Silver Scurf Disease Research Articles

Efficacy of Pseudomonas syringae in the management of potato tuber diseases in storage

Silver scurf caused by Helminthosporium solani and dry rot caused by Fusarium spp. are tuber diseases of economic importance in potato-growing areas worldwide. Recently, the two pathogens have developed resistance to thiabendazole (TBZ), a post-harvest fungicide commonly used for their control. Therefore, alternative disease control strategies are needed. The present study assessed the efficacy of the biopesticides Bio-Save 10LP (Pseudomonas syringae-strain ESC-10; Ps10) and Bio-Save 11LP (P. syringae-strain ESC-11; Ps11) against silver scurf and dry rot. Approximately 30 isolates representing the genus Fusarium were obtained from symptomatic potato specimens with dry rot from New Brunswick (NB), Nova Scotia (NS), Prince Edward Island (PE) and Alberta (AB), Canada. Species isolated were Fusarium sambucinum, Fusarium tumidum, Fusarium coeruleum, Fusarium culmorum, and Fusarium avenaceum. H. solani isolated from AB, NB and PE was included in the study as the causal agent of silver scurf. The efficacy of P. syringae against F. sambucinum and H. solani was tested in vitro. Ps10 and Ps11 inhibited the growth of H. solani up to 68% (NB isolate) and 73% (PE isolate), respectively and the inhibition was more or less comparable with that of TBZ. F. sambucinum was not significantly inhibited by Ps10; however Ps11 significantly inhibited AB, PE and NB isolates by 43%, 28% and 54%, respectively. Conversely, TBZ inhibited AB, PE and NB isolates of Fusarium spp. in vitro by 86%, 88% and 100%, respectively. TBZ in combination with either Ps10 or Ps11 did not always reduce the growth of H. solani or Fusarium spp. in vitro compared to that of TBZ alone. Storage trials conducted in NB and PE assessed the efficacy of P. syringae against H. solani or Fusarium spp. in vivo and confirmed that the application of P. syringae or TBZ alone or in combination significantly reduced the incidence and/or severity of silver scurf and Fusarium dry rot. Ps11 alone or in combination with TBZ was significantly more effective than Ps10 in controlling silver scurf disease severity. The reduction in disease severity of dry rot and silver scurf in storage due to Ps10, Ps11, or TBZ or their combinations was consistently comparable. Results indicate that the use of P. syringae (strains ESC-11 or ESC-10) as a post-harvest treatment can contribute to the management of both silver scurf and Fusarium dry rot in potato storages.

La sarna plateada (Helminthosporium solani [Dur. & Mont.]), una enfermedad de creciente importancia en papa.

This work presents a bibliographic review of the silver scurfdisease and its causal agent Helminthosporium solani (Dur.& Mont.) in potatoes (Solanum tuberosum L.). The diseasehas a worldwide distribution and for at least 15 year it hasacquired increasing importance as a limiting factor in theproduction of these tubers. The review shows the economicimportance of the disease, its detection on tubers as well asin the soil, and its isolation procedures. It also explains thelife cycle of H. solani, which is not completely known yet.It also discusses the possibilities for controlling silver scurfby the use of fungicides, tillage and cultivation methods inthe field, storage management, the use of antagonists, andthrough the breeding of new cultivars.

First Report of Helminthosporium solani Causing Silver Scurf of Potato in Hebei Province, North China.

