Spores Released Research Articles

Determining the Timing of Spore Release by Botryosphaeriaceae Species in Oregon Vineyards.

Botryosphaeria dieback, caused by a group of pathogens in the Botryosphaeriaceae family, is one of the most common grapevine trunk disease complexes (GTDs) found in Oregon vineyards. To understand the period of spores released by Botryosphaeria spp. in Oregon vineyards, four Burkard 7-day recording volumetric spore traps were placed in vineyard blocks in northern and southern Oregon. Each trap was placed near a younger (<10 years) and older (>30 years) block in both regions. Spore traps were deployed at the beginning of December 2019 and continued until March 2021. Between these timeframes, 475 and 477 days of samples were collected from each spore trap in northern and southern Oregon, respectively. DNA extraction was performed from individual day samples and followed by qPCR analysis of Botryosphaeria spores trapped in each tape sample. Weather data such as temperature, precipitation, relative humidity (RH), and wind speed were collected from nearby weather stations. Association between these data and number of spores detected were analyzed using Pearson correlation analysis. In northern Oregon, the detection occurred between December and February, and the first spore detection occurred when cumulative growing degree day (GDD) totaled to 4,357 and 4,351 units (TBase = 0°C, biofix date = January 1) during the first and second seasons, respectively. Similarly, in southern Oregon, the detection occurred between November and January, and the first spore detection occurred when cumulative GDD was 4,405 units during the second season. Hours of continuous RH >86% was significantly associated with number of spores released (P = 0.026; r = 0.42). During the spore detected dates, the RH was >86% for at least 19 consecutive hours. These findings provide an important implication to manage Botryosphaeria dieback by protecting pruning wounds during the most-spore-released periods. Furthermore, the knowledge of weather variables and their possible association with spore detection provides important information towards developing predictive models in future studies.

Telescopic peristomes, hygroscopic movement and the spore release model of Regmatodon declinatus (Leskeaceae Bryophyta).

Moss peristome hygroscopic movement plays an important role in protecting and controlling spore release. Recent studies on the peristome's hygroscopic movement and spore release have focussed on mosses with 'perfect' peristomes, such as Brachytheciaceae, whereas the hygroscopic movement type and spore release pattern of 'specialized' peristomes, such as Regmatodon declinatus, are poorly understood. We investigated the relationship between the peristome's hygroscopic movement and spore release in the 'specialized' peristome of R. declinatus by the measurement of peristome hygroscopic movement parameters and the hygroscopic movement spore release test. It was found that: (i) Exostomes (EX) are significantly shorter than endostomes (EN), triggering the hygroscopic movement of telescopic peristomes, in which the EX rapidly elongate while closing in on the EN, and the teeth rapidly converge. (ii) Spore release was minimal when peristome movement was triggered alone. The number of spores released when exposed to wind was 124 times greater than in the absence of wind. Dry capsules released seven times more spores than wet capsules. The study reveals that the hygroscopic movement of 'telescopic' peristomes of R. declinatus did not contribute significantly to spore release. More spores were released when wind and hygroscopic movement acted synergistically. Dry capsules released the maximum number of spores. It was also revealed that structural damage to capsules can facilitate complete spore release. Finally, we modelled the release of R. declinatus spores from initiation to complete release, namely the coupled release model of wind-water-capsule structural damage.

Seasonal dynamics of inoculum of Botryosphaeriaceae in macadamia orchards in Australia

AbstractMacadamia (Macadamia integrifolia and M. tetraphylla and their hybrids) is a tree nut crop affected by Botryosphaeria branch dieback. The disease results in branch and tree death in commercial orchards, so reducing the productivity of the Australian macadamia industry. There is a dearth of knowledge of the disease cycle in macadamia, which confounds disease management. This study investigated the dynamics of pathogen inoculum associated with Botryosphaeria branch dieback and the influence of environmental factors (temperature, rainfall and relative humidity) on the seasonal spore release within the orchards. Diseased and asymptomatic plant parts from macadamia trees were collected each season for 3 years in commercial orchards. Fungal structures (pycnidia and pseudothecia) mainly were (71%) observed on symptomatic wood samples. A comparison of the number of spores released from the fungal structures between summer and autumn revealed high concentrations of Lasiodiplodia pseudotheobromae from diseased wood (4.8 × 104 conidia/cm2) and Neofusicoccum luteum from blighted leaves (2.1 × 103 conidia/cm2). The peak airborne conidia dispersal period, quantified using microscopy and quantitative PCR assays, was consistently detected after rainfall and strongly associated with relative humidity over 70% and temperatures between 20 and 27°C during summer and autumn. Botryosphaeriaceae isolates obtained from the pycnidia on the macadamia trees caused severe branch dieback symptoms when inoculated on detached macadamia twigs, which suggests both airborne and rain‐splashed spores from fungal structures on the trees contribute to the disease in macadamia orchards.

