Search

In Hokkaido potato fields, tubers produced from the plants with leaf curl symptoms caused by potato leaf roll virus (PLRV) were noted to be more densely covered with Rhizoctonia sclerotia. This observation led us to hypothesize that potato infected with PLRV would have an increased susceptibility to Rhizoctonia solani. To test this hypothesis, in a pot experiment, we inoculated PLRV-infected mother tubers with Rhizoctonia. As a result, PLRV-infected plants produced significantly fewer and smaller tubers than virus-free plants did, suggesting that PLRV-infected plants are more susceptible than virus-free plants to R. solani. Virus-free seed tubers should thus be used to reduce Rhizoctonia diseases. [ABSTRACT FROM AUTHOR]

An integrated approach was made to control the black scurf of potato (Solanum tuberosum Linn.). Potato is one of the important crop and the fourth largest grown crop after rice, wheat and maize in the world. The pathogen was isolated from naturally infected tubers and the fungus was purified. In the pathogenicity test the symptoms were found on tuber, stem and stolon also. The efficacy of organic amendments (Vermicompost, Neem cake and Farm Yard Manure) was evaluated as soil application alone or in combination with the antagonist (T. harzianum). The Vermicompost and Neem cake both found effective in reducing the Black Scurf Disease Index (BSDI) while FYM was less effective in controlling the black scurf, stolon and stem canker. The Vermicompost and Neem cake also promote the growth of the plant i.e. increasing the shoot length, seed size and formation of tubers per plant was increased. The yield was also increased by the Vermicompost and Neem cake. The organic amendments can be too useful in reducing the soil-borne disease. [ABSTRACT FROM AUTHOR]

A three-year study was conducted in 1999, 2001, and 2002 to examine the influence of seed-borne inoculum and fludioxonil+mancozeb seed treatment on silver scurf (caused by Helminthosporium solani) development on progeny tubers at six locations under different potato rotations in the semi-arid U.S. Pacific Northwest. Disease-free pre-nuclear seed and diseased generation 3 seed was either treated or not treated with fludioxonil plus mancozeb, planted, and progeny tubers were harvested and then evaluated for silver scurf incidence and severity. Experiments were conducted in the southern Columbia Basin (Oregon), northern Columbia Basin (Washington), central Oregon, southern Oregon, western Idaho, and eastern Idaho under short (<3 years), normal (3-5 years), and long (>5 years) potato rotations over the three years for a total of 19 location-year-rotation combinations. Significant differences were observed among years and locations with disease incidence being highest in central Oregon. Progeny tubers from untreated generation 3 seed had significantly higher silver scurf incidence (18.4 %) and severity (1.3) compared to untreated progeny tubers from pre-nuclear seed (1.2 % and 0.04 for incidence and severity, respectively). Seed treatment with fludioxonil+mancozeb reduced incidence (3.8 %) and severity (0.2) significantly compared to the untreated control (15.8 % and 1.1 for incidence and severity, respectively). Significant ( P < 0.0001) interactions between treatments and location-year-rotation were observed and additive main effects multiplicative interaction analysis discriminated those with high incidence, severity, and variability. These data indicate that seed, not soil, is the primary source of progeny tuber infection in the field in the Pacific Northwest. For long term storage, purchase of clean seed is an essential component for managing silver scurf. [ABSTRACT FROM AUTHOR]

Potato tubers were collected and evaluated for symptoms and signs of black dot, silver scurf, and Verticillium wilt to determine the effect of extended crop rotations on disease incidences in the Columbia Basin. Incidence of tubers with black dot collected from storage significantly decreased as the number of years between potato crops increased from 3 to 5 years and beyond and significantly increased as the number of previous potato crops increased to 16. The highest incidence of black dot (range of 73 to 98%) was from fields rotated out of potatoes for 1 to 3 years. The mean incidence of black dot was 56% for fields out of potatoes for 0 to 4 years and 12% for fields out of potatoes 5 and more years. A low incidence (0 to 9%) of black dot was detected at 15 years out of potatoes. Years out of potato and number of prior potato crops accounted for 71% of the variability associated with the incidence of black dot. Severity of black dot on tuber periderm peels significantly increased as incidence of tuber periderm peels with Colletotrichum coccodes increased. Coefficient of determination was 0.87 for log severity on regressed on black dot incidence. Incidence of silver scurf was highest from fields out of potatoes for 1 year. Incidence of silver scurf infected tubers significantly increased as the number of previous potato crops increased due to short rotations between potato crops. Incidence of tubers with Verticillium dahliae was not related to years between potato crops or number of previous potato crops. The present study confirmed that black dot can be reduced with rotations out of potatoes greater than 5 years. [ABSTRACT FROM AUTHOR]

