by measuring across the upper- tion. (Tsao and Ocaña 1969). Plates were most inflorescence from tip to tip of Cultures of P. fluorescens were incubated at 22 ± 2 °C for 3 to 5 d two of the primary bracts) and overall grown on nutrient broth for 2 d on an before counting colonies. appearance of root system. Root rat- orbital mechanical shaker at 125 rpm SCREENING OF BCAS AND ing was done as follows: 1 = healthy (Lab-Line Instruments, Inc., Melrose BIORATIONALS. Each treatment was ap- root system with white roots; 2 = few Park, Ill.) and 22 ± 2 °C (71.6 ± 3.6 plied to two sets of 15 plants. The roots showing discoloration and/or °F). The concentration of bacteria was plants were 4-week-old rooted cut- tissue maceration; 3 = root system estimated using a spectrophotometer tings of ‘Freedom’ poinsettia. One set discolored with some dead roots; 4 =

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RR8 150 11/22/02, 2:27 AM root system totally disintegrated/dead. ter 2000; the second (i.e., evaluation Plant dry weight and number of bracts In addition, on five plants (first five of applications of different Mycostop/ of Mycostop-treated plants were not plants in the trough closer to the tanks) metalaxyl combinations) during the significantly different than those plants per experimental unit: fresh and dry fall of 2000 and Winter 2001. treated with either metalaxyl or Actino- weights of the plants (only dry weights STATISTICAL ANALYSIS. Statisti- Iron (Table 2). Based on root evalua- reported in the results) were measured. cal analyses were carried out using the tions, plants treated with metalaxyl EVALUATION OF APPLICATION OF PROC GLM procedure (SAS Insti- had significantly healthier root sys- DIFFERENT MYCOSTOP/METALAXYL tute, Cary, N.C.) to establish signifi- tems than those treated with Modicell, COMBINATIONS. Rooted cuttings of cance of the effects of all factors (P ≤ Actino-Iron, or Mycostop (Table 2). ‘Freedom’ poinsettias were grown as 0.05). The analyses were done sepa- On Pythium-free plants (nonin- described above and all treatments were rately for inoculated and noninoculated oculated), a growth enhancing effect either inoculated with Po20 (2 weeks treatments. Rating values for root ap- was observed on plants treated with after transplanting) or remained pearance were first converted into ranks the mycoparasite Trichoderma (i.e., Pythium free. The treatments consisted (PROC RANKS) and then analyzed TMCS 3 and RootShield), as well as of the following application combina- using PROC GLM. Differences among with Streptomyces (Mycostop) com- tions, metalaxyl (R) on week 3 fol- treatments were identified using pro- pared to the other treatments. Plants lowed by two applications of Mycostop tected LSD. were more vigorous and bracts of com- (M) at weeks 7 and 11 (R/M/M). mercial quality and bract diameters The other treatments were M/R/M Results were significantly better than the rest and M/M/R. Control treatments con- SCREENING OF BCAS AND of the treatments, including metalaxyl sisted of plants treated only with BIORATIONALS. Less than 1% of the (Table 2). metalaxyl or Mycostop at the three plants died throughout these experi- Populations of P. ultimum in the application times (R/R/R, M/M/ ments as a result of P. ultimum infec- irrigation tanks generally decreased M) and nontreated plants. At each tion; however, symptoms of root rot over time after each infestation. How- application date, a drench of only one were evident in many plants inocu- ever, tanks connected to troughs with product was applied (100 mL of solu- lated with Po20. Pythium infection diseased plants maintained a consis- tion overhead). Concentrations for reduced plant dry weight and the num- tent population [27 cfu/mL (8.0 × metalaxyl and Mycostop were 0.04 ber of bracts commercial quality in 102 cfu/fl oz) of fertilizer solution] mL·L–1 (0.005 fl oz/gal) and 0.06 nontreated control plants (P ≤ 0.05). during the course of the experiments, g·L–1 (0.008 oz/gal), respectively. This indicates that the Po20 isolate indicating that Pythium propagules The same parameters as in the used in this experiment was patho- were carried with the recirculating fer- previous experiment were measured. genic to poinsettias. tilizer solution from diseased plants EXPERIMENTAL DESIGN. All ex- Compared to control plants, into the holding tanks. However, re- periments were arranged in a split-plot plants treated with Mycostop or cent experiments by the authors sug- design with three replications per treat- Actino-Iron showed an improvement gest that movement of P. ultimum ment. There were 15 plants per repli- in the overall appearance (number of appears to be limited (unpublished cation (irrigation trough with separate bracts and plant dry weight) when the data). Pythium population density in tank). The main plot factor was the fertilizer solution was infested with Pythium-free tanks was zero through- presence or absence of Pythium and Po20 (Table 2). Plants treated with out the experiments. the subplots were the products tested Actino-Iron had plant dry weights simi- EVALUATION OF APPLICATIONS OF (treatments). All experiments were re- lar to plants treated with metalaxyl. DIFFERENT MYCOSTOP/METALAXYL peated once; the first experiments (i.e., Plants treated with Actino-Iron or COMBINATIONS. Plant mortality of screening of BCAs and biorationals) metalaxyl had similar shoot numbers Pythium-inoculated plants was high- took place during Fall 1999 and Win- (data not shown) and plant growth. est in the control treatment (25%),

