Greenhouse Pot Tests Research Articles

A potential biocontrol and growth-promoting agent Streptomyces luteoverticillatus B4 for managing cabbage Fusarium wilt and cucumber Alternaria leaf blight

Cabbage Fusarium wilt and cucumber Alternaria leaf blight are two widespread diseases caused by Fusarium oxysporum and Alternaria cucumerina that severely affect cabbage and cucumber output across the world. However, very few biocontrol actinomycete resources have been identified for these two diseases. An antagonistic actinomycete B4 was isolated and identified as Streptomyces luteoverticillatus. It is effective against a wide range of plant pathogens. The purpose of this study was to look into the inhibitory impact of S. luteoverticillatus B4 on F. oxysporum and A. cucumerina, as well as to create the theoretical groundwork and research technologies for the use of B4 as a biopesticide. It was found that B4 has the ability to detoxify organic phosphorus and produce siderophores, IAA, and glucoamylase. In the greenhouse pot test, B4 had a control efficiency of 56 % against F. oxysporum and 76 % against A. cucumerina. Further investigation into the inhibitory mechanism indicated that once the B4 fermentation broth operated on the two pathogens, their mycelial morphology was altered, and mycelial growth was suppressed, particularly for F. oxysporum. B4 could create volatile organic compounds that may have an inhibiting impact. In addition, B4 fermentation broth dramatically increased seed germination and seedling development in both cabbage and cucumber. S. luteoverticillatus B4 is a possible biocontrol agent that inhibits F. oxysporum and A. cucumerina while also encouraging cabbage and cucumber development.

Synthesis and biological activity of novel hydantoin cyclohexyl sulfonamide derivatives as potential antimicrobial agents in agriculture.

Plant disease is one of the most serious problems in agriculture that can damage crops. Chemical fungicides are widely used to control plant diseases, but have led to resistance and a series of environmental problems. It is, therefore, necessary to develop highly effective and eco-friendly antimicrobial compounds with novel structures. A series of novel hydantoin cyclohexyl sulfonamide derivatives were synthesized through an intramolecular condensation reaction. The bioassay results indicated that a majority of the title compounds displayed potent inhibitory activity against Botrytis cinerea, Sclerotinia sclerotiorum and Erwinia carotorora. The in vivo inhibition rate of compound 3h was 91.01% against B. cinerea, which was higher than that of iprodione (84.07%). Compound 3w showed excellent antifungal activity against B. cinerea with a half-maximal effective concentration (EC50 ) of 4.80 μg ml-1 , which is lower than that of iprodione. Compound 3q had an EC50 value of 1.44 μg ml-1 against S. sclerotiorum, which was close to that of iprodione (1.39 μg ml-1 ), and the inhibition rate was also similar to that of iprodione. Compounds 3i and 3w had the best inhibition efficacy against S. sclerotiorum, both on growth of the mycelium and sclerotia and in the greenhouse pot test in vitro. Further study showed that compounds 3h, 3r and 3s have superb antibacterial activity against E. carotorora with EC50 values of 2.65, 4.24 and 4.29 μg ml-1 respectively, and were superior to streptomycin sulfate (5.96 μg ml-1 ). Because of their excellent antifungal and antibacterial activity against B. cinerea, S. sclerotiorum and E. carotorora, these hydantoin cyclohexyl sulfonamide derivatives could be considered as suitable candidates for new antimicrobial agents. © 2021 Society of Chemical Industry.

Regulation of biosynthesis, perception, and functions of strigolactones for promoting arbuscular mycorrhizal symbiosis and managing root parasitic weeds.

Strigolactones (SLs) are carotenoid-derived plant secondary metabolites that play important roles in various aspects of plant growth and development as plant hormones, and in rhizosphere communications with symbiotic microbes and also root parasitic weeds. Therefore, sophisticated regulation of the biosynthesis, perception and functions of SLs is expected to promote symbiosis of beneficial microbes including arbuscular mycorrhizal (AM) fungi and also to retard parasitism by devastating root parasitic weeds. We have developed SL mimics with different skeletons, SL biosynthesis inhibitors acting at different biosynthetic steps, SL perception inhibitors that covalently bind to the SL receptor D14, and SL function inhibitors that bind to the serine residue at the catalytic site. In greenhouse pot tests, TIS108, an azole-type SL biosynthesis inhibitor effectively reduced numbers of attached root parasites Orobanche minor and Striga hermonthica without affecting their host plants; tomato and rice, respectively. AM colonization resulted in weak but distinctly enhanced plant resistance to pathogens. SL mimics can be used to promote AM symbiosis and to reduce the application rate of systemic-acquired resistance inducers which are generally phytotoxic to horticultural crops. © 2019 Society of Chemical Industry.

