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1.
Chasmothecia of Erysiphe necator form in one season, survive winter and discharge ascospores that cause primary infections and trigger powdery mildew epidemics in the next season. A strategy for powdery mildew control was developed based on (i) the reduction in overwintering chasmothecia and on (ii) spring fungicide applications to control ascosporic infections timed based on estimate risk (two to five sprays per season). Several fungicides, the hyperparasite Ampelomyces quisqualis, and a mineral oil product were first tested as separate applications in a greenhouse and in vineyards. In the greenhouse, A. quisqualis suppressed chasmothecia formation by 41 %; fungicides and mineral oil suppressed chasmothecia formation by 63 % and ascospore viability by 71 %. In vineyards, application of boscalid + kresoxim-methyl or meptyldinocap once after harvest, as well as application of A. quisqualis pre- and post-harvest, delayed disease onset and epidemic development in the following season by 1 to 3 weeks and lowered disease severity (up to the pea-sized berry stage) by 56 to 63 %. Risk-based applications of sulphur and of synthetic fungicides provided the same control as the grower spray program but required fewer applications (average reduction of 47 %). Sanitation strategies were then tested by combining products and application times (late-season, and/or pre-bud break, and/or spring). Adequate disease control with a reduced number of sprays was achieved with the following combination: two applications of A. quisqualis (pre- and post-harvest), one application of mineral oil before bud break, and model-based applications of sulphur fungicides between bud break and fruit set.  相似文献   

2.
Production and development of the chasmothecia of Erysiphe necator on Vitis vinifera leaves were studied using potted plants in controlled and outdoor environments and grapevines in a vineyard. The optimum temperature for ascocarp production was 20°C; fewer chasmothecia were produced at 15°C and even fewer at 25°C; at 10 and 30°C, no or very few chasmothecia were observed, and none reached maturity. Nonlinear equations describing ascocarp development as a function of time and temperature were developed, parameterized with data from experiments at constant temperatures, and evaluated under fluctuating temperatures. Goodness‐of‐fit showed high agreement between observed and predicted data: the model efficacy ranged from 0·74 to 0·97 (1·0 indicates a perfect fit), and the root mean square error ranged from 0·001 to 0·01 (zero indicates a perfect fit). The high proportion of the observed variability accounted for by these equations (R2 = 0·83–0·98) supported the hypothesis that temperature has a predominant role in ascocarp development under natural conditions, when all environmental factors interact. The equations tended to overestimate the production of mature chasmothecia (the coefficient of residual mass was ?0·23), but this inconsistency mainly occurred when rainfall apparently washed the mature chasmothecia from leaves during the logarithmic phase of the ascocarp developmental curve. Results from this work will be useful for predicting the development of chasmothecia in a vineyard and for timing the use of natural products, fungicides or biocontrol agents for reducing the population of chasmothecia, which are all more effective when they are applied to immature chasmothecia.  相似文献   

3.
The incidence and severity of Ascochyta blight in potted chickpea trap plants exposed for 1-wk periods near infested chickpea debris in Córdoba, Spain, or in chickpea trap crops at least 100 m from infested chickpea debris in several locations in southern Spain were correlated with pseudothecial maturity and ascospore production ofDidymella rabiei from nearby chickpea debris. The period of ascospore availability varied from January to May and depended on rain and maturity of pseudothecia. The airborne concentration of ascospores ofD. rabiei was also monitored in 1988. Ascospores were trapped mostly from the beginning of January to late February; this period coincided with that of maturity of pseudothecia on the chickpea debris. Most ascospores were trapped on rainy days during daylight and 70% were trapped between 12.00 and 18.00 h. Autumn-winter sowings of chickpea were exposed longer to ascospore inoculum than the more traditional spring sowings because the autumn-winter sowings were exposed to the entire period of ascospore production on infested chickpea debris lying on the soil surface.  相似文献   

