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1.
Splash dispersal of Fusarium culmorum and Fusarium poae spores was studied, using inoculated straw placed on tiles as the inoculum source to infect agar strips and artificially produced leaves. In addition, patterns of spread were studied with spores from inoculated artificial leaves onto agar strips. Observed patterns of spore dispersal for each species were indistinguishable, although F. culmorum produced fewer colonies than F. poae. Furthermore, spore dispersal from inoculated straw and artificial leaves were essentially identical, with one exception; colonies arose from single conidia when spread from artificial leaves, but consisted of clumps of conidia when derived from inoculated straw. Splash dispersal patterns of both species onto the upper- and undersides of artificial leaves were different. On the upperside of the leaf, most colonies were found at the tip, while on the underside of the leaf most colonies were found at the base of the leaf. This is the first time that artificially produced leaves have been used in splash dispersal experiments.  相似文献   

2.
Spread of Verticillium wilt into newly established olive orchards in Andalucía, southern Spain, has caused concern in the olive industry in the region. This spread may result from use of Verticillium dahliae-infected planting material, which can extend distribution of the highly virulent, defoliating (D) pathotype of V. dahliae to new areas. In this study, a molecular diagnostic method for the early in planta detection of D V. dahliae was developed, aimed especially at nursery-produced olive plants. For this purpose, new primers for nested PCR were designed by sequencing a 992-bp RAPD marker of the D pathotype. The use of the specific primers and different nested-PCR protocols allowed the detection of V. dahliae pathotype D DNA in infected root and stem tissues of young olive plants. Detection of the pathogen was effective from the very earliest moments following inoculation of olive plants with a V. dahliae pathotype D conidia suspension as well as in inoculated, though symptomless, plants.  相似文献   

3.
Pestalotiopsis blight and leaf spot in macadamia are caused by species of Pestalotiopsis and Neopestalotiopsis. Conidia produced by these pathogens are mostly dispersed by wind and rain splash and are the primary infecting propagules. Rapid detection and quantification of airborne conidia are essential to determine the seasonal dynamics of inoculum and critical infection periods in macadamia orchards. A quantitative PCR (qPCR) using a new primer pair and a hydrolysis probe was developed to detect and quantify airborne conidia of Pestalotiopsis and Neopestalotiopsis species. The amplification efficiency of the qPCR was 96.4% and the assay had a limit of detection of 400 fg of Pestalotiopsis/Neopestalotiopsis gDNA, which corresponds to approximately 10 conidia. The qPCR assay coupled with spore trapping was used to monitor airborne conidia dispersal under field conditions. The results showed that the assay is specific and sensitive for detecting and quantifying Pestalotiopsis/Neopestalotiopsis conidia in macadamia orchards. The detection and quantification of the pathogen inoculum will improve our understanding of disease epidemiology and the ability to manage these diseases in macadamia.  相似文献   

4.
Controlling Verticillium dahliae through irrigation systems should be an important measure within integrated management of verticillium wilt of olive in Spain. Pathogen content of water infested by V. dahliae conidia and sclerotia can be diminished following in vitro treatments with the disinfectants OX-VIRIN and OX-AGUA AL25. Three concentrations per disinfectant were assessed for their effectiveness under operational conditions of modern irrigated olive orchards. Sterilized potted soil was drip-irrigated with conidia- or sclerotia-containing water that was pumped from a storage tank and disinfected (or not, control) within the pipelines via metering pumps. The trial was carried out in autumn and spring for each type of propagule infesting the water. The inoculum dispensed through drippers and the total inoculum density accumulated in soil were estimated. Furthermore, the treated residual inoculum in soil was assessed for pathogenicity on olive plants. Conidial incorporation in soil was prevented by most disinfectant treatments in spring; while for sclerotia, prevention was observed only at the highest OX-VIRIN (51.2 mL L−1; in both seasons) and OX-AGUA AL25 (11.27 mL L−1; in autumn) concentration. The remaining disinfectant treatments reduced conidia and sclerotia accumulation in soil by over 99% and 95%, respectively. Season particularly impacted the efficacy of lower concentrations. Expression of symptoms was not observed in olive plants grown in previously treated soils. The infectivity of the residual inoculum present in some treated soils was prevented, markedly reduced or limited to the roots. These results provide a novel, interesting and feasible approach in the management of the disease.  相似文献   

