Aerial photography used for spatial pattern analysis of late blight infection in irrigated potato circles

ABSTRACT Spatial and temporal dynamics of late blight were investigated from color, infrared aerial photographs of five commercial potato fields in the Columbia Basin during epidemics in 1993, 1995, and 1998. Aerial photographs were taken one to four times at 6- to 21-day intervals. Photographs were scanned and pixels, representing approximately 1 m(2) in the field, were used in the analysis. Late blight-infected plants were aggregated as indicated by runs analysis. Significant z-tests were computed for four directions during each sampling date in each of the five fields. Absolute z-values for runs analysis increased, indicating increasing aggregation in the four directions, as disease incidence increased in the early and midphases of the epidemics in each field. Variograms indicated the existence of autocorrelation among infected plants in four directions; the range of influence increased as disease incidence increased except at the highest levels of disease. Late blight was observed to spread in fields as foci. Late blight foci enlarged in size, produced distinct daughter foci, and coalesced. A field where initial inoculum likely originated from infected seed tubers exhibited less initial aggregation than the other fields, perhaps due to a different source of primary inoculum. Aerial photography coupled with spatial analyses of late blight-infected plants was an effective technique to quantitatively assess disease patterns in relatively large fields and was useful in quantifying an intensification of aggregation during the epidemic process on a large scale.     

Late-blight epidemics on potato in Finland, 1933–2002; increased and earlier occurrence of epidemics associated with climate change and lack of rotation

Changes in the incidence and onset of potato late-blight epidemics in Finland were investigated and compared with possible changes in climate, presence of soil-borne inoculum, and aggressiveness of Phytophthora infestans populations. Datasets were constructed from leaf blight assessments in cultivar trials or fungicide tests carried out at eight experimental sites during the periods 1933–1962 and 1983–2002. Additional data were obtained from late-blight monitoring projects carried out from 1991 to 2002. From 1998 to 2002, the risk of blight outbreak was 17-fold higher compared with the periods 1933–62 and 1983–1997. Simultaneously, the outbreaks of the epidemics began 2–4 weeks earlier. The changes observed were associated with a climate more conducive to blight in the late 1990s. Lack of rotation also advanced blight epidemics by an average of 9 days in 1998–2002, but it did not have this effect in 1992–1997, suggesting that soil borne inoculum may not have been a significant threat to potato until the late 1990s. The aggressiveness of the P. infestans isolates seemed to have only minor effect on the onset of the epidemics after 1991, as the apparent infection rate remained unchanged despite weather conditions more favourable to late blight in the late 1990s. As a consequence of the more frequent and earlier epidemics, the sales of fungicides used against late blight in Finland increased 4-fold from the 1980s to 2002.     

Phytophthora infestans in a subtropical region: survival on tomato debris, temporal dynamics of airborne sporangia and alternative hosts

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.     

Spatiotemporal Description of Epidemics Caused by Phoma ligulicola in Tasmanian Pyrethrum Fields

ABSTRACT Spatial and temporal patterns of foliar disease caused by Phoma ligulicola were quantified in naturally occurring epidemics in Tasmanian pyrethrum fields. Disease assessments (defoliation incidence, defoliation severity, incidence of stems with ray blight, and incidence of flowers with ray blight) were performed four times each year in 2002 and 2003. Spatial analyses based on distribution fitting, runs analysis, and spatial analysis by distance indices (SADIE) demonstrated aggregation in fields approaching their first harvest for all assessment times between September and December. In second-year harvest fields, however, the incidence of stems with ray blight was random for the first and last samplings, but aggregated between these times. Spatiotemporal analyses were conducted between the same disease intensity measures at subsequent assessment times with the association function of SADIE. In first-year harvest fields, the presence of steep spatial gradients was suggested, most likely from dispersal of conidia from foci within the field. The importance of exogenous inoculum sources, such as wind-dispersed ascospores, was suggested by the absence of significant association between defoliation intensity (incidence and severity) and incidence of stems with ray blight in second-year harvest fields. The logistic model provided the best temporal fit to the increase in defoliation severity in each of six first-year harvest fields in 2003. The logistic model also provided the best fit for the incidence of stems with ray blight and the incidence of flowers with ray blight in four of six and three of six fields, respectively, whereas the Gompertz model provided the best fit in the remaining fields. Fungicides applied prior to mid-October (early spring) significantly reduced the area under disease progress curve (P < 0.001) for defoliation severity, the incidence of stems with ray blight, and the incidence of flowers with ray blight for epidemics at all field locations. This study provides information concerning the epidemiology of foliar disease and ray blight epidemics in pyrethrum and offers insight on how to best manage these diseases.     

