Spores Deposited Research Articles

Numerical Simulation of Aspergillus Niger Spore Deposition in Nasal Cavities of a Population in Northwest China

Background: As common pathogens in the human respiratory tract, fungal-spore-related health risks have been challenging to evaluate properly. This paper presents numerical simulations of particle deposition of Aspergillus niger spores in human nasal cavities. Methods: 30 healthy adults (including 60 nasal chambers) who lived in northwest China were recruited to conduct a nasal cavity numerical simulation using computational fluid dynamics–discrete phase model (CFD-DPM). The deposition rate in each anatomic area and its influencing variables, such as body position and respiratory flow rate, were analyzed. Results: (1) Under a resting condition, only about 5.57% ± 1.51% Aspergillus niger spores were deposited in the nasal cavity, while most of them escaped from the nasopharynx, and 0.31% ± 0.20% spores entered the maxillary sinus; (2) under an exercising condition, spores deposited in the nasal cavity were about 2.09 times as many as that in the resting state; (3) in a lying position, the A. niger spores deposited evenly on the lateral wall of the nasal cavity and the sinus when compared with a standing position. However, the deposition rate in each anatomic area did not change significantly.

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.

The aerobiology of Fusarium graminearum

Current knowledge of the aerobiology of Fusarium graminearum sensu lato is based on decades of published research documenting the processes of spore discharge, atmospheric transport, and deposition in this important pathogen of cereal crops worldwide. Spores from both local and more distant sources have been shown to cause infection in susceptible cereal crops when environmental conditions are favorable. Susceptible crops may be exposed throughout a growing season to airborne spores deposited in rain events and in night-time hours through gravitational settling. Given that spores deposited on cereal florets originate from distant as well as local sources, disease risk forecasts, based currently on weather favoring local spore production during the days before peak infection (i.e., initiation of crop flowering), might be improved by placing greater emphasis on local weather directly favoring infection at and following the time of flowering. Also, considering the genetic diversity of fungal spores introduced to local agricultural fields following atmospheric transport, crop breeders should select resistant varieties based on screening against a set of fungal isolates that represent the range of virulence observed in fungal populations across a broader geographic region. An increased understanding of the aerobiology of F. graminearum contributes to the overall knowledge of plant pathogen transport in the atmosphere.

Night-time spore deposition of the fusarium head blight pathogen, Gibberella zeae, in rotational wheat fields

Many fungal plant pathogens rely on atmospheric motion systems for transport. The movement of these pathogens in the atmosphere is characterized by processes of liberation, drift, and deposition. We observed temporal patterns of viable spore deposition of Gibberella zeae, causal agent of fusarium head blight (FHB) of wheat, over rotational wheat fields (with no visible residues of corn or wheat, potential inoculum sources of G. zeae) in Aurora, New York, United States. Viable, airborne spores of G. zeae were collected on Petri plates containing selective medium placed 30 cm above wheat canopies. Over 40 000 viable spores of G. zeae were collected over a total of 73 day (6:00 am to 8:00 pm) or night (8:00 pm to 6:00 am) sampling periods in 3 years (2002, 2004, and 2005). The vast majority of the spores was collected at night (94% in 2002, 86% in 2004, and 82% in 2005). Viable spores were deposited in all but one sampling period spanning spike emergence through kernel milk stages of local wheat. Seven major deposition events (>50 colonies, on average, per Petri plate) were observed, all at night, and three of these were coincident with rainfall. In a single wheat field in 2004, viable spores of G. zeae were collected every 2 h throughout the night (starting at 8:00 pm) for six consecutive nights. Overall, 87% of the spores were deposited from 12:00 pm until 6:00 am, with most of the spores deposited between 4:00 am and 6:00 am. In 2005, viable spores of G. zeae were collected over variable landscape environments (two winter wheat fields, two soybean fields, one alfalfa hay field, and one fallow corn field) within 1 km2 area. Temporal patterns of viable spore deposition were virtually identical over all of the landscape environments, suggesting that spores were being deposited over kilometer distances from a well-mixed atmospheric source of inoculum. Atmospheric settling (gravitational fallout of spores) coinciding with the development of an inversion layer may explain the high degree of spore deposition at night. Vertical mixing and the presence of a mixed or turbulent layer during the daylight hours may account for the relatively low number of spores collected during the day. The deposition of spores of G. zeae primarily at night in rotational wheat fields raises some interesting questions about the origin of inoculum for epidemics of FHB. Our results suggest that spore deposition may be separated from spore release in both time and space. The cumulative exposure of wheat spikes to airborne spores of G. zeae, and the deposition of these spores mainly at night, should be considered in future prediction models and management strategies for fusarium head blight.