Improvement of Alternaria Leaf Blotch and Fruit Spot of Apple Control through the Management of Primary Inoculum

Alternaria spp. is the causal agent of apple leaf blotch and fruit spot, diseases of recent appearance in Spain. The overwinter inoculum of Alternaria spp. is the source of primary infections in apple, thus the aim of this work was to optimize the control of infection through two environmentally friendly inoculum-management strategies, the removal of winter fallen leaves and the treatment of leaves with the biological agent Trichoderma asperellum to inhibit or prevent inoculum development in commercial orchards. The results of commercial orchard trials showed that leaf aspiration and application of T. asperellum on the ground have efficacy to reduce fruit spot between 50 and 80% and leaf blotch of between 30 and 40% depending on the year. The efficacies on the reduction of leaf blotch were slightly lower than of fruit spot. Disease reduction has been related to a reduction of total spores released during the season. Results of dynamics of spore release indicate that factors influencing spore release were rainfall and temperature. In conclusion, the use of environmentally friendly strategies combined with standard fungicides, and with monitoring environmental conditions, might allow a reduction in the number of phytosanitary applications, thus achieving the goal of reducing their use.

Providing the missing links in fern life history: Insights from a phenological survey of the gametophyte stage.

PremiseThe entire life cycle of ferns has been documented, yet their life histories are still poorly understood. In particular, the phenology of fern gametophytes remains largely unknown. To address this issue, we demonstrated a new ecological approach to explore the phenological link between spore release and gametophyte maturation within the life history of a tree fern species.MethodsWe conducted a serial survey of Alsophila podophylla gametophyte abundance in the field, and recorded the time of its spore release. Every two months for one year, all terrestrial fern gametophytes in an unsampled subplot were collected and identified using tissue‐direct PCR.ResultsWe found temporal differences in gametophyte abundances, with a sevenfold difference between the highest and lowest months. The number of spores released was linked to the gametophyte abundance two months later. The switch from gametophyte to juvenile sporophyte was found to be most correlated with precipitation.DiscussionThe observed fluctuation in gametophyte abundance and population structure was likely associated with the phenology of spore release and environmental factors. Importantly, these findings provide the first evidence of phenological links between different developmental stages in a fern's life history.

Timing of fungal spore release dictates survival during atmospheric transport

Fungi disperse spores to move across landscapes and spore liberation takes different patterns. Many species release spores intermittently; others release spores at specific times of day. Despite intriguing evidence of periodicity, why (and if) the timing of spore release would matter to a fungus remains an open question. Here we use state-of-the-art numerical simulations of atmospheric transport and meteorological data to follow the trajectory of many spores in the atmosphere at different times of day, seasons, and locations across North America. While individual spores follow unpredictable trajectories due to turbulence, in the aggregate patterns emerge: Statistically, spores released during the day fly for several days, whereas spores released at night return to ground within a few hours. Differences are caused by intense turbulence during the day and weak turbulence at night. The pattern is widespread but its reliability varies; for example, day/night patterns are stronger in southern regions. Results provide testable hypotheses explaining both intermittent and regular patterns of spore release as strategies to maximize spore survival in the air. Species with short-lived spores reproducing where there is strong turbulence during the day, for example in Mexico, maximize survival by releasing spores at night. Where cycles are weak, for example in Canada during fall, there is no benefit to releasing spores at the same time every day. Our data challenge the perception of fungal dispersal as risky, wasteful, and beyond control of individuals; our data suggest the timing of spore liberation may be finely tuned to maximize fitness during atmospheric transport.

Under which humidity conditions are moss spores released? A comparison between species with perfect and specialized peristomes.

