Airborne Spore Concentrations Research Articles

Effect of prevailing winds and land use on Alternaria airborne spore load

Alternaria spores are a common component of the bioaerosol. Many Alternaria species are plant pathogens, and their conidia are catalogued as important aeroallergens. Several aerobiological studies showing a strong relationship between concentrations of airborne spore and meteorological parameters have consequently been developed. However, the Alternaria airborne load variation has not been thoroughly investigated because it is difficult to assess their sources, as they are a very common and widely established phytopathogen. The objective of this study is to estimate the impact of vegetation and land uses as potential sources on airborne spore load and to know their influence, particularly, in cases of long-medium distance transport. The daily airborne spore concentration was studied over a 5-year period in León and Valladolid, two localities of Castilla y León (Spain), with differences in their bioclimatic and land use aspects. Moreover, the land use analysis carried out within a 30 km radius of each monitoring station was combined with air mass data in order to search for potential emission sources. The results showed a great spatial variation between the two areas, which are relatively close to each other. The fact that the spore concentrations recorded in Valladolid were higher than those in León was owing to prevailing winds originating from large areas covered by cereal crops, especially during the harvest period. However, the prevailing winds in León came from areas dominated by forest and shrubland, which explains the low airborne spore load, since the main Alternaria sources were the grasslands located next to the trap. Furthermore, the risk days in this location presented an unusual wind direction. This study reveals the importance of land cover and wind speed and direction data for establishing potential airborne routes of spore transport in order to improve the Alternaria forecasting models. The importance of conducting Alternaria aerobiological studies at a local level is also highlighted.

Temporal variations in fungal spores in Mardin city atmosphere, upper Mesopotamia, SE-Turkey

The present study aimed to determine the fungal spores and their concentrations in the atmosphere of Mardin (southeast Turkey) in 2014 and 2015 using the volumetric method. A total of 43 taxa, hyphal fragments, and single septate ascospores were identified by light microscopy. It was determined that the dominant fungal spores included Cladosporium (51.5%), Ustilaginales species spores (13.9%), Alternaria (6.9%), Pucciniales species spores (1.6%), Agrocybe (1.2%), Pleospora (1.1%) and hyphal fragments (15.5%). The highest atmospheric spore concentrations were observed in May and the lowest levels were determined in February in both years. Dry air spores constituted a significant ratio of the total count (73.9%) in the atmosphere of Mardin. There were significant positive correlations between atmospheric concentrations of Alternaria, Cladosporium, Ustilaginales, and Pucciniales spores and temperatures. There were significant negative correlations between airborne fungal spore concentrations and daily mean humidity. There was a significant negative correlation between Agrocybe spore concentrations and daily mean temperature and a significant positive correlation between the same and humidity and precipitation. No significant correlation was determined between the meteorological variables and Pleospora and Aspergillus/Penicillium spore concentrations.

Estimating Lung Deposition of Fungal Spores Using Actual Airborne Spore Concentrations and Physiological Data.

Exposure to bioaerosols has been implicated in adverse respiratory symptoms, infectious diseases, and bioterrorism. Although these particles have been measured within residential and occupational settings in multiple studies, the deposition of bioaerosol particles within the human respiratory system has been only minimally explored. This paper uses real-world environmental measurement data of total fungal spores using Air-o-Cell cassettes in 16 different apartments and residents' physiological data in those apartments to predict respiratory deposition of the spores. The airborne spore concentrations were measured during the spring, summer, and fall. The respiratory deposition of five most prevalent spore genera-Ascospores, Aspergillus, Basidiospores, Cladosporium, and Myxomycetes-was predicted using three empirical models: the Multiple Path Particle Dosimetry model, using both the Yeh and age-specific versions, and the Bioaerosol Adaptation of the International Committee on Radiological Protection's Lung deposition model. The predicted total deposited number of spores was highest for Ascospores and Cladosporium. While the majority of spores deposit were in the extrathoracic region, there is a significant deposition for both Aspergillus and Cladosporium in the alveolar region, potentially leading to the development of aspergillosis or allergic asthma. Although the dose-response relationship is unknown, the estimate of the actual spore deposition could be the first step in determining such a relationship.