5.
Postbloom fruit drop disease (PFD) has caused serious impacts on citrus production in the Americas, occurring sporadically and suddenly during rain in the flowering period. In São Paulo State, Brazil, Colletotrichum abscissum is the causal agent responsible for over 80% of the disease incidence. Pathogen dispersal over long distances and the origin of primary inoculum are still unclear for PFD epidemics. We tested the hypothesis that citrus propagation material can harbour C. abscissum DNA by quantifying it in leaves of budwood increase block trees (BIB) and young citrus plants (YP) using multiplex quantitative PCR (qPCR). C. abscissum DNA was detected in all citrus nurseries, regardless of the type of propagative material, the sweet orange variety, or the nursery location. Overall, 73.4% of all samples from citrus nurseries have DNA from the pathogen, with a detection limit of 10 conidia. The average of 155 conidia found in YP was higher than the conidia observed on leaf samples from BIB (p = 0.03), although leaf samples from cultivars Valencia and Pera did not differ significantly, with means around 127 and 118 conidia, respectively (p = 0.75). This is the first molecular detection of C. abscissum in citrus propagative material. The multiplex qPCR assay may be used as a protocol for an accurate diagnosis of C. abscissum in citrus propagative material, may assist a better understanding of the pathogen dispersal over long distances, and may be used for further studies involving the quantification of C. abscissum in citrus orchards.  相似文献   

6.
A wind tunnel was designed to study the effect of wind, relative humidity, leaf movement and colony age on dispersal of conidia of Uncinula necator . Wind speed as low as 2.3 m s−1 instantaneously triggered dispersal of conidia from fixed leaf discs of 18-day-old infections. Conidia were observed on sporulating leaf discs even after exposure to 17 m s−1 wind. The fraction of conidia dispersed at a given wind speed increased with colony age from 12 to 24 days. Conidia of 27-day-old colonies were less easily dispersed. No gradient of maturation of conidia along the conidial chain was observed, suggesting that even newly formed conidia were able to germinate after dispersal. Germination of dispersed conidia decreased slightly with greater colony age. Both wind and simulated rain drops caused dispersal of conidia from infected leaves. Leaf movement at wind speed of 3.5–4 m s−1 increased dispersal, and the first impact of three simulated raindrops caused release of 53% of the total conidia dispersed. Relative humidity had no effect on dispersal of conidia at different wind speeds.  相似文献   

7.
Olive leprosy, caused by the fungus Phlyctema vagabunda, is a classic fruit rot disease widespread in the Mediterranean basin. From 2009 to 2013, new disease symptoms consisting of small circular necrotic leaf lesions, coin branch canker and shoot dieback were observed in Spanish and Portuguese olive orchards showing intense defoliation. Phlyctema‐like anamorphs were consistently isolated from leaves and shoots with symptoms. Representative isolates from affected leaves, shoots and fruits were characterized based on morphology of colonies and conidia, optimum growth temperature and comparison of DNA sequence data from four regions: ITS, tub2, MIT and rpb2. In addition, pathogenicity tests were performed on apple and olive fruits, and on branches and leaves of olive trees. Maximum mycelial growth rate ranged between 0.54 and 0.73 mm per day. Conidia produced on inoculated apple fruits showed slight differences in morphology among the representative fungal isolates evaluated. Phylogenetic analysis clustered all of the Phlyctema‐like isolates in the same clade, identifying them as Phlyctema vagabunda. On fruits, influence of wounding, ripening and cultivar resistance was studied, with cv. Blanqueta being the most susceptible cultivar. On branches, a mycelial‐plug inoculation method reproduced olive leprosy symptoms and caused shoot dieback. On leaves, Koch's postulates were fulfilled and the pathogen caused characteristic necrotic spots and plant defoliation. This is the first time that the pathogenicity of P. vagabunda in olive leaves has been demonstrated.  相似文献   

