Antagonistic Pythium against pathogenic Pythium on cucumber roots1

Antagonistic microorganisms introduced into the growing medium, the seed or the root, have been shown to reduce the attack of many soil-borne plant pathogenic fungi. In 1983, three experiments with Pythium oligandrum were carried out using cucumber seedlings artificially inoculated with Pythium splendens. The seedlings cv. Ideal Nova were grown in shallow boxes containing granulated rockwool fibre (Grodania). The plants were grown at a minimum temperature of 20°C in a glasshouse. Plants were treated with the antagonist either by coating the seeds, or by applying a disc of a PDA-culture to 9-day old seedlings. The pathogen was introduced 9 or 5 days later, respectively, by adding PDA culture discs to the rockwool; 15 and 38 days later, the area with attacked roots was calculated as a percentage of the box-bottom area. The experiments showed that it is possible to control P. splendens by either method of application. P. oligandrum was able to colonize the seed and rhizosphere and suppress P. splendens for at least 38 days. If future experiments are similarly positive, the methods for use in commercial horticulture should be worked out as soon as possible.     

Use of fungal antagonists for biocontrol of damping-off and sclerotinia diseases

Two mycoparasites, Pythium oligandrum and Coniothyrium minitans, have been tested for their ability to act as disease biocontrol agents. P. oligandrum oospores, grown in a cane molasses liquid medium and coated onto cress and sugar-beet seeds using commercial thin-film or pelleting techniques, gave significant control of damping-off in cress and sugar-beet caused by Pythium ultimum and Aphanomyces cochlioides respectively, in glasshouse pot trials. In some cases, the control was equivalent to fungicide drenches or standard fungicide seed treatments, but little control was achieved with any treatment when the pathogen inoculum potential in the soil was high. Pre-planting application of a solid substrate preparation of C. minitans gave reproducible control of sclerotinia disease in the glasshouse. The degree of control was equivalent to that achieved with regular foliar sprays of vinclozolin, when there was less than 40% disease in the control plots naturally infested with Sclerotinia sclerotiorum. At higher disease levels biocontrol was lost. Nevertheless, C. minitans survived in the soil for over one year and continued to degrade sclerotia and reduce apothecial production. The commercial potential of these biocontrol agents is discussed.     

Enhanced field control of wheat take-all using cold tolerant isolates of Gaeumannomyces graminis var. graminis and Phialophora sp. (lobed hyphopodia)

Cold tolerant isolates of Gaeumannomyces graminis var. graminis ( Ggg ) and Phialophora sp. (lobed hyphopodia), which produced at least comparable growth rates at 5°C to those of pathogenic G. graminis var. tritici ( Ggt ), were shown to control take-all disease in wheat effectively in 2 years of field experiments in New South Wales, Australia. The addition of oat inoculum of these fungi at the rate of 60 kg/ha to the seeding furrow significantly ( P  ≤ 0.05) reduced disease and increased grain yields by 33–45% compared to the Ggt alone treatment. The use of 30 kg/ha of oat inoculum also significantly ( P  ≤ 0.05) reduced disease and increased grain yields by 21–44%. These high levels of take-all control were obtained consistently from four field experiments on three different soil types with different pHs. A treatment inoculated with Ggg alone showed no disease symptoms and produced grain yields similar to that of untreated wheat. This fungus is, therefore, non-pathogenic to wheat. At high rates of inoculation of Ggg and Phialophora sp. (lobed hyphopodia), 65–80% of tillering wheat plants (GS 32) had root systems colonized by these fungi. In contrast, two Pseudomonas spp. and an isolate each of Ggg and Phialophora sp. (lobed hyphopodia), which did not grow at 5°C, were ineffective in controlling take-all. Take-all assessments during heading (GS 61-83) were highly correlated ( R ²=0.6047, P ≤0.0005) with the relative yield increase or decrease of inoculated treatments compared to the Ggt alone treatment. The use of a Ggg isolate (90/3B) and a Phialophora sp. (lobed hyphopodia) isolate (KY) for take-all control has been patented. These fungi are being developed for commercial use.     