4.
ABSTRACT Mills' infection period table describes the number of hours of continuous leaf wetness required at temperatures from 6 to 25 degrees C for infection of apple leaves by ascospores of Venturia inaequalis and reports that conidia require approximately two-thirds the duration of leaf wetness required by ascospores at any given temperature. Mills' table also provides a general guideline that more than 2 days of wetting is required for leaf infection by ascospores below 6 degrees C. Although the table is widely used, infection times shorter than those in the table have been reported in lab and field studies. In 1989 a published revision of the table eliminated a potential source of error, the delay of ascospore release until dawn when rain begins at night, and shortened the times reported by Mills for ascospore infection by 3 h at all temperatures. Data to support the infection times below 6 degrees C were lacking, however. Our objective was to quantify the effects of low temperatures on ascospore discharge, ascospore infection, and infection by conidia. In two of three experiments at 1 degrees C, the initial release of ascospores occurred after 131 and 153 min. In the third experiment at 1 degrees C, no ascospores were detected during the first 6 h. The mean time required to exceed a cumulative catch of 1% was 143 min at 2 degrees C, 67 min at 4 degrees C, 56 min at 6 degrees C, and 40 min at 8 degrees C. At 4, 6, and 8 degrees C, the mean times required to exceed a cumulative catch of 5% were 103, 84, and 53 min, respectively. Infection of potted apple trees by ascospores at 2, 4, 6, and 8 degrees C required 35, 28, 18, and 13 h, respectively; substantially shorter times than previously were reported. In parallel inoculations of potted apple trees, conidia required approximately the same periods of leaf wetness as ascospores at temperatures from 2 to 8 degrees C, rather than the shorter times reported by Mills or the longer times reported in the revision of the Mills table. We propose the following revisions to infection period tables: (i) shorter minimum infection times for ascospores and conidia at or below 8 degrees C, and (ii) because both ascospores and conidia are often present simultaneously during the season of ascospore production and the required minimum infection times appear to be similar for both spore types, the adoption of a uniform set of criteria for ascosporic and conidial infection based on times required for infection by ascospores to be applied during the period prior to the exhaustion of the ascospore supply. Further revisions of infection times for ascospores may be warranted in view of the delay of ascospore discharge and the reduction of airborne ascospore doses at temperatures at or below 2 degrees C.  相似文献   

5.
ABSTRACT Greasy spot, caused by Mycosphaerella citri, produces a leaf spot disease affecting all citrus species in Florida and the Caribbean Basin. M. citri produces pseudothecia and ascospores, which are considered the principal source of inoculum, in decomposing leaves on the grove floor. In studies using a computer-controlled environmental chamber, a single rain event triggered release of most mature ascospores beginning 30 to 60 min after the rain event. Additional rain events did not bring about further release. High relative humidity without rain triggered release of low numbers of ascospores, but vibration and red/infrared irradiation had little or no effect on ascospore release. After three to four cycles of wetting and drying of leaves, all pseudothecia had matured and released their ascospores. In the field, ascospores were detectable starting about 2 h after the beginning of a rain or irrigation and most ascospores were released within 16 h. Ascospore release was greatest following rain events and somewhat less following irrigations, and low numbers of ascospores were detectable on days without precipitation. Ascospore numbers declined linearly with horizontal distance from the source and as a function of the logarithm of ascospore numbers with vertical distance. Low numbers of ascospores were detected 7.5 m above the ground and 90 m downwind from the grove. Ascospore release can be advanced by irrigating frequently during dry, nonconducive conditions to stimulate ascospore release when environmental conditions are unfavorable for infection, but the eventual effects on disease severity are uncertain.  相似文献   

