Spongospora Research Articles

Characterization of weeds and rotational crops as alternative hosts of Spongospora subterranea, the causal agent of powdery scab in Israel

Alternative hosts of Spongospora subterranea may allow multiplication and survival of the pathogen over time; thus, host range is important from an epidemiological aspect. Weeds and rotational crops, such as wheat and barley, were sampled from potato fields with a history of powdery scab (PS) and examined for the presence of S. subterranea by root staining followed by microscopic observations and by qPCR analysis after DNA extraction. The pathogen was detected in plants of 16 weed species from eight families and in volunteer plants of potato and wheat. The ability of the pathogen to infect weeds and rotational crops was further examined by artificial inoculations with sporosori in pot experiments. Successful inoculations occurred with 13 weed species from eight families and with 12 rotational crops from five families. The findings of this study indicate a wide host range in Israel; the families Malvaceae and Zygophyllaceae and the following species are reported for the first time as S. subterranea hosts: Solanum elaeagnifolium, Triticum aestivum, Cynodon dactylon, Phalaris paradoxa, Phalaris minor, Setaria verticillata, Rostaria cristata, Sinapis nigra, Arachis hypogaea, Medicago sativa, Astragalus hauraensis, Amaranthus albus, Chenopodium murale, Chenopodium opulifolium, Salsola soda, Malva nicaeensis, Chrysanthemum segetum, Verbesina encelioides, Ammi majus and Tribulus terrestris. Controlling weeds and avoiding the relevant rotational crops observed to be S. subterranea‐positive and thus potential hosts, should be taken into consideration in the management of PS, to reduce pathogen inoculum build‐up.

Development and Application of a Real-Time Reverse-Transcription PCR and Droplet Digital PCR Assays for the Direct Detection of Potato mop top virus in Soil.

Potato mop top virus (PMTV) is a continuing threat to potato production throughout the world. It has the potential to persist in the soil for long periods in the sporosori of its vector Spongospora subterranea f. sp. subterranea, which is as an important source for PMTV infection and dissemination. In this study, we used real-time quantitative reverse-transcription PCR (qRT-PCR) and reverse-transcription droplet digital PCR (RT-ddPCR) assays of the total RNA extracted directly from the soil to develop a simple, fast, and sensitive method to detect PMTV in soil samples using a specific primer with high efficiency despite a minimal amount of viral RNA. The designed primers are resilient in the presence of various PCR inhibitors in the soil when RNA is extracted. Both assays detected PMTV in all soil types used and supported the detection of <10 PMTV copies µl-1 in the RNA sample. With qRT-PCR, detection was linear, with amplification efficiencies ranging from 93.3 to 105.3% for silt loam, loamy sand, sand, and sandy loam in various experiments with R2 > 0.99. Furthermore, the RT-ddPCR assay also demonstrated a high degree of linearity (R2 > 0.99 and P < 0.0001) with the RNA extracted from the soil samples representing different textures and physiochemical characteristics that were artificially spiked with infested S. subterranea f. sp. subterranea sporosori. Additionally, both assays successfully detected PMTV in different types of naturally infested soil with PMTV carrying S. subterranea f. sp. subterranea sporosori levels ranging from 6.2 × 102 g-1 to 1.2 × 106 g-1 in soils with pH ranging from 4.9 to 7.5 and organic matter ranging from 0.9 to 5.1%, demonstrating the potential to detect PMTV in a wide variety of soils. To our knowledge, this is the first report of the development of real-time PCR and ddPCR methods for the direct detection of a soilborne virus in soil.