Management of resident plant growth-promoting rhizobacteria with the cropping system: a review of experience in the US Pacific Northwest

In view of the inconsistent performance of single or mixtures of plant growth-promoting rhizobacteria (PGPR) strains formulated for commercial use, and the high cost of regulatory approval for either a proprietary strain intended for disease control or a crop plant transformed to express a disease-suppressive or other growth-promoting PGPR trait, management of resident PGPR with the cropping system remains the most practical and affordable strategy available for use of these beneficial rhizosphere microorganisms in agriculture. A cropping system is defined as the integration of management (agricultural) practices and plant genotypes (species and varieties) to produce crops for particular end-uses and environmental benefits. The build-up in response to monoculture cereals of specific genotypes of Pseudomonas fluorescens with ability to inhibit Gaeumannomyces graminis var. tritici by production of 2,4-diacetylphoroglucinol (DAPG), accounting for take-all decline in the US Pacific Northwest, illustrates what is possible but apparently not unique globally. Other crops or cropping systems enrich for populations of the same or other genotypes of DAPG-producing P. fluorescens or, possibly and logically, genotypes with ability to produce one or more of the five other antibiotic or antibiotic-like substances inhibitory to other soilborne plant pathogens. In the U.S Pacific Northwest, maintenance of threshold populations of resident PGPR inhibitory to G. graminis var. tritici is the centerpiece of an integrated system used by growers to augment take-all decline while also limiting damage caused by pythium and rhizoctonia root rot and fusarium root and crown rot in the direct-seed (no-till) cereal-intensive cropping systems while growing varieties of these cereals (winter and spring wheat, barley and triticale) fully susceptible to all four root diseases.     

The occurrence of Phialophora-like fungi related to Gaeumannomyces graminis under various grass species and some characteristics of these fungi1

Phialophora graminicola and Phialophora sp. (lobed hyphopodia) are weakly or not pathogenic to the cereal and grass roots which they colonize and are also known to restrict the infection of these plants by Gaeumannomyces graminis. The occurrence of these fungi under 15 field-grown grass species has been studied using wheat as the test plant. P. graminicola occurred under all grass species tested but at different population levels. The lowest populations were found under Bromus erectus and B. inermis, and relatively low populations under Agrostis alba, Festuca ovina and Phalaris arundinacea. Festuca pratensis, F. rubra, F. arundinacea, Dactylis glomerata and Arrhenatherum elatius harboured the highest populations of P. graminicola. Phialophora sp. (lobed hyphopodia) was found at low population levels under 7 of the 15 grasses examined. The strains of P. graminicola isolated in these studies differed markedly in growth rate on wheat roots and in restriction of G. graminis on wheat grown in perlite (preliminary results).     

Field testing putative biological controls of take-all: rationale and results1

In seeking biological control of the wheat take-all fungus (Gaeumannomyces graminis var. tritici) by introduced organisms, the demonstration of satisfactory field performance is proving a formidable hurdle. A novel experimental design incorporating small plots, 37 x 31 cm, has been used in UK at Rothamsted and Woburn since 1983 to test different kinds of control for take-all and to explore some of the problems of providing adequate field tests of putative biocontrol agents. Three years of bacterial treatments, using different plots each year, provided no evidence of effective control of the disease. Of the few significant treatment effects, most occurred in spring and were temporary: at Woburn they were mostly decreases in take-all and at Rothamsted mostly decreases in growth of the wheat plant without concomitant changes in take-all.     

Continuous Cereal Growing in Denmark; Experimental Results1

In Denmark, results from 3 long-term trials showed that yields from barley monoculture were satisfactory on clay soil provided that sufficient nitrogen was supplied. Root diseases, in particular take-all (Gaeumannomyces graminis (Sacc.) Arx et Olivier), often stabilized at a rather low level after a period of decline. Mono-culture of winter wheat gave poor yields compared with barley monoculture. Break crops of white mustard and oats in barley monoculture had a beneficial effect, especially on sandy soil.     

Sensitivity of fungi from cereal roots to fluquinconazole and their suppressiveness towards take-all on plants with or without fluquinconazole seed treatment in a controlled environment

