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Russell J Tweddell - One of the best experts on this subject based on the ideXlab platform.
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effect of iron and nitrogen on the development of helminthosporium solani and potato Silver Scurf
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2011Co-Authors: Benjamin Mimee, Tyler J Avis, Sophia Boivin, Suha Jabaji, Russell J TweddellAbstract:Abstract Silver Scurf is a surface blemish disease of potato (Solanum tuberosum L.) tubers caused by Helminthosporium solani Durieu & Mont. Silver Scurf is becoming a disease of high economic impact. In this study, the effect of different iron (FeSO4, FeCl2) and nitrogen (NaNO2, NaNO3, NH4Cl, NH4NO3) salts on H. solani conidial germination and on potato Silver Scurf development was evaluated. The results show that iron and nitrogen salts affect in vitro germination of H. solani conidia. Conidia were particularly sensitive to FeSO4 and FeCl2. These salts completely inhibited conidial germination and were shown to be toxic at a concentration of 0.9 mM. Among the nitrogen salts tested, conidia were most affected by NaNO2 and NH4Cl, which almost completely inhibited their germination at a concentration of 169.7 mM. NaNO2 was also toxic to conidia. Among the salts tested, only FeSO4, FeCl2 and NaNO2 reduced the development of Silver Scurf. Comparison of the effect of the different tested salts leads to the con...
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integrated management of potato Silver Scurf helminthosporium solani
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2010Co-Authors: Tyler J Avis, C Martinez, Russell J TweddellAbstract:Silver Scurf is a surface blemish disease of potato (Solanum tuberosum L.) tubers, caused by Helminthosporium solani Durieu & Mont., which has gained increasing economic importance in recent years. The disease develops initially in the field but fully expands in the warehouse under storage conditions favourable to the spread of the pathogen. Control of the disease, once provided by the fungicide thiabendazole, is now difficult due to the appearance of thiabendazole-resistant strains and the lack of potato cultivars with high levels of resistance to Silver Scurf. An integrated disease management programme including appropriate cultural methods and storage conditions along with the use at planting and/or at harvest of synthetic chemical fungicides is recommended to reduce the incidence and the severity of Silver Scurf. Recent studies put forth the possibility that 'generally recognized as safe' (GRAS) compounds and microbial antagonists could eventually be integrated into Silver Scurf management strategies.
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the role of antibiosis in the antagonism of different bacteria towards helminthosporium solani the causal agent of potato Silver Scurf
Phytoprotection, 2006Co-Authors: C Martinez, Richard R Belanger, Tyler J Avis, Jeannicolas Simard, Jessica M Labonte, Russell J TweddellAbstract:Bacterial antagonists of Helminthosporium solani were submitted to different tests in order to determine the role of antibiosis in their antagonistic interaction. Among the bacterial strains tested, seven (Alcaligenes piechaudii, Aquaspirillum autotrophicum, Cellulomonas fimi, Pseudomonas chlororaphis, Pseudomonas putida (strains 94-19 and E-30) and Streptomyces griseus) were shown to produce agar diffusible metabolites inhibiting H. solani mycelial growth and/or conidial germination. Differential activity was revealed when diffusible metabolites were extracted from either pure cultures of these antagonists or dual culture in the presence of H. solani. The results presented indicate that the methodology employed could be a decisive factor in whether or not antibiosis can be identified as a mode of action of biocontrol agents.
