The Role of Ascospores and Conidia, in Relation to Weather Variables, in the Epidemiology of Stemphylium Leaf Blight of Onion.

Stemphylium leaf blight (SLB), caused by Stemphylium vesicarium, is an important foliar disease of onion in northeastern North America. The pathogen produces conidia and ascospores, but the relative contributions of these spore types to epidemics in onion is not known. Determining the abundance of ascospores and conidia during the growing season could contribute to a disease forecasting model. Airborne ascospores and conidia of S. vesicarium were trapped during the growing season of 2015 and 2016 at an onion trial in southern Ontario, Canada, using a Burkard 7-day volumetric sampler. Meteorological data were recorded hourly. Ascospore numbers peaked before the crop was planted and declined rapidly with time and at daily mean air temperatures >15°C. Conidia were present throughout the growing season and appear to be closely related to the development of SLB on onion. Daily spore concentrations were variable, but 59 to 73% of ascospores and approximately 60% of conidia were captured between 0600 and 1200 h. Spore concentrations increased 24 to 72 h after rainfall and precipitation and leaf wetness duration were consistently and positively associated with increases in numbers of conidia and subsequent SLB incidence. The first symptoms of SLB coincided with high numbers of conidia, rainfall, leaf wetness duration ≥8 h, and days with average daily temperature ≥18°C. The number of airborne ascospores was very low by the time SLB symptoms were observed. Ascospores may initiate infection on alternative hosts in early spring, while conidia are the most important inoculum for the epidemic on onions.

Passive fungal spore release from fruit and vegetable solid waste.

Food substrates in municipal solid wastes processing facilities and open dumpsites are a source for the release of fungal spores into air and can cause potential health and climate effects. Experiments were conducted in a laboratory scale flux chamber to measure the fungal growth and spore release from representative exposed cut fruit and vegetable substrates. The aerosolised spores were measured using an optical particle sizer. The results were compared to experiments conducted previously with a test species (Penicillium chrysogenum) on a synthetic media (czapek yeast extract agar). Significantly higher surface spore densities were observed for the fungi on the food substrates as compared to that on the synthetic media. The spore flux was high initially and then decreased on continued exposure to air. The spore emission flux normalised to the surface spore densities indicated that the emission from the food substrates was lower than the emissions from the synthetic media. A mathematical model was applied to the experimental data and the observed flux trends were explained in terms of the model parameters. A simple application of the data and the model to release from a municipal solid waste dumpsite was shown.

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.

Premise: The 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. Methods: We 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. Results: We 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. Discussion: The 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.

Biosynthetic Mechanism of Key Volatile Biomarkers of Harvested Lentinula edodes Triggered by Spore Release.

In this study, headspace solid-phase microextraction-gas chromatography-mass spectrometry, multivariate analyses, and transcriptomics were used to explore the biosynthesis of key volatiles and the formation of spores in Lentinula (L.) edodes. Among the 50 volatiles identified, 1-octen-3-ol, phenethyl alcohol, and several esters were considered key aromas because of their higher odor activity values. Eleven volatiles were screened as biomarkers by orthogonal partial least squares discriminant analysis, and hierarchical cluster analysis showed that these biomarkers could represent all volatiles to distinguish the spore release stage. The activities of lipoxygenase (LOX), hydroperoxide lyase, alcohol dehydrogenase, and alcohol acyltransferase were higher in L. edodes with spore release. Moreover, linolenic acid and phenylalanine metabolism were involved in aroma biosynthesis. One LOX-related gene and five aryl alcohol dehydrogenase-related genes could regulate the biosynthesis of 1-octen-3-ol, phenethyl alcohol, and phenylacetaldehyde. In addition, several key genes were involved in meiosis to regulate sporulation.

Ascospore release in apple scab underlies infrared sensation.

The agent of apple scab disease (Venturia inaequalis) is the most common pathogen in apple cultivation. Its ascospores are released in spring, mainly during daylight hours and triggered by rain events. To investigate the causes of diurnal rhythm of ascospore dissemination of the apple scab fungus ascospore releases were examined continuously with spore traps in the orchard and with laboratory assays. One of the spore traps was illuminated at night with different light sources in each year during 2011-2015. The laboratory assays were performed with different light sources with varying wavelengths and intensities. In field and laboratory conditions only light including infrared radiation stimulated ascospore release, but not with light in the visible spectrum only. Artificial illumination during night was correlated with an increase of up to 46 % of ascospores released overnight in the field. We proved that infrared radiation induces V. inaequalis to release its spores. This is the first report in which spore discharge could be stimulated during night under field conditions.