6.
A temperature‐driven, mechanistic model predicting the development of Erysiphe necator chasmothecia in vineyards was developed and validated in 38 vineyards in the Po Valley (northern Italy), Baden‐Württemberg (Germany), and South Australia between 2005 and 2011. The model, which begins operating when the first ascocarp initials are formed, predicts on a daily basis the proportions of chasmothecia at the yellow, brown and black maturity stage. The initialization date was estimated with an iterative procedure that minimized the residuals of predicted versus observed values. In all vineyards, a drop to more favourable temperatures for ascocarp production over 2–4 days in the week or in the 2 weeks before the model initialization date probably triggered chasmothecia production. Model predictions provided a good fit of observed data (coefficients of determination, model accuracy, efficacy and efficiency were all ≥0·90), with some overestimation. When predicted production of black chasmothecia (on leaves) was compared with observed dispersal of chasmothecia from vines, lack of splashing rain was probably the main cause of overestimation. When observed numbers of yellow, brown or black chasmothecia on leaves were compared with model predictions, removal of the developing chasmothecia by rainfall was probably the main cause of overestimation. Inclusion of the effect of rainfall on the removal of immature and mature chasmothecia from the powdery mildew colonies could improve the model. The model could be used to time the application of fungicides or biocontrol agents for reducing ascocarp formation and reducing primary inoculum in the following season.  相似文献   

7.
Scab is an important disease of apple and its control depends almost exclusively on frequent use of fungicides. Primary scab infection in the spring assumes several steps: ascospore maturation, liberation of ascospores that become airborne, deposition on susceptible tissues, and infection. However, the spatial heterogeneity of ascospores within the tree canopy is unknown. Aerial concentration of ascospore (ACA), ascospore concentration in rain water (ACR) and ascospore deposition (AD) were therefore measured at six heights (20–257 cm from the ground) with rotating-arm air samplers, funnels, and greased glass slides, respectively, during five rain events in 2001 and in 2002. In addition, ACR and AD were measured at eight locations within tree canopy at 196 cm height. Apple scab was assessed at the end of the primary infection period in each sampling location within the apple tree. A similar experimental design was used in 2003 to study the spatial heterogeneity of both AD and primary scab lesions. ACA and AD decreased with increasing height, while ACR increased with increasing height. Based on both variance to mean ratio and the power law relationship in both years, the ACR was heterogeneous, while AD was heterogeneous only during the peaks of ascospore release. The ACR was significantly higher at the centre of the trees and the AD was significantly higher at the centre and at the western edge of the trees. Only the cumulative AD was significantly correlated with apple scab lesions at the same location (r = 0.83). In 2003, a similar pattern of spatial heterogeneity within the tree canopy was observed for AD and primary scab lesion counts and there was a linear relationship (R 2 = 0.84) between these two variables. It was concluded that ACR and AD within the tree canopy are not randomly distributed at least during peaks of ascospore release and that AD is a good estimate of primary scab lesion development. This spatial heterogeneity should be considered when estimating ascospore deposition using mathematical models or when quantifying ascosporic inoculum using spore samplers.  相似文献   

8.
A new dynamic model for Erysiphe necator ascosporic infections on grapevine was developed. Between budbreak of vines and the time when the pool of ascospores is depleted, the model uses weather data for calculating, at daily intervals: curve of ascospore maturation; ascospore discharge events and relative proportion of the discharged ascospores; infection periods and their relative infection severity; and progress of latency period and time when secondary infections should begin. The model was validated over a 4‐year period (2005–2008) in 26 vineyards in Italy by comparing model predictions with actual observations of the first seasonal symptoms of powdery mildew. The model showed high sensitivity, specificity and accuracy. Proportions of true and false positive predictions were TPP = 0·94 and FPP = 0·26, respectively. Because a proportion of predicted infection periods did not result in actual disease onset, confidence was higher for prediction of non‐infections than for prediction of infections. Most of the false positive predictions occurred in the earlier growth stages of the host, when the surface area of susceptible tissue may be very small so that the probability that ejected ascospores land on susceptible tissue is low. An equation was then developed to describe the probability that a predicted infection period results in disease onset as a function of the growth stage of vines at the time of prediction. The new model should improve early season powdery mildew management by helping vineyard managers schedule fungicide sprays or schedule the scouting of the vineyard for detection of first disease signs.  相似文献   

