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1.
A total of 109 samples of potato seed tubers imported to Jordan from France, Netherlands and Denmark during the 2007/2008 growing seasons were surveyed for 10 different diseases caused by fungi and fungus‐like organisms to determine the prevalence of different tuberborne diseases and to evaluate the efficacy of the current visual examination procedures in detecting different potato diseases. The results demonstrated that most potato seed tuber lots imported to Jordan were infected with one or more of the following potato pests: Colletotrichum coccodes (black dot) (66.0%), Rhizoctonia solani (black scurf) (42.4%), Helminthosporium solani (silver scurf) (92.6%), and Spongospora subterranea (powdery scab) (13.8%). Just over a quarter (25.7%) of all lots examined in this study were found to exceed the acceptance limits for one or more potato diseases according to the Jordanian standards. This study suggests that the current visual examination procedure is not adequate to detect all tuberborne diseases of potato and to estimate their incidence and severity precisely.  相似文献   

2.
Methods are described for the extraction and analysis by gas-liquid and high-pressure liquid chromatography of the fungicide imazalil, 1-(β-allyloxy-2, 4-dishlorophenethyl) imidazole, on potatoes. Before storage, over 80% was recovered from potatoes treated with 0.01–3.0 mg imazalil kg?1, with a detection limit of 2 μg kg?1. Imazalil applied to potatoes at 10 g t?1 before storage decreased the incidence of gangrene (Phoma exigua), silver scurf (Helminthosporium solani), skin spot (Polyscytalum pustulans) and black scurf (Rhizoctonia solani), and was at least as effective as thiabendazole applied at 40 g t?1. At 1 g t?1 it also decreased skin spot and silver scurf. Incidence of black dot (Colletotrichum coccodes) was unaffected by these fungicide treatments.  相似文献   

3.
Controlled‐environment and field experiments were done to quantify the individual contribution of seed‐tuber and soilborne inoculum of Colletotrichum coccodes in causing black dot disease of potato tubers. Seed‐tuber and soilborne inocula of C. coccodes were quantified using an existing real‐time PCR assay and related to subsequent incidence and severity of disease. In four field trials, a controlled‐environment experiment and through the monitoring of 122 commercial crops, seed‐tuber inoculum was found to be relatively less important than soilborne inoculum in causing black dot, and the level of seed‐tuber inoculum did not significantly affect either the incidence or severity of disease or the percentage of progeny tubers deemed unmarketable. By contrast, soilborne inoculum had the potential to result in high levels of disease and the level of C. coccodes soil infestation (pg DNA g?1 soil) was found to have a significant effect. At soil infestation levels below 100 pg DNA C. coccodes g?1 soil, 7% of commercial crops had an incidence of black dot greater than 20%, increasing to 40% and 57% of crops at levels of 100–1000 pg g?1 and >1000 pg g?1 soil, respectively. These arbitrary threshold levels for soilborne inoculum related to disease risk are discussed. Interpretation of disease risk based on inoculum levels must, in the future, be informed by agronomic variables and potential control strategies.  相似文献   

4.
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 (rDNA–ITS) regions from these isolates identified three anastomosis groups (AGs), AG‐3PT, AG‐2‐1 and AG‐5. Isolates classified as AG‐3PT 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‐3PT and AG‐2‐1 isolates. Variation in the sequence and length of the rDNA–IGS1 region was also observed for selected isolates of AG‐3PT 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‐3PT. 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‐3PT 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.  相似文献   

5.
In an attempt to better understand the importance of tuber-borne inoculum in black dot development, several potato cultivars were inoculated with various Colletotrichum coccodes isolates. Symptoms developed first on underground organs (starting 2 weeks after inoculation on roots, and later on stolons and tubers) of inoculated plants; stem infections developed only after 7–10 weeks, depending on the cultivar. Infection with C. coccodes resulted in a reduction in numbers of stolons and tubers in cv. Bintje, but not in the later maturing cv. Roseval. Significant isolate by cultivar interactions were detected from the analysis of root symptoms after inoculation of three potato cultivars (Bintje, Spunta and Desiree) with five C. coccodes isolates. Such an interaction was also detected for stolon/tuber symptoms at the latest scoring date (98 days after inoculation), but not at earlier dates (58, 70 and 84 days after inoculation). These results suggest that protocols based on root colonization might be used for investigating cultivar response to black dot and pathogenicity of C. coccodes isolates, and that some specificity exists in the reaction of potato genotypes to this pathogenic fungus.  相似文献   

