THE INFLUENCE OF HOST LEAVES ON GERMINATION OF THE ASEXUAL SPORES OF SPHAEROTHECA MACULARIS (WALLR. EX. FR.) COOKE

1965 ◽  
Vol 11 (3) ◽  
pp. 539-545 ◽  
Author(s):  
J. S. Jhooty ◽  
W. E. McKeen
Keyword(s):  
Relative Humidity ◽  
Inhibitory Influence ◽  
High Moisture ◽  
Leaf Surfaces ◽  
Dry Conditions ◽  
Sphaerotheca Macularis ◽  
Glass Surfaces

Although the conidia of Sphaerotheca macularis need high moisture levels (above 90% relative humidity (R.H.)) to germinate satisfactorily on glass surfaces, they are able to germinate on host leaves under very dry conditions. The effects of some fractions, extracted from strawberry leaf surfaces, revealed that none of these fractions have a stimulating or an inhibitory influence on germination of these spores on glass surfaces at 98% R.H. The R.H. of strawberry leaf was measured and its influence on germination of these spores discussed.

WATER RELATIONS OF ASEXUAL SPORES OF SPHAEROTHECA MACULARIS (WALLR. EX. FR.) COOKE AND ERYSIPHE POLYGONI DC.

1965 ◽  
Vol 11 (3) ◽  
pp. 531-538 ◽  
Author(s):  
J. S. Jhooty ◽  
W. E. McKeen
Keyword(s):  
Relative Humidity ◽  
Water Content ◽  
Osmotic Pressure ◽  
Water Relations ◽  
Erysiphe Polygoni ◽  
Significant Change ◽  
Sphaerotheca Macularis ◽  
Glass Surfaces

The conidia of Sphaerotheca macularis germinate best at a relative humidity (R.H.) of 99 and 100% on glass surfaces, and germination does not occur if the R.H. is below 93%. Conidia of Erysiphe polygoni DC. germinate at 3% R.H. The water content of conidia of S. macularis and E. polygoni is 53 and 69% respectively. The osmotic pressure of S. macularis conidia is about 18 atm and their density varies from 1.10 to 1.11 g/ml. There is no significant change in the diameter and length of the conidia during germination.

scholarly journals Effects of relative humidity on aerosol light scattering in the Arctic

2010 ◽  
Vol 10 (8) ◽  
pp. 3875-3890 ◽  
Author(s):  
P. Zieger ◽  
R. Fierz-Schmidhauser ◽  
M. Gysel ◽  
J. Ström ◽  
S. Henne ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Light Scattering ◽  
Relative Humidity ◽  
Aerosol Particles ◽  
Aerosol Size Distribution ◽  
Hygroscopic Growth ◽  
Scattering Coefficients ◽  
Dry Conditions ◽  
Hygroscopic Particles

Abstract. Aerosol particles experience hygroscopic growth in the ambient atmosphere. Their optical properties – especially the aerosol light scattering – are therefore strongly dependent on the ambient relative humidity (RH). In-situ light scattering measurements of long-term observations are usually performed under dry conditions (RH>30–40%). The knowledge of this RH effect is of eminent importance for climate forcing calculations or for the comparison of remote sensing with in-situ measurements. This study combines measurements and model calculations to describe the RH effect on aerosol light scattering for the first time for aerosol particles present in summer and fall in the high Arctic. For this purpose, a field campaign was carried out from July to October 2008 at the Zeppelin station in Ny-Ålesund, Svalbard. The aerosol light scattering coefficient σsp(λ) was measured at three distinct wavelengths (λ=450, 550, and 700 nm) at dry and at various, predefined RH conditions between 20% and 95% with a recently developed humidified nephelometer (WetNeph) and with a second nephelometer measuring at dry conditions with an average RH<10% (DryNeph). In addition, the aerosol size distribution and the aerosol absorption coefficient were measured. The scattering enhancement factor f(RH, λ) is the key parameter to describe the RH effect on σsp(λ) and is defined as the RH dependent σsp(RH, λ) divided by the corresponding dry σsp(RHdry, λ). During our campaign the average f(RH=85%, λ=550 nm) was 3.24±0.63 (mean ± standard deviation), and no clear wavelength dependence of f(RH, λ) was observed. This means that the ambient scattering coefficients at RH=85% were on average about three times higher than the dry measured in-situ scattering coefficients. The RH dependency of the recorded f(RH, λ) can be well described by an empirical one-parameter equation. We used a simplified method to retrieve an apparent hygroscopic growth factor g(RH), defined as the aerosol particle diameter at a certain RH divided by the dry diameter, using the WetNeph, the DryNeph, the aerosol size distribution measurements and Mie theory. With this approach we found, on average, g(RH=85%) values to be 1.61±0.12 (mean±standard deviation). No clear seasonal shift of f(RH, λ) was observed during the 3-month period, while aerosol properties (size and chemical composition) clearly changed with time. While the beginning of the campaign was mainly characterized by smaller and less hygroscopic particles, the end was dominated by larger and more hygroscopic particles. This suggests that compensating effects of hygroscopicity and size determined the temporal stability of f(RH, λ). During sea salt influenced periods, distinct deliquescence transitions were observed. At the end we present a method on how to transfer the dry in-situ measured aerosol scattering coefficients to ambient values for the aerosol measured during summer and fall at this location.