ВЛИЯНИЕ БИОЛОГИЧЕСКИ АКТИВНЫХ ПРЕПАРАТОВ, УДОБРИТЕЛЬНЫХ СОСТАВОВ, ОРОШЕНИЯ НА РАСПРОСТРАНЕНИЕ БОЛЕЗНЕЙ КЛУБНЕЙ КАРТОФЕЛЯ

The purpose of the work is to identify effective factors, that reduce the spread of the complex of diseases on tubers and contribute to obtaining maximum potato productivity. It was revealed that the causative agents of ordinary scab and rhizoctoniosis had a similar reaction - their prevalence decreased with the use of fertilizers, growth regulators, but increased with the use of the studied microbiological preparations, as well as Maksim fungicide, due to the high ability of these pathogens to develop resistance. The prevalence of ordinary scab also decreased on irrigation, rhizoctoniosis - on irrigation against an increased background of fertilizers. It was revealed that the prevalence of dry rot, silver scab decreased with the use of microbiological preparations, Maksim fungicide, growth regulators and increased with the introduction of the studied fertilizer compositions. From the spread of dry rot, in addition, irrigation and a high fertilizer background were effective. The effectiveness of all biologically active preparations (Рсп 9-17%) is very high from the spread of silver scab on the dehydrator, but Maxim treatment (Рсп 25-35%) is more effective on irrigation. It was revealed that the prevalence of powdery scab decreased with the use of BAP, fertilizer compositions, and increased with an increase in the background of fertilizers. The spread of wireworm injuries decreased under the influence of most of the studied factors, increased with the introduction of Kalimag and treatment with Akvaring. KMG on drylands increases the prevalence of common scab, dry rot, wireworm. Organic and mineral fertilizer is distinguished by a stabilizing effect on the spread of common scab, dry rot and wireworm damage. The most comprehensive protection against damage to tubers by diseases and wireworms was provided by growth regulators with the properties of increasing the internal resistance of plants. It was revealed that a decrease in potato yield was accompanied by an increase in the spread of pathogens of common scab and rhizoctoniosis, powdery scab, and fusariosis. To obtain maximum potato productivity with minimal damage to tubers by diseases and wireworms, it is recommended to grow potatoes under irrigation against the background of fertilizers N100P120K120 with potato processing with a new generation growth regulator Zircon.

Detection and differentiation between potato (Solanum tuberosum) diseases using calibration models trained with non-imaging spectrometry data

The proportion of light at wavelengths across the electromagnetic spectrum that is either absorbed, transmitted or reflected from a plant leaf is dependent on leaf structure, physiology and biochemistry. Since these elements are influenced by pests, pathogens and their associated induced diseases, the detection, differentiation and diagnosis of plant diseases is theoretically possible by non-destructive analysis of the light reflected from plant leaves. In this study the utility of analysis of light over the visible and near-infrared (400–1000 nm) portion of the spectrum to detect and distinguish between several economically important potato diseases, using either Partial Least Squares and BackPropagation Neural Network spectral calibration models was explored. Models could detect and distinguish between diseases with obvious foliar symptoms (blackleg and late blight), even pre-symptomatically, correctly classifying spectra from greenhouse experiments with an accuracy of 84.6%. When these diseases were analysed separately, models could distinguish between spectra from healthy and pre-symptomatic leaves, plus three classes of late blight lesion advancement with 92% accuracy. For blackleg, models distinguished between spectra from healthy, pre-symptomatic foliage and plants expressing blackleg symptoms with a 74.6% classification accuracy. However, models trained on spectra from whole-plant readings from field trials did not have this level of accuracy, with an r2 between target and model values of 0.66 for late blight, 0.31 for blackleg symptoms and 0.41 for healthy foliage. Regardless of greenhouse or field environment, models failed to detect or distinguish between diseases with subtle foliar impacts (black dot, powdery scab and Rhizoctonia diseases). While deployment of hand-held spectrometers for disease detection on a broad-acre scale is impractical, these findings could underpin methods to analyse hyperspectral imaging data with sub-plant resolution for incorporation into precision agriculture and Integrated Pest Management programmes for potato blackleg and late blight management.

Detection and Quantification of Spongospora subterranea Sporosori in Soil by Quantitative Real-Time PCR.

Powdery scab on potato tubers is caused by the obligate soilborne biotroph Spongospora subterranea and is known to cause substantial losses in potato production. The pathogen also infects roots of susceptible hosts, forming galls which can negatively affect root function. S. subterranea is also the vector of Potato mop-top virus, which causes a tuber necrosis disease that can, depending on temperature and cultivar, render potato tubers unmarketable. In this study, we adapted a published protocol to develop a sensitive and robust quantitative real-time PCR (qPCR) assay using specific primers and probes for detecting and quantifying S. subterranea sporosori in soil types that differ in physical properties, including organic matter content and soil pH. For the first time, an external control was utilized and applied directly to the soil prior to DNA extraction, which facilitated normalization of S. subterranea sporosori soil levels from sample to sample. The duplex qPCR protocol was demonstrated to be highly sensitive, capable of detecting and quantifying as few as 1 sporosorus/g of soil, with consistently high qPCR efficiency and the coefficient of determination (R2) values ranging from 94 to 99% and 0.98 to 0.99, respectively. The protocol was successfully implemented in enumerating S. subterranea sporosori in naturally infested field soil collected from several states and in artificial potting mixes with high organic matter content ranging from 64 to 71%. The qPCR method developed can be useful for potato growers to avoid agricultural soils highly infested with S. subterranea and in the development of risk assessment models in the future that incorporate cultivar susceptibility to powdery scab and soil infestation levels.

