scholarly journals Use of a Rainfall Frequency Threshold to Adjust a Degree-Day Model of Ascospore Maturity of Venturia inaequalis

Plant Disease ◽  
2005 ◽  
Vol 89 (2) ◽  
pp. 198-202 ◽  
Author(s):  
Arne Stensvand ◽  
Håvard Eikemo ◽  
David M. Gadoury ◽  
Robert C. Seem
Keyword(s):  
New Hampshire ◽  
Venturia Inaequalis ◽  
Simple Modification ◽  
Degree Day ◽  
Rainfall Frequency ◽  
Spore Release ◽  
Ascospore Release ◽  
Frequency Threshold ◽  
Rain Events ◽  
Southern Norway

Estimates of ascospore maturity generated by a model developed previously in New Hampshire, United States, were compared with the cumulative release of ascospores in southern Norway as monitored by volumetric spore traps at one site for 12 years, and at two additional sites for 2 years. In locations and years with frequent rain events, model-estimated ascospore maturity closely approximated observed ascospore release. However, in years with protracted dry periods of 1 to 3 weeks with no or little rain, not only was spore release delayed, but release continued to lag behind predicted maturity even after several rain events subsequent to the dry interval. By halting degree-day (base = 0°C) accumulation if 7 consecutive days without rain occurred, accuracy of the model during “dry” years was greatly improved, without substantially affecting accuracy in “wet” seasons. With minimal additional effort on the part of the user, this simple modification increases the accuracy of model-derived estimates of ascospore maturity when lack of rain slows ascospore maturation.

scholarly journals A Comparison of Methods Used to Estimate the Maturity and Release of Ascospores of Venturia inaequalis

Plant Disease ◽  
2004 ◽  
Vol 88 (8) ◽  
pp. 869-874 ◽  
Author(s):  
David M. Gadoury ◽  
Robert C. Seem ◽  
William E. MacHardy ◽  
Wayne F. Wilcox ◽  
David A. Rosenberger ◽  
...  
Keyword(s):  
Venturia Inaequalis ◽  
Infected Leaf ◽  
Degree Days ◽  
Site Specific ◽  
Degree Day ◽  
Ascospore Discharge ◽  
Ascospore Development ◽  
Ascospore Release ◽  
The Mean ◽  
Highly Correlated

Maturation and release of ascospores of Venturia inaequalis were assessed at Geneva and Highland, NY, and at Durham, NH, by microscopic examination of crushed pseudothecia excised from infected apple leaves that were collected weekly from orchards (squash mounts) in 14 siteyear combinations. Airborne ascospore dose was monitored at each location in each year of the study by volumetric spore traps. Additional laboratory assessments were made at Geneva to quantify release from infected leaf segments upon wetting (discharge tests). Finally, ascospore maturity was estimated for each location using a degree-day model developed in an earlier study. Ascospore maturation and release determined by squash mounts and discharge tests lagged significantly behind cumulative ascospore release as measured by volumetric spore traps in the field. The mean date of 98% ascospore discharge as determined by squash mounts or discharge tests occurred from 23 to 28 days after the mean date on which 98% cumulative ascospore release had been detected by volumetric traps. In contrast, cumulative ascospore maturity estimated by the degree-day model was highly correlated (r2 = 0.82) with observed cumulative ascospore release as monitored by the volumetric traps. Although large differences between predicted maturity and observed discharge were common during the exponential phase of ascospore development, the date of 98% cumulative ascospore maturity predicted by the model was generally within 1 to 9 calendar days of the date of 98% cumulative ascospore recovery in the volumetric traps. Cumulative ascospore discharge as monitored by the volumetric traps always exceeded 98% at 600 degree days (base = 0°C) after green tip. Estimating the relative quantity of primary inoculum indirectly by means of a degree-day model was more closely aligned with observed ascospore release, as measured by volumetric traps, than actual assessments of ascospore maturity and discharge obtained through squash mounts and discharge tests. The degree-day model, therefore, may be a more accurate predictor of ascospore depletion than squash mounts or discharged tests, and has the added advantage that it can be widely applied to generate site-specific estimates of ascospore maturity for any location where daily temperature data are available.

scholarly journals Influence of Light, Relative Humidity, and Maturity of Populations on Discharge of Ascospores of Venturia inaequalis

1998 ◽  
Vol 88 (9) ◽  
pp. 902-909 ◽  
Author(s):  
David M. Gadoury ◽  
Arne Stensvand ◽  
Robert C. Seem
Keyword(s):  
Relative Humidity ◽  
Light Intensity ◽  
Venturia Inaequalis ◽  
Threshold Value ◽  
Field Studies ◽  
Pathogen Population ◽  
Ascospore Release ◽  
Simulated Rain ◽  
Rain Events ◽  
Combined Impact