Fungal Diseases in Two North-West Spain Vineyards: Relationship with Meteorological Conditions and Predictive Aerobiological Model

Grey mould, powdery mildew, and downy mildew are the most frequent fungal diseases among vineyards worldwide. In the present study, we analysed the influence of the fungi causing these diseases (Botrytis, Erysiphe, and Plasmopara, respectively) on two viticulture areas from North-western (NW) Spain during three growth seasons (2016, 2017, and 2018). The obtained results showed the predominant concentration of the Botrytis airborne spores, mainly from the beginning of the Inflorescence emerge phenological stage (S-5) until the end of the Flowering phenological stage (S-6). Erysiphe and Plasmopara airborne spore peak concentrations were more localised around Flowering (S-6) and Development of fruits (S-7) phenological stages. We applied a Spearman’s correlation test and a Principal Component Analysis to determine the influence of the meteorological parameters on the concentration of airborne spores. Taking into account the variables with the highest correlation coefficient, we developed multiple regression models to forecast the phytopathogenic fungal spore concentrations. The Botrytis model regression equation explained between 59.4–70.9% of spore concentration variability. The Erysiphe equation explained between 57.6–61% and the Plasmopara explained between 39.9–55.8%. In general, we found better prediction results for mean daily concentrations than sporadic spore peaks.

Spore concentrations of Blumeria graminis f. sp. tritici in relation to weather factors and disease development in Gansu, China

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is an important disease in China. In this study, airborne spore concentrations were monitored using spore samplers and real-time PCR during 2013– 2015 at three locations in Gangu, Gansu province of China. The effects of meteorological variables on spore concentration were analyzed and models were developed for forecasting dynamics of airborne conidia and disease progress. The temperature, solar radiation and rainfall were positively correlated to spore concentrations and disease development. Although there was a negative correlation between relative humidity and spore concentration, relative humidity was positively related with disease development. Stepwise regression models were obtained for predicting the dynamics of airborne conidia based on the positive degree days and accumulation of rainfall (R2 = 0.31, P < 0.01), the positive degree days (R2 = 0.16, P = 0.04) and mean temperatures (R2 = 0.24, P = 0.01) at three locations, respectively. Disease forecasting models were developed based on various meteorological variables and spore concentration, the most important variables being temperature and spore concentration. This knowledge can improve the disease forecasting of wheat powdery mildew in Gangu and help develop better disease control strategies.

Effect of environmental conditions and phenology in the dispersal of secondary Erysiphe necator conidia in a vineyard

An integrated powdery mildew management strategy to identify the principal moments of secondary Erysiphe necator conidia dispersal in a vineyard based on aerobiological, phenological and meteorological data was developed. An adaptation of the physiological P-days model was conducted to obtain a descriptive equation for the prediction of the advantageous meteorological conditions for Erysiphe necator conidia dispersal in the vineyards of the Ribeiro Designation of Origin area. Moreover, a regression model was developed to predict the conidia concentration as a function of the weather and aerobiological variables with the highest influence on airborne E. necator spores. Additionally, phenological observations were conducted during the vegetative cycle of Vitis vinifera, with the aim to identify the most susceptible phenological stages to powdery mildew infection by relating them with the detected atmospheric spore concentrations. The study was carried out from 2008 to 2018 in an experimental vineyard. The E. necator spores were trapped using a Lanzoni VPPS-2000 sampler and the phenological observations were conducted following the BBCH standardized scale. The highest total fungal spore amount per season in the atmosphere of the vineyard was detected in 2013 with 4828 spores m-3, while the lowest amount was recorded in 2009 with 883 spores m-3. In general, the highest daily airborne spore concentrations were detected during the Flowering (stage 6) or in the previous and next stages, whereas the maximum total spore amount by stage was recorded during Development of Fruits (stage 7). The proposed threshold of P-days for potential secondary infections in the Ribeiro D.O. ranges from 120 to 160 P-days. The combination of aerobiological, phenological and meteorological data provides us a useful tool for the knowledge of the Erysiphe necator conidia dispersal behaviour bringing agricultural practices closer to a sustainable system.

