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1.
Late blight, caused by the oomycete Phytophthora infestans, is a threat to potato‐cropping systems worldwide. In the Ecuadorian Andes, despite a high late blight incidence in foliage, tuber blight is rare. In this work, the hypothesis that Ecuadorian Andean soils are naturally suppressive to P. infestans tuber infection was evaluated. Soils from four potato‐growing regions were assessed for disease suppressiveness by determining the effects of soil heat treatment on P. infestans sporangia and their ability to infect potato slices after 1, 8, 15 and 30 days of exposure to soils. Tuber infection after inoculation with P. infestans‐infested soils was consistently lower during the evaluation period compared with heat‐treated soils. Fresh, untreated soils affected germination and viability of P. infestans sporangia in a site‐dependent manner. In addition, the effect of heat treatment on soil bacterial communities was assessed through terminal restriction fragment length polymorphism analysis of the 16S rDNA gene region. Heat treatment disrupted bacterial community composition, and a subset of terminal restriction fragments (TRF) was either positively or negatively correlated with tuber infection. Bacterial TRF negatively correlated with tuber infection corresponded in fragment size to taxa with known ability to inhibit pathogens and promote plant growth. Finally, bacterial isolates obtained from untreated soils, which inhibited P. infestans growth in vitro, represented 22–47% of isolates recovered, and matched classes predicted by the TRFs. This work represents a first step in understanding the mechanisms behind the low incidence of tuber blight in Andean potato‐cropping systems.  相似文献   

2.
This study investigated the value of using real‐time monitoring of Phytophthora infestans airborne inoculum as a complement to decision support systems (DSS). The experiment was conducted during the 2010, 2011 and 2012 potato production seasons in two locations in New Brunswick, Canada. Airborne sporangia concentrations (ASC) of P. infestans were monitored using 16 rotating‐arm spore samplers placed 3 m above the ground. The first cases of late blight (2010 and 2011) were detected 6–7 days after the first ASC peak, and all samplers captured their first sporangia within the same week (at 3‐ and 9‐day periods). The cumulative ASC curve and the risk curves from two DSS (PLANT‐Plus and Pameseb Late Blight) had the same shape but different magnitudes. In both locations, the negative binomial distribution fitted the data better than the Poisson distribution, which is indicative of heterogeneity, and based on Taylor's power law, the heterogeneity increased with increasing ASC. Therefore, the present results suggest that spore‐sampling network devices may be a suitable approach for early detection of incoming inoculum and, when combined with DSS, represent a potential aid for targeting the optimal time to apply a disease‐control product. In this context, cumulative ASC can be a counterweight to the DSS risk estimate: a high risk combined with significant ASC will trigger fungicide spraying. Moreover, spore sampling can be used to assess the efficiency of management strategies by means of examining the area under the inoculum progress curve.  相似文献   

3.
The effects of strip cropping of potatoes with cereals or a grass‐clover mix in and perpendicular to the main wind direction on foliar late blight severity and tuber yield were studied in large‐scale field experiments in Germany. Disease progress was assessed in 12–18 sections per plot and yields determined from the same sections. In 2000, plot size was 3 × 10 m and there were no disease reductions apparently due to interplot interference. In 2001 and 2002, with plot sizes of 6 × 18 and 6 × 36 m in strip‐cropped potatoes, disease was significantly reduced by 9–20% and 4–12%, respectively, compared to pure stands of potato, with the greatest reductions in plots planted perpendicular to the wind and neighboured by grass‐clover. The most important factors contributing to disease reduction were loss of inoculum outside of the plots and barrier effects of neighbouring non‐potato hosts. Only 0–20% of the overall yield variation could be explained by the area under the disease progress curve, depending on cultivar and year. In one year disease effects on the yield of a moderately resistant cultivar were higher than on the yield of a susceptible cultivar. This was probably caused by differences in bulking behaviour. Nutrient limitation appeared to be more important than disease in reducing yields. Yields in the edge potato rows directly neighboured by cereals were significantly reduced in all 3 years, but competition by cereals did not change the disease–yield‐loss relationship. Strip intercropping might be a useful component in an overall management strategy to reduce incoming late blight inoculum.  相似文献   

