Rhizoctonia Root Rot Of Wheat Research Articles

Disease-Suppressive Soils Induce Systemic Resistance in Arabidopsis thaliana Against Pseudomonas syringae pv. tomato

Arabidopsis thaliana accession Col-0 seedlings were transferred into an autoclaved soil/sand mixture amended with either 10 or 20% (wt/wt) soil from fields in Washington State that are suppressive to take-all or Rhizoctonia root rot of wheat. Three weeks after transplanting, these plants had population sizes of 2,4-diacetylphloroglucinol (DAPG) or phenazine-1-carboxylic acid (PCA)-producing pseudomonads of greater than 5 × 105 colony forming units per gram fresh weight of root with rhizosphere soil. When the plants were challenge-inoculated with Pseudomonas syringae pv. tomato DC3000, both soils induced systemic resistance in the leaves against bacterial speck to a level similar to that induced by P. simiae WCS417r, P. fluorescens Q2-87 (DAPG+), P. brassicacearum Q8r1-96 and L5.1-96 (both DAPG+), and P. synxantha 2-79 (PCA+). Pasteurization of the soils before adding them into the soil/sand mixture eliminated DAPG- and PCA-producing pseudomonads from the Arabidopsis rhizosphere and significantly reduced induced systemic resistance activity. However, populations of total culturable aerobic bacteria were similar in the rhizosphere of plants grown in soil/sand mixes amended with untreated or pasteurized suppressive soils. This is the first report of induction of systemic resistance in Arabidopsis by take-all and Rhizoctonia-suppressive soils and the ability of PCA-producing P. synxantha 2-79 to induce resistance. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Potential for suppression of Rhizoctonia root rot is influenced by nutrient (N and P) and carbon inputs in a highly calcareous coarse-textured topsoil

Bioassays were undertaken in a controlled environment to assess whether the potential for suppression of Rhizoctonia root rot of wheat, in a highly calcareous topsoil, was positively influenced by nutrient (nitrogen (N) or phosphorus (P)) addition and whether any disease suppression response to augmented nutrition was affected by the addition of carbon (C), either as a readily available C source (sucrose) or as wheat stubble. The soil was P deficient, which limited plant growth, populations of putatively beneficial soil microorganisms, and microbial activity and diversity. This ultimately reduced potential for suppression of Rhizoctonia solani AG8. Addition of fertiliser P to the soil increased R. solani AG8 DNA and percent root infection but not the effectiveness of the pathogen. A positive effect of P fertiliser on plant growth partially compensated for the negative effect of increased root infection. Addition of P increased DNA for Microbacterium spp. where labile C had been added and in the presence of plant roots. Stubble addition alone, after 6 weeks of incubation, increased DNA for Pantoea agglomerans, Trichoderma A and Microbacterium spp. although differences in microbial activity and diversity between stubble treatments were only detected after the bioassay had commenced and P was added. Fertiliser P addition to stubble-amended soil resulted in less Rhizoctonia infection compared with that in soil without P or stubble addition. Effectiveness of R. solani AG8 was decreased by 50% with stubble amendment. The application of N alone did not have a marked effect on plant growth or potential for suppression of Rhizoctonia root disease. Agronomic management practices that affect quantity and lability of C input to soil, when combined with strategic P fertiliser decisions, are likely to improve the potential for development of suppression of Rhizoctonia root rot disease in cereal crops on alkaline and highly calcareous soils.

Pseudomonas synxantha 2-79 Transformed with Pyrrolnitrin Biosynthesis Genes Has Improved Biocontrol Activity Against Soilborne Pathogens of Wheat and Canola.

A four-gene operon (prnABCD) from Pseudomonas protegens Pf-5 encoding the biosynthesis of the antibiotic pyrronitrin was introduced into P. synxantha (formerly P. fluorescens) 2-79, an aggressive root colonizer of both dryland and irrigated wheat roots that naturally produces the antibiotic phenazine-1-carboxylic acid and suppresses both take-all and Rhizoctonia root rot of wheat. Recombinant strains ZHW15 and ZHW25 produced both antibiotics and maintained population sizes in the rhizosphere of wheat that were comparable to those of strain 2-79. The recombinant strains inhibited in vitro the wheat pathogens Rhizoctonia solani anastomosis group 8 (AG-8) and AG-2-1, Gaeumannomyces graminis var. tritici, Sclerotinia sclerotiorum, Fusarium culmorum, and F. pseudograminearum significantly more than did strain 2-79. Both the wild-type and recombinant strains were equally inhibitory of Pythium ultimum. When applied as a seed treatment, the recombinant strains suppressed take-all, Rhizoctonia root rot of wheat, and Rhizoctonia root and stem rot of canola significantly better than did wild-type strain 2-79.