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ultrastructure of the infection process of potato tuber by helminthosporium solani causal agent of potato Silver Scurf
Fungal Biology, 2004Co-Authors: C Martinez, Danny Rioux, Russell J TweddellAbstract:Silver Scurf is an important postharvest disease affecting potato tubers worldwide, caused by Helminthosporium solani. In the present study, key steps of infection of potato tubers (cv. ‘Dark Red Norland’) by H. solani were described using transmission (TEM) and scanning electron microscopy (SEM). The fungus entered potato tubers mainly via hyphae, although germ tubes were also able to directly penetrate the tubers. An extracellular sheath was observed around hyphae growing over the surface of tubers and the host cell wall appeared lyzed at the point of penetration. Observations suggested that both mechanical and enzymatic processes are involved in periderm penetration. Hyphae of H. solani 9 h after tuber inoculation, were present intracellularly mostly in the periderm and in some cortical cells. Two days after inoculation, host cells were invaded and both infected and neighbouring host cells showed signs of necrosis (disrupted cytoplasm, absence of typical organelles or endomembrane systems, collapsed peridermal cells) that were not observed in healthy control tubers. Four days after inoculation, completing the infection cycle, conidiophores emerged from peridermal cells directly by erupting through the host cell walls.
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effect of chlorine atmospheres on sprouting and development of dry rot soft rot and Silver Scurf on potato tubers
Postharvest Biology and Technology, 2003Co-Authors: Russell J Tweddell, R Boulanger, Joseph ArulAbstract:The effect of chlorine atmospheres on sprouting and development of potato (Solanum tuberosum L.) dry rot, soft rot and Silver Scurf were evaluated. Potato tubers were inoculated with Fusarium sambucinum, Erwinia carotovora subsp. atroseptica or Helminthosporium solani, and placed in hermetic chambers at 15 °C containing 0 (control), 2, 20 and 201 mg/l of available chlorine in moist air. After 10 days (dry rot and soft rot) or 40 days (Silver Scurf) of exposure to chlorine, severity of each disease was evaluated. The results showed that pathogens displayed differences in their susceptibility to chlorine. H. solani, a surface pathogen, was more sensitive than wound-borne pathogens F. sambucinum and E. carotovora subsp. atroseptica. Exposure to 2 mg/l of chlorine in moist air for 40 days markedly reduced Silver Scurf, whereas chlorine significantly reduced dry rot and soft rot only upon exposure to higher chlorine concentration of 201 mg/l for 10 days. A 2-day exposure to 20 mg/l was found effective in controlling Silver Scurf. Continuous exposure to chlorine for 40 days was shown to significantly reduce sprouting of the tubers at concentrations of 20 and 201 mg/l in moist air.
Rosemary Loria - One of the best experts on this subject based on the ideXlab platform.
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molecular phylogenetic support from ribosomal dna sequences for origin of helminthosporium from leptosphaeria like loculoascomycete ancestors
Mycologia, 2000Co-Authors: Claudia Olivier, R A Shoemaker, Mary L Berbee, Rosemary LoriaAbstract:Internal transcribed spacer (ITS) regions and 5.8S rDNA were PCR-amplified and sequenced for 17 isolates of Helminthosporium solani, cause of the potato disease Silver Scurf, and for 10 other iso- lates obtained from culture collections as Helminthos- porium spp. Of these, five isolates had been incor- rectly identified as Helminthosporium spp. and be- longed in the genera Cochliobolus (anamorphs Bipo- laris, Curvularia), Cladosporium, and Pyrenophora (anamorph Drechslera). Sequence alignment and analyses of ITS regions and 5.8S rDNA of four true Helminthosporium species and more than 45 fungi formerly grouped in the genus Helminthosporium s. 1. revealed that the segregated Helminthosporium spe- cies did not group with Helminthosporium s. s. Three species of Helminthosporium s. s. (H. solani, type spe- cies H. velutinum, and H. chlorophorae) grouped tightly and were most closely related to the teleo- morph Leptosphaeria bicolor. For H. solani and H. ve- lutinum, 18SrDNA sequences were also determined. Phylogenetic analyses of the 18S rDNA sequences of 33 euascomycetous species confirmed the close rela- tionship of H. solani and H. velutinum to L. bicolor and placed Helminthosporium in the Pleosporales with 100% parsimony bootstrap support. Helminthos- porium asterinum did not group closely with the other species of Helminthosporium s. s., but was as closely related to discomycetes in the Leotiales as to other
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application of organic and inorganic salts to field grown potato tubers can suppress Silver Scurf during potato storage