Population Biology and Genetic Variation of Spongospora subterranea f. sp. subterranea, the Causal Pathogen of Powdery Scab and Root Galls on Potatoes in South Africa.

Spongospora subterranea f. sp. subterranea, causal agent of powdery scab and root galls of potatoes, occurs worldwide and is responsible for quality and yield losses in potato production in South Africa. Despite being one of the most important potato pathogens in South Africa, little information is available on the genetic structure and diversity of S. subterranea f. sp. subterranea, which could provide insight into the factors shaping its evolution and the role of inoculum sources in disease development. A total of 172 samples were collected from four potato growing regions in South Africa. An additional 27 samples obtained from Colombia were included for comparative purposes. The samples were screened against six informative microsatellite (simple-sequence repeat) markers. Of the 172 samples obtained from potato growing regions in South Africa, there were 75 multilocus genotypes (MLGs), only 16 of which were shared between potato growing regions, indicating substantial gene flow and countrywide dispersal of the pathogen. The presence of common MLGs among the root- and tuber-derived samples indicated a lack of specialization of S. subterranea f. sp. subterranea to either tuber or root infection. Nei's unbiased estimates of gene diversity for the clone-corrected data were low and ranged from 0.24 to 0.38. Analysis of molecular variance and discriminant analysis of principal components showed no population differentiation between different potato growing regions in South Africa and between root- and tuber-derived genotypes. The presence of MLGs, high considerable genotypic diversity, and failure to reject the null hypothesis of random mating in most populations are indicative of some kind of recombination, either sexual or asexual, in these S. subterranea f. sp. subterranea populations. Information from this study provides new insights into the genetic structure and diversity of S. subterranea f. sp. subterranea in South Africa. Continuous monitoring of the pathogen population dynamics will be helpful in implementing effective region-specific management strategies for the pathogen, especially in the development of resistant potato cultivars.

Control of potato powdery scab (Spongospora subterranea) in Israel with chloropicrin, metam sodium or fluazinam

Powdery scab, caused by Spongospora subterranea, causes significant economic damage in potato production worldwide due to reduced quality and marketability of seed and ware tubers. Three field experiments were conducted in naturally infested soil during winter 2008, 2012 and 2013 to evaluate the efficacy of soil fumigation on powdery scab on tubers, root galling and the pathogen populations in soil. Soil fumigation with metam sodium (MS) or chloropicrin (PIC) was highly effective in controlling the disease under field conditions. Powdery scab incidence and severity on tubers were significantly reduced by MS applied at 219–222 L a.i. ha−1 by 66–98%. In application of PIC at 99–396 kg a.i. ha−1 followed with immediate plastic cover, disease incidence on tubers was significantly reduced by 56–90%, whereas, uncovered PIC treatments had a lower efficacy. Root galling was also affected by the fumigants and was significantly lower in MS and PIC treatments as compared to the control. In-furrow fluazinam treatments were less effective than the fumigants, with only 18–20% reduction in disease incidence on tubers. Pathogen levels in the soil, determined shortly after fumigation, were significantly lower than in the control. However, at the end of the growing season, they were increased to high levels with no significant differences among all treatments.

Identification of differentially expressed genes in tolerant and susceptible potato cultivars in response to Spongospora subterranea f. sp. subterranea tuber infection