6.
The position of plants withRhizoctonia solani sclerotia (black scurf) on progeny tubers was mapped for an experimental field at Haren where potatoes were grown continuously and in rotation with other crops for five successive years, and for another field at Borgercompagnie with a 12 frequency of potatoes during three potato crops. Initially, the distribution of plants with black scurf on both fields was rather dense and homogeneous. In the following years the distribution became heterogeneous and patchy. The local decline ofR. solani AG 3 (the common potato pathogen) in Haren was apparently caused by an unknown factor selectively suppressingR. solani AG 3, while simultaneouslyR. solani AG 5 increased in mass. This AG 5 type proved to be an inferior competitor of AG 3 on the potato plant in a laboratory experiment. The specificR. solani antagonistVerticillium biguttatum did not play a role. A similar factor could have reduced the formation of black scurf in the experimental field at Borgercompagnie, whereV. biguttatum was also too infrequent to account for the decline.R. solani AG 5 was not present here and could not indicate the presence of a selective factor against AG 3.  相似文献   

7.
The effects of post‐harvest curing and storage temperature on severity of black dot, caused by Colletotrichum coccodes, were investigated for potato crops grown for different crop durations (days from 50% emergence to harvest) in soils that posed a low, medium and high risk of disease. In field trials over four growing seasons (2005–8), black dot severity at harvest increased with increasing crop duration, within the range 103–146 days from 50% emergence to harvest (P < 0.05). In field trials over three growing seasons (2006–8), black dot severity on tubers at harvest increased significantly with increasing soil inoculum in each year, within the range 43–4787 pg C. coccodes DNA/g soil (P < 0.05). Storage trials were conducted to measure the influence of accumulated post‐harvest temperature on black dot. In 2005, no difference in black dot severity was observed on tubers stored for 20 weeks at 2.5 and 3.5 °C. In 2006 (but not 2007), increasing the duration of curing after harvest from 4 to 14 days increased black dot severity on tubers from 8.9 to 11.2% (P < 0.01) in long duration crops (>131 days after 50% emergence) grown under high (>1000 pg C. coccodes DNA/g soil) soil inoculum. The number of days of curing did not affect disease severity for shorter duration crops grown at high soil inoculum, or on crops grown at medium or low (100–1000 and <100 pg C. coccodes DNA/g soil, respectively) soil inoculum concentrations. Soil inoculum and crop duration together provided a reasonable prediction of black dot severity at harvest and after a 20‐week storage period.  相似文献   

8.
In recent years black dot ( Colletotrichum coccodes ) has become an economically important disease problem in potato ( Solanum tuberosum ). It is characterized by silvery lesions on the tuber surface which result in a deterioration in skin quality. In addition to causing tuber blemish symptoms, C. coccodes also causes symptoms on stems and foliage, resulting in crop losses in some countries, and is implicated as a factor in the potato early dying disease complex. In the past, the incidence and severity of black dot might have been underestimated, as tuber symptoms were often mistaken for silver scurf ( Helminthosporium solani ). Inoculum of C. coccodes can be both seed tuber- and soilborne, and disease control is difficult as there are few chemical control methods and little resistance in commercial cultivars. Cultural control options offer the only potential means to control this disease at present. Current developments in rapid and specific PCR-based detection methods are being used to address epidemiological questions.  相似文献   

9.
Field trials were carried out over a 4 year period (2004–2007) to determine the effect of agronomic factors, specifically cultivar resistance, irrigation, crop duration and chemical control (in‐furrow application of azoxystrobin), on black dot development on potato tubers grown in fields where soilborne inoculum of Colletotrichum coccodes was present. In 2004, 2005 and 2006, two field trials were performed each year and in 2007, 19 mini‐field trials were carried out across Scotland and England. Cultivar resistance was clearly demonstrated to be an effective method of reducing black dot disease severity on tubers (described here as the percentage of unmarketable tubers, i.e. those with symptoms covering a surface area of >10%). In the four field trials carried out in 2004 and 2005, in irrigated and fungicide‐untreated plots, 43·8% of tubers of cv. Maris Piper were unmarketable, compared with 17·0% of tubers of cv. Sante. Assessments of disease development on underground plant parts (stems, stolons and roots) revealed that cultivar resistance acted only at the tuber level, as disease symptoms on other parts were often high irrespective of published disease resistance ratings. Irrigation increased the severity of disease on tubers in two trials (England 2004 and 2006), but its effect was less significant when rainfall was high. Delaying harvest by 2 weeks increased disease severity in all six trials, whilst application of azoxystrobin consistently reduced black dot severity. There were significant interactions between factors. The results clearly show how black dot disease severity can be reduced through an integrated approach to disease management.  相似文献   