Dispersal is a fundamental biological process that can be divided into three phases: release, transportation, and deposition. Determining the mechanisms of diaspore release is of prime importance to understand under which climatic conditions and at which frequency diaspores are released and transported. In mosses, wherein spore dispersal takes place through the hygroscopic movements of the peristome, the factors enhancing spore release has received little attention. Here, we determine the levels of relative humidity (RH) at which peristome movements are induced, contrasting the response of species with perfect (fully developed) and specialized (reduced) peristomes. All nine investigated species with perfect peristomes displayed a xerochastic behavior, initiating a closing movement from around 50%–65% RH upon increasing humidity and an opening movement from around 90% RH upon drying. Five of the seven species with specialized peristomes exhibited a hygrochastic behavior, initiating an opening movement under increasing RH (from about 80%) and a closing movement upon drying (from about 90%). These differences between species with hygrochastic and xerochastic peristomes suggest that spore dispersal does not randomly occur regardless of the prevailing climate conditions, which can impact their dispersal distances. In species with xerochastic peristomes, the release of spores under decreasing RH can be interpreted as an adaptive mechanism to disperse spores under optimal conditions for long‐distance wind dispersal. In species with hygrochastic peristomes, conversely, the release of spores under wet conditions, which decreases their wind long‐distance dispersal capacities, might be seen as a safe‐site strategy, forcing spores to land in appropriate (micro‐) habitats where their survival is favored. Significant variations were observed in the RH thresholds triggering peristome movements among species, especially in those with hygrochastic peristomes, raising the question of what mechanisms are responsible for such differences.

Temperature-related parasite infection dynamics: the case of proliferative kidney disease of brown trout.

Climate change, in particular rising temperature, is suspected to be a major driver for the emergence of many wildlife diseases. Proliferative kidney disease of salmonids, caused by the myxozoan Tetracapsuloides bryosalmonae, was used to evaluate how temperature dependence of host-parasite interactions modulates disease emergence. Brown trout (Salmo trutta fario) kept at 12 and 15 °C, were experimentally infected with T. bryosalmonae. Parasite development in the fish host and release of spores were quantified simultaneously to unravel parasite transmission potential from the vertebrate to the invertebrate host. A change to a stable plateau in infection intensity of the kidney coincided with a threshold at which spore shedding commenced. This onset of parasite release was delayed at the low temperature in accordance with reaching this infection intensity threshold, but the amount of spores released was irrespective of temperature. The production of parasite transmission stages declined with time. In conclusion, elevated temperature modifies the parasite transmission opportunities by increasing the duration of transmission stage production, which may affect the spread and establishment of the parasite in a wider range of rivers.

Experimental validation of a long-distance transport model for plant pathogens: Application to Fusarium graminearum

Fusarium graminearum, causal agent of Fusarium head blight (FHB) of wheat and barley, is a devastating plant pathogen that may be transported through the atmosphere over long distances. A Gaussian dispersal model has been developed to predict the long distance transport of plant pathogens, but this model has not yet been experimentally validated for F. graminearum. Here, we compare the results of two release-recapture studies (conducted in 2011 and 2012) of F. graminearum from known field-scale sources of inoculum to those predicted by a Gaussian dispersal spore transport model. Dispersal kernel shape coefficients were similar for both results observed in the field and predicted by the model, with both being dictated by a power law function, indicating that turbulence was the dominant factor on a kilometer scale. Dispersal kernel predictions were also conducted using a more complicated Lagrangian Stochastic (LS) dispersal model. Dispersal kernel results were similar between the Gaussian and LS dispersal models. Model predictions had a stronger correlation with the number of spores being released when using a time varying q0 emission rate (r=0.92 in 2011 and r=0.84 in 2012) than an identical daily pattern q0 emission rate (r=0.35 in 2011 and r=0.32 in 2012). Temporal patterns of spore release and spore deposition in the field were not correlated (correlation coefficient of r=−0.12 for 2011 and r=0.45 for 2012). The actual numbers of spores deposited from our known sources were monitored using microsatellites (short, repeated sequences of DNA), and were 3 and 2000 times lower than predicted if potential source strength, Qpot, was equal to the actual number of spores released in 2011 and 2012, respectively. Differences between predicted and observed results in both years may have been due in part to variability in environmental conditions and spore release rates. This work provides a unique approach for validating a Gaussian spore transport model to predict the spore transport of F. graminearum over kilometer distances, and could be applied to other airborne plant pathogens in the future.