Silver scurf disease of potato (Solanum tuberosum) caused by Helminthosporium solani Durieu & Mont. occurs worldwide. Severe occurrence of the disease, the resulting weight loss of stored potatoes, and lower market classes of potato caused by the fungus have been documented in Europe and North America (1). Tubers infected with the pathogen develop tan-to-gray lesions that have a characteristic silvery appearance when moist. In 2005, gray spots with a defined margin and silvery appearance when seen against light were observed on potato tubers of cv. Weishu No. 1. The silver symptoms were distinguished from those of black rot disease of potato caused by Colletotrichum coccodes. The potato tubers were obtained from Weichang County of Hebei Province, North China. Conidia were scraped from the spots with a sterile scalpel and identified primarily as the fungus H. solani on the basis of morphological characters of the spores. The fungus was isolated, purified, and cultured on potato dextrose agar (PDA) amended with penicillin and streptomycin. To produce conidia, the fungus was incubated on V8 juice medium at 20 ± 2°C for 15 days under near-UV light (360 to 400 nm, 12-h light/dark cycles). The culture colony developed slowly and is gray to brown. Conidia form in whorls on conidiophores that are black, unbranched, irregular, and multiseptate. Conidia are appreciably tapered, straight or slightly curved, brown, thick walled, and have two to eight pseudosepta. The size of the conidia ranged from 14 to 70 μm long and 4 to 9 μm wide. The spore suspension was adjusted to 1.5 × 105 spores per ml by using sterile distilled water containing 0.2% Tween 20. Twenty healthy tubers were washed with distilled water and then inoculated by spraying the spore suspension onto the surface with a hand atomizer, while 10 washed tubers were sprayed with distilled water as controls. Inoculated tubers were kept in containers covered with plastic and placed in an incubation chamber at 20°C for 3 weeks. Gray-to-brown blemishes with a silvery appearance as described above were observed on tubers inoculated with the fungus and the tuber surface areas infected were from 1 to 10%, whereas no infection was visible on tubers inoculated with water. The causal agent was reisolated, cultured, and identified microscopically as H. solani. H. solani has been identified from potato tubers in Yunnan Province, Southwest China (2), but to our knowledge, this is the first report of H. solani causing silver scurf of potato in Hebei Province, North China.

Occurrence and epidemiological aspects of potato silver scurf in California

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.

Control of silver scurf disease in stored potato by using hydrogen peroxide plus (HPP)

The present study showed that it is possible to control the silver scurf disease caused by the fungus Helminthosporium solani Durieu and Mont. in stored potato ( Solanum tuberosum) by fogging the storage rooms with 10% hydrogen peroxide plus (HPP). The percentage of infected tubers after 6 months of storage, following five treatments, was 2% compared with 38% in the non-treated control. Percent decay after a single treatment with 10% HPP 6 months post harvest was 16%. Furthermore, treatment with HPP controlled the growth of the fungus on the skin of infected harvested tubers.

Management of silver scurf (Helminthosporium solani) with fungicide seed treatments and storage practices

Thiabendazole insensitive strains ofHelminthosporium solani, the causal agent of silver scurf, make controlling the disease with seed treatment difficult. Potato tuber seed treatments and environmental storage management practices were investigated as means to minimize silver scurf. Fungicide seed treatments were evaluated for control ofH. solani; disease was evaluated during the growing season, at harvest, and after 5 months of storage. Silver scurf was observed on progeny tubers eleven weeks after planting. Fungicides that reduced silver scurf incidence and severity on the seed resulted in reduced incidence and severity of the disease in the progeny tubers at harvest and significantly lower disease ratings after storage. Only small increases in disease incidence (0-8%) were seen after storage. Thiophanate-methyl with mancozeb, Captan with mancozeb, and fludioxonil were among the most effective in reducing the incidence and severity of silver scurf on seed and in progeny tubers (Incidence on progeny tubers at harvest for these three treatments were 3%, 9%, and 8% respectively). Thiophanatemethyl alone was not effective for control of silver scurf (48% incidence compared to 43% incidence for the untreated control). Environmental conditions in storage affected disease development. Reduced humidity (85%) during the curing period (0–3 weeks after harvest) significantly reduced (11%) the surface area of tubers infected with silver scurf. Free moisture on the tuber surfaces during storage significantly increased (15%) tuber surface area infection.H. solani was shown to survive in soil and on some potato storage building materials for up to 9 months. The silver scurf disease of potatoes can be suppressed using effective seed treatment and storage management.

Abstracts, Meeting of the Plant Pathology Society of Alberta, Lethbridge, Alberta, November 1995