8.
This study investigated conidial dispersal in the field, and effects of simulated wind and rain on the dispersal of A. brassicicola on Chinese cabbage ( Brassica pekinensis ). Spores were sampled using a Burkard volumetric spore sampler and rotorod samplers in a Chinese cabbage crop. Disease incidence in the field was well fitted by a Gompertz curve with an adjusted r 2 of >0·99. Conidia of A. brassicicola were trapped in the field throughout the growing season. Peaks of high spore concentrations were usually associated with dry days, shortly after rain, high temperature or high wind speed. Diurnal periodicity of spore dispersal showed a peak of conidia trapped around 10·00 h. The number of conidia trapped at a height of 25 cm above ground level was greater than that at 50, 75 and 100 cm. Conidial dispersal was also studied under simulated conditions in a wind tunnel and a rain simulator. Generalized linear models were used to model these data. The number of conidia caught increased significantly at higher wind speeds and at higher rain intensities. Under simulated wind conditions, the number of conidia dispersed from source plants with wet leaves was only 22% of that for plants with dry leaves. Linear relationships were found between the number of conidia caught and the degree of infection of trap plants.  相似文献   

9.
Conidia ofAlternaria linicola produced on infected linseed crops were mainly dispersed by wind. The numbers of conidia in the air above linseed crops collected by a Burkard spore sampler were greatest between 1200 h and 1300 h, when the relative humidity was lowest. Although numbers of conidia collected decreased with increasing height within and above the crop canopy, air-borneA. linicola conidia were present up to 80 cm above the crop canopy. Conidia ofA. linicola were transported by wind up to at least 40 m downwind from an artificial line inoculum source, but their numbers decreased with increasing distance from the source. In 1991, 1992, and 1993, the dispersal ofA. linicola conidia above linseed crops followed a seasonal periodicity which was influenced by weather conditions and cultural practices. The greatest numbers of conidia were collected during July, August and early September and coincided with periods favourable for sporulation and with an increase in the incidence of the disease in the senescent crop. Air-borneA. linicola conidia produced on point or line inoculum sources (naturally infected linseed stem debris) were responsible for the spread of the disease in linseed crops. In 1992 and 1993, the disease was first detected downwind from the sources, but by the end of the growing seasons, it had spread in all directions and up to 20 m and 60 m from the sources, respectively. Disease gradients were initially steep near the inoculum sources but they became flatter with time due to the secondary spread of the disease.  相似文献   

10.
Dispersal of conidia of Fusicladium eriobotryae, the causal agent of loquat scab, was investigated in two loquat orchards in Spain from 2010 to 2012. A volumetric spore sampler, horizontally and vertically orientated microscope slides, and rain collectors were placed in loquat fields to trap conidia of F. eriobotryae. No conidia were collected in the volumetric sampler, and highly variable numbers of conidia were collected in the rain gatherers. Large numbers of conidia were collected by microscope slides, particularly by those held in a horizontal orientation compared with those held in a vertical orientation. Approximately 90 % of the F. eriobotryae conidia were collected during rainy periods. Based on ROC and Bayesian analysis, using ≥ 0.2 mm rainfall as a cut-off value resulted in a high probability of correctly predicting actual conidial dispersal, and had a low probability of failing to predict actual conidial dispersal. Based on the index of dispersion and the binary power law, the incidence of loquat scab on fruit was highly aggregated in space between and within trees, and aggregation was influenced by disease incidence. Our results demonstrate, for the first time, that F. eriobotryae is dispersed mainly in rain splash. The results will be integrated into a mechanistic, weather-driven, disease prediction model that should help growers to minimize fungicide application for the management of loquat scab.  相似文献   