Powdery scab caused by Spongospora subterranea f. sp. subterranea (Sss) has recently become one of the most devastating potato diseases of economic importance in South Africa. The use of resistant cultivars has long been considered the most effective and sustainable strategy to manage the pathogen. However, little is known about the molecular mechanisms underlying resistance of potato tubers to Sss. Using RNA‐sequencing (RNA‐seq), 2058 differentially expressed genes (DEGs) were identified from two potato cultivars (tolerant and susceptible) in response to Sss infection. Analysis of the expression patterns of 10 selected defence‐response genes was carried out at two different stages of tuber growth using RT‐qPCR to validate the RNA‐seq data. Several defence‐related genes showed contrasting expression patterns between the tolerant and susceptible cultivars, including marker genes involved in the salicylic acid hormonal response pathway (StMRNA, StUDP and StWRKY6). Induction of six defence‐related genes (StWRKY6, StTOSB, StSN2, StLOX, StUDP and StSN1) persisted until harvest of the tubers, while three other genes (StNBS, StMRNA and StPRF) were highly up‐regulated during the initial stages of disease development. The results of this preliminary study suggest that the tolerant potato cultivar employs quantitative resistance and salicylic acid pathway hormonal responses against tuber infection by Sss. The identified genes have the potential to be used in the development of molecular markers for selection of powdery scab resistant potato lines in marker‐assisted breeding programmes.

Integrated Potato (Solanum Tuberosum L.) Late Blight (Phytophthora Infestans) Disease Management in Ethiopia

Potato (Solanum tuberosum L.) is the fourth major crop of the world after rice, wheat and maize. Potato is an important crop which holds promise for food to millions of people especially in developing countries. In Ethiopia, the yield per unit area of potato is very low compared to those of other countries. There are many factors that reduce the yield of the crop among which the diseases like late blight (Phytophthora infestans) and bacterial wilt (Ralstonia (Pseudomonas) solanacearum) which play an important role. Diseases such as late blight, early blight, fusarium wilt and black leg primarily affect the crop/foliage whereas diseases such as black scurf, wart, powdery scab and common scab disfigure the tubers and reduce their market value. Major fungal and bacterial diseases affecting potato crop are reviewed here with respect to their identification, symptoms on potato plants or tubers, nature of the pathogen involved, epidemiology, control measures etc. Management of these diseases is therefore very essential. Late blight of potato can be managed using the following management (control) strategies: use of biological control agents, use of resistant varieties, intercropping, use of certified disease-free seed, use of selective fungicides and cultural practices such as destruction of cull piles by freezing or deep burying, destruction of volunteer potato plants in nearby fields throughout the season, destruction (desiccate, disc or flail and desiccate) of infected plants to avoid spread, reduction of periods of leaf wetness and high humidity within the crop canopy by appropriately timing irrigation, application of a recommended fungicide spray program (the program should start prior to the arrival of the pathogen) and desiccation of vines prior to harvest.

马铃薯微型薯粉痂病综合防治技术

马铃薯微型薯粉痂病综合防治技术

Use and Effects of Different Brassica and Other Rotation Crops on Soilborne Diseases and Yield of Potato †

Soilborne diseases are persistent problems in potato production, resulting in reductions in tuber quality and yield. Brassica rotation crops may reduce soilborne potato diseases, but how to best utilize Brassica crops in potato cropping systems has not been established. In this research, two two-year trials were established at three different sites with histories of soilborne diseases, and up to six different Brassica crops (canola, winter rapeseed, yellow and brown condiment mustards, oriental mustard, oilseed radish, and a mustard blend) and standard rotation crops (ryegrass and buckwheat) were evaluated as rotation and green manure crops. Tuber yield did not vary substantially among the rotation crops, but rotation treatments significantly affected incidence and severity of soilborne diseases at all sites. However, results were variable among sites and years. Perennial ryegrass and mustard blend rotations reduced powdery scab disease by 31–55% relative to other rotations in the only field where powdery scab was a serious problem. Mustard blend, ryegrass, and other Brassica rotations also reduced common scab, silver scurf, and black scurf at various sites, but not consistently at all sites. At one site, mustard blend and barley/ryegrass rotations reduced black scurf (by 21–58%) and common scab (by 13–34%) relative to no rotation. Overall, disease control was not correlated with biofumigation potential or rotation crop biomass production. Although both Brassica and non-Brassica rotations provided disease reduction in potato cropping systems, no single rotation crop performed consistently better than several others.

Draft Genome Resource for the Potato Powdery Scab Pathogen Spongospora subterranea.

The Plasmodiophorida (Phytomyxea, Rhizaria) are a group of protists that infect plants. Of this group, Spongospora subterranea causes major problems for the potato industry by causing powdery scab and root galling of potatoes and as vector for the Potato mop-top virus (PMTV) (genus Pomovirus, family Virgaviridae). A single tuber isolate (SSUBK13) of this uncultivable protist was used to generate DNA for Illumina sequencing. The data were assembled to a draft genome of 28.08 Mb consisting of 2,340 contigs and an L50 of 280. A total of 10,778 genes were predicted and 93% of the BUSCO genes were detected. The presented genome assembly is only the second genome of a plasmodiophorid. The data will accelerate functional genomics to study poorly understood interaction of plasmodiophorids and their hosts.