Epidemiological Characteristics of Angular Leaf Spot of Bean: A Systems Analysis

In this review, available knowledge on angular leaf spot (ALS) of bean, caused by Phaeoisariopsis griseola, is analysed and synthesised. This is done through a systems-analytical approach, and successive flowcharts of the system, in order to identify knowledge gaps and guide further research. Six connected sub-models of the ALS monocycle are used as a framework: lesion establishment, lesion extension, defoliation, sporulation, spore liberation, and spore deposition. Each of the sub-models enables the linking of processes to various effects of environmental (physical and host) factors. Disease-induced defoliation is one feature of the pathosystem, leading to a depletion of infectious tissues from the canopy, which are transferred to the ground. Consequences of defoliation may include: strong reductions of the amount of inoculum and of vacant sites in the canopy, limited maximum disease severity, and progressive accumulation of inoculum below the canopy, which may become important a later stage of disease epidemics. These elements are hypothesised to explain the typical behaviour of ALS epidemics in the field, especially late onset, high apparent rate of disease increase, and low level of terminal disease severity in the standing canopy. Epidemiological consequences of lesion expansion, sporulation, and survival of spores deposited onto the canopy are other knowledge gaps in this pathosystem.

Spatial Patterns of Viable Spore Deposition ofGibberella zeaein Wheat Fields

ABSTRACT An increased understanding of the epidemiology of Gibberella zeae will contribute to a rational and informed approach to the management of Fusarium head blight (FHB). An integral phase of the FHB cycle is the deposition of airborne spores, yet there is no information available on the spatial pattern of spore deposition of G. zeae above wheat canopies. We examined spatial patterns of viable spore deposition of G. zeae over rotational (lacking cereal debris) wheat fields in New York in 2002 and 2004. Viable, airborne spores (ascospores and macroconidia) of G. zeae were collected above wheat spikes on petri plates containing a selective medium and the resulting colonies were counted. Spores of G. zeae were collected over a total of 68 field environments (three wheat fields during 54 day and night sample periods over 2 years) from spike emergence to kernel milk stages of local wheat. Spatial patterns of spore deposition were visualized by contour plots of spore counts over entire fields. The spatial pattern of spore deposition was unique for each field environment during each day and night sample period. Spore deposition patterns during individual sample periods were classified by spatial analysis by distance indices (SADIE) statistics and Mantel tests. Both analyses indicated that the majority (93%) of the spore deposition events were random, with the remainder being aggregated. All of the aggregated patterns were observed during the night. Observed patterns of spore deposition were independent of the mean number of viable spores deposited during individual sample periods. The spatial pattern for cumulative spore deposition during anthesis in both years became aggregated over time. Contour maps of daily and cumulative spore deposition could be compared with contour maps of FHB incidence to gain insights into inoculum thresholds and the timing of effective inoculum for infection.

A settling tower for quantitative deposition of urediniospores of Uromyces viciae-fabae

An inoculation technique resulting in uniform spore deposition for obtaining reproducible and accurate data on host responses is required for quantitative studies of resistance expression. The feasibility of obtaining uniform spore deposition on Lens culinaris, a plant with compound leaves, was investigated using a settling tower. Uniformity of spore deposition on adhesive coated glass slides was assessed by dispersing 1,2,4 and 8 mg spores of Uromyces viciae-fabae, the causal agent of lentil rust, into the tower. When an 8 mg spore quantity was discharged the number of spores deposited per square centimetre did not vary significantly (P > 0.05) between the different locations of the glass slides on the target area. A linear, relation was found between mass of spores discharged into the tower and spores deposited. Counts for 1, 2, 4 and 8 mg were, respectively, 82, 244, 384 and 972 spores per square centimetre. Uniformity of spore deposition increased as the amount discharged increased, and the coefficient of variation was inversely related to the spore quantity dispersed. When plants of lentil cultivar EL-142 were exposed to spores in the settling tower, differences in numbers of lesions per square centimetre leaf area were non-significant (P > 0.05) within and between inoculation runs. Following dispersal of 8 mg urediniospores for a 3 min settling period, a mean of 140 uredinia (standard deviation = 7) occurred per square centimetre leaf area.