Evaluation of Bacillus Strains for Plant Growth Promotion and Predictability of Efficacy by In Vitro Physiological Traits.

Bacilli are commonly used as plant growth-promoting agents but can be limited in effectiveness to certain crop and soil environments. The objectives of this study were to (1) identify Bacillus strains that can be consistent in promoting the growth of corn, wheat, and soybean and (2) determine whether physiological traits expressed in vitro can be predictive of growth promotion efficacy/consistency and be used for selecting effective strains. Twelve Bacillus strains isolated from wheat rhizospheres were evaluated in greenhouse pot tests with nonsterile soil for their effects on the growth of corn, soybean, and wheat. The strains also were assessed in vitro for multiple physiological traits. All 12 strains increased corn growth significantly compared to the controls. The four most efficacious strains on corn—Bacillus megaterium R181, B. safensis R173, B. simplex R180, and Paenibacillus graminis R200—also increased the growth of soybean and wheat. No set of traits was a predictor of growth promotion efficacy. The number of traits expressed by a strain also was not an indicator of efficacy as strain R200 that was positive for only one trait showed high growth promotion efficacy. Effective strains can be identified through pot tests on multiple crop plants, but in vitro physiological assays are unreliable for strain selection.

Vermicompost Improves Tomato Yield and Quality and the Biochemical Properties of Soils with Different Tomato Planting History in a Greenhouse Study.

A greenhouse pot test was conducted to study the impacts of replacing mineral fertilizer with organic fertilizers for one full growing period on soil fertility, tomato yield and quality using soils with different tomato planting history. Four types of fertilization regimes were compared: (1) conventional fertilizer with urea, (2) chicken manure compost, (3) vermicompost, and (4) no fertilizer. The effects on plant growth, yield and fruit quality and soil properties (including microbial biomass carbon and nitrogen, -N, -N, soil water-soluble organic carbon, soil pH and electrical conductivity) were investigated in samples collected from the experimental soils at different tomato growth stages. The main results showed that: (1) vermicompost and chicken manure compost more effectively promoted plant growth, including stem diameter and plant height compared with other fertilizer treatments, in all three types of soil; (2) vermicompost improved fruit quality in each type of soil, and increased the sugar/acid ratio, and decreased nitrate concentration in fresh fruit compared with the CK treatment; (3) vermicompost led to greater improvements in fruit yield (74%), vitamin C (47%), and soluble sugar (71%) in soils with no tomato planting history compared with those in soils with long tomato planting history; and (4) vermicompost led to greater improvements in soil quality than chicken manure compost, including higher pH (averaged 7.37 vs. averaged 7.23) and lower soil electrical conductivity (averaged 204.1 vs. averaged 234.6 μS/cm) at the end of experiment in each type of soil. We conclude that vermicompost can be recommended as a fertilizer to improve tomato fruit quality and yield and soil quality, particularly for soils with no tomato planting history.

Impact of Super Absorbent Polymer and Plants on Microbial Community and Petroleum Hydrocarbon Degradation in Contaminated Soil

A greenhouse pot test, in which wheat, cabbage, spinach were cultivated separately in petroleum contaminated soil with and without super absorbent polymer (SAP), was conducted to evaluated the effect of plants and SAP on soil microbiological properties. phospholipid fatty acids (PLFAs) profiles were analyzed to reveal the microbial communities. As a measure of the functional activity of soil microbial community, the ratio of degraded to total petroleum hydrocarbon (TPH) in soil was estimated. The results indicated that SAP had an important effect on the soil microbial community and its degrading TPH activities. First, the principal component analysis (PCA) of the PLFA signatures revealed marked changes between soil with SAP and without SAP. In addition, the total amount and the profile of PLFA were significantly different between the untreated and SAP-amended soils. Using PLFA patterns as a biomarker, it was found that gram-positive bacteria (G+) were more sensitive to SAP than gram-negative bacteria (G-), and the biomass of G+ was higher in soil with SAP than in that without SAP. Second, the crop could stimulate the growth of soil microorganisms; however, the differences depended clearly on the crop species. The G+ and G- biomass was increased in cabbage, spinach soil containing SAP, but was decreased in wheat soils. The population of fungi was increased in cabbage and spinach soils containing SAP, but was decreased in wheat soil with SAP. The population of actinomycetes was decreased in all soils with SAP. Third, the ratio of degraded to TPH was slightly increased in soil with SAP treatment, but a significant change depended on the crop species. In total, 12 different PLFAs were identified, including saturated, monounsaturated, branched, and polyunsaturated species. There was a clear difference in the PLFAs composition between soils with and without SAP.