Table 1. Listing of treatments, method and rate of application and frequency of application for the control of pythium root rot during the cropping cycle of poinsettias.

Application Application Treatment technique Rate frequency Control (nontreated) Actino-Iron Incorporate to soil mix 3 g·L–1 (5 lb/yard3) of media Once before transplanting BTMz Drench 5.5 mL·L–1 (0.7 fl oz/gal) Monthly Modicelly Drench 1.5 mL·L–1 (0.2 fl oz/gal) Monthly Mycostop Drench 0.06 g·L–1 (0.008 oz/gal) Monthly Pseudomonas fluorescens Dip 106 cfu/mL (3.0 × 107 cfu/fl oz) Once at transplanting Metalaxyl (Ridomil 240 EC) Drench 0.04 mL·L–1(0.5 fl oz/100 gal) Monthly RootShield Drench 0.6 g·L–1 (8 oz/100 gal) Once after transplanting SoilGard 12 G Soil mix 0.9 g·L–1 (1.5 lb/yard3) of media Once before transplanting TMCS 3x (Trichoderma hamatum) Drench 106 cfu/mL (3.0 × 107 cfu/fl oz) Once after transplanting

zBTM = a product containing several genera of bacteria (Bacillus, Clostridium, Enterobacter, Pseudomonas, and Rhizobium) in a humic acid solution. yThe authors consider this product a biorational since no organism is alive in the product but only the product extracted from an organism is being used. xIsolate of the mycoparasite Trichoderma hamatum labelled TMCS 3 (J.A. Gracia-Garza personal collection).

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Table 2. Average number of bracts (20 plants), plant dry weight (10 plants) and root rating (10 plants) of ‘Freedom’ poinsettia (Euphorbia pulcherrima) inoculated with Pythium ultimum var. ultimum isolate Po20 (Po20) or noninoculated and treated with one of several products.