The take-all fungus, Gaeumannomyces graminis var. tritici , was highly sensitive to fluquinconazole ( in-vitro EC₅₀ 0·016–0·018 mg L⁻¹), a fungicide developed for use as a seed treatment to control take-all, and to prochloraz (EC₅₀ 0·006 mg L⁻¹). Fungi of other genera that were commonly isolated from cereal roots were sensitive in varying degrees to prochloraz but were relatively insensitive (e.g. Fusarium culmorum , EC₅₀ > 20 mg L⁻¹) or slightly sensitive (e.g. Epicoccum purpurascens , EC₅₀ 0·514 mg L⁻¹) to fluquinconazole. Gaeumannomyces graminis var. graminis and G. cylindrosporus , weak parasites that can protect roots against take-all, and an unnamed Phialophora sp., all closely related to the take-all fungus, were highly or moderately sensitive to fluquinconazole. Alternaria infectoria and E. purpurascens were most consistently effective in suppressing development of take-all on pot-grown wheat plants dual-inoculated with G. graminis var. tritici and the nonpathogen. Take-all was decreased more on dual-inoculated wheat plants grown from seed treated with fluquinconazole or fluquinconazole plus prochloraz than when only an antagonistic fungus ( A. infectoria , E. purpurascens , Fusarium culmorum or Idriella bolleyi ) or a seed treatment was applied. These fungi were less effective in combination with seed treatments on barley. Gaeumannomyces graminis var. graminis and G. cylindrosporus , tested on wheat, suppressed take-all only in the absence of fungicides. It is suggested that the performance of seed treatment containing fluquinconazole against take-all may in some circumstances be enhanced by its partial specificity for the take-all fungus.     

Take-all of wheat

Take-all, caused by the soilborne fungus Gaeumannomyces graminis var. tritici, is arguably the most-studied root disease of any crop, yet remains the most important root disease of wheat worldwide. S. D. Garrett launched the study of root diseases and soilborne pathogens as an independent field of science starting in the middle of the 20th century, inspired by and based in large part on his research on take-all during the first half of the 20th century. Because there has been neither a source of host plant resistance nor an effective and economical fungicide for use against this disease, the focus for nearly a century has been on cultural and biological controls. In spite of the intensive and extensive works towards these controls, with mostly site-or soil-specific success, the only broadly and consistently effective controls require either crop rotation (break crops), or the converse, wheat monoculture to induce take-all decline. Take-all decline has become the model system for research on biological control of plant pathogens in the rhizosphere and provided the first proof to the scientific world after decades of debate that antibiotics are both produced in soils and play a role in the ecology of soil microorganisms. On the other hand, even the best yields following take-all decline are rarely equal to those achieved with crop rotation. Because of this, the continuing trends globally to shorten rather than lengthen the rotations in wheat-based cropping systems, and the growing use of direct-seed (no-till) trashy systems to reduce costs and protect soil and water resources, new methods to control take-all are needed more than ever. With high resolution maps of the genomes of cereals and other grasses now available, including a complete sequence of the rice genome, and the interesting differences as well as striking similarities among the genomes of cereals and related grasses, gene transfer to wheat from oats, rice, maize and other grass species resistant to G. graminis var. tritici should be pursued.     

Effect of Organic Management of Soils on Suppressiveness to <Emphasis Type="Italic">Gaeumannomyces graminis</Emphasis> var. <Emphasis Type="Italic">tritici</Emphasis> and its Antagonist, <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis>

Organic management of soils is generally considered to reduce the incidence and severity of plant diseases caused by soil-borne pathogens. In this study, take-all severity on roots of barley and wheat, caused by Gaeumannomyces graminis var. tritici, was significantly lower in organically-managed than in conventionally-managed soils. This effect was more pronounced on roots of barley and wheat plants grown in a sandy soil compared to a loamy organically-managed soil. Fluorescent Pseudomonas spp. and in particular phlD⁺ pseudomonads, key factors in the take-all decline phenomenon, were represented at lower population densities in organically-managed soils compared to conventionally-managed soils. Furthermore, organic management adversely affected the initial establishment of introduced phlD⁺ P. fluorescens strain Pf32-gfp, but not its survival. In spite of its equal survival rate in organically- and conventionally-managed soils, the efficacy of biocontrol of take-all disease by introduced strain Pf32-gfp was significantly stronger in conventionally-managed soils than in organically-managed soils. Collectively, these results suggest that phlD⁺ Pseudomonas spp. do not play a critical role in the take-all suppressiveness of the soils included in this study. Consequently, the role of more general mechanisms involved in take-all suppressiveness in the organically-managed soils was investigated. The higher microbial activity found in the organically-managed sandy soil combined with the significantly lower take-all severity suggest that microbial activity plays, at least in part, a role in the take-all suppressiveness in the organically-managed sandy soil. The significantly different bacterial composition, determined by DGGE analysis, in organically-managed sandy soils compared to the conventionally-managed sandy soils, point to a possible additional role of specific bacterial genera that limit the growth or activity of the take-all pathogen.     