10.
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 fluorogenic probe were designed using the original primer sequences to perform real-time quantitative (TaqMan) PCR. The same levels of sensitivity for specific detection of H. solani in soil and tubers were obtained during first round mboxTaqMan-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.  相似文献   

11.
Black dot, caused by Colletotrichum coccodes, is a common disease of potato in Turkey, affecting tuber quality and yield. The objectives of the current study were to characterize vegetative compatibility groups (VCGs) of C. coccodes isolates from three regions in Turkey, and to assess the correlation between VCGs and aggressiveness of isolates on potato. A total of 147 C. coccodes isolates were recovered from plants showing typical black dot symptoms on stolons, roots and stems. The frequency of nitrate non‐utilizing (nit) nit1/nit3 and NitM phenotypes were 79% and 21%, respectively. Complementation between nit mutants of the isolates and eight European/Israeli EU/I‐VCG tester isolates was used to characterize the VCGs. Amongst the tested isolates, 33.3% were assigned to EU/I‐VCG6, 21.8% to EU/I‐VCG8, 15.7% to EU/I‐VCG4. EU/I‐VCG1, EU/I‐VCG3, EU/I‐VCG5 and EU/I‐VCG7 were classified at 1.4%, 3.4%, 4.8% and 5.4%, frequency, respectively. No isolate was assigned to EU/I‐VCG2 group, while 21 isolates (14.3%) were not assigned to any of the EU/I‐VCGs. The pathogenicity tests indicated significant differences in aggressiveness of the isolates with respect to sclerotia density on potato tissues. The highest densities of sclerotia on roots and crown were obtained with EU/I‐VCG6 isolates and the lowest with EU/I‐VCG1, EU/I‐VCG3 and EU/I‐VCG5 isolates. The results demonstrate that there is significant VCG diversity among C. coccodes isolates from potato plants in Turkey.  相似文献   

12.
Relationships between diseases caused by Rhizoctonia solani on different parts of potato plants ( Solanum tuberosum ) at different stages of crop growth were investigated under selected agronomic conditions. The effects of different densities of tuber-borne inoculum, date of planting, irrigation, size of seed tubers and their interactions on the incidence of stem and stolon canker during crop growth, the incidence and severity of black scurf and the yield of progeny tubers at harvest were quantified in a multifactorial experiment. Differences in the incidence of stem canker, stolon canker and black scurf were dominated by the effect of density of inoculum on seed tubers at planting. Highly positive correlations between the disease variables indicated a close relationship between the incidence of disease at each stage of crop growth although the degree of association between variables measured at an early growth stage and those measured at progressively later stages of crop growth weakened as the time interval increased. Total yield of progeny tubers was not affected by the density of tuber-borne inoculum although there was a shift in the size distribution, with a decrease in the yield of main-sized tubers and an increase in the yield of baker- and oversized tubers at the higher density of inoculum. Of the remaining factors, the effect of season tended to be more pronounced than any of the agronomic treatments although the use of irrigation and later dates of planting did influence the incidence of infection to a limited extent.  相似文献   

13.
Phosphites (Phi) are alkali metal salts of phosphorous acid, with the ability to protect plants against different pathogens. In this research, the effect of Phi applied to potato plants on severity of three important potato diseases in Argentina was assessed. Seed tubers and foliage of potato cvs Shepody and Kennebec were treated with Phi to assess effects on resistance against Phytophthora infestans, Fusarium solani and Rhizoctonia solani. Protection resulting from Phi treatment in seed tubers was high against P. infestans, intermediate against F. solani, and low against R. solani. In addition, seed tubers treated with calcium or potassium phosphites (CaPhi and KPhi, respectively) at 1% of commercial product emerged earlier than untreated ones. When Phi were foliarly applied two or four times at different doses, high levels of protection against P. infestans were achieved in both cultivars. Higher protection was observed in Kennebec when CaPhi was applied, while in Shepody this was true for KPhi. Expression of β-1,3-glucanases was induced at different times after treatment but no correlation between β-1,3-glucanases expression and foliar protection level was found. On the other hand, Phi positive protection effects did not produce negative effects in plant growth. Leaves from CaPhi-treated plants showed a darker green colour than leaves from control plants; also an increase in Rubisco protein and a delay in crop senescence was observed.  相似文献   

