scholarly journals Effects of Humidity on the Development of Grapevine Powdery Mildew

2003 ◽  
Vol 93 (9) ◽  
pp. 1137-1144 ◽  
Author(s):  
J. E. Carroll ◽  
W. F. Wilcox
Keyword(s):  
Powdery Mildew ◽  
Management Practices ◽  
Absolute Humidity ◽  
Uncinula Necator ◽  
Disease Development ◽  
Optimum Temperature ◽  
Test Range ◽  
Grapevine Powdery Mildew ◽  
Conidium Germination

The effects of humidity on powdery mildew development on grape seedlings and the germination of Uncinula necator conidia in vitro were examined. Studies were conducted at an optimum temperature of 25 ± 2°C. Disease on foliage was markedly affected by humidity levels in the test range of 39 to 98% relative humidity (RH), corresponding to vapor pressure deficits (VPD) of 1,914 to 61 Pa. Incidence and severity increased with increasing humidity to an optimum near 85% RH, and then appeared to plateau or decrease marginally at higher values. Conidial density and chain length also were proportional to humidity, but were influenced less strongly. There was a strong, positive linear relationship between humidity level and frequency of conidium germination with RH treatments of ≤84%. However, germination frequency fell sharply at RH levels above a mean of 87%. All measures of humidity were equally accurate in predicting germination responses; however, VPD was slightly more effective than RH in accounting for effects on disease development and pathogen sporulation, and both were more effective than absolute humidity. Humidity appears to play a significant role in grapevine powdery mildew epidemiology, confirming the benefits of management practices to avoid and mitigate high humidity in the vineyard canopy.

scholarly journals Effects of Sunlight Exposure on Grapevine Powdery Mildew Development

2012 ◽  
Vol 102 (9) ◽  
pp. 857-866 ◽  
Author(s):  
Craig N. Austin ◽  
Wayne F. Wilcox
Keyword(s):  
Powdery Mildew ◽  
Solar Radiation ◽  
Controlled Environment ◽  
Disease Development ◽  
Inhibitory Effects ◽  
Grapevine Powdery Mildew ◽  
Individual Experiment ◽  
Hyphal Formation ◽  
The Individual ◽  
Artificial Shading

Natural and artificially induced shade increased grapevine powdery mildew (Erysiphe necator) severity in the vineyard, with foliar disease severity 49 to 75% higher relative to leaves in full sun, depending on the level of natural shading experienced and the individual experiment. Cluster disease severities increased by 20 to 40% relative to those on check vines when ultraviolet (UV) radiation was filtered from sunlight reaching vines in artificial shading experiments. Surface temperatures of leaves in full sunlight averaged 5 to 8°C higher than those in natural shade, and in one experiment, filtering 80% of all wavelengths of solar radiation, including longer wavelengths responsible for heating irradiated tissues, increased disease more than filtering UV alone. In controlled environment experiments, UV-B radiation reduced germination of E. necator conidia and inhibited both colony establishment (hyphal formation and elongation) and maturity (latent period). Inhibitory effects of UV-B radiation were significantly greater at 30°C than at 20 or 25°C. Thus, sunlight appears to inhibit powdery mildew development through at least two mechanisms, i.e., (i) UV radiation's damaging effects on exposed conidia and thalli of the pathogen; and (ii) elevating temperatures of irradiated tissues to a level supraoptimal or inhibitory for pathogen development. Furthermore, these effects are synergistic at temperatures near the upper threshold for disease development.

Release, germination, and pathogenicity of ascospores of Uncinula necator under controlled conditions

1998 ◽  
Vol 76 (5) ◽  
pp. 777-781 ◽  
Author(s):  
F Jailloux ◽  
T Thind ◽  
M Clerjeau
Keyword(s):  
Powdery Mildew ◽  
Vitis Vinifera ◽  
Storage Conditions ◽  
Vitis Vinifera L ◽  
Uncinula Necator ◽  
Grapevine Powdery Mildew ◽  
Germination Ability ◽  
Ascospore Release ◽  
Probable Role ◽  
Leaf Disks

A laboratory technique was standardized for studying the release, maturation, germination, and pathogenicity of ascospores of Uncinula necator (Schw.) Burr. Surface disinfestation and wetting of grape (Vitis vinifera L.) leaf disks bearing cleistothecia collected in the vineyard before incubation in a humid chamber for 48 h at 20°C were found essential for obtaining the release of ascospores (8 ascospores/cm2). Storage conditions involving periodic wetting treatments of cleistothecia at 5°C during 110 days were necessary to induce both ascospore release (80 ascospores/cm2) and germination ability (62%). The matured ascospores were pathogenic on healthy leaf disks at 20°C indicating their probable role as a primary inoculum source. This technique can be helpful in studying the inheritance of characteristics such as pathogenicity and fungicidal resistance.Key words: cleistothecia, ascospores, maturation, germination, pathogenicity, Uncinula necator, grapevine, powdery mildew.