Volatile analogues of penconazole and their activity against the take-all fungus,Gaeumannomyces graminis var. tritici

Eight new sterol biosynthesis-inhibiting fungicides, structurally related to penconazole and having vapour pressures up to 118 mPa, were synthesised. Their toxicities to the cereal take-all fungus, Gaeumannomyces graminis var. tritici, on agar were measured; intrinsic activities were measured after incorporating the compounds into the agar and vapour activities were measured after their evaporation from glass and from moist soil. Vapour activity following evaporation from soil was shown to be a function of both the intrinsic activity of the compound and its partition coefficient between the air and moist soil (K_as). The latter is itself a function of vapour pressure, 1-octanol/water partition coefficient (K_ow) and the soil type. The compound most active as vapour from soil in the in-vitro test, 1-(pyridin-3-yl)-2-(4-flurorophenyl)pentane, was ineffective against take-all in wheat in a pot test in which the inoculated soil was treated unevenly, providing further evidence that the redistribution of fungicides in moist soil occurs predominantly via the water phase rather than the vapour phase.     

寡雄腐霉发酵液对温室番茄生长及灰霉病的防治作用

为了研制高效、无毒的生物农药,采用自主分离的寡雄腐霉生防菌株Pythium oligandrum CQ2010制备发酵液,研究其对温室番茄生长及灰霉病的防治作用。结果表明,寡雄腐霉发酵液(Pythium oligandrum broth,POB)能显著提高番茄叶绿素含量,增强根系活力,增加氮、磷、钾吸收,促进植株生长,使生物量比对照提高65.14%;同时能激活与叶片抗病性相关的过氧化物酶和过氧化氢酶活性,诱导植株产生抗病性反应,提高抗病能力,其效果优于寡雄腐霉卵孢子制剂;而且POB能显著抑制离体灰葡萄孢菌的菌丝生长和孢子萌发;施用POB能使番茄灰霉病发病率下降22.28%~31.05%,病情指数从52.5(对照)下降至22.5~27.5,相对防治效果达47.62%~57.14%,叶片丙二醛含量显著降低,说明POB减轻了灰葡萄孢菌对细胞膜的伤害。表明POB兼具促进番茄生长及防治灰霉病的作用。     

Dominant Colonisation of Wheat Roots by Pseudomonas fluorescens Pf29A and Selection of the Indigenous Microflora in the Presence of the Take-all Fungus

Increases in populations of fluorescent pseudomonads on wheat roots are usually associated with take-all decline, natural control of take-all, a disease caused by the fungus Gaeumannomyces graminis var. tritici (Ggt). Colonisation by Pseudomonas fluorescens strain Pf29A was assessed on the roots of healthy plants and of plants with take-all, and the effect of this bacterium on indigenous populations of fluorescent pseudomonads was studied. The efficacy of Pf29A as an agent for the biocontrol of take-all on five-week-old wheat seedlings was tested in non-sterile conducive soil in a growth chamber. RAPD (random amplification of polymorphic DNA) fingerprinting with a decamer primer was used to monitor strain Pf29A and culturable indigenous rhizoplane populations of fluorescent pseudomonad. Pf29A decreased disease severity and accounted for 44.6% of the culturable fluorescent pseudomonads on healthy plant rhizoplane and 75.8% on diseased plant rhizoplane. Fewer RAPD patterns were obtained when Pf29A was introduced into the soil with Ggt. In the presence of Ggt and necrotic roots, Pf29A became the dominant root coloniser and dramatically changed the diversity and the structure of indigenous fluorescent pseudomonad populations. The results show that Ggt and reduced lesion size on roots can trigger a specific increase in antagonist populations and that the introduction of a biocontrol agent in soil influences the structure of indigenous bacterial populations.     

Pythium rot of chingensai ( Brassica campestris L. chinensis group) caused by Pythium ultimum var. ultimum and Pythium aphanidermatum

Severe rot was found at the base of leaves and stems of chingensai (Brassica campestris L. chinensis group) in Okayama Prefecture in 2000. The causal fungi were morphologically identified as Pythium ultimum Trow var. ultimum and P. aphanidermatum (Edson) Fitzpatrick. This is the first report of rot caused by Pythium species on chingensai. We named this disease Pythium rot of chingensai.     