Spatial Aspects of Light Leaf Spot (Pyrenopeziza brassicae) Epidemic Development on Winter Oilseed Rape (Brassica napus) in the United Kingdom

ABSTRACT In microplot experiments in 1998-99 and 1999-2000, the start of light leaf spot epidemics could be predicted from weather data, using empirical equations for Pyrenopeziza brassicae apothecial (ascospore) development, ascospore infection criteria, and the latent period of P. brassicae. The dates when P. brassicae sporulation was first observed fitted predictions and initial spread of light leaf spot from an inoculum source was mostly in the prevailing wind direction, with differences between the two growing seasons attributable to differences in wind patterns. Subsequent secondary spread of disease could be predicted using temperature and rainfall data, and observations fitted predicted dates. In both 1998-99 and 1999-2000, initial spatial patterns of observed disease in January were random, because data were not significantly different from a binomial distribution (P = 0.18). Analysis of spatial data from samples in February and March indicated aggregation, because data fit was significantly different from a binomial distribution (P 相似文献   

Biological control of botrytis leaf blight of onion byGliocladium roseum applied as sprays and with fabric applicators

Gliocladium roseum (5×10⁶ conidia ml^–1) and chlorothalonil (Bravo 500) were compared in two field tests for effectiveness in suppressing leaf blight caused byBotrytis squamosa in cooking onions. The biological control agent and fungicide were applied with sprayers and with specially designed fabric applicators that were mounted interchangeably on an aluminium carriage with bicycle wheels. In the applicators, inoculum and fungicide gravitated from a reservoir down curtains of denim strips and onto portions of onion leaves contacted by the strips. Initial applications were timed using a leaf blight forecasting system (BOTCAST) and three or four subsequent applications were made at weekly intervals. When compared to water checks,G. roseum applied as sprays or by applicators reduced density of leaf spots by about 50–58% during middle and late stages of epidemics. The antagonist was about half as effective as chlorothalonil in suppressing density of spots, regardless of application method. The applicators delivered inoculum in similar densities to proximal and distal halves of leaves, and used at least 35% less volume of inoculum compared to the sprayers. Density of inoculum on leaves treated by applicators was about the same as in spray-treated leaves when canopies were sparse, but less when canopies were dense. It is concluded thatG. roseum has good potential for controlling leaf blight sufficiently to avoid economic yield losses.     

Temporal and spatial dynamics of watermelon gummy stem blight epidemics

The effect of the distance of initial inoculum on the intensity of watermelon gummy stem blight, caused by Didymella bryoniae, was studied in a naturally-infected rainfed commercial field. The shorter the distance from the focus, the sooner was disease onset and the earlier maximum disease levels were achieved. Maximum disease incidences were reached earlier than maximum severities, but eventually destructive levels were observed for both disease incidence and severity. Disease progressed at similar rates, irrespective of the radial distance from the focus. A detailed study of the disease temporal progress was conducted in inoculated rainfed experimental fields with commercial genotypes Crimson Sweet (susceptible, S) and Riviera (moderately resistant, R). The Gompertz model best described the disease progress curves, and estimated apparent infection rates were 0.049 and 0.020 respectively for S and R genotypes. In addition, spatial pattern studies were conducted during the dry season in overhead irrigated experimental plots, inoculated with point-source foci. Disease intensity gradients were better explained by the Exponential model than by the Power Law model. Gummy stem blight distribution was classified as aggregated by the Ordinary Runs procedure. Two different spatial autocorrelation methods (2DCorr and LCOR) revealed strong short distance spatial dependencies. Long distance positive correlations between quadrats were observed along with periods of higher progress rates. The dynamic patterns of the epidemics of gummy stem blight in watermelon described here are consistent with epidemics of polycyclic diseases with splash-dispersed spores.     