Release thresholds for moss spores: the importance of turbulence and sporophyte length

Summary Adequately describing the dispersal mechanisms of a species is important for understanding and predicting its distribution dynamics in space and time. For wind‐dispersed species, the transportation of airborne propagules is comparatively well studied, while the mechanisms triggering propagule release are poorly understood, especially for cryptogams. We investigated the effect of wind speed and turbulence on spore release in the moss Atrichum undulatum in a wind tunnel. Specifically, we measured the amount of spores released from sporophytes when exposed to different wind speeds, in high and low turbulence, using a particle counter. We also related spore release to variation in vibrations of the sporophyte and investigated how the vibrations were affected by wind speed, turbulence and sporophyte length (here including capsule, seta and the top part of the shoot). We show that in high turbulence, the amount of spores released increased with increasing wind speed, while in low turbulence, it did not, within the wind speed range 0.8–4.3 m s−1. However, there was a threshold in wind speed (˜2.5–3 m s−1) before large amounts of spores started to be released in turbulent flow, which coincided with incipient vibrations of the sporophyte. Thresholds in wind variation, rather than average wind speed, seemed to initiate sporophyte vibrations. The vibration threshold increased with decreasing sporophyte length. The deposition of spores near the source decreased with increasing wind variation during the time of their release, based on simulated spore deposition from another study of moss dispersal. Synthesis. We suggest that vibration of moss sporophytes is an important mechanism to regulate spore release and that turbulence and sporophyte length regulate the onset of sporophyte vibration. Spore release thresholds affect dispersal distances and have implications for our understanding and predictions of species distribution patterns, population dynamics and persistence. The mechanisms of this phase of the dispersal process are also important to explore for other species, as there may be a substantial variation depending on the species' different traits.

Incubation Temperature and Substrate Quality Modulate Sporulation by Aquatic Hyphomycetes

Frequency and amplitude of temperature oscillations can profoundly affect structure and function of ecosystems. Unless the rate of a biological process changes linearly within the range of these fluctuations, the cumulative effect of temperature differs from the effect measured at the average temperature (Jensen's inequality). Here, we measured numbers and types of spores released by aquatic hyphomycetes from oak and alder leaves that had been exposed in a Portuguese stream for between 7 and 94 days. Recovered leaves were incubated at four temperatures between 5 and 20 °C. Over this range, the sporulation response to temperature was decelerating, with an estimated optimum around 12.5 °C. Assuming a linear response, therefore, overestimates spore release from decaying leaves. The calculated discrepancy was more pronounced with recalcitrant oak leaves (greater toughness, phenolics concentration, lower N and P concentration than alder), and reached 26.6 % when temperature was assumed to oscillate between 1 and 9 °C, rather than remaining constant at 5 °C. The maximum fluctuation of water temperature over 48 h during the field experiment was approximately 3 °C, which would result in a discrepancy of up to 6 %. The composition of the fungal community (assessed by species identification of released spores) was significantly influenced by the state of decomposition, but not by leaf species or temperature. When quantifying the potential impact of global change on aquatic fungal communities, the average increase as well as fluctuations of the temperature have to be considered.

Timing and quantifying Aphanomyces astaci sporulation from the noble crayfish suffering from the crayfish plague

Aphanomyces astaci sporulation is crucial for the spreading potential of this disease agent. For the first time, we are reporting timing and quantity of A. astaci spores released from noble crayfish (Astacus astacus) suffering from crayfish plague under practical aquatic conditions. We infected nine noble crayfish with A. astaci PsI-genotype and maintained them in individual 8L tanks. Spores (zoospores and cysts) were quantified from water samples (3×1mL) taken every 12h over 10 d using A. astaci specific qPCR. A clear sporulation trend was found, together with a high individual spore estimate variation. The median spore counts from two days before death to 12h post mortem were from ∼500 to ∼2000sporesL−1. A significant sporulation increase occurred after 24h post mortem (∼12,000sporesL−1) and reached a peak after two days (∼65,000sporesL−1) before declining to or below pre mortem levels from the fourth day. The single most sporulating crayfish released from ∼75,000 to ∼400,000sporesL−1 during the mass sporulating period, yielding a maximum estimate of ∼3,200,000 spores released from a single crayfish if we assume homogeneous spore distribution. The results confirm a mass A. astaci spore release from moribund and recently dead infected noble crayfish, with a sporulation peak one to three days post mortem. The acute crayfish mortality only three days after zoospore exposure confirm the lethal potential of the PsI-genotype. The powerful sporulation potential observed here may be one of the key virulence factors of this genotype.

