Effect of Rain Distribution Alteration on Splash Dispersal of Colletotrichum acutatum

ABSTRACT Splash dispersal of Colletotrichum acutatum conidia from infected strawberry fruit was assessed using a rain simulator to determine the properties of rain (e.g., intensity [millimeters/hour] or drop size distribution) most related to dissemination. Dispersal with a simulated rain corresponding to a natural rain of about 11 mm/h was compared with dispersal of three other simulated rains that had larger and smaller drop sizes, on average, than idealized natural rains. Splash droplets were collected in sheltered petri plates with a selective medium for Colletotrichum, and colonies formed from conidia entrained in the droplets were counted and used as the measure of dispersal. Colonies were mostly confined to a 27-cm radius from the source, and density of colonies decreased exponentially with the distance squared, as indicated by the fit of a diffusion-type model to the data. Splash dispersal was more affected by drop size distribution than rain intensity or other properties of the generated rains. That is, there was a direct positive relationship between total colonies over 61 min of rain for a circular area with a 72-cm radius (Sigma) and the mass (volume) median diameter of impacting drops (D(0)') for four rain-simulation treatments. In a separate study, strawberry fruit were exposed to the same four simulated rains at two distances from a point source and for two rain durations. Although the proportion of infected fruit (y) increased with time and decreased with distance, rain treatment did not significantly affect y, as predicted based on past work with a wide range of intensities of simulated rains.     

Dispersal of Pseudocercosporella herpotrichoides and Pyrenopeziza brassicae spores in splash droplets

Splash dispersal of conidia which differ in shape and size, those of Pseudocercosporella herpo ichoides (needle-shaped, 52×2 μm) and Pyrenopeziza hrassicae (cylindrical, 12×3 μm), was studisd by allowing 5 mm drops to fall 13 m on to suspensions (depth 0.5 mm, concentration 120, 000 spores/ml) of each. The resulting splash droplets were collected on photographic film. The pattern of spore dispersal with distance and the distribution of spore-carrying droplets and spores within droplet-size categories were similar for both fungi. Regressions of square root spore number) on droplet diameter gave lines with slopes of 0.0138 for P. herpotrichoides and 0.0167 for P. brassicae.     

Effects of Single-Drop Impactions and Natural and Simulated Rains on the Dispersal of Botryosphaeria dothidea Conidia

ABSTRACT Laboratory and field experiments were conducted to study the dispersal of Botryosphaeria dothidea conidia using single-drop impactions and natural and simulated precipitations. For laboratory studies, 200 single drops were released from a height of 1 m on infected pistachio nuts. On pieces of photographic film, 50% of the droplets were collected within 20 mm (average droplet travel distance) of the target area, and the droplets ranged from 0.041 to 3.19 mm in diameter, with an average of 0.3 mm. Each droplet carried an average of 23 B. dothidea conidia. In 3 years of field experiments, rainwater was collected in funnels connected to bottles positioned at different heights inside the tree canopy and at different distances away from the edge of tree canopy in three commercial pistachio orchards in San Joaquin, Yolo, and Glenn counties in California. Numbers of conidia in rainwater varied among and within sampling seasons by sampling dates and orchards. Up to 67,000 conidia/ml were obtained in rainwater samples collected from an orchard in Yolo County. Rainwater from orchards in Yolo and Glenn counties contained a consistently higher number of conidia than rainwater collected from the orchard in San Joaquin County. Variation in numbers of conidia also existed among heights where bottles were located. There were significantly more conidia in rainwater collected inside than outside tree canopies. Inside tree canopies, bottles located at 100 and 150 cm above ground collected more B. dothidea conidia than those placed at 50 and 200 cm. Conidia were collected as far as 1 m from the tree canopy edge. Based on data from the Glenn County orchard, a linear relationship between number of conidia (Y) and rainfall amount (X) in millimeters was determined as Y = 240X - 3,867, with r(2) = 0.91, which meant that a minimum of 16.1 mm of rain was needed to disperse conidia of B. dothidea. The power law model best described the dispersal gradients of B. dothidea propagules in the 1999-2000 and 2001-02 sampling seasons, with r(2) values of >/=0.73, whereas the exponential law model fit best for the 2000-01 data, with r(2) values of >/=0.81. In a rain simulation experiment, the intensity of the rain generated by a nozzle at 138 kPa of pressure inside the tree canopy was approximately five times higher than rain recorded outside the tree canopy. Rain removed up to 65% of conidia from infected fruit. These results confirmed that B. dothidea is a splash-dispersed pathogen with relatively short distances of spore dispersal within pistachio orchards. Only pycnidia are present in pistachio orchards; therefore, the results also indicate that inoculum of B. dothidea should be entirely splashed dispersed.     