4.
A specific and sensitive PCR assay for the detection of Phytophthora infestans , the cause of late blight of potato, in soil and plant tissues was developed. A P. infestans -specific primer pair (INF FW2 and INF REV) was designed by comparing the aligned sequences of rDNA internal transcribed spacer regions of most of the known Phytophthora species. PCR amplification of P. infestans DNA with primers INF FW2 and INF REV generated a 613 bp product, and species specificity was demonstrated against DNA from nine other Phytophthora species and seven potato-blemish pathogens. In a single-round PCR assay, 0·5 pg pure P. infestans DNA was detectable. Sensitivity was increased to 5 fg DNA in a nested PCR assay using Peronsporales-specific-primers in the first round. As few as two sporangia or four zoospores of P. infestans could be detected using the nested assay. Procedures are described for detection of P. infestans in leaves, stem and seed potato tubers before expression of symptoms. A soil assay in which 10 oospores per 0·5 g soil were detectable was developed and validated using samples of field soil. The PCR assay was used to examine the long-term survival of sexual (oospores) and asexual (sporangia and mycelium) inoculum of P. infestans in leaf material buried in a replicated experiment under natural field conditions. Oospores were consistently detected using the PCR assay up to 24 months (total length of the study) after burial in soil, whereas the sporangial inoculum was detected for only 12 months after burial. Sporangial inoculum was shown to be nonviable using a baiting assay, whereas leaf material containing oospores remained viable up to 24 months after burial.  相似文献   

5.
Management of potato late blight could benefit from prediction of the risk posed to potato fields from external inoculum sources of Phytophthora infestans. Influx of inoculum depends on a complex interplay of population biological, atmospheric and spore survival processes, and is difficult to predict. This research aims at building tools for such prediction. BLIGHTSPACE is a spatio‐temporal model (parameterized for potato late blight) that has been developed and utilized to study the progress of epidemics in individual fields and networks of fields. A quasi‐Gaussian plume model was developed to provide long‐range transport of spores within BLIGHTSPACE. Numerical results compared favorably with experimental data. A further submodel for the survival of spores during long‐range transportation has been added. Integration of these three submodels will create an experimental arena for comparing control options for potato late blight.  相似文献   

6.
Phytophthora infestans is the causal agent of potato late blight. This pathogen is usually controlled by fungicides, but new European regulations have imposed changes in crop protection management that have led to a search for alternative control measures. The induction of plant defence responses by elicitors is a promising new strategy compatible with sustainable agriculture. This study investigated the effect of eliciting a defence response in potato against P. infestans using a formulation of the COS‐OGA elicitor that combines cationic chitosan oligomers (COS) and anionic pectin oligomers (OGA). Trials were conducted under greenhouse conditions to assess the ability of COS‐OGA to control P. infestans. The results showed that three foliar applications with this elicitor significantly increased potato protection against late blight in controlled conditions. The activation of potato defence genes was also evaluated by RT‐qPCR during these trials. Two pathogenesis‐related proteins, basic PR‐1 and acidic PR‐2, were rapidly and significantly up‐regulated by the elicitor treatment. Therefore, these results suggest that the COS‐OGA elicitor increases the protection of potato against P. infestans and that this protection could be explained by an increase in the expression of potato defence genes rather than by biocide activity.  相似文献   

7.
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8.
Little is known about inoculum dynamics of late blight caused by Phytophthora infestans in tropical/subtropical areas, particularly in Brazil. The objectives of the present study were to assess (i) the survival of the pathogen on stems, leaflets and tomato fruits, either buried or not in soil; (ii) the pathogenicity of P . infestans to mostly solanaceous plant species commonly found in Brazil that could act as inoculum reservoir; and (iii) the temporal dynamics of airborne sporangia. Phytophthora infestans survived in tomato plant parts for less than 36 days under greenhouse and field conditions. In greenhouse tests, pathogen structures were detected earlier on crop debris kept in dry than in wet soil conditions. Isolates of two clonal lineages of P. infestans , US-1 from tomato, and BR-1 from potato, were inoculated on 43 plant species. In addition to potato and tomato, Petunia  ×  hybrida and Nicotiana benthamiana were susceptible to the pathogen. Airborne inoculum was monitored with Rotorod and Burkard spore traps as well as with tomato and potato trap plants. Sporangia were sampled in most weeks throughout 2004 and in the first two weeks of 2005. Under tropical/subtropical conditions, airborne inoculum is abundant and is more important to late blight epidemics than inoculum from crop debris or alternative hosts.  相似文献   