scholarly journals Effects of Ontogenic Resistance upon Establishment and Growth of Uncinula necator on Grape Berries

2003 ◽  
Vol 93 (5) ◽  
pp. 556-563 ◽  
Author(s):  
Andrea Ficke ◽  
David M. Gadoury ◽  
Robert C. Seem ◽  
Ian B. Dry
Keyword(s):  
Powdery Mildew ◽  
Colony Growth ◽  
Similar Degree ◽  
Uncinula Necator ◽  
Disease Development ◽  
Phenological Stage ◽  
Appressorium Formation ◽  
Hyphal Length ◽  
Grape Berries ◽  
Ontogenic Resistance

Grape berries become resistant to powdery mildew early in development and are nearly immune to infection within 4 weeks after bloom. In this study, ontogenic resistance did not reduce attachment, germination, or appressorium formation of Uncinula necator on 3- to 4-week-old berries of Vitis vinifera ‘Chardonnay’ or 3-week-old berries of V. labruscana ‘Concord’. Pathogen ingress halted at the cuticle before formation of a penetration pore. As berries aged, hyphal elongation and colony growth slowed until finally no secondary hyphae formed on fully resistant berries. More appressoria formed per unit of hyphal length as berries aged, indicating that failure to penetrate older berries led to increased attempts to penetrate resistant fruit. Additionally, hyphae within the colonies began to die as berries aged. Finally, the number of degree-hours between germination and sporulation of the colony (latent period) increased and sporophore density decreased with berry age at time of inoculation. Thus, ontogenic resistance both slows, and eventually halts disease development on grape berries, and limits the likelihood of spread by reducing absolute supply of conidia and delaying their formation. It furthermore has a consistent, stable, and predictable impact on grape powdery mildew and operates in a similar fashion and to a similar degree in both V. labruscana and V. vinifera, although at a slightly earlier phenological stage in V. labruscana.

scholarly journals Distributions of Sensitivities to Three Sterol Demethylation Inhibitor Fungicides Among Populations of Uncinula necator Sensitive and Resistant to Triadimefon

1997 ◽  
Vol 87 (8) ◽  
pp. 784-791 ◽  
Author(s):  
Eugene O. Erickson ◽  
Wayne F. Wilcox
Keyword(s):  
Powdery Mildew ◽  
Active Form ◽  
Correlation Coefficients ◽  
The Other ◽  
Cross Resistance ◽  
Uncinula Necator ◽  
Previous Exposure ◽  
Grapevine Powdery Mildew ◽  
Dmi Fungicides ◽  
Demethylation Inhibitor

Single-conidial isolates of Uncinula necator from (i) a population representing two vineyards with no previous exposure to sterol demethylation inhibitor (DMI) fungicides (“unexposed,” n = 77) and (ii) a population representing two vineyards in which powdery mildew was poorly controlled by triadimefon after prolonged DMI use (“selected,” n = 82) were assayed to determine distributions of sensitivities to the DMI fungicides triadimenol (the active form of triadimefon), myclobutanil, and fenarimol. Median 50% effective dose (ED50) values (micrograms per milliliter) in the selected versus unexposed populations were 0.06 versus 1.9 for triadimenol, 0.03 versus 0.23 for myclobutanil, and 0.03 versus 0.07 for fenarimol, respectively. Isolates were grouped into sensitivity classes according to their ED50 values, and those from the selected population were categorized as resistant if the frequency of their sensitivity class had increased significantly relative to levels found in the unexposed population (ED50 values exceeding 0.56, 0.18, and 0.18 μg/ml for triadimenol, myclobutanil, and fenarimol, respectively). Of the 76 isolates defined as resistant to triadimenol, 64% were classified as cross-resistant to myclobutanil, 18% were classified as cross-resistant to fenarimol, and 17% were classified as resistant to all three fungicides; 25% of the isolates classified as resistant to myclobutanil also were classified as resistant to fenarimol. Similar cross-resistance relationships were revealed when all isolates were examined by regressing log ED50 values for each fungicide against those for the remaining two fungicides to determine the correlation coefficients (e.g., r = 0.85 for triadimenol versus myclobutanil and 0.56 for triadimenol versus fenarimol). The restricted levels of cross-resistance indicated by these data, particularly between fenarimol and the other two fungicides, is in sharp contrast to the high levels of cross-resistance among DMIs reported for some other pathogens and has significant implications with respect to programs for managing grapevine powdery mildew and DMI resistance.

scholarly journals Bicarbonates and Botrytis: VI. Control of Gray Mold Enhances Geranium Growth