14.
Potato seed certification is a disease management tool that minimises the risk of spreading seed tuber-borne inoculum of infectious diseases. Traditionally, certification sampling strategies have relied upon visual assessment of a seedlot from samples taken at one or two points within the load of seed tubers. However methodologies in selection of tuber samples have not been critically assessed for their precision in estimating disease load. This study presents an analysis of 37 potato seedlots over a 3 year period. Analysis of sample data using receiver operating curves (ROCs) indicates that point sampling taking two samples of 100 tubers at the beginning and end of a seedlot gives equivalent disease estimation as a continuous sampling strategy taking ten samples of 20 tubers randomly throughout the seedlot, although at lower statistical precision. This was confirmed both by visual assessment of tuber-borne disease and by analysis of pathogen DNA content from tuber peel. Across the 3 years of study, powdery scab and black scurf were the major seed tuber-borne diseases recognised and this corresponded with high levels of pathogen DNA from peel analysis for both Spongospora subterranea and Rhizoctonia solani AG3 respectively.  相似文献   

15.
Information is reviewed on root infection of potato by the plasmodiophorid Spongospora subterranea f. sp. subterranea. This pathogen has long been recognized as the cause of root galls (hyperplasia) and the economically important disease powdery scab on tubers (modified stolons). The significance for plant productivity of the zoosporangium stages of the pathogen in potato roots has only recently begun to be documented. Two experiments are described that assessed effects of S. subterranea root infection on potato plant root function and productivity. A greenhouse experiment measured root function and plant parameters for eight potato cultivars with markedly different susceptibilities to tuber powdery scab. Water uptake and plant growth were reduced by S. subterranea inoculation in all eight cultivars. The magnitudes of these negative effects, and intensities of root hyperplasia, differed among the cultivars, but were not related to respective susceptibilities to tuber powdery scab. A field trial assessed root function and plant productivity for a cultivar (Iwa) that is very susceptible to Spongospora tuber and root diseases. Soil water content beneath uninoculated plants was consistently less than for inoculated plants, indicating that inoculation reduced water uptake (root function). Inoculation reduced shoot and root dry weights, and reduced weight of tubers per plant by 42%. Spongospora subterranea causes three diseases of potato: root membrane dysfunction, root hyperplasia and tuber powdery scab. The root diseases caused by the pathogen are likely to be important both for powdery scab management and for deleterious effects on potato crop yields.  相似文献   

16.
Black dot, caused by Colletotrichum coccodes , is of potential concern to potato production in France as part of the tuber-blemishing disease complex. The lack of information about the actual distribution of the pathogen in potato-producing areas led to a survey of the occurrence of the disease. Black dot symptoms were observed on roots, stems and/or tubers of the 82 potato cultivars examined in 1994. A baiting bioassay, using cuttings of potato cultivars Bintje and Urgenta, revealed the presence of the pathogen in all 37 soil samples tested, which had been collected throughout the main French potato growing areas. In vitro , growth of five C. coccodes isolates recovered from diseased potatoes grown in western and southern France was severely affected by imazalil, tolchlofos-methyl and, to a lesser extent, mancozeb and thiabendazole. Conversely, iprodione, flutolanil and pencycuron were ineffective in reducing the growth of these isolates. These data indicate that C. coccodes is widespread in French potato cropping areas, that currently popular cultivars are susceptible to the disease, and that at least some of the fungicides commonly applied to seed tubers are ineffective against the pathogen. A better diagnosis of the disease, but also the insensitivity of the pathogen to several chemicals frequently used on seed tubers for controlling black or silver scurfs, might thus provide explanations for the apparent increase in black dot occurrence in recent years.  相似文献   

17.
Effects of crop rotation on the incidence of soil-borne pathogens and on the performance of potato were investigated in five field experiments. Rotations differed in cropping frequency of potato and in crop sequence.Incidence of stem canker caused byRhizoctonia solani was strongly influenced by the cropping frequency of potato and not by crops with which the potato was alternated in the rotation. Cropping frequency of potato also affected the occurrence of black scurf, but less pronounced than for stem canker. The antagonistVerticillium bigutatum slightly reducedR. solani (black scurf) in plots on sandy soil continuously cropped with potato. Incidence of stem canker was also strongly affected by granular nematicides applied to the soil, nitrogen level and the cultivar grown.Stem infections byVerticillium dahliae depended on the cropping frequency of potato, by the crop with which the potato was alternated in the rotation and by the density and virulence of endoparasitic nematodes, especiallyMeloidogyne spp.Crop rotation had no effect at all on incidence of common scab on tubers, whereas the effect of cropping frequency of potato on netted scab was highly significant. When cultivars were grown susceptible to both scab types, netted scab supressed common scab.  相似文献   

