Spore Release Research Articles

Irrigation can create new green bridges that promote rapid intercontinental spread of the wheat stem rust pathogen

Wheat stem rust epidemics caused by the obligate pathogenic fungus Puccinia graminis f.sp. tritici have historically driven severe yield losses on all wheat growing continents and, after many decades of control, stem rust is re-emerging as a disease of concern. In 1998, a highly virulent race able to overcome 90% of world wheat cultivars, Ug99, was identified in Uganda. Since initial detection, the pathogen has evolved many new variants and spread to many countries. The original variant spread from East Africa to the Middle East with three years between detection in Ethiopia and subsequent detection in Yemen. In 2014, another Ug99 variant (TTKTT), with one of the most complex virulence profiles, was detected in Kenya. This variant also spread from East Africa to the Middle East, but with only one year between detection in Ethiopia and subsequent detection in Iraq. Here we investigate potential airborne migration routes to account for the rapid spread of TTKTT in East Africa and beyond to the Middle East by using an integrated model combining the outputs from a meteorology-driven fungal spore dispersion model with epidemiological models to account for seasonal availability of susceptible crops and conditions for spore release and infectivity. We find viable pathways in the 2018/19 season that incorporate critical stepping-stone locations in Yemen or Saudi Arabia, but only in the presence of newly irrigated regions in Ethiopia. Our results indicate the potential and increasing importance of irrigated wheat areas in Ethiopia, Yemen and Saudi Arabia for inter-regional stem rust movements. Future movement of stem rust races out of East Africa is considered likely as irrigated areas expand. Targeted surveillance and the use of mitigation strategies including the use of durable resistant varieties in regions of irrigation are required to reduce the risks of enhanced dispersal of stem rust to other regions.

Comparison of microscopic and metagenomic approaches to identify cereal pathogens and track fungal spore release in the field

Wheat is one of the main staple food crops, and 775 million tonnes of wheat were produced worldwide in 2022. Fungal diseases such as Fusarium head blight, Septoria tritici blotch, spot blotch, tan spot, stripe rust, leaf rust, and powdery mildew cause serious yield losses in wheat and can impact quality. We aimed to investigate the incidence of spores from major fungal pathogens of cereals in the field by comparing microscopic and metagenomic based approaches for spore identification. Spore traps were set up in four geographically distinct UK wheat fields (Carnoustie, Angus; Bishop Burton, Yorkshire; Swindon, Wiltshire; and Lenham, Kent). Six major cereal fungal pathogen genera (Alternaria spp., Blumeria graminis, Cladosporium spp., Fusarium spp., Puccinia spp., and Zymoseptoria spp.) were found using these techniques at all sites. Using metagenomic and BLAST analysis, 150 cereal pathogen species (33 different genera) were recorded on the spore trap tapes. The metagenomic BLAST analysis showed a higher accuracy in terms of species-specific identification than the taxonomic tool software Kraken2 or microscopic analysis. Microscopic data from the spore traps was subsequently correlated with weather data to examine the conditions which promote ascospore release of Fusarium spp. and Zymoseptoria spp. This revealed that Zymoseptoria spp. and Fusarium spp. ascospore release show a positive correlation with relative humidity (%RH). Whereas air temperature (°C) negatively affects Zymoseptoria spp. ascospore release.

Eisenia arborea (Areschoung) domestication and mariculture development on the Pacific coast of Baja California, México