Wind dispersal of conidia of Botrytis spp. pathogenic to Vicia faba

Increasing numbers of conidia were blown from sporulating cultures of Botrytis fabae and B. cinerea as windspeed increased up to 10 m/s. Partial drying of cultures increased the number of spores blown away at low and intermediate windspeeds. Release of spores at a constant windspeed was sustained over a prolonged period. Different patterns of release from colonies of the two species when windspeed was gradually increased, or at a constant windspeed. may be related to differences in spore size affecting the drying rate. Many conidia of both species were released as clumps. A higher proportion of B. cinerea than B. fabae conidia were clumped, partly because the mean number of spores per clump was greater. Individual conidia fell more slowly in still air than did clumps. The humidity in a bean crop was more favourable to development of Botrytis lesions than that above the crop. Low windspeeds measured within crops may restrict dispersal of conidia and may result in uneven distribution of chocolate spot lesions.     

Effects of a Cover Crop on Splash Dispersal of Colletotrichum acutatum Conidia

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.     

Evaluation of the Francome MkII exhaust nozzle sprayer to apply oil-based formulations of Metarhizium flavoviride for locust control

Conidia of the fungus Metarhizium flavoviride were formulated in a paraffinic oil, ‘Shellsol’ T, and sprayed using the Francome MkII exhaust nozzle sprayer. Germination of the conidia collected from the spray was reduced by 30% as compared to unsprayed conidia. However, in bioassays, there was no detectable difference in virulence with conidia collected from the spray samples and unsprayed formulation. This indicated that, despite the recorded reduction in the concentration of active conidia, the efficacy of the formulation remained unchanged after passing through the exhaust nozzle sprayer. The droplet size spectra produced by the sprayer were investigated using the Malvern series 2600cc particle size analyser. The optimum droplets for locust control produced by this sprayer were generated by the number 1 nozzle (internal diameter 2·5 mm) with the number 1 restrictor ring (internal diameter 12.5 mm) sprayed at a pressure of 0·2 bar. The droplets thus produced had a volume median diameter of 58 μm when the nozzle protruded between 1 and 2 mm above the level of the restrictor ring. Of the droplets in the spray plume created by these conditions, 33% were between 50 and 100 μm, a range recommended as an achievable optimum for the ultra-low-volume application of Metarhizium flavoviride. The role of the exhaust nozzle sprayer as a tool for the application of M. flavoviride for locust control is discussed with reference to other vehicle-mounted ultra-low-volume sprayers. © 1997 SCI     

The incorporation of pathogen spores into rain-splash droplets: a modelling approach

Simple, theoretical, physical principles and existing experimental data were used to derive an analytical model to describe the incorporation of plant pathogen spores into splash droplets. Data were obtained from experiments on splash dispersal of spores of Pseudocercosporella herpotrichoides (cereal eyespot), Pyrenopeziza brassicae (oilseed rape light leaf spot) and Septoria nodorum (wheat glume blotch). In these experiments, incident drops of diameter 4–5 mm were allowed to fall onto spore suspensions 0.5 mm deep with 1.2 × 10⁵ to 6.5 × 10⁵ spores/mL. The analytical model was constructed as the product of three functions of droplet diameter which described, respectively, the frequency distribution of droplet diameters, the proportion of droplets carrying spores and the mean number of spores in spore-carrying droplets in each diameter category. The frequency distribution of droplet sizes was described by a log-normal distribution, the proportion of droplets carrying spores was described by an exponential function and the adimensional spore concentration in spore-carrying droplets was described by a power law. The cumulative proportions of spores in droplets in diameter categories of increasing diameter were calculated to compare observed and fitted data.     

Splash dispersal of conidia of Mycocentrospora acerina in the field

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.     