9.
A sensitive real‐time polymerase chain reaction (PCR) assay was developed for the quantification of Phytophthora infestans, the cause of foliar and tuber late blight in potato. A primer pair (PinfTQF/PinfTQR) and a fluorogenic probe (PinfTQPR) were designed to perform a quantitative assay for the detection of P. infestans in leaves, tubers and soils. The assay was shown to be specific to P. infestans and the very closely taxonomically related non‐potato pathogen species P. mirabilis, P. phaseoli and P. ipomoea, but did not detect the potato pathogens P. erythroseptica and P. nicotianae. The assay was able to reliably detect P. infestans DNA at 100 fg per reaction and was effective in quantifying P. infestans in infected leaf tissue from 24 h after inoculation and also in infected symptomless tubers and diseased tubers. Attempts to detect oospores of P. infestans in naturally and artificially infested soil samples are described and compared with baiting tests and previous literature. It was not possible to detect oospores in soil samples due to problems with DNA extraction from the oospores themselves. However, the assay was shown to detect even very low levels of asexual inoculum (sporangia and mycelium) in soil. This work assembles all the necessary features of a quantitative P. infestans assay, which have previously been somewhat disparate: the sensitivity, specificity and quantitation are fully validated, the assay is shown to work in common applications in leaf and tuber tissue and the problems with P. infestans oospore detection are explored and tested experimentally.  相似文献   

10.
Garrett KA  Mundt CC 《Phytopathology》2000,90(12):1307-1312
ABSTRACT The use of host diversity as a tool for management of potato late blight has not been viewed as promising in the past. But the increasing importance of late blight internationally has brought new consideration to all potential management tools. We studied the effect of host diversity on epidemics of potato late blight in Oregon, where there was little outside inoculum. The experimental system consisted of susceptible potato cv. Red LaSoda and a highly resistant breeding selection, inoculated with local isolates of US-8 Phytophthora infestans. Potatoes were grown in single-genotype plots and also in a mixture of 10 susceptible and 26 resistant potato plants. Half of the plots received inoculation evenly throughout the plot (general inoculation) and half received an equal quantity of inoculum in only one corner of the plot (focal inoculation). The area under the disease progress curve (AUDPC) was greater in single genotype stands of susceptible cv. Red LaSoda inoculated throughout the plot than with stands inoculated in one focus. The host-diversity effect on foliar late blight was significant in both years of the investigation; the AUDPC was reduced by an average of 37% in 1997 and 36% in 1998, compared with the mean disease level for the potato genotypes grown separately. Though the evidence for influence of inoculum pattern on host-diversity effects was weak (P = 0.15), in both years there was a trend toward greater host-diversity effects for general inoculation. Statistical significance of host-diversity effects on tuber yield and blight were found only in one of the two years. In that year, tuber yield from both the resistant and susceptible cultivar was increased in mixtures compared with single genotype stands and tuber blight was decreased in mixtures for susceptible cv. Red LaSoda.  相似文献   

11.
Potato blackleg, caused by Pectobacterium and Dickeya species, is one of the most significant bacterial diseases affecting potato production globally. Although it is generally accepted to be a seedborne disease, the processes underlying the spread of disease largely remain unknown. Spatial point pattern analysis was applied to blackleg occurrence in seed potato crops in Scotland during the period of 2010–2013 (approximately 8000 blackleg‐affected crops), to assess whether its distribution was random, regular or aggregated, and the spatial scales at which these patterns occurred. Blackleg‐affected crops derived from mother stocks with symptoms were omitted from the analyses in order to examine the statistical evidence for horizontal transmission of blackleg. The pair correlation function was used to test for global spatial autocorrelation, and results indicated significant (P < 0·05) clustering of incidence at a wide range of spatial scales. Strength of clustering (degree of aggregation) among blackleg‐affected crops was notably larger at spatial scales of 25 km or less. A hot‐ and coldspot analysis was performed to test for local spatial autocorrelation, and statistically significant clusters of high and low values of disease were found across the country. These analyses provide the first quantitative evidence of localized and large‐scale spatial clustering of potato blackleg. Understanding the mode(s) of inoculum dispersal will be important for developing new management strategies that minimize host–pathogen contacts in potato and numerous other crops affected by pathogenic Pectobacterium and Dickeya species.  相似文献   