Counts of fungal spores released during inspection of mouldy cinematographic film and determination of the gelatinolytic activity of predominant isolates

Film archivists have expressed concern regarding the release of aerial spores during inspection of mouldy cinematographic film. This study investigated the release of fungal spores during a simulated inspection procedure, and identified the key contaminants, the aim being to make recommendations to archivists regarding safe handling of such film. Eighteen films (black and white or colour) donated to the North West Film Archive, in Manchester, UK, were examined. During simulated inspection, spore release ranged from zero to several thousand spores per m3, with the films showing the most visible mould colonisation usually yielding the highest numbers of colonies. There was no significant difference between the number of spores released from black and white film in contrast with colour film reels. Major contaminants were of the genera Aspergillus or Penicillium. A. versicolor was the most common species isolated. Gelatinase assays were performed on predominant isolates, to investigate whether fungal species which released the most spores, were also the most gelatinolytic, thus posing the greatest threat to film preservation. However, this doesn't prove to be the case. Some films released spores in numbers greater than are deemed ‘safe’ levels; therefore caution is advised when dealing with very mouldy film reels.

Seasonal and Diurnal Patterns of Spore Release Can Significantly Affect the Proportion of Spores Expected to Undergo Long-Distance Dispersal

Many of the fungal pathogens that threaten agricultural and natural systems undergo wind-assisted dispersal. During turbulent wind conditions, long-distance dispersal can occur, and airborne spores are carried over distances greater than the mean. The occurrence of long-distance dispersal is an important ecological process, as it can drastically increase the extent to which pathogen epidemics spread across a landscape, result in rapid transmission of disease to previously uninfected areas, and influence the spatial structure of pathogen populations in fragmented landscapes. Since the timing of spore release determines the wind conditions that prevail over a dispersal event, this timing is likely to affect the probability of long-distance dispersal occurring. Using a Lagrangian stochastic model, we test the effect of seasonal and diurnal variation in the release of spores on wind-assisted dispersal. Spores released during the hottest part of the day are shown to be more likely to undergo long-distance dispersal than those released at other times. Furthermore, interactions are shown to occur between seasonal and diurnal patterns of release. These results have important consequences for further modelling of wind-assisted dispersal and the use of models to predict the spread of fungal pathogens and resulting population and epidemic dynamics.

A host‐pathogen simulation model: powdery mildew of grapevine

An epidemiological model simulating the growth of a single grapevine stock coupled to the dispersal and disease dynamics of the airborne conidia of the powdery mildew pathogen Erysiphe necator was developed. The model input variables were either climatic (temperature, wind speed and direction) or related to the pathogen (location and onset of primary infection). The environmental input variables dictated plant growth and pathogen spread (latent period, infection, lesion growth, conidial spore production and release). Input parameters characterized the crop production system, the growth conditions and the epidemiological characteristics of the pathogen. Output described, at each time step, number, age and pattern of healthy and infected organs, infected and infectious leaf area and aerial density of spores released. Validation of the model was achieved by comparing model output with experimental data for epidemics initiated at different times of host growth. Epidemic behaviour for two contrasting years of crop development and 7 phenological stages at the time of primary infection (PI) was examined. For PI occurring at day 115 a vine with late budbreak (1998) showed 58% of primary leaves diseased at flowering compared with only 19% for a vine with early budbreak (2003). Depending on the phenological stage at PI (1–4 leaves), the proportion of diseased primary leaves decreased from 42% to 6% at flowering. Simulations suggested that differences resulted from the interplay between the timing of the first sporulation event, the phenological stage at the time of initial infection, and the age structure and spatial distribution of the leaf population.