11.
Postbloom fruit drop (PFD) is an important citrus disease that causes up to 100% yield losses during years in which conditions are favourable for the occurrence of epidemics. The conidia of Colletotrichum acutatum and C. gloeosporioides, causal agents of PFD, are predominantly dispersed by rain splash. At the beginning of epidemics, the distribution of diseased plants is random and the disease progress rate is very high, which is unusual for pathogens spread by rain splash. As the pathogen produces abundant conidia on diseased petals, pollinating insects may contribute to disease dispersal. This study investigated honeybees (Apis mellifera) as dispersal agents of C. acutatum and C. gloeosporioides among citrus plants. Two experiments were carried out in a screenhouse in which citrus plants were protected (or not) in insect‐proof cages. The source of inoculum was placed on one side of the screenhouse, and a honeybee hive was placed on the opposite side. All uncaged plants showed symptoms of the disease, and none of the caged plants exhibited PFD symptoms. The monomolecular model showed a good fit to disease progress in both experiments. Conidium‐like structures of Colletotrichum spp. were identified attached to the bodies of the honeybees by scanning electron microscopy. These results have revealed that honeybees disperse Colletotrichum among citrus plants.  相似文献   

12.
Splash dispersal of conidia of Mycocentrospora acerina in the field   总被引：1，自引：0，他引：1  
The dispersal of conidia of Mycocentrospora acerina was studied in caraway field trials. A Burkard spore trap, rotorods, inverted Petri dishes containing sucrose agar and rain gauges were used to trap conidia of M. acerina . Sporulation was stimulated by rainfall (2 mm) and moderate temperatures (around 15°C). Solar radiation had a negative effect on sporulation. Hardly any conidia were found in the spore traps on rainless days. Short distance (9 m) spread of M. acerina is mainly caused by splash dispersal of its conidia. Trap plants at 0, 0.1, 1 and 4 m from the inoculum source were readily infected under moist conditions. Beyond 9 m from an inoculum source no infection of caraway trap plants was found. Trap plants at 9 m from an inoculum source were infected in one out of three seasons only. Long distance (>9 m) spread could not be demonstrated by the techniques used in this study. The results suggest that, usually, a caraway field is infected by inoculum sources within that field.  相似文献   

13.
Splash was shown to be an effective mechanism for short-range dispersal of conidia of Ascochyta fabae f. sp. lentis , the cause of ascochyta blight of lentil. The dispersal gradients were well described by the power law model in its linear form, In y = In a-b In x. In still air the slope of the linearized dispersal gradient, b , ranged from 2.83 to 4.07 and was steeper for 4.9 mm than for 3.9 mm incident drops. Nevertheless, for all drop sizes tested, fewer than 50% of the conidia were splashed more than 15 cm from the source. The pattern of conidium dispersal was similar for both drop sizes when horizontal windspeeds were 2.5 or 5 m/s. Wind significantly decreased the value of b (range 2.35-2.43 at 2.5 m/s, 1.71–1.91 at 5 m/s) and increased by about 2 m the maximum distance that conidia in ballistic droplets were deposited. In addition, the experiments suggested two other potentially important mechanisms for dispersal of the pathogen over longer distances, namely conidia in small air-borne droplets and windblown leaflets.  相似文献   

14.
To investigate the hypothesis that disrupting pathogen movement within the plant canopy could slow the development of aschochyta blight, the effect of pea canopy architecture on splash dispersal of Mycosphaerella pinodes‐conidia was studied in controlled conditions using a rainfall simulator generating rain events (2 mm) in still air. In intra‐plant dispersal experiments, a source constituted by a semi‐leafless pea plant with a single infectious lesion (108 pycnidia per cm2 of lesion, 1685 conidia per pycnidium) was placed in the middle of eight healthy target plants. Spore deposition was estimated by the number of lesions that developed on each stipule of the source (auto‐deposition) and target (allo‐deposition) plants after incubation. Rates of deposition on the source and target plants were 0·53 and 0·47, respectively. On the source plant, most of the spores were splashed downwards, with few spores remaining at the infectious node and very few spores moving upwards. In inter‐plant dispersal experiments, potted plants were grouped to constitute 1‐m2 canopies. A range of canopy architectures was achieved by using different plant densities and growth stages. A suspension of conidia was placed in the centre of each canopy. Resulting horizontal dispersal gradients were generally described by a negative exponential model. Canopies with a leaf area index (LAI) greater than 0·48 produced gradients with slopes that were not significantly different. A less dense canopy (LAI 0·36) produced a significantly steeper slope. Half‐distances were short and ranged between 1·6 and 6·5 cm. The barrier rate, calculated as the ratio of the mean number of lesions assessed on isolated plants to the mean number of lesions assessed on plants in canopies, increased with increasing canopy LAI.  相似文献   