9.
ABSTRACT Maturation and release of ascospores of Anisogramma anomala were monitored over a 6-year period (1988 to 1995) in European hazelnut orchards located in western Oregon. Perithecia of A. anomala were dissected from stromata collected monthly from September to May to determine spore maturation. Spore maturation began in late summer; by January, >90% of the spores were morphologically mature. Similarly, both the number of mature ascospores per perithecium and the proportion of ascospores that germinated increased through autumn. After January, the number of spores per perithecium declined until May, when few viable spores remained. Each of the 6 years, rain catch-type spore traps were placed under cankers in diseased trees from 15 September to 30 June. Based on spore collection periods of 1 to 4 weeks, three patterns for the seasonal release of A. anomala ascospores were observed: in the 1988-1989 season, >80% of the seasonal ascospore release occurred between September and January; in the 1989-1990 season, 32 to 42% of the seasonal ascospore release occurred after mid-April; and in the other 4 years, monthly releases of ascospores were relatively uniform over the 9-month seasonal period. Timing and amount of precipitation were the most important variables accounting for the differences among the yearly patterns of ascospore release. Over all years and sites, the cumulative proportion of total ascospores collected in each orchard was highly correlated (R(2) = 0.90) with cumulative precipitation. This relationship was confirmed in mist chamber experiments. A regression model was developed relating cumulative ascospore release to cumulative hours of precipitation. The model provides an estimate of the proportion of ascospores remaining to be released after budbreak, which coincides with the period of highest susceptibility to infection.  相似文献   

10.
ABSTRACT Ascospore release in 20 populations of Venturia inaequalis was generally suppressed in wind tunnel tests during darkness and simulated rain, but the following relieved this suppression: (i) exposure to low relative humidity during simulated rain and (ii) protracted incubation of leaf samples and the consequent senescence of the pathogen population. No counterpart to (i) was observed under orchard conditions. Although V. inaequalis also released a high percentage of ascospores during darkness in field studies under simulated rain late in the season of ascospore release, this phenomenon has not been reported for natural rain events. A threshold value of 0.5 muW/cm(2) at 725 nm was identified as the minimum stimulatory light intensity. Ascospore release increased with increasing light intensity from 0.5 to 5.2 muW/cm(2) at 725 nm. There was also an intrinsic increase in ascospore release as duration of rain increased. In orchards, the combined impact of both processes is probably responsible for a delay in reaching peak ascospore release at several hours after sunrise. Ascospore release during darkness will generally constitute a small proportion of the total available supply of primary inoculum. Significant ascospore release, and therefore infection periods, can be assumed to begin shortly after sunrise, when rain begins at night in orchards with low potential ascospore dose (PAD). A PAD level of 1,000 ascospores per m(2) of orchard floor per season is suggested as a threshold, above which the night-released ascospores should not be ignored.  相似文献   

11.
The primary ascospore inoculum of Sclerotinia sclerotiorum initially infects rapeseed (Brassica napus var oleifera) via petals. Infected petals fall onto leaf surfaces, resulting in infection of those organs. A scanning electron microscopy (SEM) study of this process was undertaken to elucidate the host-parasite relationship and to determine the best plant organ for detection by serology of early field infection as an aid to disease forecasting and cost-effective disease control. The behaviour of ascospores deposited on young petals and on leaves was compared. Ascospores were deposited by inverting a mature apothecium above either a leaf disc, a young petal or young petal placed on a leaf surface. Spore germination, host penetration and colonization were examined by SEM. On young petals, the following steps in pathogenesis were observed: ascospore adhesion and germination, penetration of the host from short germ tubes and collapse of epidermal cells. Petals were then covered with extensive mycelium. From these sites, the mycelium invaded leaf tissues and infection proceeded. In contrast, ascospores landing directly on leaf surfaces failed to germinate. The role of petals as sites of pre-election in the aetiology of the disease is discussed in relation to the published literature.  相似文献   