Deposition and adhesion of spores of Fusarium culmorum on hydrilla

Fusarium culmorum is a pathogen of the submerged aquatic weed Hydrilla verticillata. The deposition and attachment of macroconidia and chlamydospores of F. culmorum in water was investigated using assays with glass slides and hydrilla shoots. The number of spores deposited on leaves along the length of hydrilla shoots in test tubes did not vary significantly with depth. Macroconidia and chlamydospores deposited on the leaf did not become attached to the surface for several hours. Two-week-old macroconidia required 3 h for attachment and 6-week-old chlamydospores required 7 h. Pretreatment of macroconidia in hydrilla extract induced production of an adhesive substance from the tips of the macroconidia, which attached to glass slides and hydrilla leaves. The adhesive substance was induced after incubation for l min in hydrilla extract, and the adhesive capacity declined after 20 min of incubation. Macroconidia that adhered to glass slides began to break free after 3 h. Co-incubation of macroconidia in hydrilla extract and the lectin concanavalin A prevented adhesion of the macroconidia. Deposition and attachment of spores in the hydrilla - F. culmorum pathosystem is complex and must be understood in relation to dispersal of spores in water.

Dispersal and Disease Gradients of Anther‐Smut Infection of Silene Alba at Different Life Stages

Given the increased recognition of the importance of spatial aggregation of infected individuals on disease spread, we used a field experiment to examine spore dispersal and disease transmission at increasing distances from an inoculum source in a well—studied system, the herbaceous plant Silene alba, infected by the anther—smut fungus Ustilago violacea. Two different life stages (vegetative and floral) were examined. We measured spore deposition on flowers and, as an analog of dispersal to vegetative plants, in small vials on the ground. Spore and disease gradients (number of spores or proportion of plants infected as a function of distance) were best fit with the classic power, Y = aD—b. The slope parameter, b, were similar for spore dispersal gradients of vegetative (b = —2.38) and flowering plants (b = —1.91). However, at every distance measured, the proportion of flowers with spores was higher than the proportion of ground vials with spores, indicating overall higher relative spore dispersal to flowering plants. We also determined that disease gradients for flowering plants were more shallow (b = —0.07) than spore dispersal gradients, and vegetation infection was more spatially restricted than floral infection (no infection beyond 3.2 m for vegetative plants while floral infection was detected up to 11.2 m). The relationship between spore dispersal and disease incidence was linear for vegetative plants and curvilinear for flowering plants, with limiting returns on disease after a low threshold number of spores deposited. Overall, our study suggested that the limited dispersal of spores is likely to be important in the aggregation of diseased plants in nature; such aggregation of inoculum in turn can increase or decrease disease spread depending on how much inoculum is needed to cause infection.

ECOLOGICAL OBSERVATIONS ON THE PLANKTONIC CYANOPHYTE GLEOTRICHIA ECHINULATA1

Gleotrichia echinulata was planktonic in Green Lake (Seattle, Washington) during summer, making its initial appearance between May and early July and disappearing during September. It apparently spent 8 to 10 months of the year on the bottom where colonies developed from spores deposited by the preceding year’s bloom. The depth of spore deposition may be important in determining the success of spore maturation, and solar radiation may be a primary factor in inducing the annual return of this alga to the plankton. The maximum growth rate in 1886 was about 0.124 colony doublings per day. The vertical distribution of the colonies was controlled primarily by wind‐induced currents. The colonies had no measurable effect on light penetration even at a maximum density of over 400 colonies per liter. Laboratory studies indicated that G. echinulata can fix nitrogen. Only one herbivore in Green Lake, Lindia euchromatica, is known to feed on this species.