Plant Disease, 1999Co-Authors: Claudia Olivier, Carol R Macneil, Rosemary LoriaAbstract:Silver Scurf, caused by Helminthosporium solani, is an economically important postharvest disease of potato tubers. Organic and inorganic salts were evaluated for their ability to suppress Silver Scurf lesion development and sporulation of H. solani on potato tubers. Tubers were treated immediately after harvest with 0.2-M solutions of potassium sorbate, calcium propionate, sodium bicarbonate, sodium carbonate, ammonium bicarbonate, or water. Tween 20 was added as a surfactant to most treatments. Potassium sorbate (0.1 M), acidified potassium sorbate and calcium propionate treatments (0.2 M), and calcium chloride treatments (0.136 M) were included in additional experiments. Tubers were stored under commercial storage conditions for 4 to 6 months prior to disease evaluation. The extent of disease suppression varied among experiments; however, some treatments consistently reduced disease. Lesion formation on the tuber surface was reduced by 26 to 60% using potassium sorbate (in three of four experiments) compared to water-treated or untreated tubers. Sporulation was suppressed by 0.2 M potassium sorbate (78 to 99% reduction) in all four experiments. Sodium carbonate reduced lesion formation in two experiments and sporulation in three of four experiments. Other treatments inconsistently suppressed lesion formation or sporulation, or did not reduce disease. Addition of Tween or acidification of organic salt solutions did not improve Silver Scurf suppression in most cases. Potassium sorbate has very low mammalian toxicity and great potential as an innocuous and inexpensive postharvest fungicide for suppression of Silver Scurf during potato storage.
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detection of helminthosporium solani from soil and plant tissue with species specific pcr primers
Fems Microbiology Letters, 1998Co-Authors: Claudia Olivier, Rosemary LoriaAbstract:Two PCR primer pairs specific for Helminthosporium solani, which causes Silver Scurf on potato tubers, were designed from nucleotide sequences of the nuclear ribosomal internal transcribed spacer regions of H. solani. Both primer pairs amplified a single product with DNA from 48 North American and European isolates of H. solani, but not with DNA from 42 other fungi. Primers also amplified a single product with DNA extracted from Silver Scurf lesions on potato tubers and other plant tissue inoculated with spores of H. solani. Detection of the fungus in infested soil was only possible with nested PCR and after processing soil with a bead beater. Specific amplification of H. solani DNA can be used to study the saprophytic and pathogenic activity of this fungus in soil and plant tissue.
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detection of helminthosporium solani from soil and plant tissue with species specific pcr primers
Fems Microbiology Letters, 1998Co-Authors: Claudia Olivier, Rosemary LoriaAbstract:Two PCR primer pairs specific for Helminthosporium solani, which causes Silver Scurf on potato tubers, were designed from nucleotide sequences of the nuclear ribosomal internal transcribed spacer regions of H. solani. Both primer pairs amplified a single product with DNA from 48 North American and European isolates of H. solani, but not with DNA from 42 other fungi. Primers also amplified a single product with DNA extracted from Silver Scurf lesions on potato tubers and other plant tissue inoculated with spores of H. solani. Detection of the fungus in infested soil was only possible with nested PCR and after processing soil with a bead beater. Specific amplification of H. solani DNA can be used to study the saprophytic and pathogenic activity of this fungus in soil and plant tissue.
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postharvest application of organic and inorganic salts for suppression of Silver Scurf on potato tubers
Plant Disease, 1998Co-Authors: Claudia Olivier, D E Halseth, Eduardo S G Mizubuti, Rosemary LoriaAbstract:ABSTRACT Seven organic and inorganic salts were tested for suppression of Silver Scurf, a postharvest disease of potato tubers caused by Helminthosporium solani. Potassium sorbate, calcium propionate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium bicarbonate were added to V8 agar at concentrations of 0.06–0.2 M. Radial growth of H. solani was significantly reduced (P < 0.05) by all salts at all concentrations. All salts except sodium bicarbonate and potassium bicarbonate were fungicidal at 0.2 M. Effects of postharvest salt treatments on disease severity and sporulation of H. solani on inoculated and naturally infected potato tubers were evaluated in separate experiments. Greenhouse-grown tubers were inoculated with H. solani spore suspensions (2 × 105 spores/ml), incubated for 5 days, dipped into 0.2 M solutions of each of the salts, and incubated in a moist chamber at 22–24°C for 6 weeks. All salt treatments prevented lesion development and sporulation of...