HortScience ◽  
1995 ◽  
Vol 30 (4) ◽  
pp. 767A-767
Author(s):  
C.L. Palmer ◽  
R.W. Langhans ◽  
R.K. Horst ◽  
H.W. Israel
Keyword(s):  
Powdery Mildew ◽  
Plant Height ◽  
Disease Incidence ◽  
Dry Weight ◽  
Colony Growth ◽  
Gray Mold ◽  
Disease Development ◽  
Development Data ◽  
Low Levels

Botrytis cinerea Pers. causes gray mold on greenhouse-grown geraniums (Pelargonium ×hortorum L. H. Bailey), among many other crops. Bicarbonates effectively control rose powdery mildew (Plant Dis. 76:247–480) and inhibit B. cinerea in vitro colony growth and conidial germination (Phytopathology 84:546, 1065). To examine bicarbonate effects on gray mold incidence and geranium growth, we sprayed seedling geranium cultivars Red Elite and Scarlet Elite weekly with 0, 25, and 50 mM NH4HCO3 or KHCO3. Seedlings were transplanted in Metromix 360 and misted every 24 m for 5 s to enhance disease development. Data were collected biweekly on disease incidence, floral number, plant height, and dry weight. Both cultivars performed similarly. Disease incidence decreased with application of bicarbonates. KHCO3 at 25 mM slightly increased dry weight and height over 0 mM, whereas 25 and 50 mM NH4HCO3 greatly increased both features. Fifty mM KHCO3 decreased height slightly, but had no effect on dry weight. Floral number decreased slightly with all bicarbonate treatments. It is indicated that KHCO3 at low levels and NH4HCO3 enhance seedling geranium growth by controlling gray mold incidence and by providing additional nutrients. (Supported by H&I Agritech Inc., Ithaca, NY 14850.)

Factors influencing the germination of macroconidia and secondary conidia of Claviceps africana

2002 ◽  
Vol 53 (10) ◽  
pp. 1087 ◽  
Author(s):  
Shamsul A. Bhuiyan ◽  
Victor J. Galea ◽  
Malcolm J. Ryley ◽  
David Tay ◽  
Allan T. Lisle
Keyword(s):  
Optimum Temperature ◽  
Flower Extract ◽  
Extract Agar ◽  
Factors Influencing ◽  
Water Potentials ◽  
Secondary Conidium ◽  
Claviceps Africana ◽  
Conidium Germination ◽  
Temperature Time

The influences of temperature, time, and moisture on the germination of macroconidia and secondary conidia of Australian isolates of Claviceps africana were studied in vitro. The optimum temperature for germination of both macroconidia and secondary conidia of C. africana was 20°C. Although germination of macroconidia ceased near 31°C, approximately 30% of secondary conidia germinated at 37°C after 48 and 72 h of incubation. Sorghum flower extract agar stimulated macroconidium and secondary conidium germination, irrespective of temperature. Germination of macroconidia and secondary conidia on water agar started after 4 h of incubation at 20°C, reaching a maximum after 16–24 h and 14 h, respectively. Maximum germination of both macroconidia and secondary conidia was at ≥ –5 bars at 20°C. Germination of secondary conidia ceased at –35 bars, whereas macroconidia germinated at water potentials as low as –55 bars at 20°C.

scholarly journals Suppression of Grapevine Powdery Mildew by a Mycophagous Mite

Plant Disease ◽  
2005 ◽  
Vol 89 (12) ◽  
pp. 1331-1338 ◽  
Author(s):  
Heather S. Melidossian ◽  
Robert C. Seem ◽  
Greg English-Loeb ◽  
Wayne F. Wilcox ◽  
David M. Gadoury
Keyword(s):  
Powdery Mildew ◽  
Vitis Vinifera ◽  
Uncinula Necator ◽  
Laboratory Studies ◽  
Rapid Loss ◽  
Infection Efficiency ◽  
Grapevine Powdery Mildew ◽  
Grape Powdery Mildew

Orthotydeus lambi reduced the severity of grape powdery mildew (Uncinula necator) on fruit and foliage of Vitis vinifera ‘Chardonnay’ and ‘Riesling’ in repeated field and laboratory trials. Vines were infested with O. lambi at two densities (5 or 30 mites per leaf) at each of two times (2 to 3 weeks prebloom and 1 week postbloom). Overall, powdery mildew on the berries and foliage was suppressed by early (prebloom) mite releases at both densities, but only by the higher density in late (postbloom) releases. In a separate trial, when foliage was infested at 30 mites per leaf but mites were excluded from certain fruit clusters, severity of powdery mildew was significantly reduced on the mite-free clusters of mite-infested shoots. Thus, O. lambi may suppress powdery mildew on the fruit by reducing inoculum from foliar infections. In laboratory studies, both immature and mature mites reduced infection efficiency, colony expansion, and sporulation of the mildew colonies; but immature mites were more voracious feeders, consuming more pathogen biomass per unit of mite biomass. Mites tore at the mycelium and conidia with their palps during feeding, leading to leakage, rapid loss of hyphal turgor, and collapse of hyphae.

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