Impacts of climate change on wheat anthesis and fusarium ear blight in the UK

Climate change will affect both growth of agricultural crops and diseases that attack them but there has been little work to study how its impacts on crop growth influence impacts on disease epidemics. This paper investigates how impacts of climate change on wheat anthesis date will influence impacts on fusarium ear blight in UK mainland arable areas. A wheat growth model was used for projections of anthesis dates, and a weather-based model was developed for use in projections of incidence of fusarium ear blight in the UK. Daily weather data, generated for 14 sites in arable areas of the UK for a baseline (1960–1990) scenario and for high and low CO₂ emissions in the 2020s and 2050s, were used to project wheat anthesis dates and fusarium ear blight incidence for each site for each climate change scenario. Incidence of fusarium ear blight was related to rainfall during anthesis and temperature during the preceding 6 weeks. It was projected that, with climate change, wheat anthesis dates will be earlier and fusarium ear blight epidemics will be more severe, especially in southern England, by the 2050s. These projections, made by combining crop and disease models for different climate change scenarios, suggest that improved control of fusarium ear blight should be a high priority in industry and government strategies for adaptation to climate change to ensure food security.     

Spatial and Temporal Analyses of Bacterial Blight of Onion Caused by Xanthomonas axonopodis pv. allii

ABSTRACT Bacterial blight of onion is a severe disease, which emerged over the past decade in several onion-producing areas. This disease currently is observed in both the Old and New Worlds. Although the causative agent, Xanthomonas axonopodis pv. allii, is potentially seedborne, seed transmission and significance of seedborne initial inoculum for the development of bacterial blight of onion previously has not been assessed. This article describes experimental work designed to evaluate the biological importance of seedborne X. axonopodis pv. allii as an initial inoculum source, and examine the temporal and spatial dynamics of the disease. Over 3 years, outbreaks of bacterial blight of onion always were induced in experimental plots sown with naturally contaminated seed lots, with a contamination rate determined as 0.04%. Analyses of disease patterns indicated a likely seedborne origin for the inoculum associated with the early stages of epidemics. Spatial analyses performed with several statistical methods indicated aggregated patterns of disease incidence data. Primary foci enlarged over time, and a few distinct secondary foci sometimes were established after occurrence of wind-driven rains (with gusts up to 15 m s(-1)). Distances between primary and secondary foci ranged from less than 1 m (satellite foci) to 25 m. It remains possible that longdistance dispersal of inoculum was at least partly involved in the later stages of epidemics.     

Late Blight Forecasting in Norway 1957–19801

A regular late-blight warning service was established in Norway in 1957, run by the Plant Protection Service. The service was revised in 1965 and from that year the warnings were distributed by the Norwegian Institute of Meteorology. The criteria for warnings are described. A regression analysis of the relationship between warnings and intensity of late-blight epidemics in 1957–1980 showed no significant differences between locations, but significant differences in the relationship between years and periods. The weather in the years 1973 to 1978 caused unfavourable conditions for late blight in all parts of the country. In 1979 and 1980 the weather changed and favourable climate to late blight occurred in most regions of the country, but the progress of epidemics in 1979 was slower than expected due to reduced inoculum potential. In 1980 a more normal progress of epidemics was observed, which indicated a reestablishment of the inoculum potential in the autumn of 1979.     