Temporal variations in the diversity of airborne fungal spores in a Mediterranean high altitude site

Relationships between meteorological factors and airborne fungal spore concentrations at high altitudes are virtually unknown. We used cross-correlation analyses to test the relationships between daily variation in meteorological factors (i.e., temperature, humidity and wind speed) and airborne spore concentration, diversity (Shannon and Simpson indices) and evenness (Pielou index) in an Apennine high altitude site (Gran Sasso Massif, 2117 m elevation). Daily average concentration of spores in this high altitude site was much lower than that observed at a low altitude site in the same area, which can be explained by the environmental conditions at high altitudes. We found that diversity and evenness tended to be negatively correlated with temperature and positively with humidity and wind speed with some delay, whereas abundance tended to be positively correlated with temperature and wind, but negatively with humidity. These relationships can be explained by the fact that rain increases turnover by removing dry spores of Cladosporium (the most abundant taxon) and aerosolizing wet ones. The high dominance of the most abundant taxon is a reflection of the extreme climatic conditions at high altitudes.

Factors Affecting the Vineyard Populational Diversity of Plasmopara viticola.

Vitis vinifera is very susceptible to downy mildew (Plasmopara viticola). A number of authors have suggested different genetic populations of this fungus exist in Europe, each showing a different degree of virulence. Work performed to date indicates this diversity to be the result of different factors. In areas where gene flow is greater and recombination more frequent, the diversity of P. viticola appears to be wider. In vineyards isolated by geographic barriers, a race may become dominant and produce clonal epidemics driven by asexual reproduction. The aim of the present work was to identify the conditions that influence the genetic diversity of P. viticola populations in the vineyards of northwestern Spain, where the climatic conditions for the growth of this fungus are very good. Vineyards situated in a closed, narrow valley of the interior, in more open valleys, and on the coast were sampled and the populations of P. viticola detected were differentiated at the molecular level through the examination of microsatellite markers. The populations of P. viticola represented in primary and secondary infections were investigated in the same way. The concentration of airborne sporangia in the vegetative cycle was also examined, as was the virulence of the different P. viticola populations detected. The epidemiological characteristics of the fungus differed depending on the degree of isolation of the vineyard, the airborne spore concentration, and on whether the attack was primary or secondary. Strong isolation was associated with the appearance of dominant fungal races and, therefore, reduced populational diversity.

First fungal spore calendar for the atmosphere of Bratislava, Slovakia

Fungal spores were identified and quantified in the air of Bratislava during the 1-year period (2016) using a Burkard 7-day volumetric aerospore trap. Based on data obtained, the first spore calendar in Slovakia has been constructed for the urban area of Bratislava. The total annual spore concentration recorded during this period was 836,418 spores/m3, belonging to 53 fungal spore types. The fungal taxa contributing the highest concentration of spores were Cladosporium (71.88% of the total), Coprinus (8.84%), Leptosphaeria (3.88%), Ganoderma (3.43%) and Alternaria (2.79%). Remaining 48 spore types were less well represented (altogether 9.18% of the total). Daily monitoring data revealed a large variation in airborne spore concentrations. Fungal spores peaked during summer and autumn months (June–October) and declined from November to March. The maximum monthly total spore concentration (153,342 spores/m3) was recorded in July, while the minimum (1381 spores/m3) in January. The relationships between mean daily airborne spore concentrations of selected fungal taxa and meteorological variables were evaluated through multiple regression analysis. The percentage of variation explained by regression analyses was 49.7% for Alternaria, 46.9% for Ganoderma, 45.8% for Cladosporium, 43.9% for Leptosphaeria and 32.1% for Coprinus. Spore concentrations of most analysed airborne fungal taxa were positively associated with air temperature and/or negatively associated with relative air humidity either throughout the year or only in summer. Cladosporium spore concentration was positively related with the wind speed, whereas the association between Ganoderma spore concentration and wind speed was negative. Spores of Leptosphaeria showed significant positive association with relative air humidity and significant negative association with sunshine duration in summer. Knowledge of seasonal patterns of the type and number of spores in the air will provide clinicians and sufferers of allergic asthma and rhinitis as well as agronomists with valuable information on the prophylaxis of respiratory allergic and plant diseases, respectively.