Eisenia arborea (sensu Ecklonia arborea) is the kelp with the greatest latitudinal distribution on the Northeastern Pacific Coast. It is harvested in Mexico in small amounts for abalone farm fodder and occasionally exported to Asia for human consumption. Because the high-energy environment where it naturally grows limits its sustainable harvest, we explored the domestication and cultivation of this kelp on the west coast of Baja California, Mexico. The life history of E. arborea was completed in the laboratory following traditional methods for kelp cultivation. Gametophytes became reproductive approximately 50 days after spore release and sporophytes were visible to the naked eye after 80 days. When sporophytes reached 2–3 cm, they were transplanted to two sites on long-line systems: in an open bay (Todos Santos Bay) and in a shallow coastal lagoon (San Quintín Bay). At both sites, full differentiation occurred 6 to 8 months after deployment, with fertile blades occurring within a year. Once individuals reached maximum size, blades were harvested by pruning. Monthly, regrowth of pruned blades and new blade addition were measured. Pruned individuals reached the same weight as controls in three months. On the basis of these results, a seasonal seeding program was implemented at a third site where the presence of natural Eisenia is rare due to the lack of hard substrate but was hypothesized to provide appropriate conditions for kelp cultivation (Santa María Bay). Cultures were deployed at three different depths and growth was correlated with season, depth, and temperature. Only cultures seeded in winter developed successfully at this site. This study shows that the culture of E. arborea in a variety of ocean conditions is possible; however, site selection and seasonality are important considerations. Because E. arborea is perennial, it can be harvested periodically during the year thereby increasing yield, and because it is the warmest tolerant kelp species, it is an ideal target for ocean farming and commercial cultivation, considering climate change.

Neonectria ditissima spore release in apple plants and detached branches in Brazil

Neonectria ditissima spore release in apple plants and detached branches in Brazil

Energy status regulated umami compound metabolism in harvested shiitake mushrooms (Lentinus edodes) with spores triggered to release

The molecular mechanisms of energy status related to the umami taste of postharvest shiitake mushrooms during spore release remain poorly understood. In this study, the variations of energy status and umami taste of mushrooms were measured at 25 °C. At 24 h storage, slight spore prints of mushrooms were first pictured, respiration peaked. Significant ATP decrease and ADP increase were also observed as the initiation of postharvest senescence (P < 0.05). Meanwhile, the activities of phosphohexose isomerase, succinate dehydrogenase, glucose-6-phosphate dehydrogenase and cytochrome c oxidase and the contents of umami nucleotides and amino acids were maintained at higher levels in mushrooms with spore release. Notably, the equivalent umami concentration (EUC) was strongly correlated with energy levels (R = 0.80). Fifteen related gene expression levels in the energy metabolism pathway were downregulated. LecpdP1 and LeAK were significantly expressed in the conversion of ATP into AMP and played key roles in connecting the energy state and umami level. These results provided valuable insights on the umami taste associated with energy metabolism mechanism during postharvest mushroom spore release.

Effect of substrate on the proliferation of Myxobolus cerebralis in the mitochondrial lineages of the Tubifex tubifex host

The study goal was to examine the effects of sand and mud on the propagation of Myxobolus cerebralis, the whirling disease agent, in four mitochondrial 16S ribosomal DNA lineages (I, III, V, VI) of its oligochaete host, Tubifex tubifex (Tt). In all the lineage groups held continuously in either substrate (non-shifted) or transferred from sand to mud (shifted), substrate influenced parasite proliferation only in lineage III. Sporogenesis and release of triactinomyxon spores (TAMs) were more prevalent in lineage III Tt in mud compared to sand. Low-infection prevalence and lack of parasite development in lineage I is associated with the greater number of resistant worms and were not affected by substrate type. Substrate did not impact Tt from lineages V and VI that failed to develop any parasite stages in either substrate even after shifting from sand to mud. The relationship between the microbial community in the substrate and parasite proliferation in lineage III was described but not analyzed due to small sample size. Substrate-associated bacteria were hypothesized as essential dietary source for the oligochaete host feeding selectively on fine (mud)-microflora. Progeny was produced by all lineage groups shifted to mud with disparate survival profiles in lineage V and VI and high mortalities in lineage III. Our study demonstrates that substrate type can alter parasite proliferation in lineage III. Conversely, parasite development and infectivity were not altered in lineage V and VI that are refractory to the parasite nor among the more resistant phenotypes (I), regardless of substrate type.

