SEARCH

SEARCH BY CITATION

Keywords:

  • anastomosis group;
  • baseline sensitivity;
  • geographic distribution;
  • Rhizoctonia ;
  • Rhizoctonia solani ;
  • sedaxane

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The prevalence of Rhizoctonia spp. in European soils was determined by analysing soil samples from 282 locations. Rhizoctonia spp. were found in 68% of these samples from France, Germany, the UK, Poland, Italy, Spain, Hungary and the Czech Republic. Samples from 136 locations were further analysed by pyrosequencing. Seventy-six percent of the isolates were Rhizoctonia solani and 24% binucleate Rhizoctonia spp. Rhizoctonia solani anastomosis group (AG) 5 was detected most frequently (25%), followed by AG 9 (16%) and AG 4 (13%). For the binucleate Rhizoctonia spp., AG E was most prevalent (13%). Rhizoctonia cerealis was not detected in soil samples. Soil type or cropping history had no effect on the type of Rhizoctonia observed. Rhizoctonia solani AG 5 was the most frequently detected AG irrespective of the previous crop. The spectrum of AGs detected was similar for France, Germany and Poland but was significantly different for the UK (= 0·0016). Finally, the baseline sensitivity towards sedaxane, a new active ingredient for seed treatment, was analysed for all isolates. The results indicate a low baseline sensitivity (average EC50 of 0·028 p.p.m.) for all Rhizoctonia AGs. No difference in sensitivity was observed with the isolates obtained from different countries.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Soilborne fungi of the genus Rhizoctonia are known to be important pathogens in numerous field crops causing damping off, foliar blight and root and stem rot. Rhizoctonia cerealis (teleomorph: Ceratobasidium cereale) and Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) are the species best known for their detrimental effects in crop production. Both pathogens belong to the phylum Basidiomycota, class Basidiomycetes, but within different genera. Rhizoctonia spp. can be grouped based on the number of nuclei per hyphal septae, with R. cerealis belonging to the group of binucleate and R. solani to the multinucleate Rhizoctonia spp. (Ogoshi, 1996; Hamada et al., 2011).

Anastomosis groups (AGs) characterize the ability of hyphae from different isolates to fuse and subsequently the ability to exchange genetic information (Agrios, 2005). Although the role of anastomosis for genetic variation within Rhizoctonia is not fully understood, AGs can be seen as groups of closely related isolates (Carling, 1996). Anastomosis groups of binucleate Rhizoctonia species are indicated by the letters A–S (e.g. R. cerealis = AG D) and multinucleate species by numbers. For R. solani, as many as 13 different AGs (1–13) with further subgroups for AG 1, 2, 3, 4, 6 and 9, have been identified (Carling et al., 2002). Isolates of R. solani from different AGs were reported to differ in their host spectrum and virulence (Ogoshi, 1996; Agrios, 2005). However, even within AGs, variation in virulence, morphology and other physical characteristics have frequently been observed (Carling, 1996).

Rhizoctonia cerealis is the main causal agent of sharp eyespot in cereals and recognized worldwide as an important disease in wheat production (Hamada et al., 2011). Rhizoctonia solani has a very broad host range (Lemańczyk, 2010) including broad leaf crops such as canola/oilseed rape, potatoes, sugar beet as well as cereals (Ogoshi, 1996; Schillinger & Paulitz, 2006; Tewoldemedhin et al., 2006). Rhizoctonia solani on cereals is mainly reported from Australia (MacNish & Neate, 1996) and the northwest of the USA (Ogoshi et al., 1990; Smiley & Uddin, 1993; Schroeder & Paulitz, 2008), where AG 8 is the most commonly detected variant. In a survey of Texas (Rush et al., 1994), AG 4 was most prevalent in wheat, although AG 2-2 and AG 5 were detected as well. In South Africa, AG 2-2 and AG 4 were the most virulent AGs in barley (Tewoldemedhin et al., 2006). Reports from Poland (Lemańczyk, 2010) and Turkey (Demirci, 1998; Ünal & Dolar, 2012) showed that AG 4, AG 11, AG 2-1, AG 3, AG 5, AG 8, AG I and AG K could be detected in wheat and barley. However, there is little other data available for Europe.