길항세균을 이용한 상추 균핵병의 생물학적 방제

To isolate antagonistic bacteria against sclerotinia rot of lettuce, caused by Sclerotinia sclerotiorum, soil samples were collected from the diseased greenhouse field in Namyangju city, Gyeong-gi province from 2007 to 2008. A total of 196 bacterial isolates were isolated using serial dilution method. In dual culture assay in vitro, 26 isolates showed more than 80% of inhibition rates of mycelial growth of S. sclerotiorum. Based on 16S rDNA sequence analysis, the 26 isolates were identified as Bacillus megaterium, B. cereus, B. subtilis, Arthrobacter nicotianae, A. ramosus, Pseudomonas filiscindens, Stenotrophomonas maltophilia, Brevibacterium frigoritolerans and Sphingobacterium faecium. The 26 isolates inhibited the mycelial growth of S. sclerotiorum up to 80% and the sclerotial germination 0-100%. In the greenhouse pot test of ten isolates conducted in summer, 2 isolates B. megaterium (DK6) and B. cereus (C210) showed control efficacy on sclerotia viability of S. sclerotiorum, 20% and 35%, respectively. In the greenhouse pot test in winter, the disease incidence of the control group was 80%, whereas those of 9 isolates among 26 were approximately 20%. From the result, the 9 isolates are expected as potentially antagonistic bacteria for biological control of sclerotinia rot of lettuce caused by S. sclerotiorum.

Field and Greenhouse Response of Red Raspberry Genotypes to Root Rot

Red raspberry genotypes (Rubus idaeus L.) were evaluated for resistance to root rot at two field sites in Washington state and in a greenhouse study. Thirteen raspberry genotypes were planted in two field sites naturally infested with Phytophthora fragariae var. rubi Wilcox and Duncan and evaluated over 3 years for growth and symptom expression. In greenhouse pot tests, 14 genotypes were inoculated with an isolate of P. fragariae var. rubi at three inoculum levels and evaluated for growth, root color, and symptom expression using a 1 to 4 rating scale. Eleven of the 14 cultivars were found to be susceptible or very susceptible to root rot in the field and greenhouse. ‘Summit’ and ‘Newburgh’ possessed high levels of resistance to the pathogen. ‘Cascade Bounty’ also showed high resistance to root rot in the greenhouse, but confirmation from a field study is needed. Subjective root ratings of greenhouse-grown plants correlated well with measurements of cane numbers and cane infection in the field. The greenhouse tests were useful in identifying resistant genotypes and very susceptible genotypes but did not always match field results. Observation of at least 3 years in the field was necessary to compare relative reaction with root rot among genotypes.

Potential of Verticillium lecanii (Lecanicillium spp.) hybrid strains as biological control agents for soybean cyst nematode: Is protoplast fusion an effective tool for development of plant-parasitic nematode control agents?

Verticillium lecanii is a potentially useful biological control agent (BCA) for soybean cyst nematode (SCN), Heterodera glycines. The objective of this study was to screen hybrid strains of V. lecanii, derived from protoplast fusion, for effective control agents of SCN, and to investigate whether the protoplast fusion technique is an effective tool for development of nematode control agents. Three parental strains (Vertalec®, Mycotal®, and B-2) and their 162 hybrid strains were screened in greenhouse pot tests. Some of these hybrid strains suppressed damage on soybean plants and reduced the density of SCN in the soil. In particular, one hybrid strain, AaF42, was observed to reduce the nematode egg density by 93.2% as compared with the control. Furthermore, this strain significantly reduced the cyst and egg density as compared with the parental strains. In conclusion, some of the hybrid strains exhibited enhanced biocontrol efficacy by protoplast fusion. Therefore, the protoplast fusion technique may be a potentially valuable tool for developing nematode-antagonistic fungi as BCA.