Abstract Noteworthy diseases diagnosed on plant samples from Alberta submitted to Brooks Diagnostics Limited in 1995. Khalil I. Al-Mughrabi and Barbara J. Penner. Brooks Diagnostics Limited, P.O. Box 1701, Brooks, Alberta TIR IC5. The influence of cultivar and soil pH on take-all of wheat. M. A. Anderson, T.K. Turkington, K.G. Briggs, I. Evans, and D. Penney. Alberta Agriculture, Food and Rural Development, Lacombe, Alberta T4L 1W8, and (I.E. and D.P.) Edmonton, Alberta T6H 4P2; and (K.G.B.) University of Alberta, Edmonton, Alberta T6G 2P5 Development of a multiplex PCR-assay for detection of bean blights. Patrice Audy, André Laroche, Gilles Saindon, and Henry C. Huang. Agriculture and Agri-Food Canada, Research Center, Lethbridge, Alberta TU 4B1. Enzyme production by Helminthosporium solani, the causal agent of silver scurf disease on potato, and its relationship to thiabendazole sensitivity. Dee Ann Benard and Piara S. Bains. Soil and Crop Diagnostic Centre, 6909-116 St., Edmonton, Alberta T6H 4P2; and (P.S.B.) Crop Diversification; Centre North, R.R. 6, Edmonton, Alberta T5B 4K3. Genomic in situ hybridization to identify Haynaldia villosa chromatin in wheat lines carrying resistance to the wheat curl mite. Qin Chen, R.L. Conner, and A. Laroche. Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta TU 4BL Impact of fungicide application on the incidence of blossom blight in alfalfa in 1995. B.D. Gossen, L.M. Harrison, and J. Holley. Agriculture Canada Research Centre, Saskatoon, Saskatchewan S7N 0X2; (L.M.H.) Alberta Agriculture, Fairview, Alberta TOH 1L0; and (J.H.) Crop Diversification Centre, Brooks, Alberta TO] 0J0. Genetic differences revealed between two isolates of Paulownia witches' broom phytoplasma in Korea by the RFLP analysis of 16S rDNA sequence. S.S. Han, L. Jiang, A.H. Khadhair, C. Hiruki, W.H. Yeo, and Y.H. Kim. Department of Forest Resources, Cheonbuk National University, Korea; (L.J., A.H.K., and C.H.) Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5; and(W.H.Y.) Forestry Research Institute, Seoul, Korea Sclerotinia sclerotiorum causes blossom blight of alfalfa. J.D. Holley, R. Linowski, B. Gossen, and L. Harrison. Crop Diversification Centre, Brooks, Alberta TIR IE6; (R.L.) Medicine Hat College, Brooks Campus, Brooks, Alberta TIR IE6; (B.G.) Agriculture and Agri-Food Canada Research Centre, Saskatoon, Saskatchewan S7N OX2; and (L.H.) Provincial Building, Alberta Agriculture Food and Rural Development, Fairview, Alberta TOH ILO. Infection of canola pollen by Sclerotinia sclerotiorum. H.C. Huang, E. G. Kokko, R. S. Erickson, and R. K. Hynes. Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta TU 4B1; and (R.K.H.) Agrium Inc., 402-15 Innovation Boulevard, Saskatoon, Saskatchewan S7N 2X8. Differential display of mRNA identifies three cDNA clones that are related to the pathogenesis in tobacco stunt virus-infected tobacco leaves. L. Jiang and C. Hiruki. Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5. Attenuation of potato leafroll luteovirus infection and disease symptoms in genetically modified potato plants. L.M. Kawchuk, D.R. Lynch, G.C. Kozub, R.R. Martin, and B Farries. Agriculture and Agri-food Canada, PO Box 3000 Main, Lethbridge, Alberta TU 4B1; and (R.R.M.) Agriculture and Agri- Food Canada, 6660 NW Marine Drive, Vancouver. British Columbia V6T 1X2. Molecular diagnosis of alfalfa witches'-broom phytoplasma in three leafhopper species and alfalfa plants from the Peace River area. A.H. Khadhair, S.F. Hwang, and C. Hiruki. Alberta Environmental Centre, Bag 4000, (S.F.H.) Vegreville, Alberta T9C 1T4; and (C.H.) Department of AFNS, University of Alberta, Edmonton, Alberta T6G 2P5. Fungicidal control of entomosporium leaf and berry spot of saskatoon. Ralph M. Lange, Piara S. Bains, and Ronald J. Howard. Crop Diversification Centre, North, R.R.6, Edmonton, Alberta T5B 4K3; and (R.J.H.) Crop Diversification Centre, South, SS 4, Brooks, Alberta TIR 1E6. Identification of a DNA fragment linked to the bunt Bt- 10 resistance gene and its utilisation for marker-assisted selection in hexaploid wheat lines. André Laroche, Tigst Demeke, and Denis A. Gaudet. Agriculture and Agri-Food Canada, P.O. Box 3000 Main, Lethbridge, Alberta TU 4B1. Hybridization among pathotypes of Ustilago bullata . G.D. Turnbull and B.D. Gossen. Agriculture Canada Research Centre, Saskatoon, Saskatchewan S7M 0X2; and (B.D.G.) Alberta Environmental Centre, Vegreville, Alberta T9C JT4. The influence of tillage and nitrogen fertilizer on barley foliar diseases. T.K. Turkington, G.W. Clayton, and P.A. Burnett. Alberta Agriculture, Food & Rural Development, Lacombe, Alberta T4L 1W8; Agriculture & Agri-Food Canada, Alberta (G.W.C.) Beaverlodge, Alberta T0H 0C0; and (P.A.B.) Lacombe, Alberta T4L JWl. Preservation of dehydrated phytoplasma-infected Paulownia leaf tissue by quick drying with a microwave oven for molecular analysis. Keri Wang, AH. Khadhair, and C. Hiruki. Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, T6G 2P5.