Disease symptoms for R. solani in cereals are variable depending on the severity of infection and the causal agent, but generally damage the root system. These symptoms range from brown sunken lesions on roots, spear tips, yellowing or necrosis of the cortex causing a delayed development, to stunting or damping off of young plants resulting in bare patch disease (Mazzola et al., 1996). The compromised root health after infections also increases susceptibility of the plants to drought stress, nutrient deficiency and secondary infections by other root diseases (Cook, 2001; Hamada et al., 2011). However, R. solani infections are often misdiagnosed because they affect the underground parts of a plant.

Damage by rhizoctonia root rot is most severe in cropping systems with cereal monoculture and minimum to no till practices (Cook et al., 2002). Rhizoctonia can survive in the soil on organic debris without the presence of a living host. Tillage can reduce the inoculum on the soil surface and subsequently the disease potential in a crop (MacNish & Neate, 1996; Cook, 2001; Paulitz et al., 2002). However, under no till conditions the organic matter on the soil surface is a good source of inoculum and keeps the soil cool and moist, further favouring Rhizoctonia infections (Cook, 1992). Under these conditions, options available to reduce Rhizoctonia infections are limited. Furthermore, all wheat varieties available are susceptible to Rhizoctonia spp. (Smith et al., 2003), thereby increasing disease prevalence. An important cultivation practice to minimize the risk of Rhizoctonia infections is to ensure a sufficient period with no crop or volunteer plants and weeds in the field (Roget et al., 1987; Smiley et al., 1992; Cook, 2001; Paulitz et al., 2002). Fresh, high quality seeds and a fungicide seed treatment should also be used in order to ensure a good stand establishment. Placement of phosphorus fertilizer under the seed at sowing can also help to reduce the negative effects of rhizoctonia root rot (Cook et al., 2000; Cook, 2001).

Sedaxane is a new active ingredient from the class of pyrazole carboxamides. It inhibits fungal metabolism by binding to the succinate dehydrogenase (SDH) enzyme, and therefore belongs to the new SDH inhibitor class of fungicides. Based on its favourable physical and chemical properties, sedaxane was only developed for seed treatment use. During an extensive, worldwide field trials programme, it has shown excellent control of seed and soilborne diseases such as smuts and bunts, snow mould (Microdochium nivale), Rhizoctonia spp. and many others.

The aim of this study was to determine the distribution and prevalence of Rhizoctonia spp. in arable soils in Europe and the baseline sensitivity towards sedaxane, a novel seed treatment fungicide.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Soil sampling

Soil samples (= 282) were taken from different locations in Europe (Germany, Poland, France, the UK, the Czech Republic, Spain, Italy and Hungary) during the 2009/2010 season. Samples (500 mL) were taken from the top 15 cm of non-tilled fields prior to planting. Each sample combined at least 30 soil cores taken randomly from across the field. Information recorded at sampling included the soil type, crop, previous crop and date of sampling, as well as the geocoordinates of the location.

Isolation of Rhizoctonia from soil

Rhizoctonia isolates were obtained from the soil by using a modified baiting method as described by Paulitz & Schroeder (2005). Dry soil samples were moistened with sterile water prior to starting with the isolation procedure. Autoclaved wheat and barley grains and wooden toothpicks were placed as bait into 14 cm diameter Petri dishes containing the soil samples and incubated in darkness at room temperature for 2 days. Cereal baits were chosen because the objective of this study was to detect Rhizoctonia relevant to cereals. After incubation, baits were transferred from the soil onto Petri dishes (9 cm diameter, without vents) with ANS-agar (50 mg L−1 each of aureomycin, neomycin and streptomycin; Sigma-Aldrich) and incubated in darkness at room temperature in order to stimulate mycelial growth from the baits. After 24 h, single hyphae were cut from the agar as mycelial plugs under sterile conditions and transferred onto PDA (potato dextrose agar: 39 g L−1 PDA in sterile demineralized water; Merck) for multiplication. Rhizoctonia was distinguished both macroscopically and microscopically from other fungi by the typical hyphal morphology.