12.
The epidemiology of circular leaf spot of persimmon, caused by Mycosphaerella nawae, was studied in a semi-arid area in Spain for two consecutive years. No conidia were observed on diseased leaves and all infections were thought to be caused by ascospores formed in the leaf litter. Ascospores were released mainly in April and May, but relatively low numbers in June were able to induce severe symptoms on trap plants. Temperature was not significantly correlated with ascospore catches or disease incidence on trap plants, indicating that it was not a limiting factor for disease development during the period of study. Rainfall was above normal, but still considerably lower than in endemic areas of Korea. Most infections coincided with rains, but the disease was observed also on trap plants exposed to less than 1?mm of precipitation and even in the absence of rain. Orchards were flood irrigated once inoculum deposits in the leaf litter had already been depleted, so it was not possible to determine its effects on ascospore release and disease development. The use of a wind tunnel to determine inoculum production allowed detection of physiologically mature ascospores of M. nawae in the leaf litter 1?C2?weeks before they were released to air in the orchard. Disease progress was fitted to the monomolecular growth curve, associated with monocyclic pathogens and diseases with a variable incubation period as a function of the host phenology.  相似文献   

13.
Mondal SN  Timmer LW 《Phytopathology》2002,92(12):1267-1275
ABSTRACT Mycosphaerella citri, the cause of citrus greasy spot, produces pseudothecia and ascospores in decomposing leaf litter on the grove floor. In laboratory studies, the effect of wetting and drying and temperature on the formation, maturation, and production of pseudothecia and ascospores was evaluated on mature, detached grapefruit leaves. Production of pseudothecia was most rapid when leaves were soaked five times per week for 2 h per day, but pseudothecial density and total ascospore production were greatest when leaves were soaked three times per week for 2 h per day. In duration of wetting studies, 3 h per day, 3 days per week brought about the most rapid production, but 10 to 30 min per day resulted in production of the most pseudothecia and ascospores. Pseudothecia and ascospore production were greatest at 28 degrees C and declined rapidly at lower and higher temperatures. Maturation of pseudothecia was slow at 20 and 24 degrees C, but production was high at 24 degrees C; at 32 degrees C, pseudothecia matured rapidly, but degenerated quickly. No mature pseudothecia were produced on leaves maintained continuously under wet conditions. In field studies, leaves were placed on the grove floor monthly from April 2000 to September 2001. Pseudothecia production was rapid during the summer rainy season from June to September. Pseudothecia produced on leaves placed in the grove from October to May developed and matured more slowly but were produced in much larger numbers than in summer. The number of days to first pseudothecial initials, 50% maturation, first discharge of ascospores, leaf decomposition, as well as pseudothecial density and incidence, were negatively related to average temperature. Total ascospore production was unrelated to temperature.  相似文献   

14.
ABSTRACT The influences of Microsphaeropsis sp., M. arundinis, Ophiostoma sp., Diplodia sp., and Trichoderma sp., all antagonists of Venturia inaequalis, on ascospore production were evaluated under natural conditions and compared with urea and Athelia bombacina, a known antagonist. In the autumn, the fungi were applied to leaf disks artificially inoculated with V. inaequalis and to scabbed apple (Malus domestica) leaves incubated under controlled and natural conditions. In addition, large-scale trials were conducted with Microsphaeropsis sp. applied either as a foliar postharvest spray or as a ground application at 90% leaf fall. All fungal isolates, except Ophiostoma sp., were recovered from the leaf material that overwintered in the orchard. All treatments, except those with Ophiostoma sp., resulted in a significant reduction in V. inaequalis ascospore production on the leaf disks incubated under controlled conditions or in the orchard. In 1997, leaves with apple scab lesions treated with urea or Microsphaeropsis sp. produced significantly fewer ascospores of V. inaequalis than did nontreated leaves, with a reduction of 73.0 and 76.3%, respectively. In 1998, leaves treated with Microsphaeropsis sp., urea, Trichoderma sp., A. bombacina, and M. arundinis reduced ascospore production by 84.3, 96.6, 75.2, 96.6, and 52.2%, respectively. Based on all tests combined, the most efficient isolate was Microsphaeropsis sp. Postharvest applications of Microsphaeropsis sp. reduced the total amount of airborne ascospores trapped by 70.7 and 79.8% as compared with the nontreated plots in 1997 and 1998, respectively. Microsphaeropsis sp. provided a significant and consistent reduction in ascospore production in all tests.  相似文献   