Going With the Flow – Population Genetics of the Kelp Saccharina latissima (Phaeophyceae, Laminariales)

Saccharina latissimais the most important habitat-forming kelp in sheltered areas of North-Atlantic, and there is also an increasing interest in cultivation and utilization ofS. latissima. The cultivation activity may introduce a risk of “crop-to-wild” gene flow from the cultivated crops to natural populations. A baseline study to examine genetic structure and gene flow inS. latissimaalong the Norwegian coast was therefore done. Microsatellite analyses was carried out on samples from 21 stations, where 12 were in the coastal area from outer Oslofjord in the south to Porsanger in North-Norway, and 9 in the two longest fjords of Norway, Hardangerfjord and Sognefjord. In addition, a hydrographical model was applied, simulating the direction and potential rate of spore dispersal along the coast during the main period of spore release. The results showed a clear isolation by distance pattern along the coast, good connectivity and little genetic structure, except for a reduced connectivity between South- and North-Norway, probably due to the Lofoten archipelago representing a partial barrier for the northward dispersal of spores. In addition, indications of reduced connectivity between coastal stations and the innermost fjord stations were found. Analysing the material with and without one locus potentially under positive selection suggests some degree of genetic adaptation of sugar kelp populations in the Skagerrak area and in the two fjords. The results suggest that genetic connectivity between populations on the coast is strongly influenced by the Norwegian Coastal current.

Lichen cell factories: methods for the isolation of photobiont and mycobiont partners for defined pure and co-cultivation

BackgroundDue to their huge biodiversity and the capability to produce a wide range of secondary metabolites, lichens have a great potential in biotechnological applications. They have, however, hardly been used as cell factories to date, as it is considered to be difficult and laborious to cultivate lichen partners in pure or co-culture in the laboratory. The various methods used to isolate lichen fungi, based on either the ascospores, the conidia, or the thallus, have so far not been compared or critically examined. Therefore, here we systematically investigate and compare the known methods and two new methods to identify the most suitable technology for isolation of fungi from lichens.ResultsWithin this study six lichen fungi species were isolated and propagated as pure cultures. All of them formed colonies within one month. In case of lichens with ascocarps the spore discharge was the most suitable method. Spores were already discharged within 2 days and germinated within only four days and the contamination rate was low. Otherwise, the soredia and thallus method without homogenization, as described in this work, are also well suited to obtain pure fungal cultures. For the isolation of algae, we were also successful with the thallus method without homogenization.ConclusionWith the methods described here and the proposed strategic approach, we believe that a large proportion of the lichen fungi can be cultivated within a reasonable time and effort. Based on this, methods of controlled cultivation and co-cultivation must now be developed in order to use the potential of lichens with regard to their secondary metabolites, but also for other applications.

Phase-change-mediated transport and agglomeration of fungal spores on wheat awns.

Wheat and other staple crops are devastated by fungal diseases. Many fungal plant pathogens are spread via active or passive discharge of microscopic spores. Here, we described the unique transport of spores of the fungal pathogen Epicoccum tritici, causal agent of black sooty mould, on wheat awns. The unique multi-scale architecture of wheat awns, coupled with condensation and evaporation of dew droplets, facilitated the transport and agglomeration of spores of the fungus. First, dew droplets spontaneously transported spores from the tips of awn hairs to the neighbouring stomatal ridges, driven by gradients in Laplace pressure and surface wettability. Subsequently, spores agglomerated into dry clusters due to the Cheerios effect and evaporation, increasing the likelihood of passive spore removal via wind shear and/or rainsplash. Future plant breeding approaches should consider the development of modified spike structures, such as those without awns or awn hairs, to reduce the potential for spread of fungal plant pathogens.

Ascertaining the interactions of brown seaweed-derived biostimulants and seawater temperature on spore release, germination, conchocelis, and newly formed blades of the commercially important red alga Neopyropia yezoensis?