DNA isolation

Rhizoctonia isolates were cultured on PDA plates covered by a layer of cellophane for easy and agar-free recovery of the mycelium. Mycelium was then scraped from the surface of culture plates, transferred into 2 mL reaction tubes and freeze-dried (Christ alpha 1-4 LD plus) for 24 h. After adding glass beads, samples were disrupted and homogenized directly in the reaction tubes using a swing mill (Retsch MM301). Genomic DNA was extracted from 20 mg mycelium powder using the NucleoSpin Plant II Kit (Macherey-Nagel) according to the manufacturer's protocol.

Determination of anastomosis groups for Rhizoctonia spp. by pyrosequencing

The AGs were determined for 288 isolates of Rhizoctonia spp. from 136 locations. Pyrosequencing was used to distinguish the different AGs of Rhizoctonia spp. based on differentiating sequences within the internal transcribed spacer (ITS) region of their rDNA (White et al., 1990). Analysis of the rDNA-ITS region has been shown to be the most reliable identification method for Rhizoctonia spp. (Sharon et al., 2006, 2008). PCR primers RHI-its1-f (5′-TAGGTGAACCTGCGGAAGGAT-3′) and RHI-its1-r (5′-Bio-CCAAGAGATCCGTTGTTGAAACTTAG-3′; biotin modification on 5′ end required for single strand denaturation step following PCR) and sequencing primer RHI-so-ce-s (5′-TGCGGAAGGATCATTA-3′) were used. These primers anneal close to the 3′ end of the highly conserved 18S region and the 5′ end of the 5·8S region, respectively, in order to provide optimum coverage of all Rhizoctonia species/probes tested. Sequences of the ITS1 intron between those highly conservative regions show high variability, which is fairly homologous within each AG, but distinguishes between the AGs of Rhizoctonia spp. The PCR reaction was carried out in a Primus 96 Cycler (Peqlab) containing 500 nmol of each primer, 200 μmol dNTPs (each), 2 mm MgCl2, 1 ×  Gold Buffer, 1·25 U AmpliTaq Gold Polymerase (Applied Biosystems), 10–20 ng DNA and H2O in a total volume of 25 μL. Cycler conditions for amplification were as follows: initial denaturation at 95°C for 5 min, 40 cycles of denaturation at 95°C for 15 s, annealing at 59°C for 30 s and elongation at 72°C for 30 s, followed by a final extension at 72°C for 5 min. After denaturation of PCR amplicons with NaOH and binding the biotin-labelled DNA strands to streptavidin sepharose beads, sequencing was performed on a PyroMark Q96 ID Pyrosequencer (QIAGEN). The single-stranded sequence analysis (SQA) used detects approximately 50–70 bp downstream from the ITS1 intron. Resulting sequences were compared to an appropriate set of reference sequences from the NCBI database (www.ncbi.nlm.nih.gov) using the alignment tool IdentiFire. Despite the relatively short number of base pairs, an acceptable comparison to the NCBI database was possible due to the high variability within the ITS1 area. The determination of AGs is based on the homologies within the sequence analysed. Generally there was a high level of homology. The level of required homology for the region used for identification was set to 85% because even within an AG, 100% identity cannot always be obtained. In 73% of the cases homology was ≥95%.

Sensitivity assays

Sedaxane sensitivity was determined using a fungicide/PDA dilution assay in 16·2 mm well diameter, 24-well tissue culture plates. Isolates selected for the sensitivity assay included all AGs detected from Poland, Germany, France and the UK (= 105). Rhizoctonia cerealis isolate Rc196-47 was included in these assays as a reference because the excellent activity of sedaxane against R. cerealis is well known. The fungicide concentrations were graded logarithmically by a factor of three in order to obtain an accurate complete dose–response reaction and EC50 evaluation. The test concentrations were prepared by diluting appropriate volumes of a stock solution of sedaxane in sterile demineralized water. Pure PDA representing the untreated control and seven fungicide-amended PDA solutions (10 μL fungicide solution added to 1 mL PDA for each well resulting in effective concentrations of 0·003, 0·01, 0·03, 0·1, 0·3, 1·0 and 3·0 mg L−1 active ingredient) were then transferred into the 24-well plates. Each well was inoculated with an agar plug. The tissue culture plates were put into plastic bags to reduce evaporation, and incubated at 18°C in darkness. Growth was assessed visually 48 h after inoculation in relation to the untreated control (100% growth). EC50 values (concentration at which growth was inhibited by 50% relative to the untreated control) were calculated for each isolate by probit analysis (Weber, 1980).