Claudia Olivier - One of the best experts on this subject based on the ideXlab platform.
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molecular phylogenetic support from ribosomal dna sequences for origin of helminthosporium from leptosphaeria like loculoascomycete ancestors
Mycologia, 2000Co-Authors: Claudia Olivier, R A Shoemaker, Mary L Berbee, Rosemary LoriaAbstract:Internal transcribed spacer (ITS) regions and 5.8S rDNA were PCR-amplified and sequenced for 17 isolates of Helminthosporium solani, cause of the potato disease Silver Scurf, and for 10 other iso- lates obtained from culture collections as Helminthos- porium spp. Of these, five isolates had been incor- rectly identified as Helminthosporium spp. and be- longed in the genera Cochliobolus (anamorphs Bipo- laris, Curvularia), Cladosporium, and Pyrenophora (anamorph Drechslera). Sequence alignment and analyses of ITS regions and 5.8S rDNA of four true Helminthosporium species and more than 45 fungi formerly grouped in the genus Helminthosporium s. 1. revealed that the segregated Helminthosporium spe- cies did not group with Helminthosporium s. s. Three species of Helminthosporium s. s. (H. solani, type spe- cies H. velutinum, and H. chlorophorae) grouped tightly and were most closely related to the teleo- morph Leptosphaeria bicolor. For H. solani and H. ve- lutinum, 18SrDNA sequences were also determined. Phylogenetic analyses of the 18S rDNA sequences of 33 euascomycetous species confirmed the close rela- tionship of H. solani and H. velutinum to L. bicolor and placed Helminthosporium in the Pleosporales with 100% parsimony bootstrap support. Helminthos- porium asterinum did not group closely with the other species of Helminthosporium s. s., but was as closely related to discomycetes in the Leotiales as to other
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application of organic and inorganic salts to field grown potato tubers can suppress Silver Scurf during potato storage
Plant Disease, 1999Co-Authors: Claudia Olivier, Carol R Macneil, Rosemary LoriaAbstract:Silver Scurf, caused by Helminthosporium solani, is an economically important postharvest disease of potato tubers. Organic and inorganic salts were evaluated for their ability to suppress Silver Scurf lesion development and sporulation of H. solani on potato tubers. Tubers were treated immediately after harvest with 0.2-M solutions of potassium sorbate, calcium propionate, sodium bicarbonate, sodium carbonate, ammonium bicarbonate, or water. Tween 20 was added as a surfactant to most treatments. Potassium sorbate (0.1 M), acidified potassium sorbate and calcium propionate treatments (0.2 M), and calcium chloride treatments (0.136 M) were included in additional experiments. Tubers were stored under commercial storage conditions for 4 to 6 months prior to disease evaluation. The extent of disease suppression varied among experiments; however, some treatments consistently reduced disease. Lesion formation on the tuber surface was reduced by 26 to 60% using potassium sorbate (in three of four experiments) compared to water-treated or untreated tubers. Sporulation was suppressed by 0.2 M potassium sorbate (78 to 99% reduction) in all four experiments. Sodium carbonate reduced lesion formation in two experiments and sporulation in three of four experiments. Other treatments inconsistently suppressed lesion formation or sporulation, or did not reduce disease. Addition of Tween or acidification of organic salt solutions did not improve Silver Scurf suppression in most cases. Potassium sorbate has very low mammalian toxicity and great potential as an innocuous and inexpensive postharvest fungicide for suppression of Silver Scurf during potato storage.