Helminthosporium solani is a slow-growing fungal pathogen belonging to the family Massarinaceae. It causes blemishes on potato tubers, affecting processing and fresh market trade. Despite its worldwide distribution, little is known about the biology of H. solani. Here we report the generation of a draft genome sequence of H. solani with an estimated genome size of ~35 megabases, for use in phylogenetic and pathogenicity studies of this fungal pathogen. This sequence is also the first reference genome within the family Massarinaceae. We identified a large suite of genes in the H. solani genome that encode putative cell wall degrading enzymes. Based on comparison with other genomes, we speculate that H. solani is a hemibiotroph or necrotroph. The presence of a large number of genes in the glycoside hydrolase (GH) 10 and 43 families, which aid in the hydrolysis of glucoronoarabinoxylan, also suggests that H. solani may be able to survive on grass hosts and indicates the need to re-examine the life cycle and host range of this pathogen. [ABSTRACT FROM AUTHOR]

Isolates (a total of 129) of Rhizoctonia solani were collected from black scurf on potato tubers from different potato-growing regions in New Zealand. Sequence analysis of the nuclear ribosomal DNA internal transcribed spacer (r DNA- ITS) regions from these isolates identified three anastomosis groups ( AGs), AG-3 PT, AG-2-1 and AG-5. Isolates classified as AG-3 PT were widely distributed, whereas AG-2-1 and AG-5 were confined to distinct locations. Sequence heterogeneity was identified in the ITS regions of 100 AG-3 PT and AG-2-1 isolates. Variation in the sequence and length of the r DNA- IGS1 region was also observed for selected isolates of AG-3 PT and AG-2-1. Phylogenetic studies found all AG-2-1 isolates belong to AG-2Nt, a subset of AG-2-1 previously associated with solanaceous crops in other countries. AG-2-1 isolates were consistently more aggressive than those of AG-3 PT. Delayed emergence, severe infection on stolons, formation of aerial tubers and considerable yield losses were associated with AG-2-1, but they caused negligible black scurf. In contrast, AG-3 PT caused black scurf on progeny tubers but variable effects on stem emergence and stolons. Furthermore, AG-2-1 isolates caused severe tuber malformation, but isolates of other AGs did not. This is the first report on the AG composition, genetic variability and pathogenicity of R. solani isolates associated with black scurf of New Zealand potatoes. [ABSTRACT FROM AUTHOR]

Silver scurf, caused by Helminthosporium solani, and black dot, caused by Colletotrichum coccodes, cause tuber blemishes on potato ( Solanum tuberosum L.) which affect processing and fresh market trade. Tubers from ten cultivars were collected at harvest from three organic farms in Wisconsin and categorized as symptomatic or asymptomatic based on visual symptoms of silver scurf and black dot and/or signs of H. solani and C. coccodes. Tuber incubation and PCR assays were performed on asymptomatic tubers to detect H. solani and C. coccodes. Tuber incubation and PCR assays were in slight to fair agreement (kappa coefficient <0.4) for detecting both pathogens. Most asymptomatic tubers tested were positive by one or both assays for H. solani (75 %) or C. coccodes (94 %). Minituber inoculation assays were also performed to screen potato lines for resistance to silver scurf. Of the 14 lines tested, a diploid interspecific hybrid, C287, had consistently low sporulation, suggesting it has partial resistance to silver scurf. Since the majority of tubers harvested are already infected with one or both pathogens further research should focus on organically acceptable management practices that may inhibit disease development in field and in storage. [ABSTRACT FROM AUTHOR]

Abstract: Common scab, black scurf and silver scurf belong to serious diseases of cultivated potato that especially impair tuber quality. Tuber infection in 44 potato (Solanum tuberosum ssp. tuberosum L.) varieties was evaluated using two measures – severity and incidence of infected tubers. Both measures were highly correlated. An important result derived from this study supports fungicide application against potato late blight secondarily acts on reducing tuber infection by all evaluated pathogens. Therefore, the conventional potato growing seems to be more effective compared to ecological growing. The pedigree analysis of 44 varieties indicated the presence of Solanum demissum genotypes in the variety genome may negatively affect variety response to Helminthosporium solani presence. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Many naturally occurring plant volatile compounds are known for their anti-fungal properties. In this study, acetaldehyde and 2E-hexenal were chosen as prototype volatiles in order to investigate the use of volatile compounds for control of blemish pathogens in fresh-pack potato packaging. Pure cultures of the three main potato blemish pathogens, Pectobacterium atrosepticum (bacterial soft rot), Colletotrichum coccodes (black dot), and Helminthosporium solani (silver scurf), were used in the study. Pathogen cultures were exposed to the pure volatiles that were injected into the atmosphere of sealed jars for 4–8days at 23°C. Results showed that 2E-hexenal was the most effective of the two volatiles with 5μL/L providing complete inhibition of growth for all three pathogens in vitro. Cytological studies showed that a concentration of 2.5μL/L of 2E-hexenal was capable of inhibiting germination in both fungal pathogens. These results suggest that the primary mode of action of 2E-hexenal was inhibiting germination for fungi and suppressing bacterial growth. The quantities required to achieve pathogen inhibition are extremely low. This study suggests that these volatiles may be used to effectively manage potato postharvest blemish diseases in storage. [Copyright &y& Elsevier]