scholarly journals Production and Germination of Conidia of Trichoderma stromaticum, a Mycoparasite of Crinipellis perniciosa on Cacao

2002 ◽  
Vol 92 (10) ◽  
pp. 1032-1037 ◽  
Author(s):  
S. Sanogo ◽  
A. Pomella ◽  
P. K. Hebbar ◽  
B. Bailey ◽  
J. C. B. Costa ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Air Temperature ◽  
Environmental Conditions ◽  
Growth Characteristics ◽  
Fruiting Bodies ◽  
High Moisture ◽  
Crinipellis Perniciosa ◽  
Broom Disease ◽  
Moisture Conditions ◽  
Incubation Temperatures

Growth characteristics of the fungus Trichoderma stromaticum, a mycoparasite on the mycelium and fruiting bodies of Crinipellis perniciosa, the causal agent of witches'-broom disease of cacao, were evaluated under controlled environmental conditions. The ability of T. stromaticum to produce conidia and germinate on dry brooms was evaluated at three constant temperatures (20, 25, and 30°C) and two constant relative humidities (75 and 100%). T. stromaticum produced abundant conidia on brooms at 100% relative humidity and incubation temperatures of 20 and 25°C, but none at 30°C. Sporulation of T. stromaticum was not observed at 75% relative humidity at any temperature. At 100% relative humidity and either at 20 or 25°C, treatment of brooms with T. stromaticum suppressed C. perniciosa within 7 days. In contrast, at 30°C, treatment with T. stromaticum had no effect on the pathogen in brooms maintained at either 75 or 100% relative humidity. Mycelium of C. perniciosa grew from brooms at all temperatures at 100% relative humidity. Conidial germination on broom tissue approximated 80% at temperatures from 20 to 30°C. Results suggest that applying T. stromaticum under high-moisture conditions when the air temperature is below 30°C may enhance the establishment of this mycoparasite in cacao plantations.

scholarly journals Effect of relative humidity on SOA formation from isoprene/NO photooxidation: role of particle-phase esterification under dry conditions

2011 ◽  
Vol 11 (2) ◽  
pp. 5407-5433 ◽  
Author(s):  
H. Zhang ◽  
J. D. Surratt ◽  
Y. H. Lin ◽  
J. Bapat ◽  
R. M. Kamens
Keyword(s):  
Mass Spectrometry ◽  
Relative Humidity ◽  
Chemical Characterization ◽  
Ultra Performance Liquid Chromatography ◽  
Gas Chromatography Mass Spectrometry ◽  
Particle Phase ◽  
Particle Volume ◽  
Flight Mass Spectrometry ◽  
Dry Conditions ◽  
Detailed Chemical

Abstract. The effect of relative humidity (RH) on secondary organic aerosol (SOA) formation from the photooxidation of isoprene under initially high-nitric oxide (NO) conditions was investigated in a dual outdoor smog chamber. Based upon particle volume concentration measurements and the detailed chemical characterization of isoprene SOA using gas chromatography/mass spectrometry (GC/MS) and ultra performance liquid chromatography/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-Q-TOFMS), enhanced SOA formation was observed under lower RH conditions (15–40%) compared to higher RH conditions (40–90%). 2-methylglyceric acid (2-MG) and its corresponding oligoesters, which have been previously shown to form from further oxidation of methacryloylperoxynitrate (MPAN), were enhanced in the particle-phase under lower RH conditions. In addition, an abundant unknown SOA tracer likely derived from the further oxidation of MPAN was detected and enhanced under lower RH conditions. In contrast, the 2-methyltetrols, which are known to form from the reactive uptake of isoprene epoxydiols (IEPOX) under low-NO conditions in the presence of acidified aerosol, did not substantially vary under different RH conditions; however, isoprene-derived organosulfates were found to be enhanced under high-RH conditions, indicating the likely importance of the aqueous aerosol phase in their formation. Based upon the detailed chemical characterization results, particle-phase organic esterification is proposed to explain the observed enhancements of isoprene SOA mass under lower RH conditions. This is one of only a few chamber studies that have examined the effect of RH on isoprene SOA formation. In comparison to our recent results obtained from aromatic SOA formation, the effect of RH on isoprene SOA formation is reversed. The results of this study highlight the importance of elucidating the key reactive intermediates that lead to SOA formation, especially since RH likely affects their ability in forming SOA. Furthermore, ignoring the effects of RH may significantly affect the accuracy of both regional and global SOA models.