Preparation of polylactide-based microspheres enclosing acetamiprid and evaluation of efficacy against cotton aphid by soil application

Concern for the environment has increased interest in reducing the amount of pesticides applied to agricultural land. This can be accomplished by immobilization of the pesticides in polymer supports, which prevents volatilization, degradation and leaching losses, and provides controlled release of the pesticides. In the present study, acetamiprid, a novel pesticide, was enclosed in polylactide (PLA)-based microspheres using solvent evaporation method via oil-in-oil (O/O) emulsion. Amount of acetamiprid released from PLA microspheres was less than 5% in phosphate buffered saline. On the other hand, incorporation of water-soluble polymer, such as poly(ethylene glycol) (PEG) and poly(oxyethylene) diglycolic acid, into the PLA microspheres resulted in increased amount of released acetamiprid (∼70%). Planting hole application by greenhouse pot test demonstrated that the efficacy of the PLA/PEG microspheres enclosing acetamiprid against cotton aphids was superior to that of PLA microspheres enclosing acetamiprid. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Incorporating straw may induce sulfide toxicity in paddy rice

Sulfide toxicity to rice plants has been randomly observed in isolated sites in rice fields and experimental plots in the Sacramento Valley. Plants suffering from sulfide toxicity show signs of retarded growth and reduced yields, including the characteristic blackened roots and, in the most severe cases, death. Because the environmental conditions causing sulfide toxicity are not clear, we carried out a greenhouse pot test. The treatments included straw and sulfate additions to a rice soil to induce sulfide production. Our results contribute to an improved definition of conditions leading to sulfide production, toxicity and impact to rice plants.

Potato germplasm resistant to corky ringspot disease

Potato germplasm was assessed for resistance to corky ringspot disease (CRS) incited by transmission of tobacco rattle virus (TRV). TRV is transmitted by the stubby root nematode,Paratrichodorus allius, in the Pacific Northwest, and characterized by necrotic areas in the tuber. Four tests were conducted at two different problem fields in Umatilla, OR and Pasco, WA. The fields differed in the virulence of the virus isolates. Some clones and named varieties showed resistance only in the field with the relatively mild Umatilla isolate, while others remained symptomless at both sites. The host suitability of test potatoes to threeP. allius populations from the region was determined in greenhouse pot tests, and expressed as reproductive values [Rf = (final population of nematode at 55 days) / (initial population)]. TheRf values for the nematodes were not correlated with resistance ratings based on visual scoring of CRS symptoms in field grown potatoes. Thus, it appears that CRS resistance is based on reaction of potato genotypes to virus and not the vector. The availability of resistant clones inin vitro form is indicated.

Novel 1,3,5-triazine derivatives with herbicidal activity

New fluoroalkyl-substituted 1,3,5-triazine derivatives were synthesized and screened for herbicidal activity using a greenhouse pot test. Surprisingly, a series of 2-alkyl-4-fluoroalkyl-6-aralkylamino-1,3,5-triazines e.g. 6-(4-bromo-benzylamino)-2-methyl-4-trifluoromethyl-1,3,5-triazine was found to possess strong pre- and post-emergence herbicidal activities, although the conventional herbicidal 1,3,5-triazines generally should have a 2-substituted-4,6-diamino-1,3,5-triazine structure for herbicidal activity. Our compounds show strong Photosynthetic Electron Transport inhibitory activity (PI 50 c 7). Although their herbicidal effect is considered to be caused by a process similar to that for the conventional 1,3,5-triazine herbicide atrazine, they can control atrazine-resistant Chenopodium album effectively, and will thus form promising trial compounds for new triazine herbicide design.