Comparison of rain effects on splash dispersal of three colletotrichum species infecting strawberry

ABSTRACT Rain simulation studies were performed to compare splash dispersal of three Colletotrichum species: C. acutatum (C. acutatum-O isolate from Ohio and C. acutatum-M isolate from Mississippi), C. fragariae (isolate from Mississippi), and C. gloeosporioides (isolate from Florida). Conidial dispersal was assessed by counting colonies formed from spore-bearing splash droplets deposited in sheltered petri plates containing a selective medium. Colonies were converted to number of conidia based on germination rates of spores on the media. The interpolated total number of dispersed conidia over a 61 min rain and 72 cm from the point source (Sigma) was calculated. For all species, a rain intensity of 30-mm/h resulted in significantly greater dispersal than an intensity of 11-mm/h. C. fragariae had the lowest amount of spore dispersal, and C. acutatum-O had the highest dispersal. C. acutatum-M and C. gloeosporioides were intermediate in magnitude of conidial splash dispersal. However, differences were directly attributed to differences in spore density per fruit at the source. When Sigma was corrected for source strength (Sigma(r)), the species were very similar, with only C. acutatum-M having a mean Sigma(r) significantly less than the others. Proportions and rates of spore removal (per minute) from source fruits were higher for C. acutatum-O and C. gloeosporioides than for other isolates. Wash-off rates of conidia deposited on healthy fruits were the same for all species. Deposition flux density of spores that had been uniformly sprayed over the entire soil surface of the experimental area was affected by species. A significant difference in means was observed between C. acutatum and C. fragariae-the latter had a somewhat lower flux density. This is the first demonstration that closely related species infecting the same plant species are similar in terms of splash dispersal.     

Dry-dispersal and rain-splash of brown (Puccinia recondita f.sp. tritici) and yellow (P. striiformis) rust spores from infected wheat leaves exposed to simulated raindrops

The dispersal of spores from lesions of brown ( Puccinia recondita f.sp. tritici ) or yellow ( P. striiformis ) rusts of wheat by impacting drops was studied. Using a generator of uniform-size drops, drops of 2.5, 3.4, 4.2 and 4.9 mm in diameter were released from rest at heights of 5, 50 and 100 cm above horizontal and primary leaves uniformly covered with sporulating lesions. Dry-dispersal and rain-splash occurred simultaneously in response to drop impaction. A coloration technique allowed separate counting of dry-dispersed and rain-splashed spores caught on slides. More spores were rain-splashed than dry-dispersed. Neither removal mechanism affected in-vitro germination of spores, which was higher in brown than in yellow rust. For both rusts, the number of both dry-dispersed and rain-splashed spores, as well as their travel distance, increased with drop diameter and fall height. The fall speed of incident drops in relation to diameter and fall height was obtained by solving numerically the equation of vertical drop motion. The number of spores removed by a given impacting drop was found to be a power function of the calculated kinetic energy of the impacting drop. Based on this experimental relationship, a simulation study showed the relevance of rain type in the removal of spores.     

Effects of wind, relative humidity, leaf movement and colony age on dispersal of conidia of Uncinula necator, causal agent of grape powdery mildew

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.     

Studies on the spread of the olive scab pathogen,Spilocaea oleagina1

Investigations were carried out to study the occurrence and effectiveness of wind dispersal of conidia of the olive spot pathogen Spilocaea oleagina. Dissemination in absence of rain was confirmed both by collecting conidia at various distances from an inoculum source and by using trap plants. The dispersal gradient of conidia was very steep: 3–10% of leaves of olive seedlings placed 20 m from diseased trees became infected.     

小麦白粉病菌分生孢子田间传播的初步研究

2015年度采用定容式孢子捕捉器对田间空气中小麦白粉病菌分生孢子传播的初步研究表明,在病害发生初期病菌分生孢子捕捉量比较低,但随着菌源中心病害的逐渐加重,病菌分生孢子在距菌源中心20 m和40 m远处捕捉量随之增大。线性弧度相关分析结果发现,距菌源中心北向20 m和40 m处的孢子捕捉量与风向存在显著正相关性;距菌源中心不同距离处的孢子捕捉量之间均存在极显著正相关性,且在相同方向上,距菌源中心20 m处孢子捕捉量显著高于40 m处孢子捕捉量。     

小麦白粉菌分生孢子离体后存活时间与温度的定量关系研究

<正>小麦白粉病是我国小麦生产上的重要病害之一,由专性寄生真菌Blumeria graminis f.sp.tritici引起。此病害是典型的气传病害,病菌分生孢子可借助高空气流远距离传播为害~([1]),高空传播距离与病菌的分生孢子存活时间有直接关系,而温度是     