15.
An innovative inoculation process, involving the drilling of a trunk hole in 3 year-old olive trees and injecting a dense conidial suspension of Verticillium dahliae, was developed to study differentiation in foliar symptom expression between olive cultivars tolerant or susceptible to the pathogen. It was demonstrated that V. dahliae conidia could be translocated and colonize the xylem at the same distance above and below the point of trunk injection in both cultivars. However, the pathogen could be subsequently isolated at statistically significant percentages in susceptible cv. Amphissis compared to the tolerant cv. Kalamon, indicating operation of resistance mechanisms in the vascular phase of the disease. Consequently symptom development in the susceptible cultivar was at least sixfold more intensive compared to the tolerant cultivar, 6–11 months after trunk inoculation. Perennial olive orchard experiments, aimed at selecting Verticillium-resistant root-stocks, were conducted by applying the novel method in 2–3 year-old root-stock suckers of Amphissis olive trees and in the tolerant cvs Lianolia of Corfu and Koroneiki. It was indicated that potentially resistant root-stocks could be obtained following the trunk drilling technique. Resistance differentiation between cvs Amphissis and Kalamon was further verified through root inoculation by various V. dahliae microsclerotial concentrations and demonstrated that the trunk drilling inoculation procedure is equally efficient in resistance evaluation of olives to Verticillium wilt. The trunk inoculation procedure could be useful in selecting and screening root-stocks for resistance to V. dahliae and other vascular pathogens and could elucidate resistance mechanisms in woody plants against vascular wilt diseases.  相似文献   

16.
A study was carried out to investigate the relative infectivity of aerial and submerged conidia of Metarhizium flavoviride to Schistocerca gregaria and Zonocerus variegatus. The effect of formulation and application method on initial infectivity and field persistence of these conidia was investigated. Strain IMI 330189 was highly virulent to S. gregaria but showed relatively low virulence to Z. variegatus. Direct contact with conidia from the initial spray application resulted in 100% mortality of S. gregaria for all formulation and application combinations. The mean survival time of infected locusts was significantly shorter for treatments using a knapsack sprayer containing submerged conidia in water plus 10 ml litre−1 ‘Codacide’™ (seven days), than treatments with aerial conidia in oil using ULV techniques (8.9 days) or submerged conidia in modified (water plus adjuvants) ULV (MULV) (nine days) or in water-based (VLV) applications (9·3 days). Both aerial and submerged conidia persisted long enough in the environment to effect significant mortality via secondary pick-up of spray residue from vegeta-tion. Persistence was greatest in the ULV and MULV treatments, where the oil component of the formulations provided greater protection of the conidia from environmental stresses. The consequences of secondary pick-up of conidia from the different treatments on total mortality from a single application were examined using a simple host–pathogen model. This predicted that the ULV treatment would be much more effective than the other treatments under conditions where direct contact with the spray was limited. The results of these investigations are discussed in the context of development of optimum spray strategies for control of locusts and grasshoppers, and other pests, under different environmental conditions.  相似文献   