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 μW/cm2 at 725 nm was identified as the minimum stimulatory light intensity. Ascospore release increased with increasing light intensity from 0.5 to 5.2 μW/cm2 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 m2 of orchard floor per season is suggested as a threshold, above which the night-released ascospores should not be ignored.

scholarly journals Discharge and Dissemination of Ascospores by Venturia inaequalis During Dew

Plant Disease ◽  
1998 ◽  
Vol 82 (7) ◽  
pp. 761-764 ◽  
Author(s):  
Arne Stensvand ◽  
Terje Amundsen ◽  
Lars Semb ◽  
David M. Gadoury ◽  
Robert C. Seem
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
Weather Conditions ◽  
Fair Weather ◽  
Peak Period ◽  
Ascospore Discharge ◽  
Dew Formation ◽  
Spore Release ◽  
Ascospore Release ◽  
Drying Conditions

Abundant airborne ascospores of the apple scab pathogen (Venturia inaequalis) have never before been observed during periods of dew. We studied ascospore release in V. inaequalis in two orchards in southeastern Norway using Burkard 7-day volumetric spore traps. At Ås in 1990, 1992, and 1997, and at Svelvik in 1992, a total of 14.8, 1.4, 0.27, and 26.9%, respectively, of the season's total spore release was trapped during periods of dew. Dew followed by spore release was observed 22 days at the two locations. During one night with dew at Ås in 1990 and two nights with dew at Svelvik in 1992, approximately 13 and 20%, respectively, of the season's total spore numbers were observed. High numbers of spores were trapped prior to sunrise, and on an average, 48.4% of the spores were trapped prior to 0400 in the morning. Episodes in which more than 1% of the season's inoculum was released during dew occurred around bloom of apple, which is the peak period for ascospore discharge, and followed more than 2 days of fair weather (clear, warm days and cool, humid nights). The ordinary suppression of ascospore release in V. inaequalis during darkness has been overcome in previous studies under laboratory conditions when protracted periods favorable for ascospore maturity occur without opportunity for ascospore discharge. This is the first confirmed report of relatively large (>10% of the season's total inoculum) numbers of airborne ascospores in orchards during dew. The sequential occurrence of specific weather conditions, for example (i) fair-weather days, (ii) cool nights with abundant dew formation, (iii) significant release and dispersal of airborne ascospores, and (iv) poor drying conditions or additional hours of leaf wetness due to fog or rain, would be required for dew-released ascospores to constitute a threat of infection. Absent the foregoing, release during dew is more likely to deplete the ascospore supply with no consequent increase in the overall risk of disease.

scholarly journals A Computer-Controlled Environmental Chamber for the Study of Aerial Fungal Spore Release

1997 ◽  
Vol 87 (10) ◽  
pp. 1078-1084 ◽  
Author(s):  
T. R. Gottwald ◽  
T. M. Trocine ◽  
L. W. Timmer
Keyword(s):  
Data Acquisition ◽  
Environmental Conditions ◽  
Venturia Inaequalis ◽  
Data Acquisition System ◽  
Environmental Data ◽  
Acquisition System ◽  
Leaf Wetness ◽  
Environmental Chamber ◽  
Spore Trap ◽  
Spore Release

An environmental chamber was designed to study aerial release of spores of ascomycetes and hyphomycetes, based on a device developed by C. M. Leach. Relative humidity (RH), temperature, red (660 nm) and infrared (880 nm) light, leaf wetness, wind speed, vibration, and rain events are controlled and monitored within the chamber via an RTC-HC11 real-time controller and data-acquisition system. A BASIC11 computer program is uploaded to and controls the system. The program requests values for environmental parameters that change through time according to user specifications. The controller interacts with a stepper motor, solenoids, and relay switches via a feedback system based on data received from solid-state RH, temperature, and leaf-wetness sensors. The data-acquisition system records environmental data from the chamber in RAM (random access memory) that can be downloaded to a personal computer for correlation with spore-release data. Spores released from fungal specimens on plant tissues and cultures placed in the chamber and subjected to the desired environmental conditions are collected on a continuous volumetric spore trap at an exhaust port from the chamber. The performance of the device was examined by measuring spore release of Mycosphaerella citri, Alternaria solani, and Venturia inaequalis under various environmental conditions.

scholarly journals Botryosphaeriaceae Species Spore-Trapping Studies in California Vineyards