18.
Powdery scab of potato, once established in a field, is difficult to control because of the longevity of the resting spores (cystosori) of the causal organism, Spongospora subterranea f.sp. subterranea. Host resistance is likely to be the most efficient in a long-term control strategy for preventing build-up of field inoculum and spread of the disease. Resistance screening of potato cultivars is mostly done in laborious field trials where disease development is likely to be unpredictable. A bioassay with potato tissue cultured plantlets and cystosori as inoculum is described and was tested for its potential to screen potato cultivars at an early stage for their relative susceptibility to powdery scab by comparing the lab results with field data. With cystosori inoculum of Swiss origin, the laboratory test showed clear differences between the potato cultivars in the severity of zoosporangial root infection which correlated better with ranked tuber infection data, compared to root galling. There are apparent differences in the relative trends in susceptibility between roots and tubers of five selected cultivars when using naturally infested soil instead of prepared cystosori as inoculum in the lab bioassay. Furthermore, differences in the severity of zoosporangial root infection of two selected cultivars were found when cystosori from different countries where used as inoculum. A possible host genotype × pathogen interaction is discussed. The bioassay has the potential to screen and select for resistant material at an early breeding stage thus making field trials not unnecessary but more economical. It will allow the use of a standard set of pathogen collections and facilitate testing for inoculum virulence in infested soils.  相似文献   

19.
A series of chemical and biological control agents were tested for compatibility with the Rhizoctonia-specific biocontrol fungus Verticillium biguttatum aimed at designing novel control strategies for black scurf (Rhizoctonia solani) and other tuber diseases in potato. The efficacy of chemicals, alone and in combination with V. biguttatum was tested in in vitro assays on nutrient agar plates, in bio-assays with minitubers and in the field. Generally, there were both antagonistic, neutral and additive interactions with V. biguttatum among the combinations tested; there were no indications for synergistic interactions. Broad-spectrum fungicides (azoxystrobin, chlorothalonil, thiabendazole) were fungitoxic to V. biguttatum as shown in in vitro assays, and hampered black scurf control by V. biguttatum in bio-assays. Oomycete-specific chemicals (cymoxanil and propamocarb) and various biocontrol strains (Gliocladium spp., Pseudomonas spp. and Trichoderma spp.) did not interfere with the growth of V. biguttatum on agar nutrient plates and did not affect black scurf control by V. biguttatum in co-applied treatments in the minituber bio-assay. Rhizoctonia-specific (pencycuron, flutalonil) fungicides co-applied with V. biguttatum showed additive effects on black scurf control. When combinations of V. biguttatum and cymoxanil or propamocarb were applied to immature potato tubers at green crop lifting, a reduction of both black scurf and Pythium- or Phytophthora-incited tuber rot was observed at harvest. In conclusion, the biocontrol fungus V. biguttatum is compatible with selected chemical control systems and may improve control efficacy in combination with Rhizoctonia-specific fungicides or may extend control spectrum in combination with Oomycete-specific fungicides.  相似文献   

20.
A collection of 241 isolates of Rhizoctonia solani obtained from potato plants grown in different areas in France was characterized for anastomosis grouping, symptomatology on tubers of different cultivars and sensitivity to three fungicides. Most isolates collected belonged to (anastomosis groups (AGs)) AG 3, but 2% and 4% of the isolates were AG 5 and AG 2-1. AG 3 and AG 2-1 isolates were mostly obtained from sclerotia on tubers, but all AG 5, some AG 3 and some AG 2-1 isolates were recovered from superficial tuber alterations, like deformations, corky or scabby lesions. Sclerotia were formed on tubers produced by healthy stem cuttings grown in soil artificially infested with AG 3, but not on tubers grown in soil infested with either AG 5 or AG 2-1. No variation in susceptibility to sclerotial formation was observed among five potato cultivars. In all cases, a large proportion of tubers showed superficial corky lesions, often associated with deformations. The proportion of tubers with lesions and deformations was highest in soil infested with AG 2-1 and significantly lower on cv. Samba in all treatments. All isolates were highly sensitive to flutolanil, iprodione and pencycuron, except the AG 5 isolates, moderately sensitive to pencycuron. These results show that, although AG 3 is the most common R. solani group on potato in France, AG 5 and AG 2-1 may be present. Isolates differed for pathogenicity. In vitro sensitivity to fungicides varied among AGs.  相似文献   

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