Sensitivity of Rhizoctonia Isolates to Phenazine-1-Carboxylic Acid and Biological Control by Phenazine-Producing Pseudomonas spp.

Rhizoctonia solani anastomosis groups (AG)-8 and AG-2-1 and R. oryzae are ubiquitous in cereal-based cropping systems of the Columbia Plateau of the Inland Pacific Northwest and commonly infect wheat. AG-8 and R. oryzae, causal agents of Rhizoctonia root rot and bare patch, are most commonly found in fields in the low-precipitation zone, whereas R. solani AG-2-1 is much less virulent on wheat and is distributed in fields throughout the low-, intermediate-, and high-precipitation zones. Fluorescent Pseudomonas spp. that produce the antibiotic phenazine-1-carboxylic acid (PCA) also are abundant in the rhizosphere of crops grown in the low-precipitation zone but their broader geographic distribution and effect on populations of Rhizoctonia is unknown. To address these questions, we surveyed the distribution of PCA producers (Phz+) in 59 fields in cereal-based cropping systems throughout the Columbia Plateau. Phz+ Pseudomonas spp. were detected in 37 of 59 samples and comprised from 0 to 12.5% of the total culturable heterotrophic aerobic rhizosphere bacteria. The frequency with which individual plants were colonized by Phz+ pseudomonads ranged from 0 to 100%. High and moderate colonization frequencies of Phz+ pseudomonads were associated with roots from fields located in the driest areas whereas only moderate and low colonization frequencies were associated with crops where higher annual precipitation occurs. Thus, the geographic distribution of Phz+ pseudomonads overlaps closely with the distribution of R. solani AG-8 but not with that of R. oryzae or R. solani AG-2-1. Moreover, linear regression analysis demonstrated a highly significant inverse relationship between annual precipitation and the frequency of rhizospheres colonized by Phz+ pseudomonads. Phz+ pseudomonads representative of the four major indigenous species (P. aridus, P. cerealis, P. orientalis, and P. synxantha) suppressed Rhizoctonia root rot of wheat when applied as seed treatments. In vitro, mean 50% effective dose values for isolates of AG-8 and AG-2-1 from fields with high and low frequencies of phenazine producers did not differ significantly, nor was there a correlation between virulence of an isolate and sensitivity to PCA, resulting in rejection of the hypothesis that tolerance in Rhizoctonia spp. to PCA develops in nature upon exposure to Phz+ pseudomonads.

Biological control of wheat root diseases by the CLP-producing strain Pseudomonas fluorescens HC1-07.

Pseudomonas fluorescens HC1-07, previously isolated from the phyllosphere of wheat grown in Hebei province, China, suppresses the soilborne disease of wheat take-all, caused by Gaeumannomyces graminis var. tritici. We report here that strain HC1-07 also suppresses Rhizoctonia root rot of wheat caused by Rhizoctonia solani AG-8. Strain HC1-07 produced a cyclic lipopeptide (CLP) with a molecular weight of 1,126.42 based on analysis by electrospray ionization mass spectrometry. Extracted CLP inhibited the growth of G. graminis var. tritici and R. solani in vitro. To determine the role of this CLP in biological control, plasposon mutagenesis was used to generate two nonproducing mutants, HC1-07viscB and HC1-07prtR2. Analysis of regions flanking plasposon insertions in HC1-07prtR2 and HC1-07viscB revealed that the inactivated genes were similar to prtR and viscB, respectively, of the well-described biocontrol strain P. fluorescens SBW25 that produces the CLP viscosin. Both genes in HC1-07 were required for the production of the viscosin-like CLP. The two mutants were less inhibitory to G. graminis var. tritici and R. solani in vitro and reduced in ability to suppress take-all. HC1-07viscB but not HC-07prtR2 was reduced in ability to suppress Rhizoctonia root rot. In addition to CLP production, prtR also played a role in protease production.

Can placement of seed away from relic stubble limit Rhizoctonia root rot in direct-seeded wheat?

