Colonization byCladosporium spp. of painted metal surfaces associated with heating and air conditioning systems

Summary Cladosporium cladosporioides andC. hebarum colonized painted metal surfaces of covering panels and register vents of heating, air conditioning and ventilation systems. Hyphae penetrated the paint film and developed characteristic conidiophores and conidia. The colonies were tightly appressed to the metal surface and conidia were not readily detectable via standard air sampling procedures.     

Powdery mildew of tobacco (Erysiphe cichoracearum DC)

A Hirst volumetric spore trap, at a height of 30 cm., was used to assess the diurnal distribution of Erysiphe conidia in the air in tobacco crops infected with E. cichoracearum in Rhodesia. Air temperature and humidity, and the length of time leaves were wet each day, were also recorded at the same height, amongst the plants. In four seasons, most conidia were caught between 13.00 and 15.00 hr. There were close positive correlations in 1962 between numbers of conidia per m.3 of air per hour and saturation deficit and air temperature during the same hours (10.00–18.00 hr.) Correlations of total Erysiphe conidia per day with temperature and humidity were very variable; temperature had no apparent effect during three seasons, but in one (1961)there was a highly significant positive correlation between numbers of conidia and the daily duration of temperatures > 25d? C. More conidia were also caught when the air was dry for long periods that season, though temperature probably had the greater effect. In 1962, more conidia were caught per day the longer the air was humid (s.D. 0–1 mb.) In 1961, the amount of rain per day had no apparent effect on numbers of conidia, but in 1962 more were caught the greater the daily rainfall. However, rain, which nearly always fell in the afternoon, also removed most conidia from the air that afternoon. Neither windspeed nor duration of leaf wetness appeared to affect spore dispersion.     

Studies on the Concentration of Ramularia beticola Conidia in the Air Above Sugar Beet fields in Denmark

Concentrations of Ramularia beticola Faut. & Lamb. conidia in the air above 3 sugar beet (Beta vulgaris L.) field were registered for a period of 41 days altogether. A significant diurnal periodicity was revealed. Two periods of 3 and 5 days, respectively, included peaks of several thousands of conidia per m³ of air. The conidial concentrations were related to temperature, relative humidity (RH) and vapour pressure of the air, and to wind speed, dew point, rainfall and hours of sunshine. A significant effect of vapour pressure was observed for 2 fields. In one field with very low conidial concentrations, vapour pressure was nearly significant. In this field only wind speed significantly influenced dispersal of conidia. In an analysis of covariance including all data, 50% of the variation was explained by field, time of day, vapour pressure and number of hours of RH above 95% in the preceding 24h.     

Effects of wetting on the persistence of quiescent conidia of Isaria fumosorosea

Quiescent conidia of Isaria fumosorosea were submitted to various wetting–drying cycles under different regimes of temperature and air humidity. Germination and viability of conidia collected on cultures freshly host-passed (P2) were not affected at 25 °C during five cycles at increasing wet phase duration (2–12 h per daily cycle) under any moisture conditions (13–86% RH). Infectivity levels remained stable, but mortality was slightly postponed. In vitro-cultured inocula (P5) were significantly affected after only one cycle at higher air humidity (75 and 86% RH) and temperature (35 and 40 °C). The persistence of I. fumosorosea conidia suspended in water soluble extracts of leaf surfaces (corn and cabbage) confirmed the better persistence of P2 conidia and the relatively higher detrimental effect of lower air humidity conditions when combined with moderate temperatures. Quiescent conidia deposited in situ on potted plants of cabbage showed a higher persistence on wet foliage and on foliage submitted to wetting–drying cycles, than on dry foliage. These results underline that constraints prevailing in targeted environments and ecological fitness of fungal isolates have to be taken into account for assessing microbial control strategies.     

Airborne Aspergillus fumigatus conidia: a risk factor for aspergillosis

Aspergillus fumigatus is an opportunistic fungal pathogen that causes invasive aspergillosis, a usually fatal infection. The disease has risen in prominence in recent years due to the increasing numbers of severely immunocompromised patients becoming infected. The fungus is ubiquitous in the environment, producing large numbers of conidia that are dispersed in the air. Humans inhale numerous conidia everyday, but infections are not seen in healthy individuals. As inhalation of conidia is the main route of infection, considerable efforts are required to prevent infection in susceptible patients. This review summarises the current knowledge on airborne concentrations of A. fumigatus conidia, their background levels in outdoor air and seasonal distribution patterns. New and established methods of air sampling for airborne A. fumigatus conidia are discussed. Common environmental sources of the fungus are reviewed, including its presence in compost heaps. Finally, the lack of stringent guidelines on the monitoring and control of airborne A. fumigatus concentrations in hospitals is discussed.     