15.
Polystigma ochraceum is a major leaf pathogen of almond in Fars Province of Iran. Over a 4-year study period it was found that ascospore discharge began at flowering and continued for 4–5 weeks. The maximum discharge occurred at petal fall. The incubation period was estimated to be 4–5 weeks under experimental conditions. Although the mature ascospores could produce short germ tubes in distilled water or water agar, the fungus could not be cultured or grown on conventional media from either ascospores, pycnidiospores or stromatic tissues under laboratory conditions.
Of several systemic and non-systemic fungicides evaluated under field conditions, triforine at 100–400 μ/ml was most effective. Other fungicides which significantly reduced leaf infection were, in order of efficacy, copper oxychloride (2000 μg/ml), copper hydroxide (2000 mUg/ml), Bordeaux mixture (10 000 μg/ ml) and mancozeb (2000 μg/ml). Carbendazim and thiophanate methyl (500 μg/ml) increased the level of infection. One application of the fungicide at petal fall and then two at 14-day intervals were found to be effective in reducing the disease.  相似文献   

16.
Pseudothecia containing abundant ascospores of Mycosphaerella brassicicola were produced in vitro on Brussels sprout decoction agar at 15°C under a 16-hour photoperiod of different light regimes. Spermogonia containing spermatia were also produced on the decoction agar. Ascospores were released when cultures were misted with SDW and placed under continuous light. Germination of ascospores was highest between 20°C and 25°C and spores remained viable at relative humidities above 93.5%. Exposure of ascospores to 55% relative humidity for 24 h reduced their germination to 75%. A polyclonal antiserum raised against whole ascospores was used to detect, by immunofluorescence, the ascospore and mycelial wall of M . brassicicola , following reaction with anti-rabbit IgG FITC conjugate. Autofluorescence of spore and mycelial components of other fungal species could be eliminated using the counterstains Evan's blue and eriochrome black at 0.2% and 0.5%, respectively, in phosphate buffered saline (pH 7.2). A procedure was developed to detect, by immunofluorescence, ascospores of M . brassicicola on artificially inoculated Melinex spore tape. Coating of the spore tape with bovine serum albumin provided a suitable support medium and blocking agent for detection of ascospores in the field. The potential use of the system for selective detection of ascospores of M . brassicicola in infected crops of vegetable brassicas in the presence of other ascosporic fungi is discussed. Keywords : ascospores, immunofluorescence, Mycosphaerella brassicicola , spore production, spore trapping .  相似文献   

17.
ABSTRACT Relationships between environmental factors and release of ascospores of Anisogramma anomala, the causal agent of eastern filbert blight, were examined in four European hazelnut (Corylus avellana) orchards during a 2-year period. In each orchard, Burkhard volumetric spore traps and automated weather-monitoring equipment were deployed for 12-week periods beginning at budbreak, when hazelnut becomes susceptible to infection. Ascospores of A. anomala were released when stromata on the surface of hazelnut branches were wet from rain but not from dew. Release of ascospores ceased after branch surfaces dried. The duration of free moisture on branch surfaces regulated the initiation and rate of ascospore release, but no significant effects of temperature, relative humidity, wind, or light on ascospore release were apparent. Most (>90%) ascospores were captured during precipitation events that exceeded 20 h in duration, which represented about 10% of the total precipitation events each season. Quantitative relationships between the hourly capture of A. anomala ascospores and hours since the beginning of a precipitation event were developed. With the onset of precipitation, the hourly rate of ascospore capture increased until the fifth hour of rain, remained relatively constant between the fifth and twelfth hours, and then declined gradually. During the 12-week spore-trapping periods, the likelihood and rates of ascospore release associated with precipitation were highest at budbreak and then declined through April and May until early June, when the reserve of ascospores in the perithecia was depleted. Large numbers of ascospores were captured in the volumetric spore traps, indicating that ascospores may be commonly dispersed long distances on air currents as well as locally by splash dispersal within the canopy, as reported previously. The results indicate that monitoring seasonal precipitation patterns may be useful for estimating the quantity and temporal distribution of airborne inoculum during the period that the host is susceptible to infection.  相似文献   