Synthesis and Herbicidal Activity of New Oxazolidinedione Derivatives

A series of new 3-(substituted phenyl)-5-alkylidene-1,3-oxazolidine-2,4-dione derivatives was synthesized by reacting substituted phenyl isocyanates with 2-hydroxy-3-alkenoates prepared through an acid-catalyzed isomerization of 3,3-disubstituted glycidates, and their herbicidal activities against various weeds as well as the crop safeties were examined. 1,2) The herbicidal activities of these oxazolidinedione derivatives were primarily influenced by the substituents on the phenyl group and by the structure of the alkylidene moiety. The compounds having a 2,4-dihalo-5-alkoxyphenyl moiety exhibited relatively higher herbicidal activities while the introduction of a long chain alkylidene group at the 5-position of the oxazolidine ring reduced the activity. The crop safety was found to be markedly affected by the substituent at the 5-position of the phenyl group and a cyclopentyloxy group seemed to be the most preferable one. Among the compounds synthesized, 3-(4-chloro-5-cyclopentyloxy-2-fluorophenyl)-5-isopropylidene-1,3-oxazolidine-2,4-dione (KPP-314) was selected as a promising paddy rice herbicide. In greenhouse pot tests, KPP-314 exhibited an excellent activity against annual lowland weeds by pre- and post-emergence soil treatments at 150 to 450 g a.i./ha with a wide safety margin between rice plant and Echinochloa oryzicola.

Insecticidal activity of monoterpenoids to western corn rootworm (Coleoptera: Chrysomelidae), twospotted spider mite (Acari: Tetranychidae), and house fly (Diptera: Muscidae).

Acute toxicities of 34 naturally occurring monoterpenoids were evaluated against 3 important arthropod pest species; the larva of the western corn rootworm, Diabrotica virgifera virgifera LeConte; the adult of the twospotted spider mite. Tetranychus urticae Koch; and the adult house fly. Musca domestica L. Potential larvicidal or acaricidal activities of each monoterpenoid were determined by topical application, leaf-dip method, soil bioassay, and greenhouse pot tests. Phytotoxicity was also tested on a corn plant. Citronellic acid and thymol were the most topically toxic against the house fly, and citronellol and thujone were the most effective on the western corn rootworm. Most of the monoterpenoids were lethal to the twospotted spider mite at high concentrations; carvomenthenol and terpinen-4-ol were especially effective. A wide range of monoterpenoids showed some larvicidal activity against the western corn rootworm in the soil bioassay. Perillaldehyde, the most toxic (LC50 = 3 micrograms/g) in soil, was only 1/3 as toxic as carbofuran, a commercial soil insecticide (LC50 = 1 microgram/g). Selected monoterpenoids also effectively protected corn roots from attack by the western corn rootworm larvae under greenhouse conditions. alpha-Terpineol was the best monoterpenoid in the greenhouse pot test. The acute toxicity of monoterpenoids was low relative to conventional insecticides. Some monoterpenoids were phytotoxic to corn roots and leaves. l-Carvone was the most phytotoxic, whereas pulegone was the safest. The results with thymyl ethyl ether, one of the synthetic derivatives of thymol, showed a potential of derivatization to reduce monoterpenoid phytotoxicity.

Antibacterial Activity of Validamycin A against Pseudomonas solanacearum and Its Efficacy against Tomato Bacterial Wilt.

Validamycin A (VM-A), the active ingredient of Validacin®, inhibits fungal growth by inhibiting trehalase activity. Therefore, VM-A was tested against Pseudomonas solanacearum for its efficacy in controlling tomato bacterial wilt. In media containing trehalose as the sole carbohydrate, VM-A at 50μg/ml inhibited growth of P. solanacearum to rates similar to that of the bacteria in media without carbohydrate for seven days after inoculation. VM-A also gave excellent control of tomato bacterial wilt in greenhouse pot tests, when directly injected into plant stems. In field tests, foliar sprays of VM-A at 250μg/ml five days before and two days after inoculation had reduced disease by 47.4% by four weeks after inoculation. In the tomato stem between 0 and 5cm above the soil line, the bacteria population in the non-treated plot reached 3.84×1010cfu/g fresh weight, whereas that in the VM-A (500μg/ml)-treated plot reached 2.13×109cfu/g fresh weight. Inhibition of bacteria growth by VM-A may delay the appearance of disease symptoms of tomato bacterial wilt.

Activity of a Sulfonylurea Herbicide Azimsulfuron(DPX-A8947) in Combination with Bensulfuron Methyl and Effects of Environmental Factors.