Powdery mildew of tobacco (Erysiphe cichoracearum DC.): Some effects of methods of inoculation and air humidity on germination of conidia and growth of hyphae on leaves*

Germination of conidia of Erysiphe cichoracearum and hyphal growth in 3 days at 23° C. and 6 mb. saturation deficit was similar, whether conidia were applied dry or suspended for up to 1 hr. in glass-distilled water before being sprayed on tobacco leaves. Growth of single conidial colonies whose hyphae were more than 333 μ long, was positively correlated with numbers per cm.² of leaf (P < 0.01) on three of the eleven times tested, mostly when conidia were sparsely distributed; ten of the regressions were positive. A greater percentage of conidia germinated at 0–1.7 mb. saturation deficit than at 7–9 mb. Subsequent growth of hyphae was greater in the drier air.     

Conidia of the tomato powdery mildew <Emphasis Type="Italic">Oidium neolycopersici</Emphasis> initiate germ tubes at a predetermined site

The emergence of germ tubes from the conidia of powdery mildew fungi is the first morphological event of the infection process, preceding appressoria formation, peg penetration and primary haustoria formation. Germination patterns of the conidia are specific in powdery mildew fungi and therefore considered useful for identification. In the present study, we examined conidial germination of the tomato powdery mildew Oidium neolycopersici KTP-01 in order to clarify whether germ tube emergence site in KTP-01 conidia is determined by the first contact of the conidia to leaves (as found for the conidia of barley powdery mildew), or alternatively is predetermined and is unrelated to contact stimulus. Highly germinative conidia of KTP-01 were collected from conidial pseudochains on conidiophores in colonies on tomato leaves using two methods involving an electrostatic spore attractor and a blower. In the electrostatic spore attraction method, the conidia were attracted to the electrified insulator probe of the spore collector—this being the first contact stimulus for the conidia. In addition, the blowing method was used as a model of natural infection; pseudochain conidia were transferred to detached leaves by air (1 m/s) from a blower. Thus, landing on the leaves was the first contact for the conidia. Furthermore, conidia were also blown onto an artificial membrane (Parafilm-coated glass slides forming a hydrophobic surface) or solidified agar plates in Petri dishes (hydrophilic surface). Eventually, almost all conidia on the probe and on tomato leaves or artificial hydrophobic and hydrophilic surfaces synchronously germinated within 6 h of incubation, indicating that the first contact of the conidia with any of the aforementioned substrata was an effective germination induction signal. Germ tube emergence sites were exclusively subterminal on the conidia. Moreover, the germ tubes emerged without any relation to the sites touched first on the conidia. Thus, the present study strongly indicates that conidia of O. neolycopersici produce germ tubes at a predetermined site.     

Levels of Airborne Botrytis cinerea Conidia Trapped Among Pepper (Capsicum annuum L.) and Eggplant (Solanum melongena L.) Crops Cultivated in Polyethylene Greenhouses on the Málaga Coastal Plain (Southern-Spain)

The levels of B. cinerea conidia in the air of greenhouses with pepper or eggplant crops at El Morche (Málaga, Spain) were studied during the 1981–82 and 1982–83 growing seasons. The number of conidia collected, the temperatures and relative humidities recorded during different periods were analyzed and fitted to different regression models. Several types of transformation were made to straighten the curves. In both seasons, the regression analyses of the pepper crop data showed no statistical significance, but those for eggplant crops did. The levels of significance for the eggplants were good and those of the 1981–82 experiment were the best. During the 24 h period prior the conidia collection, there was a negative correlation between temperatures measured 6 and 8 h prior to conidia sampling and the number of conidia collected. When the 2nd pair of variables was used, B. cinerea conidia collections were less the longer the periods of temperatures between 20 and 30°C with relative humidities above 70%. This type of information would facilitate a more rational physical and chemical control of the disease in greenhouse vegetable crops to prevent or reduce crop losses.     