Susceptibility of opium poppy and pyrethrum to root infection by Spongospora subterranea

AbstractSpongospora subterranea, which causes powdery scab of potato, infects a diverse range of plant species. Crop rotation as a powdery scab management tool will be compromised if pathogen hosts exist between potato crops. Opium poppy (Papaver somniferum) and pyrethrum (Tanacetum cinerariifolium) are important crops within intensive vegetable production rotations in NW Tasmania. Measurements of S. subterranea soil inoculum within a commercial field showed pathogen amounts were substantially elevated following an opium poppy crop, which suggested host status. In glasshouse testing, opium poppy and pyrethrum were confirmed as hosts of S. subterranea, with opium poppy the more susceptible of the two. Both species were less susceptible than tomato, a known host. Observations of early growth suggested inoculation impacts on all three plant species, although at 16 (tomato and opium poppy) or 26 (pyrethrum) weeks postinoculation, only tomato had significantly reduced shoot and root development. The role of rotation crops in inoculum persistence and the possible role of S. subterranea as a minor pathogen of nonpotato crops are discussed.

Effect of Diverse Compost Products on Soilborne Diseases of Potato

ABSTRACTSoilborne diseases result in major economic losses for potato producers. Compost application can reduce soilborne diseases, however the effects of compost products on potato disease severity and incidence are still unclear. Diverse compost products were compared for their effects on soilborne diseases of potato in New Brunswick, Canada using field and growth room experiments. In the field, five products were applied at 45 Mg ha−1 dry weight to field plots in October of 2014 and 2015. In the growth room experiment, seven products were mixed to a 5% w/w ratio with naturally infested soil. Tubers were assessed for disease severity and incidence and compared with a no compost addition control. Severity of symptoms of silver scurf, black scurf (BS), common scab (CS), and powdery scab varied among treatments, experiments, and years. In the field experiment, BS severity was significantly greater in the control than in the poultry manure compost treatment (3.26% versus 0.90%) in 2016. Common scab severity and incidence in the field were positively related to soil pH and negatively related to soil particulate organic matter C and compost C concentrations. In the growth room experiment, CS severity was significantly greater in the control (8.98%) than in the municipal source separated organic compost and sea-waste compost treatments (1.72 and 2.47%, respectively). In this study, compost products had a significant, but inconsistent, suppressive effect on soilborne potato diseases. The quantity of compost C, rather than compost quality, was likely the most important factor in disease suppression in this study.

Organismos asociados a daños en tubérculos de papa en postcosecha

&lt;p&gt;La papa (&lt;em&gt;Solanum tuberosum&lt;/em&gt; L.) es uno de los cultivos de mayor consumo humano a nivel mundial. El cultivo es amenazado desde sus inicios por distintos organismos; algunos de ellos ocasionan daños superficiales en los tubérculos, que reducen la calidad y apariencia lo que provoca el rechazo por el consumidor. De un total de 34 muestras de tubérculos de papa destinados para consumo humano, obtenidas mediante muestreo visual dirigido, en la Central de Abastos de Ecatepec, se identificaron a los microorganismos asociados a algún daño físico o alteración superficial; además, de manchas atípicas en la superficie de tubérculos. Del total de las muestras en el 50% se identificaron a las bacterias &lt;em&gt;Enterobacter aerogenes&lt;/em&gt;, &lt;em&gt;Pseudomonas fluorescens&lt;/em&gt; y &lt;em&gt;Streptomyces&lt;/em&gt; sp. En el 41% se identificaron a hongos y protozoarios como &lt;em&gt;Fusarium oxysporum&lt;/em&gt;, &lt;em&gt;F. solani&lt;/em&gt;, &lt;em&gt;F. verticillioides&lt;/em&gt;, &lt;em&gt;Rhizoctonia solani&lt;/em&gt;, &lt;em&gt;Alternaria&lt;/em&gt; sp., &lt;em&gt;Colletotrichum&lt;/em&gt; sp., &lt;em&gt;Clonostachys&lt;/em&gt; sp., &lt;em&gt;Geotrichum&lt;/em&gt; sp., y &lt;em&gt;Spongospora subterranea&lt;/em&gt; f. sp. &lt;em&gt;subterranea&lt;/em&gt;. Del 9% de las muestras restantes no se identificó ningún organismo relacionado al daño.&lt;/p&gt;