scholarly journals First Confirmation of Sphaerotheca macularis on Strawberry Plants in Southwestern Spain

Plant Disease ◽  
2002 ◽  
Vol 86 (9) ◽  
pp. 1049-1049 ◽  
Author(s):  
B. de los Santos ◽  
C. Blanco ◽  
M. Porras ◽  
C. Barrau ◽  
F. Romero
Keyword(s):  
Relative Humidity ◽  
Powdery Mildew ◽  
Leaf Surface ◽  
Pathogenic Fungi ◽  
Tween 20 ◽  
Conidial Suspension ◽  
Lower Leaf Surface ◽  
White Mycelium ◽  
Sphaerotheca Macularis ◽  
Symptoms And Signs

In February 2001, in seven small tunnel production fields in southwestern Spain, symptoms and signs of powdery mildew were detected on strawberry (Fragaria × ananassa) cvs. Camarosa, Andana, and Carisma. On ‘Camarosa’ plants, white patches of mycelium developed on the lower leaf surface. Later, the leaf edges rolled upward, and reddish or necrotic irregular spots appeared on the lower leaf surface. Some immature fruits were abnormally hard and covered with a dense white mycelium. Symptoms were much less severe on ‘Andana’ and ‘Carisma’. Microscopic observations revealed conidia in chains, ellipsoidal to barrel-shaped, with fibrosin granules. Mean dimensions of conidia (N= 70) were 31.2 μm ± 2.8 × 20.39 μm ± 4.1. Cleistothecia were not detected. Based on these characteristics, the causal agent was identified as Sphaerotheca macularis (Wallr.:Fr.) Lind. (1). Pathogenicity was confirmed by inoculating leaves of 2-month-old potted ‘Camarosa’ plants. S. macularis obtained from field-grown plants was maintained on ‘Camarosa’ strawberry leaves in a growth chamber (20°C and 100% relative humidity). Inoculum was obtained from freshly sporulating infected leaves 11 days after inoculation. Conidia of S. macularis were gently brushed into 100-ml distilled water containing two drops of Tween 20. Ten strawberry ‘Camarosa’ plants were inoculated by misting with a conidial suspension (104 conidia per ml) (2). The plants were incubated at 100% relative humidity for 48 h in the greenhouse (15 to 25°C). Colonies of powdery mildew were observed on leaves after 18 days. To our knowledge, this is the first confirmation of S. macularis on strawberry in Spain. References: (1) K. G. Mukerji. No. 188 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, UK, 1968. (2) R. Reuveni et al. Crop Prot. 19:335, 2000.

Micromovement of Propachlor from Granules in Soil

Weed Science ◽  
1973 ◽  
Vol 21 (3) ◽  
pp. 185-188 ◽  
Author(s):  
M. P. Molnau ◽  
W. G. Lovely ◽  
H. P. Johnson
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Exposure Time ◽  
Horizontal Movement ◽  
Dry Conditions ◽  
Soil Area

Movement of 2-chloro-N-isopropylacetanilide (propachlor) from a granule to the soil was classified as horizontal, below the granule, above the granule, and into an area within a 3-ppmw contour. The influence of depth of placement, moisture content, temperature, relative humidity, and exposure time on each of the movement classifications was determined. Horizontal movement increased as the temperature, moisture, and exposure time increased. Propachlor tends to move down into the soil under dry conditions and up when the soil is moist. The size of the soil area that contained 3 ppmw was greater for granules placed in the soil than for granules placed on the surface. The size of the area increased as the moisture increased.

scholarly journals Downy Mildew of Stock, Caused by Peronospora parasitica, in California

Plant Disease ◽  
2000 ◽  
Vol 84 (1) ◽  
pp. 103-103 ◽  
Author(s):  
S. T. Koike
Keyword(s):  
Relative Humidity ◽  
Downy Mildew ◽  
Fungal Growth ◽  
Peronospora Parasitica ◽  
Cut Flower ◽  
Coastal Regions ◽  
Leaf Surfaces ◽  
Humidity Chamber ◽  
Chlorotic Leaf ◽  
Leaf Symptoms

During the spring and fall of 1999, commercial plantings of the cut flower stock (Matthiola incana) in coastal regions of California developed a severe foliar disease. Abaxial leaf surfaces supported the extensive white fungal growth typical of a downy mildew. Adaxial surfaces of newly infected leaves did not show symptoms, but with time, leaves exhibited extensive, diffuse chlorotic areas and slight twisting. Infected plants were not acceptable for the cut flower market and, therefore, were not harvested. Sporangiophores had main trunks with dichotomous branches ending in slender curved tips that were 2.8 μm long. Sporangia were ovoid, measuring 22 to 25 μm long and 19 to 22 μm wide. The fungus was identified as Peronospora parasitica. Pathogenicity was established by gently pressing diseased leaves onto stock plants (cv. Avalanche), incubating plants in a humidity chamber (20 to 22°C, 100% relative humidity) for 48 h, and keeping plants in a greenhouse. Diffuse chlorotic leaf symptoms developed after 10 days, and the same fungus later developed on abaxial surfaces. Uninoculated plants did not develop downy mildew. Inoculations were conducted a second time, and the results were the same. This is the first documentation of P. parasitica on stock in California.