Plant Disease ◽  
2010 ◽  
Vol 94 (6) ◽  
pp. 717-724 ◽  
Author(s):  
J. R. Úrbez-Torres ◽  
M. Battany ◽  
L. J. Bettiga ◽  
C. Gispert ◽  
G. McGourty ◽  
...  
Keyword(s):  
Strong Relationship ◽  
Early Spring ◽  
Seasonal Abundance ◽  
Petroleum Jelly ◽  
Riverside County ◽  
Spore Release ◽  
Spore Trapping ◽  
Rain Events ◽  
Microscope Slides ◽  
Glass Microscope

The seasonal abundance of Botryosphaeriaceae spp. spores was studied in California vineyards by using glass microscope slides covered with petroleum jelly placed on grapevine cordons and Burkard volumetric spore traps at seven and two different locations, respectively. Correlation analysis was used to determine which meteorological variables (precipitation, relative humidity, temperature, and wind speed) influenced Botryosphaeriaceae spp. spore release. Among all variables, regression analysis resulted in a strong relationship between spore release and precipitation. Additionally, a positive relationship between irrigation and spore release was also observed in the Riverside County vineyard. During the study period, spore discharge of Botryosphaeriaceae spp. occurred from the first fall rain through the last spring rains, coinciding with September to April. However, based on the results obtained from the spore traps, most spores (over 60%) were trapped following rain events during the winter months of December, January, and February, which coincides with the grapevine pruning season. Botryosphaeriaceae spp. spore release was much lower in fall and early spring (22%) and very few or no spores were trapped in late spring and summer (3%). This work suggests that a delay of pruning time in California may be warranted to reduce grapevine infection because the current timing coincides with the greatest period of spore discharge.

scholarly journals Evaluation of three models for predicting Venturia inaequalis ascospore release in Southern Brazil

2013 ◽  
Vol 66 ◽  
pp. 303-307 ◽  
Author(s):  
S.A.M. Alves ◽  
R.M. Beresford
Keyword(s):  
Venturia Inaequalis ◽  
Seasonal Pattern ◽  
Black Spot ◽  
Bud Break ◽  
Growth Season ◽  
Start Date ◽  
Winter Temperatures ◽  
Ascospore Release ◽  
Principal Source ◽  
Best Fit

Ascospores of Venturia inaequalis constitute the principal source of primary inoculum for epidemics of apple black spot (scab) Mathematical models that describe ascospore release have been developed in USA New Zealand and Italy These models are based upon degreeday accumulation In this work the seasonal pattern of released ascospores of V inaequalis in Vacaria Brazil was evaluated During four apple growth seasons (2009 to 2012) the natural release of ascospores from five orchards was recorded The cumulative percentage of ascospore release was predicted using three different degreeday models The released ascospore data showed the best fit to the model developed in Italy with a start date of 22 August rather than the phenological stage of apple bud break It is concluded that in regions with warm winter temperatures models that use bud break to initiate ascospore maturation will tend to underestimate availability of ascospores at the beginning of the apple growth season

scholarly journals Sensitivity to climate change of the mass balance of glaciers in southern Norway

1993 ◽  
Vol 39 (133) ◽  
pp. 656-665 ◽  
Author(s):  
Tron Laumann ◽  
Niels Reeh
Keyword(s):  
Mass Balance ◽  
Atlantic Coast ◽  
Elevation Gradient ◽  
Greenland Ice Sheet ◽  
Climatic Conditions ◽  
Model Parameters ◽  
Average Mass ◽  
Degree Day ◽  
Temperature And Precipitation ◽  
Southern Norway

Abstract A degree-day model developed for parameterizing melt rates on the Greenland ice sheet is adapted to the climatic conditions on glaciers in southern Norway. The model is calibrated by means of observed average mass-balance-elevation relationships (1963–90) for three glaciers in a west-east transect in southern Norway and 30 year normals (1961–90) of temperature and precipitation observed at nearby climate stations. The calibration gives a surprisingly small variation of the model parameters (degree-day factors for snow-and ice-melt, and precipitation-elevation gradient) from one glacier to another. The derived values of the parameters are used to estimate the change of the mass-balance-elevation relationship for different climatic scenarios. The study indicates that a low-lying glacier in the maritime, high-precipitation environment near the Atlantic coast is more sensitive to both temperature and precipitation changes than the high elevated glaciers in the dry, more continental climate farther away from the coast. However, all of the glaciers studied will lose mass in a warmer climate, unless the warming is accompanied by a dramatic increase in the precipitation of 25–40% deg−1 warming.

scholarly journals Distribution of the Infection Time of Ascospores of Venturia inaequalis