Airborne Alternaria and Cladosporium fungal spores in Europe: Forecasting possibilities and relationships with meteorological parameters

Airborne fungal spores are prevalent components of bioaerosols with a large impact on ecology, economy and health. Their major socioeconomic effects could be reduced by accurate and timely prediction of airborne spore concentrations. The main aim of this study was to create and evaluate models of Alternaria and Cladosporium spore concentrations based on data on a continental scale. Additional goals included assessment of the level of generalization of the models spatially and description of the main meteorological factors influencing fungal spore concentrations.Aerobiological monitoring was carried out at 18 sites in six countries across Europe over 3 to 21 years depending on site. Quantile random forest modelling was used to predict spore concentrations. Generalization of the Alternaria and Cladosporium models was tested using (i) one model for all the sites, (ii) models for groups of sites, and (iii) models for individual sites.The study revealed the possibility of reliable prediction of fungal spore levels using gridded meteorological data. The classification models also showed the capacity for providing larger scale predictions of fungal spore concentrations. Regression models were distinctly less accurate than classification models due to several factors, including measurement errors and distinct day-to-day changes of concentrations. Temperature and vapour pressure proved to be the most important variables in the regression and classification models of Alternaria and Cladosporium spore concentrations.Accurate and operational daily-scale predictive models of bioaerosol abundances contribute to the assessment and evaluation of relevant exposure and consequently more timely and efficient management of phytopathogenic and of human allergic diseases.

Variation in airborne fungal spore concentrations among five monitoring locations in a desert urban environment

Fungal spores are biological particles that are ubiquitous in the outdoor air. Spores of several very common fungal species are known allergens, with the potential to cause respiratory illnesses by exacerbating asthma and allergic rhinitis. The National Allergy Bureau typically has one monitoring station established per city to determine fungal spore counts for an entire metropolitan area. However, variations in fungal spore concentrations could occur among different locations. The objective of this study was to measure and compare airborne fungal spore concentrations in five locations in Las Vegas for the year 2015 to determine if there are differences among microenvironments in the city. Twenty-four-hour or 7-day air samples were collected from five sites across the Las Vegas Valley. Samples were analyzed with a light microscope for fungal spores and counts were converted to concentrations of spores per volume of air. Mixed-model methods were used to evaluate mean differences. Results showed that smuts (basidiomycetes) were the dominant spore type for all five sites during the spring season. Cladosporium species were responsible for the second most dominant spore type with the highest concentrations occurring during the summer and fall months. Results obtained from the five stations established in Las Vegas show that there are important variations among the sites regarding fungal spore concentrations. The data suggest that more sites and additional monitoring of outdoor allergens are needed to provide information necessary to inform the community of outdoor air quality conditions and their potential effects on public health. This study presents new outdoor fungal spore data for the southwest region of the USA, focused in the Las Vegas Valley.