Statistical analysis

The statistical software package jmp v. 8.0.2 (SAS Institute Inc.) was used for all analyses. Pearsons χ2 test of independence was applied on the contingency table to determine if categorical variables such as soil class, previous or current crop, date of sampling or sampling location had an effect on the number of isolates or the AGs detected. Cases with less than five expected values had to be excluded for statistical reliability.

anova using GLIMMIX procedure (sas v. 9.3; SAS Institute Inc.) considering multinomial distribution and cumulative logit link function was used to analyse differences in virulence.

The differences in response of the variables were analysed by comparing the frequency of the distribution in the classes. For the analysis of the crop effect, categories with < 3 isolates were excluded.

One-way anova on EC50 was used to analyse the differences between AGs in their sensitivity towards sedaxane. A t-test at α = 0·05 level was applied to determine if there was a difference in sensitivity towards sedaxane between the binucleate and multinucleate anastomosis groups.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Prevalence of Rhizoctonia spp. in Europe

Rhizoctonia isolates were obtained from 68% of the 282 locations sampled. More than four isolates were obtained from 25% of the locations, 3–4 isolates from 20% and 1–2 isolates from 24% of the locations (Table 1). Most (70%) of the isolates analysed were identified as R. solani. Binucleate Rhizoctonia spp. were identified in 22% of the samples analysed. For 8% of the samples, the AG could not be determined.

Table 1. Percentage of soil samples from which Rhizoctonia solani was isolated, as well as the number of isolates obtained per location, listed by country
Sample originNo. of soil samplesNo. samples with R. solani detectionPercentage of soil samples with
1–2 isolates3–4 isolates>4 isolates
Germany6558231817
France3964182126
United Kingdom6063636363
Poland9382828282
Spain967676767
Italy36703333
Hungary757291414
Czech Republic4100252550
Total number28268242025

Rhizoctonia solani AG 5 was detected most frequently (32% of the locations), followed by AG 9 (22%), AG 4 HG II (17%), AG 2-1 (7%), AG 11 (5%) and AG 8 (3%). All AGs detected are summarized in Table 2. AG 5 was the multinucleate AG most frequently detected in Germany (56%, locations = 27), Poland (51%, locations = 39), France (22%, locations = 23), and Hungary (33%, locations = 3), but could not be detected in Italian (= 2), Spanish (= 6) and Czech Republic (= 4) soil samples. AG 9 was most frequently detected in the UK from 34% of all locations tested (= 32). Overall, AG 9 showed the same distribution as AG 5 (Table 2). AG 8 was only detected in one location from the UK (3%, = 32) and in three samples from Spain (50%, = 6).

Table 2. Anastomosis groups (AGs) of Rhizoctonia solani detected in soil samples by pyrosequence analysis of isolates. Results are given as number of positive locations per AG, listed by country
CountryNo. of locationsNo. of locations with AG detected
MultinucleateBinucleate
1 IB2-13 PT3 TB4 HG I4 HG II4 HG III56 Gv28911ABoCEIK
  1. a

    Percentage of locations that were positive for each AG.

Czech Republic414
Germany27211915614
Spain611313
France231131543211541
United Kingdom3245311121414
Hungary3111
Italy21111
Poland391411720871
Sum136110471231441430731224510
%a 1735117132132252111847

For the binucleate Rhizoctonia spp., AG E (18%) was the anastomosis group most frequently detected, followed by AG K (7%). Rhizoctonia cerealis was not detected in any of the soil samples analysed.

Statistical analysis could not be conducted on all AGs detected and countries sampled because of low numbers of isolates per category. However, there was a significant difference when prevalence of the most frequent AGs (AG 5, AG 9, AG 4 HG II and AG E) was compared for the UK, Germany, Poland and France (= 0·0016), with the UK showing a significant difference in its Rhizoctonia spectrum compared to the other countries. Whilst AG 4 HG II was the second most frequent multinucleate AG in France, Germany and Poland, this AG was not detected in samples from the UK. Furthermore, AG 9 was the multinucleate AG detected at most locations in the UK (34%), followed by AG 3 TB (16%) and AG 2-1 (13%). AG 5, the most frequent AG in all other countries, was only detected at 9% of UK locations.