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detection of helminthosporium solani from soil and plant tissue with species specific pcr primers
Fems Microbiology Letters, 1998Co-Authors: Claudia Olivier, Rosemary LoriaAbstract:Two PCR primer pairs specific for Helminthosporium solani, which causes Silver Scurf on potato tubers, were designed from nucleotide sequences of the nuclear ribosomal internal transcribed spacer regions of H. solani. Both primer pairs amplified a single product with DNA from 48 North American and European isolates of H. solani, but not with DNA from 42 other fungi. Primers also amplified a single product with DNA extracted from Silver Scurf lesions on potato tubers and other plant tissue inoculated with spores of H. solani. Detection of the fungus in infested soil was only possible with nested PCR and after processing soil with a bead beater. Specific amplification of H. solani DNA can be used to study the saprophytic and pathogenic activity of this fungus in soil and plant tissue.
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detection of helminthosporium solani from soil and plant tissue with species specific pcr primers
Fems Microbiology Letters, 1998Co-Authors: Claudia Olivier, Rosemary LoriaAbstract:Two PCR primer pairs specific for Helminthosporium solani, which causes Silver Scurf on potato tubers, were designed from nucleotide sequences of the nuclear ribosomal internal transcribed spacer regions of H. solani. Both primer pairs amplified a single product with DNA from 48 North American and European isolates of H. solani, but not with DNA from 42 other fungi. Primers also amplified a single product with DNA extracted from Silver Scurf lesions on potato tubers and other plant tissue inoculated with spores of H. solani. Detection of the fungus in infested soil was only possible with nested PCR and after processing soil with a bead beater. Specific amplification of H. solani DNA can be used to study the saprophytic and pathogenic activity of this fungus in soil and plant tissue.
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postharvest application of organic and inorganic salts for suppression of Silver Scurf on potato tubers
Plant Disease, 1998Co-Authors: Claudia Olivier, D E Halseth, Eduardo S G Mizubuti, Rosemary LoriaAbstract:ABSTRACT Seven organic and inorganic salts were tested for suppression of Silver Scurf, a postharvest disease of potato tubers caused by Helminthosporium solani. Potassium sorbate, calcium propionate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium bicarbonate were added to V8 agar at concentrations of 0.06–0.2 M. Radial growth of H. solani was significantly reduced (P < 0.05) by all salts at all concentrations. All salts except sodium bicarbonate and potassium bicarbonate were fungicidal at 0.2 M. Effects of postharvest salt treatments on disease severity and sporulation of H. solani on inoculated and naturally infected potato tubers were evaluated in separate experiments. Greenhouse-grown tubers were inoculated with H. solani spore suspensions (2 × 105 spores/ml), incubated for 5 days, dipped into 0.2 M solutions of each of the salts, and incubated in a moist chamber at 22–24°C for 6 weeks. All salt treatments prevented lesion development and sporulation of...
D W Cullen - One of the best experts on this subject based on the ideXlab platform.