Rhizoctonia root rot of wheat can be a problem in no-till systems, especially during the transition from conventional tillage. There are no effective chemical controls or resistant varieties, leaving only cultural methods to manage this disease. In a no-till system, residue and inoculum of soilborne pathogens are not moved by cultivation, therefore the inoculum may be concentrated in the seeding row of the previous year. Using GPS tracking systems with sub-meter accuracy, the seeding row could be placed away from the row of the previous year. We tested the hypothesis that seeding away from the relic row may reduce Rhizoctonia root rot. In two field experiments, plants were sampled at three distances from the seed row, as well as from fumigated plots. Intact soil cores were also removed from the field, planted with seeds at various distances from the previous row, and grown in the greenhouse under controlled conditions. Pasteurized cores served as controls. Disease levels were higher in the field in the second year, but there was no consistent effect of seed row placement on disease or plant parameters. However, soil fumigation and pasteurization had significant effects, indicating that soilborne pathogens were active. Inoculum of Rhizoctonia is not produced in the crowns and lower stems of the plant, but the pathogen survives in living and dead roots of the previous year crop, volunteers, and grassy weeds. Thus, high inoculum densities may be present in between the relic rows, as well as within the rows. If this is the situation with Rhizoctonia, precision placement of seed rows would not be efficacious.

Influence of depth of soil disturbance on root growth dynamics of wheat seedlings associated with Rhizoctonia solani AG-8 disease severity in sandy and loamy sand soils of Western Australia

Rhizoctonia root rot (bare-patch disease) of cereals caused by Rhizoctonia solani AG-8 is reported to become more severe when the crop is sown under no-tillage practice. Disturbing the soil with tillage is an effective way to reduce the impact of disease. Glasshouse and field studies were conducted to evaluate the effects of the depth and intensity of soil disturbance and soil moisture conditions at the time of disturbance on rhizoctonia root rot of wheat ( Triticum aestivum L. cv. Aroona) seedlings. Results of glasshouse studies showed that intensity of soil disturbance was important for reducing the disease if the soil was disturbed at the surface (0–5 cm). Disturbing the soil at 10–20 cm below the surface without disturbing the surface soil proved to be more effective in reducing the disease than surface disturbance even when the soil was disturbed at lower intensity. Total wheat root length and rooting depth increased when soil below the seed was disturbed. Disturbance of wet soil before sowing resulted in less reduction of root and shoot weights following inoculation with R. solani AG-8 than in relatively dry soil. Similar results were obtained from a field study conducted near Newdegate (WA, Australia) on a Orthic Solonetz soil (sandy loam), with tillage of the field soil 10–15 cm below the surface producing maximum dry root and shoot weights in a rhizoctonia patch area mapped in the previous year.

Soil moisture affects disease severity and colonisation of wheat roots by Rhizoctonia solani AG-8

Experiments were conducted to study how the soil moisture affects rhizoctonia root rot of wheat, colonisation of root by Rhizoctonia solani AG-8, spread of fungus in the soil and microbial activity of soil. Four soil moisture levels ranging from 15 to 75% water-holding capacity of a sandy soil at saturation, which equated to a soil water potential range of −10 to −3 kPa, were tested. It was found that the disease severity decreased up to 69%, as the soil became wetter. The soil moisture status at and above 20% WHC however, did not significantly affect the spread of the fungus in soil. Colonisation of roots by young unpigmented hyphae of the fungus diminished with increasing soil moisture, from 80% of root length colonised under relatively dry conditions (15% WHC) to 20–25% under wet conditions (75% WHC). Soil microbial activity increased with increasing soil moisture and may be associated with suppression of pathogen activity through competition.

Decline in root rot (Rhizoctonia solani AG-8) in wheat in a tillage and rotation experiment at Avon, South Australia

Studies of a tillage x rotation field experiment begun in 1978 at Avon, South Australia, have demonstrated a decline in rhizoctonia root rot of wheat. In direct-drilled treatments the severity of rhizoctonia root rot culminated in 1983, with patches of poor plant growth accounting for up to 46% of the crop area, and then declined to negligible levels by 1990. Disease severity was significantly less in cultivated than direct-drilled treatments. In cultivated treatments the onset of decline was more difficult to determine, but by 1990 there was negligible rhizoctonia root rot in either tillage treatment, with no increase in disease from 1990 to 1994. Decline in rhizoctonia root rot occurred largely independent of rotation, although there were significant differences in root damage and patch area between rotations, with disease generally being more severe in wheat following pasture than following peas, medic, or wheat. When inoculum of R. solani was added to soil collected from the experimental site in 1985, wheat grown in soil from direct-drilled plots had significantly less disease than wheat grown in soil from cultivated treatments, indicating a possible development of suppression.