Effect of soil type

For all soil types, Rhizoctonia spp. were found in at least 50% of the samples analysed. No effect of the soil type or soil class on either the number of isolates or the AGs detected was observed in this study (Table 3).

Table 3. Effect of soil class, previous crop, current crop and location on the detection of Rhizoctonia spp.
 Total numberd.f.< χ2Categories included in analysis
  1. a

    AG 5, AG 9, AG 4 HG II, AG E included in analysis.

Location × most frequent AGsa17090·002Germany, France, UK, Poland
Soil class × isolates detected23130·399All crops
Previous crop × isolate detection21420·299Barley, oilseed rape, wheat
Previous crop × isolate detection21520·069Maize, oilseed rape, wheat
Previous crop × number of isolates detected26330·126Oilseed rape, wheat
Previous crop × most frequent AGsa14230·132Oilseed rape, wheat
Current crop × isolates detection18710·347Oilseed rape, wheat
Current crop × number of isolates detected18730·601Oilseed rape, wheat
Current crop × most frequent AGsa14530·068Oilseed rape, wheat

Effect of previous or current crop

The previous or current crop did not have a significant effect on the detection of isolates or the number of isolates detected when results for the crops with > 5 per category were compared. There was also no difference in detection of the different AGs for wheat and oilseed rape, the previous crop most frequently sampled. All AGs were detected after wheat. AG 5, the most frequently detected AG, was detected after all crops except for peas (= 1). These results are summarized in Table 3.

Sensitivity towards sedaxane

All Rhizoctonia isolates tested were sensitive to sedaxane, a new seed treatment which targets seed and soilborne diseases. The EC50 values ranged between 0·001 and 0·093 p.p.m., with the average EC50 at 0·028 p.p.m. (Table 4). There was no difference in sensitivity between multinucleate and binucleate AGs (= 0·521). Furthermore, there was no difference observed in sensitivity between the different AGs isolated from European soils except for AG A (= 2), which had a slightly higher average EC50 value of 0·078 p.p.m. (< 0·001; Table 4). Rhizoctonia cerealis (AG D) was also included in the sensitivity assay as a reference, because it is known that sedaxane is highly active against this pathogen. The EC50 for R. cerealis was 0·058 p.p.m.

Table 4. Sensitivity of Rhizoctonia spp. towards sedaxane
Anastomosis groupEC50 (p.p.m.)aIsolates
  1. a

    Values followed by the same letter do not differ statistically (t-test at α = 0·05).

AG 1-IB0·021 bc2
AG 2-10·020 c8
AG 3 PT0·022 bc5
AG 3 TB0·043 abc5
AG 4 HG II0·028 bc13
AG 50·028 bc28
AG 80·025 abc1
AG 90·024 c8
AG 110·020 bc3
AG A0·078 a2
AG Bo0·021 abc1
AG C0·014 bc2
AG E0·028 bc3
AG I0·016 c4
AG K0·036 bc6
AG D0·058 ab3

No difference could be observed (= 0·7086) when the average as well as the minimum and maximum EC50 values for the AGs from different countries were compared (Table 5).

Table 5. Sensitivity of Rhizoctonia spp. from different countries towards sedaxane. The average EC50 (MEC50), the standard error (SE) and the lower and upper 95% confidence interval of the EC50 value is given
Country n MEC50SELower 95%Upper 95%
UK220·0310·0030·0240·037
France230·0260·0030·0200·033
Germany230·0280·0030·0210·034
Poland300·0260·0030·0200·031

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

In this first survey analysing the occurrence of Rhizoctonia spp. in European soils, Rhizoctonia was detected in 68% of the soil samples analysed. For 45% of the soil samples >3 isolates were obtained. Therefore, Rhizoctonia spp. can be expected in most European soils where farming practices and climatic conditions at sowing favour Rhizoctonia (cereal monoculture and minimum tillage). In this survey, R. solani AG 5 was the most prevalent multinucleate AG (32%) detected, followed by AG 9 (22%) and AG 4 HG II (17%). The R. solani AG most frequently reported for cereals globally is AG 8. Reports on AG 8 are mostly from cereals from the Pacific Northwest of the USA (Ogoshi et al., 1990; Schroeder & Paulitz, 2008) and Australia (MacNish & Neate, 1996) were it is known to be the causal agent of bare patch, a major disease in those regions (Gill et al., 2000; Cook, 2001; Schroeder & Paulitz, 2008). AG 8 has also been reported occasionally from the UK and Turkey (MacNish & Neate, 1996; Ünal & Dolar, 2012). However, in this survey, AG 8 was only detected in samples from the UK (one field) and Spain (three fields), despite the fact that the isolation method used was originally developed for isolating AG 8 from soil by Paulitz & Schroeder (2005). Consequently, Rhizoctonia AG 8 does not seem to be widely present in European soils.