A survey of the prevalence of skin blemish diseases in potatoes after the growing seasons of 2008 and 2009 was carried out on 247 potato lots representing different cultivars and production regions in Norway. The results showed the presence of silver scurf ( Helminthosporium solani) in all lots. Skin spot ( Polyscytalum pustulans) and black scurf ( Rhizoctonia solani) were found in 80% of the lots, and black dot ( Colletotrichum coccodes) and common scab caused by Streptomyces spp. were present in 50-70%. Also, powdery scab ( Spongospora subterranea) occurred in 65-80% of the lots, and root-lesion nematodes ( Pratylenchus spp.) were detected in 60% of the sub-samples that exhibited symptoms of common scab. [ABSTRACT FROM AUTHOR]

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 conclusion that ions Fe++ and NO2 − have toxic effects on the conidia and repressive effects on silver scurf development while NO3 − and NH4 + have no toxic effect on conidia and no repressive effect on silver scurf development. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Potato mop-top virus (PMTV) causes disease in both the growing plant and tubers (spraing) of potato and is transmitted by the plasmodiophorid Spongospora subterranea, the cause of powdery scab. The effect of temperature during plant growth on the transmission of PMTV from infected seed tubers and from infested growing media was investigated in a series of glasshouse experiments. Symptoms developed on foliage of plants derived from infected seed tubers but none developed when PMTV was transmitted by S. subterranea in soil. The incidence of foliar symptoms was greatest on plants grown at 12°C, less at 16°C, few at 20°C and absent at 24°C. The transmission of PMTV from infected seed tubers was not significantly affected by temperatures between 12 and 24°C, but when the virus was transmitted by S. subterranea, minimal tuber infection occurred at 24°C and no differences were recorded at temperatures between 12 and 20°C. The incidence of powdery scab on tubers was greatest at 12 and 16°C and very low at 20 and 24°C. However, the incidence and severity of root galling caused by S. subterranea, was greatest at 20 and very low at 24°C. The incidence of powdery scab was greater on tubers of plants derived from infected seed tubers grown in a fluctuating temperature regime of 12 h at 20°C followed by 24 h at 12°C than on those grown at a constant 20°C, whereas the incidence of tuber infection by PMTV and spraing was similar for both regimes. This demonstrates that infection of roots can occur at a higher temperature than that for powdery scab on tubers and that this root infection can enable the transmission of PMTV into the potato plant. [ABSTRACT FROM AUTHOR]

This work presents a bibliographic review of the silver scurf disease and its causal agent Helminthosporium solani (Dur. & Mont.) in potatoes (Solanum tuberosum L.). The disease has a worldwide distribution and for at least 15 year it has acquired increasing importance as a limiting factor in the production of these tubers. The review shows the economic importance of the disease, its detection on tubers as well as in the soil, and its isolation procedures. It also explains the life cycle of H. solani, which is not completely known yet. It also discusses the possibilities for controlling silver scurf by the use of fungicides, tillage and cultivation methods in the field, storage management, the use of antagonists, and through the breeding of new cultivars. [ABSTRACT FROM AUTHOR]

Isolates of Helminthosporium solani, the causal agent of silver scurf of potato, collected from multiple locations consistently show white sectoring and rings, differential coloration, and reduced sporulation in culture. It has been accepted that this growth pattern is normal for H. solani cultures. Scanning electron microscopy confirmed the presence of a contaminating fungus in close association with cultures of H. solani. Repeated hyphal tip isolation techniques were used to separate H. solani from the fungal contaminant. Resultant pure cultures of H. solani were uniformly black in color, without white sectors or rings. The contaminating fungus was identified as Acremoniurn strictum. The purpose of this study was to elucidate the relationship between A .strictum and H. solani, and evaluate the impact of the fungicolous A .strictum on the growth and biology of H. solani. In vitro studies demonstrated that A. strictum significantly reduced sporulation of H. solani isolates from 65 to 35%, spore germination from 53 to 43%, and mycelial growth from 40 to 32% compared with noncontaminated cultures of H. solani. These data indicate that A. strictum is antagonistic to H. solani, and can be considered a mycoparasite. A. strictum reduced H. solani conidia production on minitubers, thereby reducing inoculum for infection. However, treatment with A. strictum does not reduce silver scurf of previously infected tubers. Further studies are warranted to determine the full potential of A. strictum as a biological control agent of H. solanii-incited silver scurf of stored potato tubers and the most effective manner of use. [ABSTRACT FROM AUTHOR]