Variation in pyrone production, lytic enzymes and control of rhizoctonia root rot of wheat among single-spore isolates of Trichoderma koningii

Fifty-four single-spore isolates were obtained from two wheat field strains of Trichoderma koningii. These isolates inhibited the growth of Rhizoctonia solani to varying levels when tested on potato dextrose agar. 6-Pentyl-α-pyrone was isolated only from the extracts obtained from those isolates which showed strong inhibition of the pathogen on agar. Six isolates, three pyrone producers and three non-producers, were tested for protection of wheat against rhizoctonia root rot under controlled conditions. Only the pyrone producers significantly reduced root rot when applied to the soil and incubated for 14 d with the pathogen before planting. Those not producing pyrone did not reduce the disease when applied to the soil either with or without an incubation period in soil. There was no relationship between the disease protection ability of the isolates and their mycoparasitic ability or their production of chitinase, glucanase, cellulase or xylanase. This indicates that the pyrone antibiotic may have an important role in the reduction of rhizoctonia root rot of wheat by the effective strains and that the ability to produce the antibiotic may vary among asexually produced progenies.

Effect of Flutriafol on Saprophytic Survival and Growth of Rhizoctonia Solani (Ag-8).

The effect of flutriafol (a sterol-inhibiting triazole fungicide) on saprophytic survival and growth of Rhizoctonia solani (AG-8, causal agent of rhizoctonia root rot of wheat) in vitro and in soil was investigated with agar plate tests, a soilsandwich experiment and soil bioassays. At a concentration of 25 μg/mL agar, flutriafol reduced the growth of R. solani in vitro, but at 2.5 μg/mL it reduced growth of only two of the three isolates tested. Mycelium from plugs removed from plates of agar containing inhibitory concentrations of flutriafol retained pathogenicity to wheat seedlings. Flutriafol reduced growth of the fungus in unsterilised and autoclaved soil when applied at 190 μg/100 g, but not at 19 μg/100 g. Less fungal growth occurred in unsterilised than autoclaved soil at all concentrations of flutriafol. Bioassays of fungal mycelium placed in soil treated with flutriafol showed that pathogen survival was unaffected by the fungicide. Flutriafol appears to have a negligible effect on saprophytic survival and growth of R. solani (AG-8) at rates which could be considered commercially acceptable in the field.

Evaluation of in-furrow fungicide treatments to control rhizoctonia root rot of wheat

The efficacy of eight fungicides, placed in-furrow at sowing, to reduce rhizoctonia root rot and increase yields of wheat was examined in glasshouse and field experiments. Under glasshouse conditions three of the fungicides, coated on clay granules at a rate equivalent to 400 g a.i. ha −1, reduced root rot of wheat grown in soil inoculated with Rhizoctonia solani. None of the chemicals stimulated growth of wheat in the absence of disease, but three retarded growth. Experiments at six sites with different soil types and rhizoctonia risk in north-west Victoria, Australia, showed that the fungicide-coated granules were generally ineffective at reducing both incidence and severity of rhizoctonia root rot of wheat. However, tebuconazole was effective at two sites and at one of these flutriafol, RH-7592, cyproconazole and diniconazole also reduced disease severity. Yields were increased by 51% with tebuconazole at one site, by 40% with diniconazole at another and by between 23 and 30% with RH-7592, diniconazole, flutriafol and flutolanil, at a third site.

Effects of Fungal Root Pathogens on the Population Dynamics of Biocontrol Strains of Fluorescent Pseudomonads in the Wheat Rhizosphere

The influences of Gaeumannomyces graminis var. tritici (which causes take-all of wheat), Rhizoctonia solani AG-8 (which causes rhizoctonia root rot of wheat), Pythium irregulare, P. aristosporum, and P. ultimum var. sporangiiferum (which cause pythium root rot of wheat) on the population dynamics of Pseudomonas fluorescens 2-79 and Q72a-80 (bicontrol strains active against take-all and pythium root rot of wheat, respectively) in the wheat rhizosphere were examined. Root infection by either G. graminis var. tritici or R. solani resulted in populations of both bacterial strains that were equal to or significantly larger than their respective populations maintained on roots in the absence of these pathogens. In contrast, the population of strain 2-79 was significantly smaller on roots in the presence of any of the three Pythium species than on noninfected roots and was often below the limits of detection (50 CFU/cm of root) on Pythium-infected roots after 40 days of plant growth. In the presence of either P. aristosporum or P. ultimum var. sporangiiferum, the decline in the population of Q72a-80 was similar to that observed on noninfected roots; however, the population of this strain declined more rapidly on roots infected by P. irregulare than on noninfected roots. Application of metalaxyl (which is selectively inhibitory to Pythium spp.) to soil naturally infestated with Pythium spp. resulted in significantly larger rhizosphere populations of the introduced bacteria over time than on plants grown in the same soil without metalaxyl. It is apparent that root infections by fungal pathogens may either enhance or depress the population of fluorescent pseudomonads introduced for their control, with different strains of pseudomonads reacting differentially to different genera and species of the root pathogens.