18.
Apple scab caused by the fungus Venturia inaequalis can result in significant crop losses if not managed effectively. Sanitation as part of an integrated management strategy aims to significantly reduce primary inoculum to lower the disease pressure. This study evaluates the possibility of molecular detection and quantification of ascospore discharge and the use of this method to test for efficacy of orchard sanitation treatments. A method to detect and quantify airborne ascospores was developed using volumetric spore traps (VSTs). V. inaequalis specific primers were tested on daily VST samples from two orchard sections (leaf litter removed compared to leaf litter left) during spring. A molecular method to detect and quantify ascospores was tested by amplifying genomic regions of the mitochondrial CYP51A1 gene, and the ITS region using SYBR® green. Timing of ascospore discharge was compared to predicted infection risk and a degree day model using weather data. The average spore detection limit was estimated to be at levels of 1 pg μl?1 DNA (approximately 37 ascospores) per daily spore trap reading using CYP51A1 primers. Using the CYP51A1 primer pair, primary inoculum was estimated to be 51 % lower in the orchard sections where leaves had been removed, indicating that this method could be used to evaluate the efficacy of alternative control strategies such as leaf removal to reduce potential ascospore dose. This is the first report of combining VSTs and quantitative PCR to monitor airborne V. inaequalis ascospores.  相似文献   

19.
During European canker monitoring in an apple experimental orchard, 14 mummified fruit (two and three trees with 10 and four positive records in 2018 and 2019, respectively) showed perithecia. Perithecium production on apple fruit, confirmation of pathogenicity of Neonectria ditissima isolated from mummified fruit, and ascospore release from fruit tissues has rarely been reported, and their role in the epidemiology of European canker has been largely overlooked. Thus, the objectives of our study were to (a) prove the presence of both conidia and ascospores of N. ditissima in mummified fruit in an experimental field, confirming pathogenesis in different apple cultivars, and (b) monitor production of the two types of inoculum in infected apple fruit over time. Canker incidence in this orchard was 47% of trees with symptoms in 2018 and 48% in 2019. Molecular and morphological tests confirmed that the fungus detected in the mummified apple fruit was N. ditissima. Apple fruit with sporodochia and perithecia washed immediately after collection from the orchard showed conidia but no ascospores of N. ditissima. However, after 4 days’ incubation, perithecia on mummified fruit showed many ascospore cirri. Koch's postulates were fulfilled on apple plants and mature fruit. Fruit inoculated with N. ditissima released spores for over a year under Brazilian field conditions. The release of both spore types peaked in May (Brazilian leaf fall) and October (spring); release of conidia also peaked in February (early harvest). These results support our hypothesis that fruit can serve as primary inoculum for European canker in Brazilian apple orchards.  相似文献   

20.
The results of observation for three seasons in oilseed rape crops of the production and release of ascopores of Pyrenopeziza brassicae , the cause of light leaf spot disease of brassicas, are presented. Large apothecia (1–2 mm in diameter) take at least 3 weeks to develop on leaf petioles after infected leaves die, but small apothecia (50–200 um) may form on leaf lamellae after about 15 days. Apothecia were found on all 12 oilseed rape varieties examined. Spore trapping experiments in infected crops show that ascospore release is associated with rain, but most ascospores are released after rainfall when the crop debris bearing apothecia are wet. Ascospores can be released for up to 5 days after rain. Laboratory measurements show that apothecia can continue to release ascospores for up to 3 weeks even when they are subjected to wet and dry cycles. The consequences of the widespread occurrence of the sexual stage of P. brassicae are discussed and possible cycles of disease and spore production in oilseed crops are suggested.  相似文献   

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