Po20 inoculated Noninoculated Bracts Plant dry Avg root Bracts Plant dry Treatment (no.)z wt (g)y ratingx (no.) wt (g) Control (nontreated) 1.3 cw 6.5 c 3.55 cd 2.4 ab 9.8 bcd Actino-Iron 2.0 b 9.3 ab 3.33 c 1.9 c 9.0 bcd BTMv 1.7 bc 6.6 c 3.40 cd 2.1 c 9.5 bcd Modicell 1.6 bc 7.6 abc 2.96 b 2.3 b 10.7 bc Mycostop 2.2 ab 8.1 ab 3.37 cd 2.4 abc 13.9 a Pseudomonas fluorescens 1.2 c 5.9 c 3.67 d 2.1 c 9.0 bcd Metalaxyl (Ridomil 240 E.C.) 2.7 a 9.6 a 1.97 a 1.9 c 7.8 d RootShield 1.9 b 7.4 bc 3.57 cd 2.8 ab 11.1 b SoilGard 12 G 1.3 c 6.0 c 3.56 cd 1.3 d 8.3 cd TMCS 3 (Trichoderma hamatum)u 1.7 bc 6.8 c 3.40 cd 2.9 a 11.2 b LSD (P ≤ 0.05) 0.58 2.1 0.54 2.43

zNumber of bracts of commercially acceptable quality. y28.4 g = 1.0 oz. xRoot rating was done as follows: 1 = healthy root system with white roots; 2 = few roots showing discoloration and/or tissue maceration; 3 = root system discolored with some dead roots; and 4 = root system totally disintegrated. wTreatments followed by different letters differed statistically at the 0.05 level of significance according to a protected LSD. vBTM = A product containing several genera of bacteria (Bacillus, Clostridium, Enterobacter, Pseudomonas, and Rhizobium) in a humic acid solution. uIsolate of the mycoparasite Trichoderma hamatum labelled TMCS 3 (J.A. Gracia-Garza personal collection).

followed by the treatment consisting larger (P ≤0.05) than the other treat- mend to introduce the BCAs early in of a single metalaxyl application at ments (Fig. 1), including the chemical the cropping system to allow for ad- week 11 (8.5%). There was no plant control (R/R/R). There were no dif- equate colonization of the root sys- mortality when treated with metalaxyl ferences in plant and root characteris- tems and/or the growing substrate. either at week 3 or 7 (Table 3). None tics for the noninoculated treatments BCAs are better suited as a preventa- of the noninoculated plants died. (root data shown in Fig. 1). tive rather than a curative treatment. Analysis of the overall appearance of Similar trends in the population Some BCAs such as those containing the plant (plant and root rating) for dynamics of P. ultimum in the tanks Trichoderma, appear to have a growth- the inoculated treatments indicated was observed in these experiments as enhancing effect when the population significant differences (P ≤ 0.05) among in the previous test. of the pathogen is either low or nonex- the treatments. Plants treated with R/ istent as shown in Table 2. Some of M/M, M/R/M or R/R/R appeared Discussion these BCAs might not be strong com- healthier (visually) than the rest of the Use of BCAs or products of bio- petitors against aggressive pathogens treatments as well as quantitatively by logical origin is a feasible alternative to but might be deleterious to weaker the number and size of the bracts the use of chemicals for some organisms, competing in the rhizo- (Table 3). However, only the root pathosystems, as seen in these tests. sphere for nutrients. In addition, plants fresh weights of the treatments R/M/ However, often companies producing may react to the colonization of some M and M/R/M were significantly biologically based products recom- BCAs by releasing some defense

Table 3. Mortality rate, number of bracts and bract diameter (cm) and root fresh weight (g) of ‘Freedom’ poinsettia (Euphorbia pulcherrima) inoculated with Pythium ultimum var. ultimum isolate Po20 (Po20), as well as mortality rate and root fresh weight (g) for noninoculated treatments. Plants were nontreated (control) or treated with three drench applications of metalaxyl (R/R/R), three applications of Mycostop (M/M/M) or a combined application of metalaxyl (R) and Mycostop (M) at 3, 7 or 11 weeks after transplanting.