In one survey conducted in the Pacific Northwest of the USA, after AG 8 (42%), AG 4 had the next highest frequency (32%; Ogoshi et al., 1990), also one of the more commonly detected AGs in the present survey.

However, AG 9 and AG 5, the AG most frequently found in this survey, were only reported from a single site in the study conducted by Ogoshi et al. (1990). In Europe, survey data focusing on Rhizoctonia spp. in wheat is limited to a survey conducted in Turkey where isolates were obtained from crown and subcrown tissues (Demirci, 1998). Rhizoctonia AG 4 was detected in 38%, AG 3 in 28% and AG 5 in 21% of the cases. However, little comparable data has been published to date and the different sampling strategies (plant versus root or soil samples) do not allow a direct comparison in many cases. Currently one survey from the USA (USDA-Agricultural Research Service) and one from Canada (University of Guelph) are being used to establish the prevalence of Rhizoctonia in soil samples from the USA and seedlings from Canada. The results from these surveys showed that, overall (except for the Pacific Northwest where AG 8 was most frequent), AG 2-1 was the most prevalent anastomosis group of R. solani isolated in the USA and Canada. In Canada, where plant seedlings were analysed, AG 4 and AG 5 were also isolated from wheat seedlings in higher numbers (G. Boland, University of Guelph, Canada, personal communication). For the USA, where soil samples were analysed using the same isolation procedure as this survey, R. solani AG 4 was frequently detected, whereas AG 5 was not isolated from any of the samples (K. Schroeder & T. Paulitz, USDA-ARS, Washington State University, USA, personal communication; Schroeder et al., 2011). The study by Schroeder et al. also identified that Rhizoctonia oryzae (Waitea circinata) was even slightly more prevalent than R. solani in their study (38 vs 27%). The present survey did not detect R. oryzae, but the isolation process was designed for the detection of R. solani and R. cerealis, therefore the presence of R. oryzae in Europe cannot be ruled out.

A species that is well known in Europe to be pathogenic in cereals, but was not detected in this survey, was R. cerealis (AG D). This could possibly be ascribed to its rapid degradation in soil and that it was therefore no longer viable when the baiting was conducted. On the other hand, R. cerealis was also reported to have a significantly slower growth rate than R. solani (Hamada et al., 2011) and could possibly have been missed this way. When whole plant leaf samples from a field trial with artificial R. cerealis soil inoculation were analysed, using the same sequencing methodology as described in this study, R. cerealis was detected in three of the four samples, but not in soil samples from the same field. Rhizoctonia cerealis was only detected in soil either directly after inoculation or when inoculation took place using sterilized soil (Syngenta/Epilogic, unpublished data). Furthermore, in a survey by Epilogic analysing wheat stem samples from Germany, 50% of the samples were positive for R. cerealis (Syngenta/Epilogic, unpublished data). In order to further understand this, both plant and soil sampling should be done in future studies.

In this survey, no impact of soil type or the previous crop on the number of isolates or AGs detected was observed. There are a number of additional factors in the soil other than class that could have an impact on Rhizoctonia such as organic matter content, microbial activity of the soil, compaction, pH, soil preparation, cropping history and climatic conditions (Gill et al., 2000, 2001, 2004; Schroeder & Paulitz, 2008). Therefore, information on the soil type alone might not be sufficient to understand the occurrence of specific AGs in a given soil.

All AGs could be isolated from the soil after wheat, the crop that was most frequently sampled (= 139). Likewise AG 5, the most frequent AG, was isolated from almost all crops. No trend could be found in the detection of AGs with respect to particular crops. The data obtained in this survey did not allow for statistical analysis for all AGs × crop combinations because of the low numbers of isolates for some combinations. However, those combinations with sufficient data points showed that the previous crop did not impact on the type of AGs detected. This is in line with the fact that Rhizoctonia spp. are reported to have a broad host range and crop rotations do not have a major impact on this disease (Cook et al., 2002). Nevertheless, in order to draw solid conclusions, a study dedicated to crop effects would be required.