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conventional pcr and real time quantitative pcr detection of helminthosporium solani in soil and on potato tubers
European Journal of Plant Pathology, 2001Co-Authors: D W Cullen, A K Lees, Ian K. Toth, James M. DuncanAbstract:Silver Scurf is an economically important blemish disease of potato caused by the fungus Helminthosporium solani. Two sets of PCR primers, Hs1F1/Hs2R1 (outer) and Hs1NF1/Hs2NR1 (nested) were designed to unique sequences of the nuclear ribosomal internal transcribed spacer (ITS1 and ITS2) regions of H. solani. Nested PCR was used to increase the specificity and sensitivity of single round PCR. Each primer set amplified a single product of 447 bp and 371 bp respectively, with DNA from 71 European and North American isolates of H. solani, and the specificity of primers was confirmed by the absence of amplified product with DNA from other fungal and bacterial plant pathogens. A simple and rapid procedure for direct extraction of DNA from soils and potato tubers was modified and developed to yield DNA of a purity and quality suitable for PCR within 3 h. The sensitivity of PCR for the specific detection of H. solani in seeded soils was determined to be 1.5 spores g −1 of soil. H. solani was also detected by PCR in naturally infested soil and from peel and peel extract from infected and apparently healthy tubers. Specific primers and a TaqMan TM fluorogenic probe were designed using the original primer sequences to perform real-time quantitative (TaqMan TM ) PCR. The same levels of sensitivity for specific detection of H. solani in soil and tubers were obtained during first round TaqMan-based PCR as with conventional nested PCR and gel electrophoresis. This rapid and quantitative PCR assay allows an accurate estimation of tuber and soil contamination by H. solani, thus providing a tool to study the ecology of the organism and to serve as a crucial component for disease risk assessments. Abbreviations: BSA – bovine serum albumin; CTAB – hexadecyltrimethylammonium bromide; cv – cultivar; dNTPs – deoxynucleoside triphosphates; ITS – internal transcribed spacer; PCR – polymerase chain reaction; PVPP – polyvinylpolypyrrolidone; SASA – Scottish Agricultural Science Agency; SCRI – Scottish Crop Research Institute; TBZ – thiabendazole.
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a pcr based method for detection of potato pathogen helminthosporium solani in Silver Scurf infected tuber tissue and soils
Journal of Microbiological Methods, 2001Co-Authors: Deena Errampalli, Janet Saunders, D W CullenAbstract:Abstract Silver Scurf caused by Helminthosporium solani causes significant economic losses in table stock, seed and processing potatoes. Specific polymerase chain reaction (PCR) primers, Hs1F1/Hs2R1, from H. solani were used for the amplification of a 447-bp product from 20 tissue samples and 54 single spore H. solani isolates, from eastern Canada (27 isolates), western Canada (13 isolates) and North Dakota in USA (14 isolates), but not from other potato fungal pathogens. In addition to PCR analysis, all 54 isolates were studied using conventional detection methods, visual disease symptoms and/or colony morphology and microscopic examination of the morphology of conidiophores and conidia. The PCR assay successfully detected H. solani and the PCR results correlated well with assessments based on conventional techniques. The detection of H. solani by PCR (1 day) is rapid and offers an alternative to the time consuming conventional diagnostic techniques (4–5 weeks). Nested PCR assay was necessary for the detection of H. solani in soils and thus can provide a sensitive technique to study the epidemiology of Silver Scurf in soils.
G. A. Hide - One of the best experts on this subject based on the ideXlab platform.
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the control of Silver Scurf and development of thiabendazole resistance in helminthosporium solani as affected by the rate of fungicide applied to potato seed tubers
Potato Research, 1994Co-Authors: Sharon M. Hall, G. A. HideAbstract:Seed tubers were immersed in suspensions of thiabendazole (Storite) or thiabendazole plus imazalil (Extratect) at different concentrations and planted in a field experiment. During the following 2 years samples of the produce were planted after treatment with the same fungicide formulation used on the seed.
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the occurrence of thiabendazole resistant isolates of polyscytalum pustulans and helminthosporium solani on seed potato tubers in relation to fungicide treatment and storage
Plant Pathology, 1994Co-Authors: S F Carnegie, G. A. Hide, A M Cameron, Sharon M. HallAbstract:Tubers infected with thiabendazole-sensitive isolates of Polyscytalum pustulans and Helminthosporium solani were treated annually for 4 years with benomyl, thiabendazole or a formulated mixture of thiabendazole and imazalil, and grown at three farms in Scotland. The proportion of thiabendazole-resistant isolates of H. solani increased, and isolates producing black colonies became more common with successive annual applications of thiabendazole or benomyl. Silver Scurf was not reduced after three annual applications. When these fungicides were applied once to untreated seed the incidence of resistant isolates of H. solani was much less in 1988 than in 1991 when tubers had been grown on farms for 3 years from untreated seed. The proportion of resistant isolates of P. pustulans increased with the number of successive applications of thiabendazole or benomyl but at differing rates on each farm. At one farm, skin spot was not reduced by three annual applications of these fungicides whereas at the other farms it was reduced by 90–100% by four annual applications. A smaller proportion of resistant isolates of P. pustulans and H. solani was obtained after applying the mixture of thiabendazole and imazalil than after benomyl or thiabendazole alone. Their occurrence was not related to the number of fungicide applications. The mixture also reduced both diseases by more than 75% over the 4 years. At one farm where resistant isolates of H. solani were present, tubers were infected when stored on trays but not when stored in bags.