Fungal spores affecting vineyards in Montilla-Moriles Southern Spain

The most common Vitis vinifera diseases are powdery mildew (Uncinula necator), grey mould (Botrytis cinerea) and downy mildew (Plasmopara viticola). Greater knowledge of the factors involved in fungus reproduction and plant infection will help to fine-tune treatment application calendars, thus cutting farmers’ costs and reducing adverse environmental effects. The main aim of this study was to investigate the relationship between airborne spore concentrations, weather-related parameters and grapevine phenology. Phenological observations and airborne spore detection were carried out during the Vitis vinifera growing period (February–August) from 2015 to 2017. Phenological data were collected weekly for four grape varieties (Pedro Ximenez, Verdejo, Muscat a petit grains and Chardonnay). Airborne fungal spores were monitored using one Hirst-type volumetric spore trap, following the standard protocol developed by the Spanish Aerobiology Network (REA) and the European Aeroallergen Society (EAS), and 4 Passive Spore Traps (PST), following the protocol proposed by Kelly et al. (Phytopathology, 105, 905–916, 2015). During this study, U. necator was the most common, followed by B. cinerea and P. viticola. A significant correlation was found between the all PSTs weekly spore concentrations and the Hirst sampler but the seasonal spore integral was always higher for the Hirst-type sampler than for PSTs. Airborne U. necator spore concentrations were higher prior to blooming, and correlated with average temperature and rainfall. B. cinerea recorded the highest concentrations during leaf development, inflorescence emergence and flowering; airborne spore concentrations were correlated with both dew point and daily average temperature. P. viticola presented lower concentration but it was most frequently recorded spore during the stages prior to blooming, and displayed stronger correlations with humidity, dew point and average temperature. Weather conditions over the study period in the Montilla-Moriles Protected Designation of Origin (PDO) area probably gave rise to spore concentrations lower than those reported for vineyards elsewhere in Spain, but higher than those recorded locally in areas where not associated with vineyards. The Hirst-type sampler yielded spore data representative of the whole study area. Knowledge of the factors influencing fungal spore concentration will help to fine-tune treatment calendars, and thus reduce the economic and environmental effects of treatment.

Inter-seasonal and altitudinal inoculum dynamics for wheat stripe rust and powdery mildew epidemics in Gangu, Northwestern China

Inter-seasonal and altitudinal dynamics of airborne spores of wheat stripe rust and powdery mildew pathogens were studied in northwestern China (Gangu, Gansu) in this study. Burkard spore traps were placed in three locations of Gansu county of the Gansu province at various altitudes, named South mountain, Valley and North mountain. Airborne spore samples were collected from March 2013 to December 2015, totaling 1365 collections for each pathogen. The airborne spore concentration of both pathogen, quantified using duplex real-time PCR assay, were consistently higher in the spring and summer than in fall and winter seasons. The within-crop season airborne inoculum levels were associated with disease severity levels. No difference was found in the Area Under the Spore Concentration Progress Curve (AUSCPC) between spring and summer for both pathogens as well as among the three locations, and there was significant correlation of ten-day spore concentrations between any two of the three locations. Our findings suggest that Gangu is an important source of oversummering inoculum for both diseases with frequent exchange of airborne spores within this region. The time-series analysis demonstrated that the airborne spore concentrations of Pst for all the 10-day-spore-sum during 3 years at three locations were all significantly described by the Autoregressive Integrated Moving-Average (ARIMA) (1, 0, 0) models, while, those of Bgt fitted different models, which contributed to predicting the tendency of airborne spore concentrations for both pathogens in Gangu.

Dew point temperature affects ascospore release of allergenic genus Leptosphaeria

The genus Leptosphaeria contains numerous fungi that cause the symptoms of asthma and also parasitize wild and crop plants. In search of a robust and universal forecast model, the ascospore concentration in air was measured and weather data recorded from 1 March to 31 October between 2006 and 2012. The experiment was conducted in three European countries of the temperate climate, i.e., Ukraine, Poland, and the UK. Out of over 150 forecast models produced using artificial neural networks (ANNs) and multivariate regression trees (MRTs), we selected the best model for each site, as well as for joint two-site combinations. The performance of all computed models was tested against records from 1 year which had not been used for model construction. The statistical analysis of the fungal spore data was supported by a comprehensive study of both climate and land cover within a 30-km radius from the air sampler location. High-performance forecasting models were obtained for individual sites, showing that the local micro-climate plays a decisive role in biology of the fungi. Based on the previous epidemiological studies, we hypothesized that dew point temperature (DPT) would be a critical factor in the models. The impact of DPT was confirmed only by one of the final best neural models, but the MRT analyses, similarly to the Spearman’s rank test, indicated the importance of DPT in all but one of the studied cases and in half of them ranked it as a fundamental factor. This work applies artificial neural modeling to predict the Leptosphaeria airborne spore concentration in urban areas for the first time.