Data from this European survey shows that Rhizoctonia spp. can be expected to be present in the soil irrespective of the soil type and previous crop in the field. The impact on the crop will therefore depend on other factors such as climatic conditions and farming practice.

The mean baseline sensitivity towards sedaxane was relative low, with an MEC50 of 0·028 p.p.m. and a small range of variability (EC50 min 0·001 p.p.m. and EC50 max 0·093 p.p.m.) confirming the excellent activity of this active ingredient towards Rhizoctonia. This was also supported by the fact that there was no difference in sensitivity for isolates from different countries. A seed treatment with sedaxane can therefore be an additional tool in protecting seedlings from Rhizoctonia infections during early stages of plant development.

This disease has been shown to be very important in other regions, such as the Pacific Northwest of the USA (Paulitz et al., 2002; Schroeder & Paulitz, 2008). Currently in Europe, awareness is still low. However, as a result of shifts in cultivation practices such as implementation of no or minimum till, growers are becoming increasingly aware of Rhizoctonia as a pathogen impacting root health. Damage to the health of the plant root at early stages affects proper development at later stages, and the ability of the plant to gain its full yield potential.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The authors want to express their thanks to Claudia Madel and Katharina Swoboda from EpiLogic/EpiGene GmbH and Michelle Moesch from Syngenta Crop Protection for all their input in the laboratory and excellent project assistance.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • Agrios G, 2005. Plant Pathology. Burlington, MA, USA: Elsevier Academic Press.
  • Carling DE, 1996. Grouping in Rhizoctonia solani by hyphal anastomosis. In: Sneh B, Jabaji-Hare S, Neate S, Dijst G, eds. Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology, and Disease Control. Dordrecht, the Netherlands: Kluwer Academic Publishers, 1435.
  • Carling DE, Baird RE, Gitaitis RD, Brainard KA, Kuninaga S, 2002. Characterisation of AG13, a newly reported anastomosis group of Rhizoctonia solani. Phytopathology 92, 8939.
  • Cook RJ, 1992. Wheat root health management and environmental concern. Canadian Journal of Plant Pathology 14, 7685.
  • Cook RJ, 2001. Management of wheat and barley root diseases in modern farming systems. Australasian Plant Pathology 30, 11926.
  • Cook RJ, Ownley BH, Zhang H, Vakoch D, 2000. Influence of paired-row spacing and fertilizer placement on yield and root diseases of direct-seeded wheat. Crop Science 40, 107987.
  • Cook RJ, Schillinger WF, Christensen NW, 2002. Rhizoctonia root rot and take-all of wheat in diverse direct-seed spring cropping systems. Canadian Journal of Plant Pathology 24, 34958.
  • Demirci E, 1998. Rhizoctonia species and anastomosis groups isolated from barley and wheat in Erzurum, Turkey. Plant Pathology 47, 105.
  • Gill JS, Sivasithamparam K, Smettem KRJ, 2000. Soil types with different texture affects development of Rhizoctonia root rot of wheat seedlings. Plant and Soil 221, 11320.
  • Gill JS, Sivasithamparam K, Smettem KRJ, 2001. Effect of soil moisture at different temperatures on Rhizoctonia root rot of wheat seedlings. Plant and Soil 231, 916.
  • Gill JS, Hunt S, Sivasithamparam K, Smettem KRJ, 2004. Root growth altered by compaction of a sandy loam soil affects severity of Rhizoctonia root rot of wheat seedlings. Australian Journal of Experimental Agriculture 44, 595.
  • Hamada MS, Yin Y, Chen H, Ma Z, 2011. The escalating threat of Rhizoctonia cerealis, the causal agent of sharp eyespot in wheat. Pest Management Science 67, 14119.