12.
The relationship between initial soil inoculum level of Spongospora subterranea f. sp. subterranea (Sss) and the incidence and severity of powdery scab on potato tubers at harvest was investigated. In all experiments soil inoculum level of Sss (sporeballs/g soil) was measured using a quantitative real‐time PCR assay. Of 113 commercial potato fields across the UK, soil inoculum was detected in 75%, ranging from 0 to 148 Sss sporeballs/g soil. When arbitrary soil inoculum threshold values of 0, <10 and >10 sporeballs/g soil were set, it was observed that the number of progeny crops developing powdery scab increased with the level of inoculum quantified in the field soil preplanting. In four field trials carried out to investigate the link between the amount of inoculum added to the soil and disease development, disease incidence and severity on progeny tubers was found to be significantly (P < 0·01) greater in plots with increasing levels of inoculum incorporated. There was a cultivar effect in all years, with disease incidence and severity scores being significantly greater in cvs Agria and Estima than in Nicola (P < 0·01).  相似文献   

13.
Phoma koolunga is a recently recognized pathogen in the ascochyta blight complex of field pea (Pisum sativum). Unlike the other three ascochyta blight pathogens, survival of P. koolunga is poorly understood. Survival of this fungus was examined on field pea stubble and as pseudosclerotia on the surface of, and buried in, field soil. Pseudosclerotia were formed in plates containing potato dextrose agar (PDA) mixed with sand or amended with fluorocytocin. After 1 month, P. koolunga was recovered on amended PDA from 93% of stubble sections retrieved from the soil surface, 36% of buried stubble sections and 100% of pseudosclerotia buried in field soil, pasteurized or not. The frequency of recovery of P. koolunga decreased over time and the fungus was not recovered from stubble on the soil surface at 15 months, nor was it recovered from stubble buried in soil at 11 months or later, or from pseudosclerotia buried for 18 months. In a pot bioassay, most ascochyta blight lesions developed on plants inoculated with stubble retrieved from the soil surface after 1 month. Infectivity of the inoculum decreased over time. Disease on plants inoculated with stubble that had been buried or left on the soil surface for up to 6 and 5 months, respectively, and pseudosclerotia retrieved at 14 months and later from field soil did not differ from the non‐inoculated control. These results suggest that field pea stubble may play a role in survival of P. koolunga, especially if it remains on the soil surface. In addition, pseudosclerotia were able to persist in soil and infect field pea plants into the next season.  相似文献   

14.
Late blight, caused by Phytophthora infestans, has emerged as the most destructive disease of potato and tomato in South India since 2008. One hundred and fifty‐seven isolates of Phytophthora infestans, 63 from potato and 94 from tomato, were collected from major potato and tomato production areas of South India between 2010 and 2012. Their phenotypic and genotypic characteristics were determined and compared with reference isolates. Isolates were characterized based on mating type, in vitro metalaxyl sensitivity, mitochondrial DNA haplotype, RG57 DNA fingerprinting patterns, SSR markers and aggressiveness on potato and tomato, in order to monitor population changes in P. infestans. All isolates were A2 mating type, metalaxyl resistant, mtDNA haplotype Ia and had RG57 and SSR fingerprints almost identical to the 13_A2 clonal lineage reported in Europe. Variation at the D13 and SSR4 loci allowed discrimination of minor variants, designated as 13_A2_3, 13_A2_3b, 13_A2_3c and 13_A2_1. A comparison of the lesion diameters caused by 157 isolates on detached leaflets of three potato and tomato cultivars showed all isolates to be equally aggressive, confirming that the same clonal population is infecting both hosts. This study demonstrates that the 13_A2 lineage was responsible for severe late blight outbreaks on potato and tomato in South India and has replaced the prior population represented by the US‐1 and other genotypes. Revised management strategies will be required to combat this destructive 13_A2 clonal lineage and monitoring of the population across other potato‐ and tomato‐growing regions of India is warranted.  相似文献   