Changes in airborne fungal flora along an urban to rural gradient

Exposure to bioaerosols has been associated with respiratory allergies and asthma. This highlights a need to characterize the fungal flora along an urbanization gradient. In this study, the airborne fungal flora, the concentration of dominant fungi and their seasonal variation along an urbanization gradient were investigated through viable count and direct microscopic count. Thirty-one fungal species including Cladosporium, Aspergillus, Penicillium, Fusarium and Trichoderma were identified. Characteristics of fungal floras differed significantly among seasons. The lowest spore concentration presented in winter, constituting the baseline data of airborne fungi. Urban and rural areas had significantly different airborne fungal floras and spore concentration. Aspergillus flavus and C. oxysporum were the dominant fungi in summer and autumn, respectively. Spatial distributions of dominant fungi, A. flavus and C. oxysporum, in their dominant seasons were similar and in both cases their spore concentration increased along a gradient of vegetation coverage. This pattern seems to be a result of the relatively lower plant tissue and soil in the urban. Contrasting with the dominance of allergenic C. herbarum in temperate areas, the dominant fungus in tropical Taiwan was C. oxysporum.

Occurrence of Puccinia spp. spores in Madeira Island and their phytopathological importance

The genus Puccinia represents rust infections, which are responsible for great productivity losses in crops of commercial and ornamental plants worldwide. This work is aimed at determining the occurrence of Puccinia spp. spores in Madeira Island in order to infer the exposure risks from a phytopathological point of view. A phytopathological analysis was performed in 203 local plant samples between January 2003 and December 2012. During the same period the airborne concentrations of rust spores were monitored following well-established guidelines. Aerobiological data was compared with meteorological records. Based on macro and microscopic analyses, five species of rusts were identified: P. horiana, P. buxi, P. porri, P. pelargonii-zonalis, and P. sorghi, and they were found mostly in spring and summer. A total of 20 samples out of 203 analysed plants (9.8%), were infected with Puccinia spores, i.e., P. horiana (5.9%), P. buxi (1.47%), P. porri and P. pelargonii-zonalis (0.98%), and P. sorghi (0.5%). During the studied period Puccinia spores attained an annual average concentration of 126 spores m−3 and most of them were recorded between March and October. Meteorological factors were determinant in fluctuations in spore concentration. Relative humidity was the parameter that favoured the biggest release and dispersal of the rust spores, whereas rainfall revealed a significant negative effect. Rusts do not represent an important plant pathogen in Madeira Island, as shown by the low infection frequencies and levels of airborne spore concentrations.

Phenotypic and genotypic diversity of airborne fungal spores in Dem\xe4novsk\xe1 Ice Cave (Low Tatras, Slovakia)

This paper is the first aero-mycological report from Demänovská Ice Cave. Fungal spores were sampled from the internal and external air of the cave in June, 2014, using the impact method with a microbiological air sampler. Airborne fungi cultured on PDA medium were identified using a combination of classical phenotypic and molecular methods. Altogether, the presence of 18 different fungal spores, belonging to 3 phyla, 9 orders and 14 genera, was detected in the air of the cave. All of them were isolated from the indoor samples, and only 9 were obtained from the outdoor samples. Overall, airborne fungal spores belonging to the genus Cladosporium dominated in this study. However, the spores of Trametes hirsuta were most commonly found in the indoor air samples of the cave and the spores of C. herbarum in the outdoor air samples. On the other hand, the spores of Alternaria abundans, Arthrinium kogelbergense, Cryptococcus curvatus, Discosia sp., Fomes fomentarius, Microdochium seminicola and T. hirsuta were discovered for the first time in the air of natural and artificial underground sites. The external air of the cave contains more culturable airborne fungal spores (755 colony-forming units (CFU) per 1 m3 of air) than the internal air (from 47 to 273 CFU in 1 m3), and these levels of airborne spore concentration do not pose a threat to the health of tourists. Probably, the specific microclimate in the cave, including the constant presence of ice caps and low temperature, as well as the location and surrounding environment, contributes to the unique species composition of aeromycota and their spores in the cave. Thus, aero-mycological monitoring of underground sites seems to be very important for their ecosystems, and it may help reduce the risk of fungal infections in humans and other mammals that may arise in particular due to climate change.