The role of rain in dispersal of the primary inoculum of Plasmopara viticola

Although primary infection of grapevines by Plasmopara viticola requires splash dispersal of inoculum from soil to leaves, little is known about the role of rain in primary inoculum dispersal. Distribution of rain splashes from soil to grapevine canopy was evaluated over 20 rain periods (0.2 to 64.2 mm of rain) with splash samplers placed within the canopy. Samplers at 40, 80, and 140 cm above the soil caught 4.4, 0.03, and 0.003 drops/cm(2) of sampler area, respectively. Drops caught at 40 and 80 cm (1.5 cm in diameter) were larger than drops at 140 cm (1.3 cm). Leaf coverage by splashed drops, total drop number, and drop size increased with an increase in the maximum intensity of rain (mm/h) during any rain period. Any rainfall led to infection in potted grapevines placed outside on leaf litter containing oospores, if the litter contained germinated oospores at the time of rain; infection severity was unrelated to rain amount or intensity. Results from vineyards also indicate that any rain can carry P. viticola inoculum from soil to leaves and should be considered a splash event in disease prediction systems. Sampling for early disease detection should focus on the lower canopy, where the probability of splash impact is greatest.     

西洋参疫病菌的水滴飞溅传播规律

本项研究通过实验模拟手段揭示了水滴飞溅散布对西洋参疫病菌传播的机制。从定量的角度确立了西洋参疫病菌传播数量与水平距离、水滴碰撞速率的数学模型: Ln(Y)=b_0 b_1D b_2V 在自然雨滴的直径范围内,垂直下落高度在3.5m以内,飞溅传播直径约1m,在三维空间里,以低于碰撞源水平面的传播效果最为明显。     

Conidial dispersal by Alternaria brassicicola on Chinese cabbage (Brassica pekinensis) in the field and under simulated conditions

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.     

Patterns of Splash Dispersed Conidia of Fusarium poae and Fusarium culmorum

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.     

Production of conidia by Peronosclerospora sorghi on sorghum crops in Zimbabwe

Factors affecting the production of conidia of Peronosclerospora sorghi , causing sorghum downy mildew (SDM), were investigated during 1993 and 1994 in Zimbabwe. In the field conidia were detected on nights when the minimum temperature was in the range 10–19°C. On 73% of nights when conidia were detected rain had fallen within the previous 72 h and on 64% of nights wind speed was < 2.0 m s⁻¹. The time period over which conidia were detected was 2–9 h. Using incubated leaf material, conidia were produced in the temperature range 10–26°C. Local lesions and systemically infected leaf material produced 2.4–5.7 × 10³ conidia per cm². Under controlled conditions conidia were released from conidiophores for 2.5 h after maturation and were shown to be well adapted to wind dispersal, having a settling velocity of 1.5 × 10⁻⁴ m s⁻¹. Conditions that are suitable for conidia production occur in Zimbabwe and other semi-arid regions of southern Africa during the cropping season.     

黑附球菌抗紫外线保护剂的筛选

为减少紫外线对黑附球菌 Epicoccum purpurascens 分生孢子的影响,提高分生孢子在田间的生物活性,在室内检测了6种紫外线吸收剂和4种光稳定剂之间的不同组合(复合型抗紫外线保护剂)对黑附球菌XF1菌株分生孢子抗紫外线的保护作用。结果表明:不同复合型抗紫外线保护剂对XF1分生孢子的保护效率差异较大,其中苯并三唑类与六甲基磷酰三胺的组合(a3b1)及苯甲酮与六甲基磷酰三胺的组合(a4b1和a5b1)保护作用较强,在253.7 nm波长紫外灯下照射40 min,保护效率均达90%以上;水杨酸苯酯类与六甲基磷酰三胺的组合(a1b1)对分生孢子的保护效率较低,仅为37.12%;水杨酸苯酯类、苯并三唑类、苯甲酮类与光稳定剂770(b2)的组合(a1b2、a3b2、a4b2和a5b2)则无保护作用。对于选出的3种复合型抗紫外线保护剂(a3b1、a4b1、a5b1),其最适宜的溶剂组合为 V (正己烷)∶V (花生油)=1∶1,a4b1和a5b1使用时的质量浓度应大于7.5 mg/mL,而a3b1的质量浓度应大于10 mg/mL。采用波长为253.7 nm的紫外灯照射90 min,所选出的3种复合型抗紫外线保护剂对分生孢子的保护效率均保持在88%以上;照射180 min后,保护效率均大于63%。