15.
Potato late blight caused the Irish Potato Famine and still causes billions of dollars of annual crop damage. Tracking and predicting its spread remains problematic. Growers overspray potato fields with fungicide as a precaution, irrespective of the prevalence or actual risk of the disease. This study created a new weather‐based mathematical model for the spread of late blight at a regional scale using empirical data, and validated it using a novel approach for presence‐only data. The model was tested using a contrapositive ‘proof’ by comparing predicted to actual weather patterns to examine its accuracy. The model was then used to create risk maps showing the likelihood of future outbreaks in the region. Such risk maps can help growers optimize late blight suppression and fungicide use by alerting them to the most probable day at which they are at the most risk, using real‐time weather data from the previous few days. These risk maps would be updated daily to account for conditions needed for sporulation. Overall, this work offers a methodology to understand and model a disease's spread in time and space.  相似文献   

16.
Late blight remained a significant disease for potato growers in Europe long after the famine of the 1840s. Of the four mitochondrial haplotypes of Phytophthora infestans, only the Ia mitochondrial DNA (mtDNA) haplotype has been identified previously in infected potato leaves from famine‐era herbarium specimens collected in England, Ireland and Europe in the 19th century. Long‐term soil fertility experiments were conducted on potato between 1876 and 1901 in Rothamsted to investigate effects of combinations of organic manures and mineral fertilizers on disease and yield. This report identifies for the first time the same Ia mtDNA haplotype of P. infestans in three diseased tubers from 1877 from the long‐term Rothamsted trials, thus providing the earliest evidence of the presence of the founder Ia mtDNA haplotype of P. infestans in potato tubers in England. Soil amendments had a significant impact on disease and yield. A real‐time PCR assay was used to detect and quantify P. infestans in tubers. The level of pathogen DNA was greatest in tubers from highest yielding plots that received combinations of inorganic nitrogenous and mineral fertilizers and least in tubers from plots with organic farmyard manures or non‐nitrogenous mineral fertilizers. The Ia mtDNA haplotype was also confirmed from diseased potato leaves during the same time period. Thus, the founder Ia mtDNA haplotype survived in potato tubers after 1846 and was present over 30 years later in the UK.  相似文献   

17.
The conidia and resting hyphae of the northern anthracnose pathogen of Trifolium species, Kabatiella caulivora, were effectively carried by, and maintained long‐term viability on, a range of materials, including metals, fabrics, woods and plastics. Conidia and hyphae became thick‐walled and melanized with time. There were significant (P < 0.001) differences in conidia/resting hyphae survival between carrier materials and between temperature regimes. At 23 °C/8 °C day/night, conidia and resting hyphae remained viable on steel, corrugated iron, galvanized steel, all tested fabrics, wood and random mixed materials for up to 8 months. At 36 °C/14 °C day/night, conidia and resting hyphae remained viable for up to 8 months, but only on cotton, denim, fleece, silk, leather, paper, plastic and all wood materials. At 45 °C/15 °C day/night, conidia and resting hyphae remained viable up to 8 months only on fleece wool, Eucalyptus marginata (jarrah wood) and paper. There were significant differences between carrier materials in their abilities to retain conidia and resting hyphae after washing (P < 0.001). Metabolic activity was confirmed for conidia and resting hyphae recovered after 8 months and K. caulivora colonies successfully re‐established on potato dextrose agar. Findings confirmed the critical importance of materials as long‐term carriers of viable K. caulivora conidia and resting hyphae, highlighting the potential for spread of a highly virulent K. caulivora race within and outside Australia via farming equipment, clothing and other associated materials. Results also have wider biosecurity implications for the transportation of fungal‐infested carrier materials previously considered as low risk.  相似文献   