Atmospheric concentrations and intradiurnal pattern of Alternaria and Cladosporium conidia in Tétouan (NW of Morocco)

Fungal spores of Alternaria and Cladosporium are ubiquitous components of both indoor and outdoor air samples and are the main causes of human respiratory allergies. Monitoring these airborne fungal spores during 2009–2014 was carried out by means of Hirst-type spore trap to investigate their airborne spore concentrations with respect to annual load, seasonality and overall intradiurnal pattern. Alternaria and Cladosporium spores are present throughout the year in the atmosphere of Tetouan, although they show seasonal variations. Despite important differences between years, their highest levels presented a first peak during spring and a higher second peak in summer or autumn depending on the year. The spore concentrations were homogeneously distributed throughout the day with slight increase of 7.6 and 3.7% on average between 12–14 and 14–16 h for Alternaria and Cladosporium, respectively. The borderline of 3000 sp/m3 of Cladosporium linked to the occurrence of allergic diseases was exceeded between 13 and 31 days. Airborne spores of Alternaria overcame the threshold value of 100 sp/m3 up to 95 days, suggesting that Cladosporium and Alternaria could be clinically significant aeroallergens for atopic patients.

Temporal Dynamics of Botrytis cinerea and Sclerotinia sclerotiorum in Seed Alfalfa Fields of Southern Alberta, Canada.

Blossom blight of seed alfalfa (Medicago sativa L.), caused by the fungal pathogens Botrytis cinerea and Sclerotinia sclerotiorum, is a potentially devastating disease on the Canadian Prairies in moist growing seasons. Monitoring the airborne spore concentrations of these pathogens could facilitate disease forecasting in the region. Nineteen seed alfalfa fields in southern Alberta, Canada were assessed throughout the growing seasons of 2014 and 2015. Trace levels of blossom blight symptoms were found in both years; however, plated floret and pod samples indicated that, overall, B. cinerea increased over the growing season whereas S. sclerotiorum decreased. In both seasons, Burkard 7-day volumetric spore samplers collected daily aerosol samples, and weather stations recorded environmental variables in three fields. Conidia and ascospores collected were quantified each day with a real-time polymerase chain reaction assay. Spore quantification indicated that both B. cinerea and S. sclerotiorum numbers remained low in July and increased in August. Both species had multiple days with high spore discharge, with seasonal maxima of 21,137 conidia and 2,265 ascospores. Exploratory model development indicated that spore discharge of both fungi is associated with environmental stressors such as large changes in relative humidity or high temperatures on preceding days.

A Quantitative Dynamic Simulation of Bremia lactucae Airborne Conidia Concentration above a Lettuce Canopy.

Lettuce downy mildew, caused by the oomycete Bremia lactucae Regel, is a major threat to lettuce production worldwide. Lettuce downy mildew is a polycyclic disease driven by airborne spores. A weather-based dynamic simulation model for B. lactucae airborne spores was developed to simulate the aerobiological characteristics of the pathogen. The model was built using the STELLA platform by following the system dynamics methodology. The model was developed using published equations describing disease subprocesses (e.g., sporulation) and assembled knowledge of the interactions among pathogen, host, and weather. The model was evaluated with four years of independent data by comparing model simulations with observations of hourly and daily airborne spore concentrations. The results show an accurate simulation of the trend and shape of B. lactucae temporal dynamics of airborne spore concentration. The model simulated hourly and daily peaks in airborne spore concentrations. More than 95% of the simulation runs, the daily-simulated airborne conidia concentration was 0 when airborne conidia were not observed. Also, the relationship between the simulated and the observed airborne spores was linear. In more than 94% of the simulation runs, the proportion of the linear variation in the hourly-observed values explained by the variation in the hourly-simulated values was greater than 0.7 in all years except one. Most of the errors came from the deviation from the 1:1 line, and the proportion of errors due to the model bias was low. This model is the only dynamic model developed to mimic the dynamics of airborne inoculum and represents an initial step towards improved lettuce downy mildew understanding, forecasting and management.