Plant Disease ◽  
2020 ◽  
Vol 104 (2) ◽  
pp. 465-473 ◽  
Author(s):  
Vincent Philion ◽  
Valentin Joubert ◽  
Marc Trapman ◽  
Anne-Grete R. Hjelkrem ◽  
Arne Stensvand
Keyword(s):  
Venturia Inaequalis ◽  
Apple Scab ◽  
Simulation Software ◽  
Infection Time ◽  
Different Temperatures ◽  
Ontogenic Resistance ◽  
Wetting Time ◽  
Rain Events ◽  
Time Required

In many areas where spring is wet, fungicides are applied in relation to rain events that trigger ejection of ascospores of Venturia inaequalis, which cause primary infections of apple scab. Past studies established the rate of ejection during rain in relation to light and temperature, and determined the wetting time required for infection. Simulation software uses this information to calculate risk and help time sprays accordingly. However, the distribution of the infection time required by a population of spores landed on leaves was never studied, and assumptions were used. To estimate this, we inoculated ascospores of V. inaequalis on potted trees at different temperatures for specific wetting times. Lesions were enumerated after incubation. Lesions increased with wetness time and leveled off once the slowest spores infected the host, closely matching the monomolecular model. Wetness hours were best adjusted for temperature using the Yin equation. The minimum infection time on the youngest leaves was about 5 h, matching results from previous studies, whereas half the lesions appeared after 7 h of infection. Infection times for leaves with ontogenic resistance were longer. Our results improve current software estimates and may improve spraying decisions.

Daily and seasonal spore dispersal by Mycosphaerella pinodes and development of mycosphaerella blight of field pea

2005 ◽  
Vol 83 (3) ◽  
pp. 302-310 ◽  
Author(s):  
Jin Xiu Zhang ◽  
W G Dilantha Fernando ◽  
Allen G Xue
Keyword(s):  
Disease Severity ◽  
Field Pea ◽  
Mycosphaerella Pinodes ◽  
Rain Event ◽  
Spore Dispersal ◽  
Rainfall Events ◽  
Inoculum Source ◽  
Practical Applications ◽  
Spore Release ◽  
Rain Events

Daily and seasonal spore dispersal of Mycosphaerella pinodes (Berk & Bloxam) Vestergren and the relationship of spore dispersal to distance and disease severity were investigated in a pea field in western Canada during two consecutive years. Most ascospores were released in response to rain events, during the first 23–27 d after the inoculum source area was infested with naturally diseased pea residue, whereas most pycnidiospores were trapped during the first 20 d. For both ascospores and pycnidiospores, the highest peaks of spore release occurred during the first 14–20 d after infestation. Few spores were trapped after day 27 after infestation. Daily peaks of ascospore and pycnidiospore release occurred between 1700 and 0400 hours. Most ascospores were released 1–2 d after a rain event and the largest peak appeared the first day after rain. In contrast, most pycnidiospores were released on the same day as rain occurred or the following day. The release of both spore types was associated with rainfall events ≥2 mm during the first 27 d after infestation but not with rainfall events after 27 d. Ascospore density was negatively correlated with distance from the inoculum source (r ≤ –0.92) and positively related to the disease severity (r ≥ 0.92). Disease severity decreased with increasing distance from the inoculum source. The patterns of spore dispersal associated with rain events have practical applications in the disease forecasting and spraying of chemicals to control the disease.Key words: field pea, mycosphaerella blight, rainfall, spore release.

scholarly journals A new apple scab risk model that integrates ascospore release infection risk and susceptible leaf area

2004 ◽  
Vol 57 ◽  
pp. 20-24 ◽  
Author(s):  
R.M Beresford ◽  
W.R. Henshall ◽  
J.W. Palmer
Keyword(s):  
Leaf Area ◽  
Risk Model ◽  
Venturia Inaequalis ◽  
Apple Scab ◽  
Black Spot ◽  
Infection Risk ◽  
Weather Data ◽  
Scab Control ◽  
Ascospore Release ◽  
Maturation Rate

A new model has been developed for assessing daytoday variation in risk of infection of apples by Venturia inaequalis the scab or black spot pathogen The model comprises three components ascospore availability wetnessbased infection risk based on Mills periods and susceptible leaf area The ascospore and wetnessbased infection risk components were adapted from previous models whereas the susceptible leaf area component is new When the model used weather data from Hawkes Bay and Nelson in spring 2003 the predicted risk incidence was determined mostly by wetnessbased infection risk but the magnitude of risk periods was greatly influenced by predicted ascospore release The susceptible leaf area component predicted a hitherto unidentified increase in infection risk after the peak in ascospore maturation rate had occurred The model is intended to assist in fungicide selection and timing for scab control in New Zealand apples but needs to be field tested before implementation

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