The effectiveness of various seed-tuber treatments was evaluated for control of silver scurf on potato (Solon urn tube rosum), caused by Helminthosporium solani, at four locations in Washing- ton and Oregon using seed-tubers from the same source. Disease incidence was determined at harvest and following storage, and differed significantly among locations. The highest incidence of disease was observed at Redmond, OR and the lowest was at Hermiston, OR. Significantly less silver scurf occurred on progeny-tubers, regardless of location, when seed was treated with the fungicide treatments fludioxonil, fludioxonil + quintozene, azoxystrobin, or thiophanate- methyl + mancozeb compared with the nontreated control. A sample of H. solani from seed planted in the Columbia Basin of Washington and Oregon was assessed for resistance to thiabendazole (TBZ) and thiophanate-methyl (TPM). Sensitivity of 20 isolates of H. solani to TBZ was determined on V8 media amended with TBZ. Four isolates, selected as a subset from the 20 isolates tested for TBZ sensitivity, were tested for resistance to TPM, mancozeb, and TPM + mancozeb on amended V8 media. Isolates differed significantly in sensitivity to both chemicals. Thirteen isolates out of the 20 tested were resistant to TBZ. One out of the four subsets of isolates was resistant to both TBZ and TPM. TBZ sensitivity was not related to geographic origin of the isolates. Variation in resistance was evident on a small scale as seen with one resistant and one sensitive isolate collected from the same tuber. This is the first report that silver scurf incidence is affected by location despite the same tuber-seed source and also the first report of TBZ and TPM resistant isolates of H. solani from the Columbia Basin (Oregon and Washington) production area. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Evaluates the efficacy of different fungicides applied to potato seed tubers for control of silver scurf. Influence on total and marketable yields; Effects on silver scurf severity; Influence of experimental locations on silver scurf development.

Investigates silver scurf as an economically important disease of potatoes. Biology of the pathogen; Epidemiology of the disease; Pathogen detection; Integrated control measures for the management of silver scurf in both field and potato tuber stores.

When potato tubers with small amounts of silver scurf at lifting (less than 10 per cent of surface cover) were stored over periods of about five months in a dry condition, very little silver scurf developed irrespective of storage temperature. At high humidity, there was little disease after storage at 5°C and very little at temperatures below 4°C: moderate to severe infection (20 per cent or more of surface area covered) occurred at storage temperatures of about 6°C or above. Weight losses of tubers with severe silver scurf (50 per cent surface area affected) stored in a dry atmosphere for 27 weeks were greater than those of tubers with moderate (25 per cent area cover) and slight infection (5 per cent area cover), 8.5, 5.9 and 4.5 per cent respectively. However, tubers stored in a dry atmosphere showed greater weight losses than tubers stored in a humid atmosphere, despite having less silver scurf infection. Low storage temperatures aggravated symptoms of skin spot. Slightly affected seed tubers gave rise to more silver scurf in the subsequent crop than tubers with over 75 per cent surface affected, and crops from light sandy soils showed more infection at lifting than crops from heavier soils. These differences persisted during storage, but were largely masked if storage conditions favoured disease development, indicating that in normal stocks there is always an adequate inoculum, at lifting to produce severe symptoms. Very small amounts of inoculum giving little silver scurf after storage, resulted from using seed from stem-cutting material or by treating seed with benomyl. [ABSTRACT FROM AUTHOR]

Discusses the abstract of the article "Involvement of antibiosis in the biocontrol of potato silver scurf by different bacteria," by C. Martinez, J.-N. Simard, J. Labonte, R.R. Belanger and R.J. Tweddell, submitted to the 2003 Canadian Phytopathological Society Annual Meeting in Montreal, Quebec.

A correction to the article "Influence of Location, Year, Potato Rotation, and Chemical Seed Treatment on Incidence and Severity of Silver Scurf on Progeny Tubers" that was published in the 2015 issue is presented.

Presents an abstract of the study `Chemical control of silver scurf and anthracnose of potatoes with prochloraz,' by F.D.N. Denner et al which was presented at the 33rd annual congress of the South African Society for Plant Pathology held from January 15-18, 1995 in South Africa.