Early development ofChondrus ocellatus holm (Gigartinaceae, Rhodophyta)

Chondrus is an economically important red algae widely used for food and biochemical purpose. It early development is crucial for the culture and seedling propagation. We chose tetraspores and carpospores ofChondrus ocellatus as examples for experiment of the culture, induction and release in laboratory condition, aiming to understand early development ofC. ocellatus and to apply in seedling production. MatureC. ocellatus were collected in Qingdao, China, from Nov. to Dec. 2004. After the gametophyte and tetrasporophyte were brushed and washed with sterilized seawater, the algal materials were treated in 1.5% KI for 20 min, then were dried for 1h to stimulate the releasing of spores. After the spores released overnight, it were cultured in PES medium, incubated at 18 °C, 10±2 μmol/(m2·s1) in 12∶12h (light: dark). The observation and recording under microscope were carried out. Continuous observation of the early development showed that both tetraspore and carpospore are similar to each other. In general, three stages of the early development were shown being division, discoid crust and seedling stages. To the division stage, the most obvious feature was the increasing of cell number; during the discoid crust stage, the discoid crust had a three-dimensional axis, and it began to differentiate into two types of cells: the basal cells and the apical cells; and to the seedling stage, several protuberances-like appeared on the discoid crusts and formed juvenile seedlings. Carpospores and tetraspores exhibited a similar development process that included division stage, discoid crust stage and seedling stage.

Assessment of the aerosolization potential for fungal spores in moldy homes

The airborne fungal concentration measured with air samplers during specific time intervals may not adequately represent the indoor air quality because of the sporadic nature of spore release from sources. The conventional source evaluation (e.g. swab and tape sampling) characterizes the mold source but does not relate to the fraction of spores that can be aerosolized from a contaminated material. As an alternative to these methods, we have recently developed and laboratory-tested a novel Fungal Spore Source Strength Tester (FSSST). It allows assessing the potential of aerosolization of fungal spores from contaminated surfaces under the most favorable release conditions. In this study, the FSSST was used to characterize the release of spores from four building materials in mold-problem homes. The spores of different species were efficiently aerosolized by the FSSST, exhibiting a total spore release rate ranging approximately from 10(2) to 10(3) cm2/min. For all tested materials, <2% of the spores on the contaminated surface were released during the tests. The airborne spore concentration estimated from the release rate data was found in most cases to be significantly greater than the concentration actually measured in these environments with simultaneous air sampling. The results suggest that the FSSST can be used for the assessment of maximum potential exposure to airborne spores released from identified sources in homes. A recently developed FSSST was found to be suitable to measure the aerosolization potential of indoor fungal sources at the most favorable release conditions. The FSSST generates the data that allows assessing the strength of mold sources in homes with respect to their maximum ability to contaminate indoor air with fungi. The novel approach bridges two conventional methods, the air sampling and the direct source evaluation (e.g. swab sampling), thus providing a better representation of the airborne fungal exposure than these methods individually. The device prototype can be used for evaluating the effectiveness of environmental interventions by taking samples before and after the intervention. As a broader application, the FSSST can be utilized for assessing the release of various hazardous biological and non-biological particles from contaminated surfaces.

Fungal spore source strength tester: laboratory evaluation of a new concept

The airborne fungal spore concentration measured with air samplers during specific time intervals does not always adequately represent the maximum spore concentration levels, because of the sporadic nature of spore release. Hence, a reliable method is needed to directly assess the indoor fungal sources with respect to their spore aerosolization potential. In this study, the newly developed fungal spore source strength tester (FSSST), which aerosolizes spores from growth surfaces and samples the airborne fungi into a bioaerosol sampler, was evaluated in the laboratory. The FSSST's operational flow rates of 30 and 12.5 l/min were tested. The fungal spores released from moldy surfaces were measured with an optical particle counter. Simultaneously, the spores were collected by a bioaerosol sampler: either with a 37-mm filter cassette or with the BioSampler. Three material types, ceiling tile, gypsum board and plastic sheet coated with agar, were tested after they were inoculated with the fungus Aspergillus versicolor. In addition, gypsum board naturally contaminated with various fungi (obtained from a mold-problem home) was tested in the laboratory using the FSSST. In all three laboratory-inoculated materials, the release rate of A. versicolor was found to be higher when the FSSST operated at 30 l/min than at 12.5 l/min. Nevertheless, even at 12.5 l/min the number of spores aerosolized from the source during 10 min was found sufficient to reflect the highest level of release that may occur in indoor environments. At 12.5 l/min, the release rate of A. versicolor during the first 10-min period was (23.9±17.7)×10 4 cm −2 for ceiling tile, (1.3±0.3)×10 4 cm −2 for gypsum board and (0.13±0.08)×10 4 cm −2 for agar surface (based on the samples collected with the BioSampler). The spore release rate was higher during the first 10 min than during the second 10 min of the FSSST application. It was observed that the particles aerosolized from the A. versicolor culture included spore aggregates and single spores, as well as mycelial fragments. Overall, 0.6±0.3% of spores detected on 1 cm 2 of ceiling tile inoculated with A. versicolor were aerosolized during the 10-min source testing. The respective number was 9.2±1.0% for the laboratory-inoculated gypsum board, 0.002±0.001% for the laboratory-inoculated plastic covered with agar and 1.8±0.2% for naturally contaminated gypsum board. Our data suggest that the FSSST provides very favorable conditions for the spore aerosolization and thus can be used in the field to assess the maximum potential spore release from a fungal source.