Zoosporangial root infection of tomato by Spongospora subterranea in hydroponic and glasshouse culture results in diminished plant growth

AbstractTomato plants are highly susceptible to root infection by Spongospora subterranea and are commonly used as bioassay hosts. The impacts of root infection with S. subterranea on plant productivity and yield have been debated. Recent experiments with potato, the major economic host of S. subterranea, have indicated significantly reduced plant growth and potato yield following heavy infection. However, there have been very few similar studies that have examined the possible impacts of S. subterranea infection on tomato plant growth. Three tomato cultivars, “Grape,” “Roma” and “Truss,” were challenged with S. subterranea inoculum in hydroponic culture. Moderate to severe zoosporangial infections were observed with minor but statistically significant differences in susceptibility among the three tomato cultivars. Zoosporangial root infection in the absence of root gall formation resulted in significantly diminished shoot lengths and plant fresh weights in pathogen challenge tests conducted both in hydroponic culture and glasshouse‐grown plants in potting mix. Root lengths were reduced, but the differences were statistically significant in a single trial only. The findings from this study demonstrate that, as with potato, root infection by S. subterranea can result in reduced tomato plant growth and that root gall production associated with root infection was not necessary for this retardation of growth response. This further suggests that possible yield impacts in other crop species that are hosts for S. subterranea root infection are worthy of examination.

Germinate to exterminate: chemical stimulation of Spongospora subterranea resting spore germination and its potential to diminish soil inoculum

Hoagland's solution (HS), a defined nutrient supplement for plants, has been previously reported to stimulate zoospore release from resting spores of the potato pathogen Spongospora subterranea f. sp. subterranea. This study obtained direct empirical evidence for an increase in zoospore release with HS treatment, and identified Fe‐EDTA as the stimulant component of HS. Stimulation of resting spores by HS and Fe‐EDTA resulted in greater and earlier zoospore release compared to a distilled water control, and in the presence of a susceptible tomato host plant resulted in enhanced root infection. Given the labile nature of S. subterranea zoospores, it was postulated that stimulation of premature release of zoospores from the dormant resting spores in absence of susceptible hosts could reduce soil inoculum levels. In two glasshouse trials in the absence of host plants, both Fe‐EDTA and HS soil treatments reduced S. subterranea soil inoculum levels, providing proof of concept for the ‘germinate to exterminate’ approach to inoculum management.

PM 7/28 (2) Synchytrium endobioticum

Specific scopeThis Standard describes a diagnostic protocol for Synchytrium endobioticum.This Standard should be used in conjunction with PM 7/76 Use of EPPO diagnostic protocols.Specific approval and amendmentApproved in 2003‐09. Revision approved in 2017‐06.

Proceedings of the 3rd International Powdery Scab Workshop

Proceedings of the 3rd International Powdery Scab Workshop

Biocontrol of powdery scab of potato by seed tuber application of an antagonistic fungus, Aspergillus versicolor, isolated from potato roots

An environmentally friendly measure to control potato powdery scab caused by a protozoan pathogen Spongospora subterranea f.sp. subterranea (Sss) was developed by focusing on antagonistic microorganisms that were considered compatible with potato root. Five hundred and eight soil fungi, isolated from potato root cultivated in soil suspensions from four potato fields in Hokkaido, were screened for suppressiveness of root infection by Sss in a hydroponic culture system and for powdery scab severity in greenhouse and field experiments. Antagonistic isolate Im6-50, identified as Aspergillus versicolor, was selected as a potent biological control agent. In a 3-year field test, A. versicolor Im6-50 suppressed powdery scab with a protection value of 54–70 (100 = complete protection) when applied directly on seed tubers compared with a protection value of 77–93 by the synthetic fungicide fluazinam. A. versicolor Im6-50 was detected from the surface of daughter tubers and from the soil in which the inoculated seed tubers were cultivated by PCR using species-specific primers. The establishment of A. versicolor Im6-50 on the stolon of inoculated potato plants and in the rhizosphere is considered to contribute to the mechanism for disease suppression.