Improved polymerase chain reaction (PCR) detection ofGaeumannomyces graminis including a safeguard against false negatives

A previously reported method for polymerase chain reaction (PCR) detection ofGaeumannomyces graminis was modified to simplify it, improve its specificity and decrease the possibility of contamination of the assay. The modified method also allowed discrimination between theG. graminis varieties (tritici andavenae) that are pathogenic to wheat and oats respectively and the variety weakly pathogenic to wheat (var.graminis). An internal positive control for the PCR was also added to the test by including a second pair of primers in the reaction. This positive control has wider application in PCR tests for detection of other fungi.     

The effects of various crops on the survival and carry-over of the wheat take-all fungus Gaeumannomyces graminis var. tritici

The effects of various crops on the saprophytic survival and carry-over of Gaeumannomyces graminis var. tritici were studied in the glasshouse and field.
In the glasshouse, survival of G. g. tritici was greater in unplanted pots than in pots planted with either cereals or non-cereals. In the field, fallow and various non-cereal crops reduced carryover of take-all but the disease was severe after wheat, barley and triticale. Grain yields were higher after fallow and non-cereals than after cereal crops.     

Control of fungal pathogens — preharvest Use of coniothyrium minitans and pythium oligandrum as disease biocontrol agents

When disease levels are low,Coniothyrium minitans gives biological control of Sclerotinia disease in lettuce andPythium oligandrum control of damping-off in cress and sugar beet equivalent to standard fungicide treatments, but both fail as the inoculum potential of the pathogens increases. Possible approaches for improving the use and efficacy of these biocontrol agents are discussed.     

Utilisation d'antagonistes pour l'enrobage des semences: efficacité et mode d'action contre les agents de la fonte des semis1

Le screening de 224 cultures microbiennes a fourni 17 souches de champignons, 5 bactéries et 1 actinomycète efficaces, en enrobage des semences, contre la fonte des semis de la betterave dans un sol contaminé par Pythium spp. en chambre climatisée. L'examen de ces 23 souches a permis de sélectionner Pseudomonas sp., Pythium oligandrum et Chaetomium globosum. Appliqués respectivement sous la forme de cellules bactériennes, d'oospores ou d'ascospores, les trois antagonistes ont présenté une efficacité constante contre Pythium ultimum. Sur les semences stockées, Pseudomonas sp. et P. oligandrum ont conservé leurs propriétés plusieurs mois, C. globosum pendant au moins 2 ans. Pseudomonas sp. et P. oligandrum protégeaient les betteraves contre P. ultimum et Phoma betae (contaminant les semences), mais pas contre Rhizoctonia solani. C. globosumétait efficace contre les trois pathogènes. Il était aussi actif contre P. ultimum et R. solani sur coton. Son efficacité contre Aphanomyces cochlioides sur betterave est à l'examen. Le mycoparasitisme de P. oligandrum, l'antibiose de C. globosum et Pseudomonas sp. ainsi que des dégradations aux hyphes des pathogènes par Pseudomonas sp. et C. globosum ont été observés in vitro.     

Biological means of plant protection in glasshouses in Belarus1

Biological control methods introduced and developed for Belarussian glasshouse crops are described. The agents used against arthropod pests include the natural enemies Phytoseiulus persimilis, Encarsia formosa and Amblyseius spp., the fungi Verticillium lecanii, Beauveria bassiana and Aschersonio, and the preparation Bitoxibacillin (based on Bacillus thuringiensis var. thuringiensis). Against fungal pathogens, Trichodermin (based on Trichuderma Iignorum) and peat oxyhumates are used.     

Differentiation of Gaeumannomyces graminis from other turf-grass fungi by amplification with primers from ribosomal internal transcribed spacers

A region comprising the 5.8S RNA gene and internal transcribed spacers 1 and 2 of the take-all patch fungus, Gaeumannomyces graminis var. avenae , was cloned and sequenced using primers from the flanking 17S and 26S ribosomal RNA genes. The sequenced region showed 99% similarity between the two G. graminis isolates, and 70–80% similarity between these two isolates and several other species of fungi. From the sequence, oligonucleotide primers were selected which permitted specific amplification of DNA from G. graminis vars. avenae and graminis using the polymerase chain reaction (PCR). The assay could detect DNA of G. graminis strains obtained from a wide variety of hosts, but did not amplify DNA from many other fungi, including the important turf-grass root pathogens Magnaporthe poae and Leptosphaeria korrae. The primers also did not amplify DNA from G. graminis var. tritici, M. rhizophila or Phialophora graminicola. The PCR-based assay shows promise as a diagnostic tool for the take-all pathogen in turf-grass pathology.