Seaweed-derived extracts are commonly used as biostimulants in agriculture and, more recently, to cultivate other types of seaweeds. Here, we examined if Ascophyllum marine plant extract powder (aka AMPEP) and Kelpak® influenced changes in the life history of the commercially important, Neopyropia yezoensis. N. yezoensis was cultured in von Stosch enriched (VSE) medium with different concentrations (0, 0.001, and 1 mL L−1) of AMPEP and Kelpak® for up to six days. Cultivars were then allowed to grow in VSE at either 15, 20, or 25 °C, 12:12 L:D photoperiod, and 100 μmol photon m−2 s−1 of PAR for up to 42 days. Spore release, germination, and appearance of newly formed blades per treatment were tracked and quantified using photographs. Results showed that temperature was the main factor driving the transition between developmental stages. However, interactive effects were observed. The concentration of 0.001 mL L−1 Kelpak® seemed to promote early germination and formation of conchocelis tufts at 15 °C. The same concentration of AMPEP and Kelpak® at 20 °C appeared to have a delayed positive effect on blade formation. These preliminary results do not show significant evidence that the application of Kelpak® and AMPEP, as tested, could affect the transition between life stages or provide enhancements on thermal tolerance.

Checklist of Amazonian gasteroid fungi (Agaricomycetidae, Phallomycetidae, Basidiomycota)

ABSTRACT The Amazon rainforest is the largest tropical rainforest in the world, with high biodiversity of organisms. Despite the increasing knowledge about fungal diversity in the last few years, many fungal taxa, including gasteroid clades, are still poorly known. Gasteroid fungi are recognized by the maturation of basidiospores inside the basidiomata and by the passive release of spores. We conducted a detailed survey of published data on the species that occur in Amazon forests. We confirmed the occurrence of 83 species distributed in 22 genera, eight families and four orders. The most representative genera was Geastrum, followed by Cyathus, Lycoperdon and Phallus. We present an identification key for Amazonian gasteroid genera and a map of record distribution. This review is expected to contribute to identify distribution gaps for further research on gasteroid fungi and to subsidize policies for the conservation of fungi in the Amazon region.

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.

High-speed video and plant ultrastructure define mechanisms of gametophyte dispersal.

Dispersal of gametophytes is critical for land plant survivorship and reproduction. It defines potential colonization and geographical distribution as well as genetic mixing and evolution. C. T. Ingold's classic works on Spore Discharge in Land Plants and Spore Liberation review mechanisms for spore release and dispersal based on real‐time observations, basic histology, and light microscopy. Many mechanisms underlying spore liberation are explosive and have evolved independently multiple times. These mechanisms involve physiological processes such as water gain and loss, coupled with structural features using different plant tissues. Here we review how high‐speed video and analyses of ultrastructure have defined new biomechanical mechanisms for the dispersal of gametophytes through the dissemination of haploid diaspores, including spores, pollen, and asexual reproductive propagules. This comparative review highlights the diversity and importance of rapid movements in plants for dispersing gametophytes and considerations for using combinations of high‐speed video methods and microscopic techniques to understand these dispersal movements. A deeper understanding of these mechanisms is crucial not only for understanding gametophyte ecology but also for applied engineering and biomimetic applications used in human technologies.

First Long-Time Airborne Fungal Spores Study in Dublin, Ireland (1978–1980)

Ambient fungal spores within the atmosphere can contribute to a range of negative human, animal and plant health conditions and diseases. However, trends in fungal spore seasonality, species prevalence, and geographical origin have been significantly understudied in Ireland. Previously unpublished data from the late 1970s have recently been collected and analysed to establish historical fungal spore trends/characteristics for Dublin. Historical spore concentrations were largely dominated by Alternaria, Ascospores, Basidiospores, Botrytis, Cladosporium, Erysiphe and Rusts. The main fungal spore season for Dublin commenced in April with the fructification of Scopulariopsis and Ganoderma. However, the vast majority of other spore types did not reach peak spore release until late summer. The correlation between ambient spore concentration, and meteorological parameters was examined using Multivariable Regression Tree (MRT) analysis. The notable correlations found for fungal spore concentrations tended to involve temperature-based parameters. The use of a non-parametric wind regression was also employed to determine the potential geographical origin of ambient fungal spores. The impact of wind direction, and high windspeed on fungal spores was established, ultimately highlighting the importance of studying and monitoring fungal spores within Ireland, rather than attempting to rely on data from other regions, as most fungal spores collected in Dublin appeared to originate from within the island.