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effects of wounding fungicide treated potato seed tubers on Silver Scurf disease on daughter tubers at harvest
Potato Research, 1994Co-Authors: G. A. HideAbstract:Silver Scurf on daughter tubers at harvest was decreased by treating seed tubers with imazalil or thiabendazole in March but significantly increased when the treated tubers were wounded the day before planting in May. The disease was also increased by wounding seed tubers not treated with fungicide. Black dot was decreased by seed treatment with imazalil but was not affected by wounding.
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control of skin spot and Silver Scurf on stored cv king edward potatoes by chemical and non chemical methods
Annals of Applied Biology, 1994Co-Authors: G. A. Hide, Sharon M. Hall, P J ReadAbstract:Summary In 3 years, seed tubers of cv. King Edward were planted in field experiments and diseases assessed on the daughter tubers after storage for 24–26 wk. In 1991 and 1992, the seed tubers were treated with a mixture of thiabendazole and imazalil at two rates. Tubers were harvested on several dates from late August to early October and dried under different conditions before storage. In 1990, Silver Scurf after storage was decreased equally by dry curing for 2 wk and windrowing for 2 h whereas skin spot was decreased most by dry curing, and these effects were greater the earlier tubers were harvested. In 1991, dry curing for 2 wk decreased skin spot and Silver Scurf more than dry curing for 1 wk, and skin spot was slightly decreased by windrowing for 2 h; windrowing improved the control of both diseases when tubers were subsequently dry cured. In 1991 and 1992 fungicide treatment of seed tubers greatly decreased skin spot after storage and was also effective against Silver Scurf, but increased black dot when tubers were harvested in September or October. Skin spot was controlled equally well by the two rates of fungicide but Silver Scurf was less well controlled when the dose was decreased by 75%. It is suggested that amounts of fungicide applied to seed tubers could be decreased provided that the efficiency of application is improved and that crops are harvested early and dried before storage.
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Development of resistance to thiabendazole in Helminthosporium solani (Silver Scurf) as a result of potato seed tuber treatment
Plant Pathology, 1993Co-Authors: G. A. Hide, Sharon M. HallAbstract:Applying thiabendazole to potato seed tubers affected with Silver Scurf caused by Helminthosporium solani sensitive to thiabendazole decreased the severity of disease on progeny tubers at harvest, but about 50% of the isolates from these were resistant to the fungicide. The disease was not decreased when samples of the progeny tubers were treated with thiabendazole and planted in the following year, and the incidence of resistant isolates increased. Resistant isolates continued to be present when tubers were planted in the next 2 years without fungicide treatment. Treatment with a mixture of thiabendazole and imazalil also decreased the disease and fewer isolates were resistant than when treated with thiabendazole alone, although the proportion increased after treatment with the mixture in the following year. When seed tubers were infected with thiabendazole-resistant H. solani, Silver Scurf on progeny tubers was not affected by thiabendazole applied to the seed tubers but was decreased by the mixture of thiabendazole and imazalil. Imazalil was equally effective against H. solani sensitive or resistant to thiabendazole. Some isolates of H. solani had grey aerial mycelium and of 516 of these isolates obtained in 4 years 29% were resistant to the fungicide. Other isolates produced small, black colonies and their frequency increased with thiabendazole treatment of seed tubers. Of 244 of these isolates, 62% were resistant.