Assessment of airborne primary inoculum availability and modelling of disease onset of ascochyta blight in field peas

Ascochyta blight is a serious disease affecting field peas. In France, disease management relies mainly on scheduled chemical applications without taking into account the actual disease risk. A better understanding of the factors affecting disease onset would therefore help in the timing of the first application. Field experiments involving eight sowing dates between mid-September and mid-December were conducted for two consecutive years. The seasonal dynamics of airborne inoculum were investigated through trap plants. The weekly availability of airborne primary inoculum was extremely low during autumn and winter and was partially influenced by mesoclimatic conditions. Disease onset occurred between mid-October and early March depending on the sowing date. Generally, the later the sowing date, the longer the period between sowing and disease onset. This was due to an increase in the period between sowing and emergence. Disease onset was observed 14–35 days after emergence. A disease onset model based on the calculation of weather-dependent daily infection values (DIVs) was established, assuming that disease onset occurs once the temperature and moisture requirements for incubation are met. Cumulative daily infection values (cDIVs) were determined by sowing date and experiment through addition of consecutive DIVs between emergence and disease onset. A frequency analysis of cDIVs was performed to determine the 10th and 90th percentiles of the distribution. An analysis of the observed and predicted values showed that observed disease onset dates were almost always included in the forecast window defined by these two percentiles. This study is the first attempt to predict ascochyta blight onset in field peas and should contribute to development of a more rational fungicide application strategy.     

Genetic Structure of Atmospheric Populations of Gibberella zeae

ABSTRACT Gibberella zeae, causal agent of Fusarium head blight (FHB) of wheat and barley and Gibberella ear rot (GER) of corn, may be transported over long distances in the atmosphere. Epidemics of FHB and GER may be initiated by regional atmospheric sources of inoculum of G. zeae; however, little is known about the origin of inoculum for these epidemics. We tested the hypothesis that atmospheric populations of G. zeae are genetically diverse by determining the genetic structure of New York atmospheric populations (NYAPs) of G. zeae, and comparing them with populations of G. zeae collected from seven different states in the northern United States. Viable, airborne spores of G. zeae were collected in rotational (lacking any apparent within-field inoculum sources of G. zeae) wheat and corn fields in Aurora, NY in May through August over 3 years (2002 to 2004). We evaluated 23 amplified fragment length polymorphism (AFLP) loci in 780 isolates of G. zeae. Normalized genotypic diversity was high (ranging from 0.91 to 1.0) in NYAPs of G. zeae, and nearly all of the isolates in each of the populations represented unique AFLP haplotypes. Pairwise calculations of Nei's unbiased genetic identity were uniformly high (>0.99) for all of the possible NYAP comparisons. Although the NYAPs were genotypically diverse, they were genetically similar and potentially part of a large, interbreeding population of G. zeae in North America. Estimates of the fixation index (G(ST)) and the effective migration rate (Nm) for the NYAPs indicated significant genetic exchange among populations. Relatively low levels of linkage disequilibrium in the NYAPs suggest that outcrossing is common and that the populations are not a result of a recent bottleneck or invasion. When NYAPs were compared with those collected across the United States, the observed genetic identities between the populations ranged from 0.92 to 0.99. However, there was a significant negative correlation (R = -0.59, P < 0.001) between genetic identity and geographic distance, suggesting that some genetic isolation may occur on a continental scale. The contribution of long-distance transport of G. zeae to regional epidemics of FHB and GER remains unclear, but the diverse atmospheric populations of G. zeae suggest that inoculum may originate from multiple locations over large geographic distances. Practically, the long-distance transport of G. zeae suggests that management of inoculum sources on a local scale, unless performed over extensive production areas, will not be completely effective for the management of FHB and GER.     

Host diversity can reduce potato late blight severity for focal and general patterns of primary inoculum

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.     