Aerial diffusion of phytopathogenic fungi

Summary Aeriobiological studies are essential for understanding the distribution, ecology and deposition patterns of both phytopathogenic and nonpathogenic fungal spores which are carried away from their source. Many spores and conidia are devitalized during aerial transportation as a consequence of being exposed to atmospheric agents. Nonetheless, a sufficient number remain viable, causing infections of various kinds, some of which extremely serious and with an epidemic trend.In order to predict the onset of fungi-induced diseases, it is necessary to be able to determine the inoculum source of the pathogenic agent. As air is the main vector transporting pathogenic fungal spores and conidia, periodical monitoring is required. Thus, having established the critical stages of plant infection, necessary precautionary measures can be undertaken in order to control diseases onset and development.It is therefore necessary to gain a through understanding of spore takeoff and dispersal mechanisms so as to determine how the spores and conidia are transported by air currents onto the plants and how they cause infective impaction. Spores and conidia suspended in the atmosphere can be collected by means of appropriate traps filtering a predetermined amount of air at predetermined time intervals in order to be able to make predictions as to the possibility of plant infection. Volumetric air sampling allows not only to determine the concentration of spores and conidia in a given period of time but also to establish the hours of the day in which they are present in highest concentrations and in which therefore they are more liable to cause infection. This information may be used in estimating the incidence of disease symptoms, the duration of infection and the seriousness of the disease.On the basis of this data, mathematical models for predicting epidemics can be worked out.     

Temporal and spatial dispersal of cladobotryum conidia in the controlled environment of a mushroom growing room

Cladobotryum spp. are responsible for cobweb disease of mushrooms. In two commercial and one experimental mushroom-growing room, Cladobotryum conidia were released into the air in direct response to physical disturbance of disease colonies during either crop watering or treatment by covering with salt to 10 mm. Conidia were detected using a Burkard spore trap or agar-based trap plates. A maximum concentration of approximately 25,000 conidia m(-3) was recorded in a small (75-m(3)) experimental growing room in the hour following the salting of 16 cobweb patches (0.55 m(2)). Concentrations of 100 and 40 conidia m(-3) were recorded in the two larger commercial growing rooms in the hour following the salting of 18 and 11 patches of cobweb (diameter, approximately 50 to 200 mm), respectively. In controlled experiments, disturbed conidia were dispersed rapidly throughout a small growing room, with 91 to 97% of conidia settling out within 15 min. Eighty-five percent of conidia settled out within a 0.5-m radius when air-conditioning fans were switched off, consistent with airborne spore dispersal. Alternative methods for treating diseased areas to minimize conidial release and distribution were investigated and included covering disease colonies with damp paper tissue prior to salt application (tissue salting) and holding a dust extractor above disease colonies during salt application. Both methods resulted in no detectable airborne conidia, but the tissue paper salting technique was more convenient. Prevention of airborne conidial release and distribution is essential to avoid mushroom spotting symptoms, secondary colonies, and early crop termination.     

Methods for reducing particle concentrations of Aspergillus fumigatus conidia and mouldy hay dust

The effectiveness of commercially available domestic air purifiers to reduce airborne Aspergillus fumigatus conidia and mouldy hay dust was investigated. It was found that the rate of particle clearance is a function of the volume of air passing through the purifiers but that the low throughflow of air makes their use of little value in clearing particles from a normal sized room. Vacuum cleaners were more effective than air purifiers because of their higher air throughput, so too were high volume fan systems in conjunction with simple filtration units. Ionizers had no effect but steam condensation was very efficient at clearing airborne particles.     

Temporal and Spatial Dispersal of Cladobotryum Conidia in the Controlled Environment of a Mushroom Growing Room

Cladobotryum spp. are responsible for cobweb disease of mushrooms. In two commercial and one experimental mushroom-growing room, Cladobotryum conidia were released into the air in direct response to physical disturbance of disease colonies during either crop watering or treatment by covering with salt to 10 mm. Conidia were detected using a Burkard spore trap or agar-based trap plates. A maximum concentration of ~25,000 conidia m⁻³ was recorded in a small (75-m³) experimental growing room in the hour following the salting of 16 cobweb patches (0.55 m²). Concentrations of 100 and 40 conidia m⁻³ were recorded in the two larger commercial growing rooms in the hour following the salting of 18 and 11 patches of cobweb (diameter, approximately 50 to 200 mm), respectively. In controlled experiments, disturbed conidia were dispersed rapidly throughout a small growing room, with 91 to 97% of conidia settling out within 15 min. Eighty-five percent of conidia settled out within a 0.5-m radius when air-conditioning fans were switched off, consistent with airborne spore dispersal. Alternative methods for treating diseased areas to minimize conidial release and distribution were investigated and included covering disease colonies with damp paper tissue prior to salt application (tissue salting) and holding a dust extractor above disease colonies during salt application. Both methods resulted in no detectable airborne conidia, but the tissue paper salting technique was more convenient. Prevention of airborne conidial release and distribution is essential to avoid mushroom spotting symptoms, secondary colonies, and early crop termination.     