Fungal spore source strength tester: laboratory evaluation of a new concept

The airborne fungal spore concentration measured with air samplers during specific time intervals does not always adequately represent the maximum spore concentration levels, because of the sporadic nature of spore release. Hence, a reliable method is needed to directly assess the indoor fungal sources with respect to their spore aerosolization potential. In this study, the newly developed fungal spore source strength tester (FSSST), which aerosolizes spores from growth surfaces and samples the airborne fungi into a bioaerosol sampler, was evaluated in the laboratory. The FSSST's operational flow rates of 30 and 12.5 l/min were tested. The fungal spores released from moldy surfaces were measured with an optical particle counter. Simultaneously, the spores were collected by a bioaerosol sampler: either with a 37-mm filter cassette or with the BioSampler. Three material types, ceiling tile, gypsum board and plastic sheet coated with agar, were tested after they were inoculated with the fungus Aspergillus versicolor . In addition, gypsum board naturally contaminated with various fungi (obtained from a mold-problem home) was tested in the laboratory using the FSSST. In all three laboratory-inoculated materials, the release rate of A. versicolor was found to be higher when the FSSST operated at 30 l/min than at 12.5 l/min. Nevertheless, even at 12.5 l/min the number of spores aerosolized from the source during 10 min was found sufficient to reflect the highest level of release that may occur in indoor environments. At 12.5 l/min, the release rate of A. versicolor during the first 10-min period was (23.9±17.7)×10 4 cm −2 for ceiling tile, (1.3±0.3)×10 4 cm −2 for gypsum board and (0.13±0.08)×10 4 cm −2 for agar surface (based on the samples collected with the BioSampler). The spore release rate was higher during the first 10 min than during the second 10 min of the FSSST application. It was observed that the particles aerosolized from the A. versicolor culture included spore aggregates and single spores, as well as mycelial fragments. Overall, 0.6±0.3% of spores detected on 1 cm 2 of ceiling tile inoculated with A. versicolor were aerosolized during the 10-min source testing. The respective number was 9.2±1.0% for the laboratory-inoculated gypsum board, 0.002±0.001% for the laboratory-inoculated plastic covered with agar and 1.8±0.2% for naturally contaminated gypsum board. Our data suggest that the FSSST provides very favorable conditions for the spore aerosolization and thus can be used in the field to assess the maximum potential spore release from a fungal source.

Source strength of fungal spore aerosolization from moldy building material

The release of Aspergillus versicolor, Cladosporium cladosporioides, and Penicillium melinii spores from agar and ceiling tile surfaces was tested under different controlled environmental conditions using a newly designed and constructed aerosolization chamber. This study revealed that all the investigated parameters, such as fungal species, air velocity above the surface, texture of the surface, and vibration of contaminated material, affected the fungal spore release. It was found that typical indoor air currents can release up to 200 spores cm −2 from surfaces with fungal spores during 30-min experiments. The release of fungal spores from smooth agar surfaces was found to be inadequate for accurately predicting the emission from rough ceiling tile surfaces because the air turbulence increases the spore release from a rough surface. A vibration at a frequency of 1 Hz at a power level of 14 W resulted in a significant increase in the spore release rate. The release appears to depend on the morphology of the fungal colonies grown on ceiling tile surfaces including the thickness of conidiophores, the length of spore chains, and the shape of spores. The spores were found to be released continuously during each 30-min experiment. However, the release rate was usually highest during the first few minutes of exposure to air currents and mechanical vibration. About 71–88% of the spores released during a 30-min interval became airborne during the first 10 min.