Comparative analyses of spot blotch and tan spot epidemics on wheat under optimum and late sowing period in South Asia

In South Asia, foliar blight of wheat (Triticum aestivum L.) is a disease complex caused by Cochliobolus sativus (the spot blotch pathogen) and Pyrenophora tritici-repentis (the tan spot pathogen) which can reduce yields by >30?%. Little is known about the effects of wheat genotypes and their planting time on foliar blight epidemics. Field experiments were conducted to determine the infection potential and epidemic development of C. sativus and P. tritici-repentis on two susceptible (Sonalika and BL1473) and two tolerant (NL750 and Milan/Shanghai-7) wheat genotypes under optimum (November 26) and late (December 11 and December 26) planting conditions. The dynamics of airborne conidia were studied using air samplers. The highest aerial concentrations of conidia and disease incidence of both pathogens on all four wheat genotypes were detected during the first 3?weeks of March under both optimum and late seeding conditions in both years. Compared to optimum sowing time (i.e. November 26), wheat genotypes had higher disease severity when planted late on December 11 and 26. The disease complex reduced grain yield by 20.5, 27.2 and 37.3?% for November 26, December 11 and December 26 plantings, respectively in 2004. The corresponding differences were 17.7, 23.6 and 30.2?% in 2005. The findings of this study provide valuable information on the epidemiology of spot blotch and tan spot, which could help in developing strategies for managing these diseases in South Asian region through the selection of suitable genotypes and planting dates.     

Evaluation of the temporal distribution of <Emphasis Type="Italic">Fusarium graminearum</Emphasis> airborne inoculum above the wheat canopy and its relationship with Fusarium head blight and DON concentration

With the aim of unravelling the role of airborne Fusarium graminearum inoculum in the epidemic of Fusarium head blight (FHB) caused by this species in wheat spikes, a network of Burkard air samplers was set up in five wheat fields distributed in Belgium from 2011 to 2013. Each year from April to July, the daily amounts of F. graminearum inoculum above the wheat canopy were quantified using a newly developed TaqMan qPCR assay. The pattern of spore trapping observed was drastically different per year and per location with a frequency of detection between 9 and 66% and a mean daily concentration between 0.8 and 10.2 conidia-equivalent/m³. In one location, air was sampled for a whole year. Inoculum was frequently detected from the wheat stem elongation stage until the end of the harvesting period, but high inoculum levels were also observed during the fall. Using a window-pane analysis, different periods of time around wheat flowering (varying in length and starting date) were investigated for their importance in the relation between airborne inoculum and FHB parameters (FHB severity, frequency of F. graminearum infection and DON). For almost all the combinations of variables, strong and significant correlations were found for multiple window lengths and starting times. Inoculum quantities trapped around flowering were highly correlated with F. graminearum infection (up to R?=?0.84) and DON (up to R?=?0.9). Frequencies of detection were also well correlated with both of these parameters. DON concentrations at harvest could even be significantly associated with the F. graminearum inoculum trapped during periods finishing before the beginning of the anthesis (R?=?0.77). Overall, these results highlight the key role of the airborne inoculum in F. graminearum epidemics and underline the importance of monitoring it for the development of disease forecasting tools.     

Spatiotemporal development of Ascochyta blight in chickpea from primary infection foci: insights from plant,pathogen and the environment interactions to inform an epidemic risk

European Journal of Plant Pathology - Ascochyta blight epidemics have been observed in many countries since the early 1900s but studies on an interaction between the amount of inoculum,...     