Transmission of Helminthosporium solani from potato seed tubers and effects of soil conditions, seed inoculum and seed physiology on silver scurf disease

SUMMARYThe transmission of silver scurf (Helminthosporium solani) disease of potatoes was examined in field experiments at Cambridge University Farm in 1988–90. Treatment factors examined were seed size, seed age, seed incubation, soil moisture regime and planting date. A laboratory experiment investigated the viability of conidia of Helminthosporium in soil stored under different conditions.Incubation of seed at high humidity before planting increased sporulation of Helminthosporium on seed tubers after planting and fewer conidia were produced from small seed than from larger seed. Delay in planting caused more rapid growth of Helminthosporium on seed tubers after planting.Early planting and late harvesting increased the severity of silver scurf on progeny tubers. Severity of silver scurf was also increased by ageing seed and by incubating seed. Weight loss of potato tubers during storage tended to be greater from treatments with most severe silver scurf in all years but a significant linear regression of weight loss on silver scurf severity was found in only one year out of three from a late harvest. The viability of conidia added to soil was found to decrease rapidly so that by 10 weeks after addition, < 1% of conidia were apparently viable.

Effects of wounding fungicide-treated potato seed tubers on silver scurf disease on daughter tubers at harvest

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.

Resistance to thiabendazole in isolates of Helminthosporium solani, the cause of silver scurf disease of potatoes

Isolates of Helminthosporium solani were obtained from potato tubers and cultured on agar containing thiabendazole. Some grew on agar containing 100 mg/l and these were classified as resistant, whereas sensitive isolates produced no mycelial growth on agar containing 5 mg/l. Isolates were also found that were intermediate in their sensitivity to the fungicide. All isolates from Scottish virus tested stem cutting stocks (VTSC) on two farms were resistant whereas those from another farm were sensitive to the fungicide. The proportion of resistant isolates from eight English once‐grown seed stocks ranged from 0 to 96%. There has been no previous report of fungicide resistance in H. solani and the possible reasons for these results and their implications are discussed.

Control of silver scurf (Helminthosporium solani) disease of potato with benomyl and thiabendazole

SUMMARYBenomyl and thiabendazole, applied as dusts to seed potatoes before chitting (sprouting), reduced the incidence of silver scurf disease on the progeny at lifting and during subsequent storage. Treatment of seed tubers 4 months prior to planting almost completely suppressed sporulation during storage, even under conditions very favourable for the growth of the fungus.The fungicides appeared not to act systemically because developing tubers grown from treated seed were just as susceptible to infection after inoculation as those from untreated. Control was due to effective inhibition of sporulation on the surface of diseased seed tubers after planting.There was no reduction in the amount of disease in subsequent generations of potato crops without further fungicidal treatment. Seed virtually free from silver scurf, produced from seed treated with fungicide in the previous year, yielded progeny with as much disease as progeny from untreated seed stocks.

Use of 2-aminobutane as a fumigant for control of gangrene, skin spot and silver scurf diseases of potato tubers

Fumigation of tubers with 2-aminobutane (sec-butylamine) gas at a dosage of 200 mg/kg in simply made fumigation chambers gave very good control of the diseases gangrene (caused byPhoma exigua var.foveata) and skin spot (Oospora pustulans) if treatment was done within 14 days of harvesting. Some control of silver scurf disease (Helminthosporium solani) was also obtained, but results were always poorer than with gangrene or skin spot. Fumigation did not control tuber blight (Phytophthora infestans), dry rot (Fusarium solani var.caeruleum) and did not kill the sclerotia ofRhizoctonia solani.