Azimsulfuron (DPX-A8947) is one of sulfonylurea herbicides developed by E. I. du Pont de Nemours and Co. Inc. as a paddy rice herbicide. Azimsulfuron is also an acetolactate synthase (ALS) inhibitor. Results of greenhouse pot tests indicated that azimsulfuron at a rate as low as 6g a. i./ha affords excellent control of sedge and perennial weeds, whereas a higher rate is required to give excellent control on annual broad leaf weeds. Especially activity of Cyperus serotinus and Eleochalis kuroguwai was significantly higher than that of bensulfuronmethyl (BSM). Azimsulfuron afforded a comparable rice safety to that of BSM at 75g a. i./ha up to 12g a. i./ha under the tested conditions. Data from glass tube studies, in which plants were directly exposed to chemicals, suggest that the high selectivity between rice and Cyperus serotinus may mainly be attributed to physiological or biochemical factors in plants as in the case of BSM which is rapidly metabolized in rice plants. In greenhouse studies, a mixture of azimsulfuron with BSM was found to be effective. Addition of azimsulfuron significantly improved the activity of BSM on perennial sedges without causing rice injury and reduced the total quantity of chemicals used. This combination controlled the tested weeds well even under environmental factors such as water leaching, overflow of paddy water and low temperature. The results obtained suggest that azimsulfuron is a promising rice herbicide especially in combination with BSM in terms of high biological activity and rice safety.

Environmental evaluation of calcium magnesium acetate for highway deicing applications

Calcium magnesium acetate (CMA) was identified in the early 1980s as a material that is potentially effective for deicing highways, feasible to manufacture commercially, and environmentally acceptable. Its environmental acceptability required definitive testing prior to widespread application. This paper reports the results of comprehensive laboratory and controlled field plot experiments designed to determine CMA transport characteristics and environmental fate and its impacts on terrestrial and aquatic ecosystems. Preliminary modeling predicted routine and maximum CMA concentrations and mass loadings in highway runoff and spray as a basis for designing experimental treatments. In experiments testing CMA effects on a number of soil physical properties, only permeability exhibited any substantial change; however, the general increases in this characteristic are not a cause for concern relative to CMA use. Laboratory assessments of soils dosed with CMA solutions showed potential acetate mobility, yet field measurements yielded only minor evidence of CMA transport in the soil and ground water. The laboratory experiments also demonstrated a potential to release certain trace metals, preexisting in soils, through ion exchange reactions involving calcium and magnesium, a trend confirmed in the field, although with less strength and consistency. The quantities released in these experiments would pose no environmental hazards, but it is unknown whether mobilization from heavy metal-contaminated actual roadside soils would do so. CMA biodegradation was investigated at several temperatures in both soils and water. At 20 and 10°C, a high level of decomposition was achieved within 2 weeks in soils, and most of the ultimate BOD was exerted within 5 and 10 days, respectively, in water. These levels of decomposition required 4 weeks in soils and 100 days in water at 2°C. Biodegradation in water was associated with the leading potential environmental impact of concern, the ability of CMA in concentrations that could be found in highway runoff to deplete dissolved oxygen in water; this issue is the subject of a companion paper. In greenhouse pot tests of CMA effects on various herbaceous and woody plant species, only root zone concentrations well above any normally expected value killed seedlings. Field applications of similarly high concentrations did not affect the yield, cover, vigor, rooting, or leaf condition of the plot flora. A series of laboratory bioassays on zooplankton and fish resulted in high rates of survival and reproduction at any routinely expected CMA concentration, so long as oxygen was not allowed to deplete.

Caffeic Acid Identified as an Inhibitory Compound in Asparagus Root Filtrate

A potential allelochemical was isolated and identified from methanol extracts of asparagus (Asparagus officinalis L.) fresh root tissue. Fractions were collected by cellulose column chromatography and tested for inhibition by an asparagus seed germination bioassay. The fraction showing the greatest inhibition contained caffeic acid, as identified by melting point, thin-layer chromatography, and infrared spectrum analysis. Seed germination bioassays and greenhouse pot tests showed depression of seedling emergence when asparagus seeds were exposed to various dosages of crude filtrate, a methanol extract from crude filtrate, and caffeic acid.

Evaluation of a Strain ofMyrothecium roridumas a Potential Biocontrol Agent AgainstPhytophthora cinnamomi

Potential antagonists of Phytophthora cinnamomi were evaluated from among 36 fungi and 110 bacteria isolated from the rhizosphere of avocado roots growing in a soil suppressive to Phytophthora where P. cinnamomi had been present for 40-50 yr. Strain TW of Myrothecium roridum proved to be the most active antagonist in controlling P. cinnamomi in repeated greenhouse pot tests with highly susceptible seedlings of Persea indica inoculated with P. cinnamomi