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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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variation in allyl isothiocyanate production within brassica species and correlation with fungicidal activity
Journal of Chemical Ecology, 1999Co-Authors: Claudia Olivier, Steven F Vaughn, Eduardo S. G. Mizubuti, Rosemary LoriaAbstract:Brassica nigra (black mustard) and B. juncea (Indian mustard) genotypes were tested for pathogen suppression and release of allyl isothiocyanate (AITC), a fungitoxic volatile produced in mustard tissue after enzymatic hydrolysis of allyl glucosinolate (sinigrin). In bioassays, 28 genotypes of B. nigra and 35 genotypes of B. juncea were screened for inhibition of the potato pathogens Helminthosporium solani and Verticillium dahliae by volatiles released from macerated leaf tissue. Release of AITC from plant tissue was quantified by gas chromatography; isothiocyanate profiles were determined by headspace analysis. All mustard genotypes produced compounds that suppressed radial growth of both fungi. Growth suppression and AITC release differed significantly (P 1.2 mg AITC/g plant tissue were fungicidal to both pathogens. Headspace analysis confirmed that allyl glucosinolate was the major glucosinolate in all genotypes of B. nigra tested; most genotypes also produced 2-phenylethyl-isothiocyanate (ITC). Brassica juncea genotypes produced variable amounts of AITC and other volatiles with antimicrobial activity, including 2-phenylethyl-ITC, benzyl-ITC, and 3-butenyl-ITC. Evaluating mustards from geographically diverse locations allowed selection of mustard genotypes that may be useful in breeding programs designed to develop disease-suppressing green manure cultivars.
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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.
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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variation in allyl isothiocyanate production within brassica species and correlation with fungicidal activity
Journal of Chemical Ecology, 1999Co-Authors: Claudia Olivier, Steven F Vaughn, Eduardo S. G. Mizubuti, Rosemary LoriaAbstract:Brassica nigra (black mustard) and B. juncea (Indian mustard) genotypes were tested for pathogen suppression and release of allyl isothiocyanate (AITC), a fungitoxic volatile produced in mustard tissue after enzymatic hydrolysis of allyl glucosinolate (sinigrin). In bioassays, 28 genotypes of B. nigra and 35 genotypes of B. juncea were screened for inhibition of the potato pathogens Helminthosporium solani and Verticillium dahliae by volatiles released from macerated leaf tissue. Release of AITC from plant tissue was quantified by gas chromatography; isothiocyanate profiles were determined by headspace analysis. All mustard genotypes produced compounds that suppressed radial growth of both fungi. Growth suppression and AITC release differed significantly (P 1.2 mg AITC/g plant tissue were fungicidal to both pathogens. Headspace analysis confirmed that allyl glucosinolate was the major glucosinolate in all genotypes of B. nigra tested; most genotypes also produced 2-phenylethyl-isothiocyanate (ITC). Brassica juncea genotypes produced variable amounts of AITC and other volatiles with antimicrobial activity, including 2-phenylethyl-ITC, benzyl-ITC, and 3-butenyl-ITC. Evaluating mustards from geographically diverse locations allowed selection of mustard genotypes that may be useful in breeding programs designed to develop disease-suppressing green manure cultivars.
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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.
May Bente Brurberg - One of the best experts on this subject based on the ideXlab platform.
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a three way transcriptomic interaction study of a biocontrol agent clonostachys rosea a fungal pathogen Helminthosporium solani and a potato host solanum tuberosum
Molecular Plant-microbe Interactions, 2017Co-Authors: Erik Lysoe, Merete Wiken Dees, May Bente BrurbergAbstract:Helminthosporium solani causes silver scurf, which affects the quality of potato. The biocontrol agent Clonostachys rosea greatly limited the severity of silver scurf symptoms and amount of H. solani genomic DNA in laboratory experiments. Transcriptomic analysis during interaction showed that H. solani gene expression was highly reduced when coinoculated with the biocontrol agent C. rosea, whereas gene expression of C. rosea was clearly boosted as a response to the pathogen. The most notable upregulated C. rosea genes were those encoding proteins involved in cellular response to oxidative stress, proteases, G-protein signaling, and the methyltransferase LaeA. The most notable potato response to both fungi was downregulation of defense-related genes and mitogen-activated protein kinase kinase kinases. At a later stage, this shifted, and most potato defense genes were turned on, especially those involved in terpenoid biosynthesis when H. solani was present. Some biocontrol-activated defense-related genes in...
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a three way transcriptomic interaction study of a biocontrol agent clonostachys rosea a fungal pathogen Helminthosporium solani and a potato host solanum tuberosum
Molecular Plant-microbe Interactions, 2017Co-Authors: Erik Lysoe, Merete Wiken Dees, May Bente BrurbergAbstract:Helminthosporium solani causes silver scurf, which affects the quality of potato. The biocontrol agent Clonostachys rosea greatly limited the severity of silver scurf symptoms and amount of H. solani genomic DNA in laboratory experiments. Transcriptomic analysis during interaction showed that H. solani gene expression was highly reduced when coinoculated with the biocontrol agent C. rosea, whereas gene expression of C. rosea was clearly boosted as a response to the pathogen. The most notable upregulated C. rosea genes were those encoding proteins involved in cellular response to oxidative stress, proteases, G-protein signaling, and the methyltransferase LaeA. The most notable potato response to both fungi was downregulation of defense-related genes and mitogen-activated protein kinase kinase kinases. At a later stage, this shifted, and most potato defense genes were turned on, especially those involved in terpenoid biosynthesis when H. solani was present. Some biocontrol-activated defense-related genes in potato were upregulated during early interaction with C. rosea alone that were not triggered by H. solani alone. Our results indicate that the reductions of silver scurf using C. rosea are probably due to a combination of mechanisms, including mycoparasitism, biocontrol-activated stimulation of plant defense mechanisms, microbial competition for nutrients, space, and antibiosis.