Infection of Sentinel Cotton Aphids (Homoptera: Aphididae) by Aerial Conidia ofNeozygites fresenii(Entomophthorales: Neozygitaceae)

Uninfected adultAphis gossypii(Homoptera: Aphididae) apterae (sentinel aphids) on cotton leaves were exposed for 8 h to the air over a commercial cotton field in Louisiana during the night of 1–2 July 1995. At 0015 h there were 90,437 primary conidia/m³air of the fungusNeozygites fresenii(Entomophthorales: Neozygitaceae) at the midfield position as determined from Rotorod samples. Forty-eight percent (n = 106) of the sentinel aphids exposed for 8 h at midfield were infected by aerial conidia ofN. fresenii.Exposure of sentinel aphids outside the cotton field, at 10 and 100 m downwind and 10 m upwind, resulted in 34.8% (n = 131), 24.0% (n = 129), and 17.4% (n = 146) infected aphids, respectively. These data demonstrate that wind-dispersed aerial conidia ofN. freseniiare infective and rapidly and efficiently disperse the pathogen throughout aphid populations within and between fields.     

Patterns of airborne conidia of Stemphylium vesicarium, the causal agent of brown spot disease of pears, in relation to weather conditions

Seven-day volumetric spore samplers were installed in pear orchards of northern Italy, in the years between 1993 and 2002, and operated continuously during the development of brown spot epidemics (mid-April–mid-August), caused by Stemphylium vesicarium. Aerial concentration of conidia was recorded at 2 h intervals to study their diurnal and seasonal patterns and the influence of weather conditions. The diurnal periodicity of aerial conidia showed a peak around midday and low counts in the dark. The increase in spore concentration was significantly correlated with the reduction of relative humidity and wetness in early morning, and the increase of wind in late morning and afternoon. Conidia of S. vesicarium became easily airborne to form a regular component of the air-spora in pear orchards, while ascospores were caught only sporadically. Differences between years concerned total spore counts and numbers of peaks (defined as days with more than 30 conidia/m³ air per day). Periods with highest spore counts occurred in late-May to early-June (in 2 years), mid to end of June (5 years), or after mid-July (3 years). There was a significant correlation between spore peaks and days with favourable weather conditions, defined as days with air temperature between 15 and 25°C and high humidity, particularly a wet period longer than 10 h. Occurrence of one or more consecutive days with favourable weather conditions determined an increase in the airborne concentration of conidia, which usually lasted some days and then decreased.     

Effects of Metarhizium robertsii on the bloodsucking mosquito Aedes flavescens and non‐target predatory insects (Odonata)

The effects of different concentrations and methods of treatment with Metarhizium robertsii Bisch., Rehner & Humber conidia on the non‐target aquatic dragonfly larvae Lestes sponsa Hansemann, Lestes dryas Kirby and Aeshna affinis Vander Linden and on the target bloodsucking mosquito larvae Aedes (O.) flavescens (Muller) were analysed. We found that dragonflies are significantly less susceptible than mosquitoes to the fungus. Larvae of L. sponsa larvae were more susceptible to wet conidia than dry conidia. However, the mortality of the air‐breathing larvae of A. affinis was significantly higher after treatment with dry conidia relative to aqueous suspension. The results help to minimize the negative effects of entomopathogenic fungi on non‐target predator insects under the control of mosquito larvae.     

Optimising inoculum yield and shelf life of Plectosphaerella cucumerina,a potential bioherbicide for Cirsium arvense

Plectosphaerella cucumerina was identified as a potential bioherbicide for controlling Cirsium arvense in Canada and New Zealand. The current study evaluated production conditions using two isolates (one from each country) to determine whether the yield and shelf life of inoculum are suitable for mass production. Mycelial growth and sporulation in culture both increased from 15°C to 25°C and declined at higher temperatures with no mycelial growth at 37°C. The Canadian isolate produced fewer conidia than a New Zealand isolate. Potato dextrose-based liquid media with moderate to high concentrations of carbohydrates (25%, 50%, and 100%) maximised conidia production and these base media produced conidia with the highest germination rate (>80%) both at harvest and after 4 weeks stored at 4°C in 2.5% glycerol, 40% milk glycerol or after air drying. However, after 10-week storage, the conidia failed to germinate. Sporulation occurred during growth on all solid substrates tested (rice, rolled barley, and triticale), but conidial germination was highest on rice and barley, both before and after air drying. By contrast to conidia, 90% of mycelia-infested barley grains were viable after 3 years of storage at room temperature, although viability was lost by this time on the other substrates. This study has shown that the nutritional base is an important determinant of sporulation and shelf life for P. cucumerina. Although the yield of conidia in liquid medium was adequate to justify further development of P. cucumerina as a bioherbicide, improvement in its shelf life, or alternate formulation types that extend the shelf life, must be made for commercial efficiency.     