Spatial Patterns of Viable Spore Deposition of Gibberella zeae in Wheat Fields

ABSTRACT An increased understanding of the epidemiology of Gibberella zeae will contribute to a rational and informed approach to the management of Fusarium head blight (FHB). An integral phase of the FHB cycle is the deposition of airborne spores, yet there is no information available on the spatial pattern of spore deposition of G. zeae above wheat canopies. We examined spatial patterns of viable spore deposition of G. zeae over rotational (lacking cereal debris) wheat fields in New York in 2002 and 2004. Viable, airborne spores (ascospores and macroconidia) of G. zeae were collected above wheat spikes on petri plates containing a selective medium and the resulting colonies were counted. Spores of G. zeae were collected over a total of 68 field environments (three wheat fields during 54 day and night sample periods over 2 years) from spike emergence to kernel milk stages of local wheat. Spatial patterns of spore deposition were visualized by contour plots of spore counts over entire fields. The spatial pattern of spore deposition was unique for each field environment during each day and night sample period. Spore deposition patterns during individual sample periods were classified by spatial analysis by distance indices (SADIE) statistics and Mantel tests. Both analyses indicated that the majority (93%) of the spore deposition events were random, with the remainder being aggregated. All of the aggregated patterns were observed during the night. Observed patterns of spore deposition were independent of the mean number of viable spores deposited during individual sample periods. The spatial pattern for cumulative spore deposition during anthesis in both years became aggregated over time. Contour maps of daily and cumulative spore deposition could be compared with contour maps of FHB incidence to gain insights into inoculum thresholds and the timing of effective inoculum for infection.     

Multi‐scale modelling of infection pressure from Phytophthora infestans*

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.     

Biological Control of Botrytis cinerea in Cyclamen with Ulocladium atrum and Gliocladium roseum Under Commercial Growing Conditions

ABSTRACT The effect of treatments with conidial suspensions of Ulocladium atrum and Gliocladium roseum on leaf rot of cyclamen caused by Botrytis cinerea was investigated under commercial greenhouse conditions. Spraying U. atrum (1 x 10(6) conidia per ml) or G. roseum (2 x 10(6) conidia per ml and 1 x 10(7) conidia per ml) at intervals of 2 to 3 weeks during the production period and spraying U. atrum (1 x 10(6) conidia per ml) at intervals of 4 to 6 weeks resulted in a significant reduction of natural infections of petioles by B. cinerea. U. atrum or G. roseum (1 x 10(7)conidia per ml) was as effective as the standard fungicide program. B. cinerea colonized senesced leaves within the plant canopy and infected adjacent petioles and leaves later. The antagonists colonized senesced leaves and reduced B. cinerea development on these leaves. Thus, the inoculum potential on petioles adjacent to necrotic leaf tissues was reduced. The fate of U. atrum conidia on surfaces of green cyclamen leaves during a 70-day period after application was studied. The number of conidia per square centimeter of leaf surface remained relatively constant during the entire experiment. Sixty percent of the conidia sampled during the experiments retained the ability to germinate. When green leaves were removed from the plants to induce senescence and subsequently were incubated in a moist chamber, U. atrum colonized the dead leaves. Senesced leaves also were colonized by other naturally occurring fungi including B. cinerea. On leaves treated with U. atrum from all sampling dates, sporulation of B. cinerea was significantly less as compared with the untreated control. Our results indicate that early applications of U. atrum before canopy closure may be sufficient to achieve commercially satisfactory control of Botrytis leaf rot in cyclamen.     

Detection and quantification of airborne inoculum of Sclerotinia sclerotiorum using quantitative PCR

This paper reports the development of a new specific diagnostic technique to accurately quantify airborne inoculum of Sclerotinia sclerotiorum and discusses its potential use in disease-forecasting schemes, using examples of three contrasting epidemic seasons: 2007, when there was a severe epidemic of sclerotinia stem rot (SSR) in England and high numbers of airborne ascospores were trapped at Rothamsted, and, in contrast, 2003 and 2004, when the incidence of SSR in England was low and low numbers of airborne ascospores were trapped at Rothamsted. DNA was extracted from wax-coated plastic tapes, such as those used in Burkard (Hirst-type) spore traps and rotating-arm traps. A SYBR-green quantitative PCR (qPCR) method produced a linear relationship between ascospore numbers and S. sclerotiorum DNA (mean 0·35 pg DNA per spore) and was able to detect DNA representing as few as two ascospores. The technique was insensitive to DNA of the host plant, Brassica napus , and other plant pathogens, including Sclerotinia minor , S. trifoliorum and Botrytis cinerea , and common airborne fungal genera such as Cladosporium and Penicillium . There was no relationship between rainfall and numbers of airborne ascospores of S. sclerotiorum present at Rothamsted during the period of infection in the severe SSR season (2007).