Evaluation of methods for the chemical control of rhizoctonia root rot of wheat

In a preliminary screening test of 14 fungicides against rhizoctonia root rot of wheat in pots, six triazole compounds were effective in reducing disease severity. Of these, triadimenol or triadimefon and flutriafol were further investigated in a series of glasshouse experiments and a small plot trial. Flutriafol at 200 g a.i. ha −1 equivalent was more effective as a soil-applied fungicide than triadimefon, but triadimenol was more effective than flutriafol as a seed-applied fungicide. In combinations as seed and soil applications, the fungicides were more effective in reducing the severity of rhizoctonia root rot when flutriafol, at either 100 g or 200 g a.i. ha −1, was mixed through the soil rather than placed in a smaller volume of soil adjacent to the seed. However, when flutriafol was placed on double superphosphate to give a rate of 100 or 200 g a.i. fungicide ha −1 adjacent to the seed it reduced disease severity and increased plant weight, with or without a triadimenol seed treatment. Similarly, in small field plots disease severity was reduced by flutriafol-amended double superphosphate at 200 g in 1988 and at 100 g and 200 g a.i. ha −1 in 1989.

Use of three screening techniques for the evaluation of fungicides to control rhizoctonia root rot of wheat

SummaryTwenty fungicides were screened for their abilities to reduce the saprophytic growth of Rhizoctonia solani on agar and in soil, and to control root rot of wheat (Triticum aestivum) in pots of soil. Thirteen showed some activity against the in vitro growth of R. solani, the most promising being Sandoz 619F and flutolanil, although none of these reduced saprophytic growth of the fungus in soil. Only benomyl and thiabendazole, which were ineffective on agar and against disease in pots, reduced saprophytic growth in soil. None of the fungicides reduced the number of plants infected in the pot experiments and only six (flutriafol, diniconazole, Schering 539865, propiconazole, Bayer HWG1608 and flutolanil) of the thirteen active on agar (+ triadimefon which was not) reduced root rot severity. The results of this study indicate the differing reactions towards R. solani of chemicals in the three screening tests and confirm the potential for chemical control of rhizoctonia root rot of wheat.

Use of Guazatine and Flutriafol for the Control of Take-All and Rhizoctonia Root Rot of Wheat.

A series of experiments with artificially inoculated soil was undertaken to test the efficacy of the fungicide guazatine against take-all and Rhizoctonia root rot of wheat (caused by Gaeumannomyces graminis var. tritici and Rhizoctonia solani, respectively) and to develop a chemical control technique against Rhizoctonia root rot. Guazatine was ineffective as a soil-applied fungicide against both diseases but, as a seed dressing in combination with soil-applied flutriafol, it reduced incidence and severity of Rhizoctonia root rot at 4 weeks though not that of take-all. In the glasshouse, flutriafol-amended double superphosphate at rates equivalent to 100 g and 200 g a.i./ha |+- guazatine seed dressing (0.5 g a.i./kg seed) reduced Rhizoctonia root rot and improved plant growth at 8 weeks. In small field plots, flutriafol-amended fertiliser at 200 g a.i/ha reduced Rhizoctonia root rot severity. Flutriafol-amended fertiliser therefore shows potential for the control of Rhizoctonia root rot of wheat at relatively low concentrations.

Effect of short chemical fallow on Rhizoctonia bare patch and root rot of wheat at Esperance, Western Australia

The effects of short chemical fallows after ryegrass pasture on rhizoctonia bare patch and root rot ofwheat were studied in 2 experiments at the Esperance Downs Research Station, 35 km north of Esperance, W.A. In 1 experiment the subterranean-clover dominant pasture was sprayed with a paraquat-diquat mixture prior to resowing with annual ryegrass at densities ranging from 3 to about 400 plants m-2. The ryegrass was allowed to grow for either 42 or 63 days prior to treatment with a desiccant herbicide (paraquat-diquat) followed by a short chemical fallow of 26 or 5 days, respectively, before sowing with wheat using minimum tillage. Some treatments were cultivated twice to 10 cm. Neither the ryegrass density nor the length of chemical fallow had any effect (P=0.05) on rhizoctonia bare patch score or incidence or severity of root rot. However, cultivation caused 76% reduction in mean patch score and a 38 and 68% reduction in mean rhizoctonia incidence and severity respectively. Yield was negatively correlated with rhizoctonia incidence and severity: each 1% increase in incidence percentage resulted in 17 kg ha-1 reduction in grain yield of wheat. In another experiment, chemical fallow periods of 66, 52, 24 or 1 day prior to sowing wheat had no effect (P= 0.05) on rhizoctonia root rot incidence.