Detection of airborne Stachybotrys chartarum macrocyclic trichothecene mycotoxins on particulates smaller than conidia

Highly respirable particles (diameter, <1 microm) constitute the majority of particulate matter found in indoor air. It is hypothesized that these particles serve as carriers for toxic compounds, specifically the compounds produced by molds in water-damaged buildings. The presence of airborne Stachybotrys chartarum trichothecene mycotoxins on particles smaller than conidia (e.g., fungal fragments) was therefore investigated. Cellulose ceiling tiles with confluent Stachybotrys growth were placed in gas-drying containers through which filtered air was passed. Exiting particulates were collected by using a series of polycarbonate membrane filters with decreasing pore sizes. Scanning electron microscopy was employed to determine the presence of conidia on the filters. A competitive enzyme-linked immunosorbent assay (ELISA) specific for macrocyclic trichothecenes was used to analyze filter extracts. Cross-reactivity to various mycotoxins was examined to confirm the specificity. Statistically significant (P < 0.05) ELISA binding was observed primarily for macrocyclic trichothecenes at concentrations of 50 and 5 ng/ml and 500 pg/ml (58.4 to 83.5% inhibition). Of the remaining toxins tested, only verrucarol and diacetylverrucarol (nonmacrocyclic trichothecenes) demonstrated significant binding (18.2 and 51.7% inhibition, respectively) and then only at high concentrations. The results showed that extracts from conidium-free filters demonstrated statistically significant (P < 0.05) antibody binding that increased with sampling time (38.4 to 71.9% inhibition, representing a range of 0.5 to 4.0 ng/ml). High-performance liquid chromatography analysis suggested the presence of satratoxin H in conidium-free filter extracts. These data show that S. chartarum trichothecene mycotoxins can become airborne in association with intact conidia or smaller particles. These findings may have important implications for indoor air quality assessment.     

Experimental determination of viability loss of Penicillium bilaiae conidia during convective air-drying

A study was conducted on the drying of Penicillium bilaiae, a fungal micro-organism used to promote soil-bound phosphorous uptake in several crop species, such as wheat, canola and pulse crops. A wet pellet formed from a mixture of the inoculant and a starch-based carrier was air-dried to the appropriate water activity to extend the shelf-life of the viable fungal conidia. Convective air-drying was examined as a low-energy alternative to the more expensive freeze-drying technology that is currently in use. Experiments were conducted to measure the loss of conidia viability during drying in a fixed-bed, thin-layer convective dryer. The dryer air inlet temperature and relative humidity were controlled in experiments to determine the effect of thermal and dessicative stresses on conidial viability. The measured survivor fraction was determined to be dependent on solids temperature, moisture content and drying rate. Thermal stresses became significant for process temperatures above 30°C, while the survivor fraction fell sharply below a dry basis moisture ratio of 30%. Slower drying kinetics associated with high inlet air relative humidity were found to significantly improve the recovery of viable conidia. By minimising environmental stresses, survivor fractions of up to 75% could be achieved, but this result fell dramatically with the introduction of more severe conditions. A general linear statistical model is used to quantify experimental error and the significance level of each factor.     

飞虱虫疠霉分生孢子在不同温湿度组合条件下的存活率*

用荧光染色法研究了不同温度（１０～３０℃）和湿度（５１～１００％ＲＨ）组合条件下飞虱虫疠 霉 Ｐａｎｄｏｒａ ｄｅｌｐｈａｃｉｓ分生孢子的存活率。在无放回抽样观察中,孢子弹射后第２４ ｈ的存活 率在５１％、７４％、８５％、９０％、９５％和１００％ＲＨ与不同温度的组合中分别为４２～８１％、６９～８９％、７０～ ９５％、 ６７～１００％、 ７６～１００％和 ５６～１００％。存放４个月后,不同温度下的孢子存活率在 ５１％、 ７４％、 ８５％和 ９０％ＲＨ下分别为 ５５～７４％、 ５２～８７％、 ３８～７３％和 １～６５％。而在≥９５％ ＲＨ下孢子存活率 ２４ｈ 后锐减,至第７ ｄ几乎全部失活。以上结果表明,弹射后的飞虱虫疠霉孢子在头２４ ｈ的存活 易受低湿影响,但存活下来的孢子能继续在低湿下存活较久;饱和或接近饱和的高湿度最不 利孢子长久存活。