Po20 inoculated Noninoculated Mortality Bracts Bract diam Root fresh Mortality Root fresh Treatment (%) (no.)z (cm)y wt (g)x (%) wt (g) Control 25 2.3 bcw 24.0 b 7.7 b 0 10.9 b R/R/R 0 2.8 a 31.4 a 7.6 b 0 13.1 b M / M / M 4.2 2.1 c 22.9 b 11.2 ab 0 13.5 b R/M/M 0 2.6 ab 31.2 a 13.4 a 0 12.7 a M/R/M 0 2.7 ab 31.4 a 13.5 a 0 14.5 a M/M/R 8.5 2.1 c 26.1 b 8.8 b 0 10.6 b

zNumber of bracts of commercially acceptable quality. y2.5 cm = 1.0 inch. x28.4 g = 1.0 oz. wTreatments followed by different letters differ statistically at the 0.05 levels of significance according to a protected LSD.

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RR8 152 11/22/02, 2:28 AM mechanisms that indirectly suppress Gracia-Garza, J.A. 2001 Fusarium weak pathogens resulting in more vig- oxysporum Schlecht. f. sp. cyclaminis orous plants. Gerlach. [fusarium wilt of cyclamen], p. In these tests, some products/ 452–456. In: P. Mason and J Huber (eds.). organisms did not perform well; how- Biological control programmes in Canada 1981–2000. Chapter 89. CABI Publ., ever, these should not be considered as Oxford, U.K. an ineffective biological product for all pathosystems. Often, BCAs require Honeycutt, E.W. and M. Benson. 2001. specific conditions for optimal perfor- Formulation of binuclate Rhizoctonia spp. mance. What can be effective in one and biocontrol of Rhizoctonia solani on system may be ineffective against an- impatients. Plant Dis. 85:1241–1248. other system; for instance, a product Kortemaa, H., H. Rita, K. Haahtela, and may perform better at controlling A. Smolander. 1994. Root-colonization damping-off in bedding plants than in ability of antagonistic Streptomyces a system such as the one studied in this griseoviridis in rhizosphere and project (Honeycutt and Benson, nonrhizosphere sand. J. Phytopathol. 2001). Moreover, BCAs are in many 145:137–143. instances specific to a particular plant Liang, X. Y., H.C. Huang, L.J. Yanke, and pathogen. In tests with other soil- G.C. Kozub. 1996. Control of damping- borne pathogens, similar to those pre- off of safflower by bacterial seed treatment. sented here we have obtained a large Can. J. Plant Pathol. 18:43–49. range of responses depending on the Mahadevan, B. and D.L. Crawford. 1997. pathogen against which they are being Properties of the chitinase of the antifungal used (Gracia-Garza, 2001). A thor- biocontrol agent Streptomyces lydicus ough investigation of the pathogen WYEC 108. Enzyme Microbial Technol. and the natural environmental condi- 20:489–493. tions where the BCAs are expected to McCullagh, M., R. Utkhede, J. Menzies, perform should be conducted in order Z. Punja, and T.C. Paulitz. 1996. Evalua- to fully explore the usefulness of the tion of plant-growth promoting few biological alternatives presently rhizobacteria for biological control of available against plant pathogens. At pythium root rot of cucumber grown in present, in Canada, only two biocontrol rockwool and effects on yield. Euro. J. agents have been registered against Plant Pathol. 102:747–755. ornamental crops, Mycostop, and more Miller, P.M. 1955. V8 juice agar as a recently, Rootshield. In the U.S., sev- general-purpose medium for fungi and eral of the biocontrol agents used in bacteria. Phytopathology 45:461–462. this study are already commercially Rankin, L. and T.C. Paulitz. 1994. Evalu- available for growers of poinsettia and ation of rhizosphere bacteria for biological other ornamental crops. control of pythium root rot of greenhouse cucumbers in hydroponic culture. Plant Literature cited Dis. 78:447–451. Daugthery, M. 1998. Fungicide resistance Tsao, P. and G. Ocaña. 1969. Selective in pathogens of greenhouse crops, p. 59– isolation of species of from 65. In: J. Hall and K. Robb (eds.). Pro- natural soils on an improved antibiotic ceedings for the 14th Conf. Insect and medium. Nature 233:636–638. Disease Management on Ornamentals. Soc. Amer. Flor., Alex., Va.

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