David M Rizzo - One of the best experts on this subject based on the ideXlab platform.
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occurrence and epidemiological aspects of potato silver scurf in california
Horticultura Brasileira, 2004Co-Authors: Marcos G Cunha, David M RizzoAbstract:A new potato tuber disease has been observed in the Tulelake region, California, USA, since 1995, with tuber symptoms suggestive of silver scurf disease (Helminthosporium solani). In this work we isolated, identified and demonstrated the nature of the causal agent of this potato disease in California. In addition, the distribution of H. solani in potato fields and the inoculum potential at harvest time were investigated. Disease progress and H. solani spore populations were also characterised under commercial storage conditions. The main fungal genera associated with potato tubers in storage were Helminthosporium solani, Colletotrichum sp., Fusarium sp., and Rhizoctonia sp. The results of Koch's postulates indicated that H. solani is responsible for the outbreak of silver scurf in the Tulelake region. In a disease survey in three commercial potato fields naturally infested, H. solani infections occurred in all fields. However, the extension of the infections differed significantly between the fields. During potato storage, silver scurf usually increased over time. The percentage of the tuber surface covered by silver scurf varied from 3.5% up to 35.5% during the storage period. The number of H. solani lesions per tuber also progressively increased from 6% up to 35%, six months after storage. H. solani spore populations also increased over time in all studied potato stores; nevertheless, they followed no consistent pattern, exhibiting multiple and variable peaks of increase and reduction during the period of storage.
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Occurrence and epidemiological aspects of potato silver scurf in California Ocorrência e aspectos epidemiológicos da sarna prateada da batateira na Califórnia
Associação Brasileira de Olericultura, 2004Co-Authors: Marcos G Cunha, David M RizzoAbstract:A new potato tuber disease has been observed in the Tulelake region, California, USA, since 1995, with tuber symptoms suggestive of silver scurf disease (Helminthosporium solani). In this work we isolated, identified and demonstrated the nature of the causal agent of this potato disease in California. In addition, the distribution of H. solani in potato fields and the inoculum potential at harvest time were investigated. Disease progress and H. solani spore populations were also characterised under commercial storage conditions. The main fungal genera associated with potato tubers in storage were Helminthosporium solani, Colletotrichum sp., Fusarium sp., and Rhizoctonia sp. The results of Koch's postulates indicated that H. solani is responsible for the outbreak of silver scurf in the Tulelake region. In a disease survey in three commercial potato fields naturally infested, H. solani infections occurred in all fields. However, the extension of the infections differed significantly between the fields. During potato storage, silver scurf usually increased over time. The percentage of the tuber surface covered by silver scurf varied from 3.5% up to 35.5% during the storage period. The number of H. solani lesions per tuber also progressively increased from 6% up to 35%, six months after storage. H. solani spore populations also increased over time in all studied potato stores; nevertheless, they followed no consistent pattern, exhibiting multiple and variable peaks of increase and reduction during the period of storage.A partir de 1995, uma nova doença foi observada em tubérculos de batata provenientes da região de Tulelake, Califórnia, USA, com sintomas que sugeriam a doença conhecida como sarna prateada, causada por Helminthosporium solani. Assim, os objetivos deste trabalho foram: a) isolar, identificar a natureza do agente causal dessa doença de batata na Califórnia; b) investigar a distribuição de H. solani nos campos de batata de Tulelake e o seu potencial de inóculo no momento da colheita; c) caracterizar o progresso da doença e populações de esporos de H. solani em condições de armazenamentos comerciais. Em armazéns comerciais, os principais gêneros de fungos associados aos tubérculos doentes foram Helminthosporium solani, Colletotrichum sp., Fusarium sp. e Rhizoctonia sp. Os resultados dos postulados de Koch indicaram que H. solani é o responsável pelos ataques de sarna prateada na região de Tulelake. Em campos de batata naturalmente infestados, observou-se que infecções de H. solani ocorreram em todos os três campos estudados, entretanto, a extensão das infestações diferiram significativamente entre os campos. Durante o armazenamento, a incidência da sarna prateada aumentou progressivamente em todos os armazéns. A percentagem da superfície do tubérculo afetada por sarna prateada aumentou de 3,5% para 35,5% durante o período de armazenamento. O número de lesões de H. solani por tubérculo também aumentou de 6 para 35 lesões por tubérculo após 6 meses de armazenamento. As populações de esporos de H. solani também aumentaram significativamente ao longo do período de armazenamento em todos os armazéns estudados. Entretanto, esses aumentos não foram contínuos, ou seja, as populações apresentaram múltiplos picos de aumento e redução durante o período de armazenamento
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development of fungicide cross resistance in Helminthosporium solani populations from california
Plant Disease, 2003Co-Authors: M G Cunha, David M RizzoAbstract:ABSTRACT Helminthosporium solani populations on potato from the Tulelake area in California frequently have been exposed to thiophanate-methyl but not benomyl. Assessment of three H. solani populations found that 182 of 238 isolates were resistant to both thiophanate-methyl and benomyl and 56 isolates were sensitive to both fungicides. None of the isolates exhibited a differential reaction to the two fungicides. The effective concentrations that reduced growth by 50% for resistant isolates of H. solani were approximately 400 mg/liter for thiophanate- methyl and 35 mg/liter for benomyl. Two point mutations were detected in the β-tubulin gene from H. solani isolates from California; however, only the mutation at the 455-nucleotide position (codon 198) was strongly associated with thiophanate-methyl resistance. This mutation led to a change of glutamic acid to alanine at codon 198. Independent of fungicide resistance, a mutation at the 836-site was detected in all California isolates. A polymerase chain reac...