  • Lemańczyk G, 2010. Occurrence of sharp eyespot in spring cereals grown in some regions of Poland. Journal of Plant Protection Research 50, 50512.
  • MacNish GC, Neate SM, 1996. Rhizoctonia bare patch of cereals – an Australian perspective. Plant Disease 80, 96571.
  • Mazzola M, Smiley RW, Rovira AD, Cook RJ, 1996. Characterization of Rhizoctonia isolates, disease occurrence and management in cereals. In: Sneh B, Jabaji-Hare S, Neate S, Dijst G, eds. Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology, and Disease Control. Dordrecht, the Netherlands: Kluwer Academic Publishers, 25968.
  • Ogoshi A, 1996. Introduction – the genus Rhizoctonia. In: Sneh B, Jabaji-Hare S, Neate S, Dijst G, eds. Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology, and Disease Control. Dordrecht, the Netherlands: Kluwer Academic Publishers, 19.
  • Ogoshi A, Cook RJ, Bassett EN, 1990. Rhizoctonia species and anastomosis groups causing root rot of wheat and barley in the Pacific Northwest. Phytopathology 80, 7848.
  • Paulitz TC, Schroeder KL, 2005. A new method for the quantification of Rhizoctonia solani and R. oryzae from soil. Plant Disease 89, 76772.
  • Paulitz TC, Smiley R, Cook RJ, 2002. Insights into the prevalence and management of soilborne cereal pathogens under direct seeding in the Pacific Northwest, U.S.A. Canadian Journal of Plant Pathology 24, 41628.
  • Roget DK, Venn NR, Rovira AD, 1987. Reduction of Rhizoctonia root rot of direct-drilled wheat by short-term chemical fallow. Australian Journal of Experimental Agriculture 27, 42530.
  • Rush CM, Carling DE, Harveson RM, Mathieson JT, 1994. Prevalence and pathogenicity of anastomosis groups of Rhizoctonia solani from wheat and sugarbeet in Texas. Plant Disease 78, 34952.
  • Schillinger WF, Paulitz TC, 2006. Reduction of Rhizoctonia bare patch in wheat with barley rotations. Plant Disease 90, 3026.
  • Schroeder KL, Paulitz TC, 2008. Effect of inoculum density and soil tillage on the development and severity of Rhizoctonia root rot. Phytopathology 98, 30414.
  • Schroeder KL, Shetty KK, Paulitz T, 2011. Survey of Rhizoctonia spp. from wheat soils in the U.S. and determination of pathogenicity on wheat and barley. Phytopathology 101, 161.
  • Sharon M, Kuninaga S, Hyakumachi M, Sneh BB, 2006. The advancing identification and classification of Rhizoctonia spp. using molecular and biotechnological methods compared with the classical anastomosis grouping. Mycoscience 47, 299316.
  • Sharon M, Kuninaga S, Hyakumachi M, Naito S, Sneh B, 2008. Classification of Rhizoctonia spp. using rDNA-ITS sequence analysis supports the genetic basis of the classical anastomosis grouping. Mycoscience 49, 93114.
  • Smiley RW, Uddin W, 1993. Influence of soil temperature on Rhizoctonia root rot (R. solani AG8 and R. oryzae) of winter wheat. Phytopathology 83, 77785.
  • Smiley RW, Ogg AG, Cook RJ, 1992. Influence of glyphosate on Rhizoctonia root rot, growth and yield of barley. Plant Disease 76, 93742.
  • Smith JD, Kidwell KK, Evans MA, Cook RJ, Smiley RW, 2003. Evaluation of spring cereal grains and wild Triticum germplasm for resistance to Rhizoctonia solani AG-8. Crop Science 43, 7019.
  • Tewoldemedhin YT, Lamprecht SC, McLeod A, Mazzola M, 2006. Characterization of Rhizoctonia spp. recovered from crop plants used in rotational cropping systems in the Western Cape Province of South Africa. Plant Disease 90, 1399406.
  • Ünal F, Dolar SF, 2012. First report of Rhizoctonia solani AG 8 on wheat in Turkey. Journal of Phytopathology 160, 524.
  • Weber E, 1980. Grundriß der Biologischen Statistik. Stuttgart, Germany: Gustav-Fischer-Verlag.
  • White TJ, Bruns TD, Lee SS, Taylor JW, 1990. Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In: Innis MA, Gelfand DH, Sninsky JJ, White TJ, eds. PCR Protocols: A Guide to Methods and Applications. New York, USA: Academic Press, 31522.