17.
ABSTRACT A rain simulator, with generated rains of 11 and 30 mm/h, was used to determine the effect of a cover crop or intercrop on the splash dispersal of Colletotrichum acutatum conidia. Dispersal through sudangrass, which can be used as a 'living mulch', was tested at two planting densities (140 or 280 kg/ha) and two heights (5 and 20 cm) and compared with a control consisting of a bare soil. Dispersal of C. acutatum conidia was assessed by counting colonies formed from spore-bearing splash droplets deposited in sheltered petri plates containing a selective medium. Both a cover crop and rain intensity significantly affected splash dispersal as measured by the interpolated total number of colonies (denoted by Sigma) from 0 to 72 cm from the inoculum source and in a time span of 61 min of generated rain (P < 0.001). However, there was no significant interaction of cover crop and intensity (P > 0.90). Dispersal with a 30-mm/h rain was higher than dispersal with a 11-mm/h rain, and presence of a cover crop significantly reduced dispersal compared with bare soil (P < 0.001). Of the treatments with sudangrass, cover crop planting density did not affect dispersal overall, but there was greater spore dispersal with the taller sudangrass at the higher planting density, due in part to the higher rate of water splashing with the tall grass compared with the short grass. Spore deposition in the petri plates could be functionally related to distance and time using a diffusion-type model, and parameter estimates could be used to explain the effects of cover crop on Sigma. Although the relationship between cover crop properties and splash dispersal is complex, results show the potential beneficial effects of the cover crop on disease management.  相似文献   

18.
BACKGROUND: Fenhexamid, a sterol biosynthesis inhibitor effective against Botrytis, inhibits the 3‐ketoreductase (Erg27) involved in C‐4 demethylation. Several fenhexamid‐resistant phenotypes have been detected in Botrytis cinerea populations from French vineyards. The field isolates with the highest resistance levels display amino acid changes in Erg27 (F412S, F412I or F412V). RESULTS: Fenhexamid‐resistant mutants were generated by site‐directed mutagenesis of the erg27 gene in a sensitive recipient strain to overcome the impact of different genetic backgrounds. The wild‐type erg27 allele was replaced by the three mutated alleles (erg27F412S/I/V) by homologous recombination. These isogenic strains were shown to be fenhexamid‐resistant and were used to quantify the impact of F412 mutations on fungal fitness. Several parameters, including radial growth, the production of sclerotia and conidia, freezing resistance and aggressiveness, were quantified in laboratory conditions. Analysis of variance demonstrated significant differences between the mutant and parental strains for some characters. In particular, the mutants grew more slowly than the wild‐type strain and displayed variations in the production of sclerotia and conidia with temperature and susceptibility to freezing. CONCLUSIONS: The results highlight a moderate but significant impact of F412 mutations on the survival capacity of B. cinerea strains displaying high levels of resistance to fenhexamid in laboratory conditions, potentially limiting their dispersal and persistence, particularly in terms of overwintering, in field conditions. Copyright © 2011 Society of Chemical Industry  相似文献   

19.
Attachment and adhesion of conidia of a wheat-isolate of Stagonospora nodorum to leaf and artificial surfaces was studied. Attachment of conidia was a non-viable process, separate from adhesion, that occurred rapidly and irreversibly. Attachment involved conidial-surface carbohydrates and was partially influenced by surface hydrophobicity. The subsequent adhesion, via the secretion of extracellular matrix from conidia, was a viable process that induced the complete cover of conidia in response to wheat leaf surface components containing epi-cuticular wax and to a lesser extent to barley but inducing only partial covering on glass. Results suggest that specific surface components from the compatible host promote rapid attachment and adhesion of S. nodorum conidia.  相似文献   

20.
In six field experiments, seed treatment with Clonostachys rosea (IK726) significantly reduced disease caused by Fusarium culmorum. IK726 was active against the pathogen at average soil temperatures at sowing ranging from 6.2 to 12 °C. Both in the field experiments and in growth chamber experiments conducted in sand, dried and stored conidia of IK726 controlled F. culmorum as effectively as freshly harvested conidia. A high correlation was found between disease index ratings from field experiments and from corresponding growth chamber sand tests. Amendment with the stickers Pelgel or Sepiret did not influence control activity. The effective dosages of IK726 (cfu/seed) were estimated in bioassays and were very similar for freshly harvested conidia and for dried conidia. With a density of > 5×103 conidia per seed more than 80% disease control was repeatedly obtained with both types of conidia.  相似文献   

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