18.
ABSTRACT A means for determining the rate of release, Q (spores per square meter per second), of spores from a source of inoculum is paramount for quantifying their further dispersal and the potential spread of disease. Values of Q were obtained for Phytophthora infestans sporangia released from an area source of diseased plants in a potato canopy by comparing the concentrations of airborne sporangia measured at several heights above the source, with the concentrations predicted by a Lagrangian Stochastic simulation model. An independent estimate of Q was obtained by quantifying the number of sporangia per unit area of source at the beginning of each sampling day by harvesting diseased plant tissue and enumerating sporangia from these samples. This standing spore crop was the potential number of sporangia released per area of source during the day. The standing spore crop was apportioned into time segments corresponding to sporangia concentration measurement periods using the time trace of sporangia sampled above the source by a Burkard continuous suction spore sampler. This apportionment of the standing spore crop yielded potential release rates that were compared with modeled release rates. The two independent estimates of Q were highly correlated (P = 0.003), indicating that the model has utility for predicting release rates for P. infestans sporangia and the spread of disease between fields.  相似文献   

19.
The oomycete Phytophthora infestans, the cause of late blight, is one of the most important potato pathogens. During infection, it secretes effector proteins that manipulate host cell function, thus contributing to pathogenicity. This study examines sequence differentiation of two P. infestans effectors from 91 isolates collected in Poland and Norway and five reference isolates. A gene encoding the Avr‐vnt1 effector, recognized by the potato Rpi‐phu1 resistance gene product, is conserved. In contrast, the second effector, AvrSmira1 recognized by Rpi‐Smira1, is highly diverse. Both effectors contain positively selected amino acids. A majority of the polymorphisms and all selected sites are located in the effector C‐terminal region, which is responsible for their function inside host cells. Hence it is concluded that they are associated with a response to diversified target protein or recognition avoidance. Diversification of the AvrSmira1 effector sequences, which existed prior to the large‐scale cultivation of plants containing the Rpi‐Smira1 gene, may reduce the predicted durability of resistance provided by this gene. Although no isolates virulent to plants with the Rpi‐phu1 gene were found, the corresponding Avr‐vnt1 effector has undergone selection, providing evidence for an ongoing ‘arms race’ between the host and pathogen. Both genes remain valuable components for resistance gene pyramiding.  相似文献   

20.
ABSTRACT The effect of components of primary inoculum dispersal in soil on the temporal dynamics of Phytophthora blight epidemics in bell pepper was evaluated in field and growth-chamber experiments. Phytophthora capsici may potentially be dispersed by one of several mechanisms in the soil, including inoculum movement to roots, root growth to inoculum, and root-to-root spread. Individual components of primary inoculum dispersal were manipulated in field plots by introducing (i) sporangia and mycelia directly in soil so that all three mechanisms of dispersal were possible, (ii) a plant with sporulating lesions on the soil surface in a plastic polyvinyl chloride (PVC) tube so inoculum movement to roots was possible, (iii) a wax-encased peat pot containing sporangia and mycelia in soil so root growth to inoculum was possible, (iv) a wax-encased peat pot containing infected roots in soil so root-to-root spread was possible, (v) noninfested V8 vermiculite media into soil directly as a control, or (vi) wax-encased noninfested soil as a control. In 1995 and 1996, final incidence of disease was highest in plots where sporangia and mycelia were buried directly in soil and all mechanisms of dispersal were operative (60 and 32%) and where infected plants were placed in PVC tubes on the soil surface and inoculum movement to roots occurred with rainfall (89 and 23%). Disease onset was delayed in 1995 and 1996, and final incidence was lower in plants in plots where wax-encased sporangia (6 and 22%) or wax-encased infected roots (22%) were buried in soil and root growth to inoculum or root-to-root spread occurred. Incidence of root infections was higher over time in plots where inoculum moved to roots or all mechanisms of dispersal were possible. In growth-chamber studies, ultimately all plants became diseased regardless of the dispersal mechanism of primary inoculum, but disease onset was delayed when plant roots had to grow through a wax layer to inoculum or infected roots in tension funnels that contained small volumes of soil. Our data from both field and growth-chamber studies demonstrate that the mechanism of dispersal of the primary inoculum in soil can have large effects on the temporal dynamics of disease.  相似文献   

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