Influence of training on sweating responses during submaximal exercise in horses

2000 ◽  
Vol 89 (6) ◽  
pp. 2463-2471 ◽  
Author(s):  
L. J. McCutcheon ◽  
R. J. Geor
Keyword(s):  
Relative Humidity ◽  
Core Temperature ◽  
Heat Dissipation ◽  
Fold Increase ◽  
Moderate Intensity ◽  
Dry Conditions ◽  
Fluid Losses ◽  
Sweating Threshold ◽  
Intensity Training ◽  
Cool Conditions

Sweating responses were examined in five horses during a standardized exercise test (SET) in hot conditions (32–34°C, 45–55% relative humidity) during 8 wk of exercise training (5 days/wk) in moderate conditions (19–21°C, 45–55% relative humidity). SETs consisting of 7 km at 50% maximal O2 consumption, determined 1 wk before training day (TD) 0, were completed on a treadmill set at a 6° incline on TD0, 14, 28, 42, and 56. Mean maximal O2consumption, measured 2 days before each SET, increased 19% [TD0 to 42: 135 ± 5 (SE) to 161 ± 4 ml · kg−1 · min−1]. Peak sweating rate (SR) during exercise increased on TD14, 28, 42, and 56 compared with TD0, whereas SRs and sweat losses in recovery decreased by TD28. By TD56, end-exercise rectal and pulmonary artery temperature decreased by 0.9 ± 0.1 and 1.2 ± 0.1°C, respectively, and mean change in body mass during the SET decreased by 23% (TD0: 10.1 ± 0.9; TD56: 7.7 ± 0.3 kg). Sweat Na+concentration during exercise decreased, whereas sweat K+concentration increased, and values for Cl− concentration in sweat were unchanged. Moderate-intensity training in cool conditions resulted in a 1.6-fold increase in sweating sensitivity evident by 4 wk and a 0.7 ± 0.1°C decrease in sweating threshold after 8 wk during exercise in hot, dry conditions. Altered sweating responses contributed to improved heat dissipation during exercise and a lower end-exercise core temperature. Despite higher SRs for a given core temperature during exercise, decreases in recovery SRs result in an overall reduction in sweat fluid losses but no change in total sweat ion losses after training.

Desiccation tolerance of Muellerius capillaris first-stage larvae from Israeli arid and French temperate habitats and their compatibility to the land snail Theba pisana

Parasitology ◽  
1999 ◽  
Vol 119 (6) ◽  
pp. 621-626 ◽  
Author(s):  
A. SOLOMON ◽  
J. CABARET ◽  
I. GLAZER ◽  
I. PAPERNA
Keyword(s):  
Relative Humidity ◽  
Post Infection ◽  
Land Snail ◽  
Free Living ◽  
Larval Stages ◽  
Survival Capacity ◽  
Dry Conditions ◽  
Theba Pisana ◽  
French Isolate ◽  
Muellerius Capillaris

The survival capacities of Muellerius capillaris (Nematoda: Protostrongylidae) free-living larval stages (L1) of an Israeli desert isolate (Nubian isolate) (92 mm rain per annum) and a French isolate from a temperate habitat (650 mm rain per annum) were compared under humid and extreme dry conditions. Under the dry conditions (7% relative humidity [r.h.] and 33% r.h. at 23 °C), both isolates exhibited the same remarkable survival capacity for periods of 17 and 28 days, respectively (>92% survival, P>0·1). However, during and after recovery from the anhydrobiotic state, different behaviour patterns of L1 were observed in each isolate. Under humid conditions (97% r.h.) for 10 days, both isolates exhibited similarly low survival percentages (13·4±4·6%, S.E., survival for the Nubian isolate, 3±3% for the French isolate, P>0·05). In water, the French isolate was less active, survived better (52±8·4% vs 28·7±3·7, by day 28, P<0·05) and retained a better morphological appearance (shrunk less) than the Nubian isolate. Larval development of the French isolate in the land snail Theba pisana was significantly faster than that of the Nubian isolate, reaching a higher proportion of infective stages (L3) on day 36 post-infection (78·6% vs 56% P>0·05). However, similar infection intensities were recovered in snails infected with either of the isolates (59·8±10·3, S.E., n=14, for the French isolate, 53±6, n=13, for the Nubian isolate, P<0·05).

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