Hyphal compartmentalization and sporulation in Streptomyces require the conserved cell division protein SepX

Filamentous actinobacteria such as Streptomyces undergo two distinct modes of cell division, leading to partitioning of growing hyphae into multicellular compartments via cross-walls, and to septation and release of unicellular spores. Specific determinants for cross-wall formation and the importance of hyphal compartmentalization for Streptomyces development are largely unknown. Here we show that SepX, an actinobacterial-specific protein, is crucial for both cell division modes in Streptomyces venezuelae. Importantly, we find that sepX-deficient mutants grow without cross-walls and that this substantially impairs the fitness of colonies and the coordinated progression through the developmental life cycle. Protein interaction studies and live-cell imaging suggest that SepX contributes to the stabilization of the divisome, a mechanism that also requires the dynamin-like protein DynB. Thus, our work identifies an important determinant for cell division in Streptomyces that is required for cellular development and sporulation.

Maturation of conchosporangia and spore release in Neopyropia yezoensis under LED irradiation with different light qualities

Maturation of conchosporangia and spore release in <i>Neopyropia yezoensis</i> under LED irradiation with different light qualities

On-line monitoring of industrial interest Bacillus fermentations, using impedance spectroscopy

Impedance spectroscopy is a technique used to characterize electrochemical systems, increasing its applicability as well to monitor cell cultures. During their growth, Bacillus species have different phases which involve the production and consumption of different metabolites, culminating in the cell differentiation process that allows the generation of bacterial spores. In order to use impedance spectroscopy as a tool to monitor industrial interest Bacillus cultures, we conducted batch fermentations of Bacillus species such as B. subtilis, B. amyloliquefaciens, and B. licheniformis coupled with this technique. Each fermentation was characterized by the scanning of 50 frequencies between 0.5 and 5 MHz every 30 min. Pearson’s correlation between impedance and phase angle profiles (obtained from each frequency scanned) with the kinetic profiles of each strain allowed the selection of fixed frequencies of 0.5, 1.143, and 1.878 MHz to follow-up of the fermentations of B. subtilis, B. amyloliquefaciens and B. licheniformis, respectively. Dielectric profiles of impedance, phase angle, reactance, and resistance obtained at the fixed frequency showed consistent changes with exponential, transition, and spore release phases.

Fern fronds that move like pine cones: humidity-driven motion of fertile leaflets governs the timing of spore dispersal in a widespread fern species.

The sensitive fern, Onoclea sensibilis, is a widespread species in eastern North America and has an atypical timing of spore dispersal among temperate ferns. During early summer, this dimorphic species produces heavily modified spore-bearing fronds with leaflets tightly enveloping their sporangia and spores. These fronds senesce and persist above ground as dead mature structures until the following early spring when the leaflets finally open and spores are dispersed. While this timing of spore dispersal has been observed for over 120 years, the structural mechanisms underpinning this phenology have remained elusive. Based on field observations, growth chamber manipulations and scanning electron microscopy, the mechanisms underlying this distinctive timing of spore dispersal in the sensitive fern were investigated. I show that fertile leaflets of the sensitive fern move in direct response to changes in humidity, exhibiting structural and functional parallels with multicellular hygromorphic structures in seed plants, such as pine cones. These parallels include differences in cellulose microfibril orientation in cells on the abaxial and adaxial sides of the leaflet. The dynamics of this hygroscopic movement concomitant with regular abscission zones along the pinnules and coordinated senescence lead to the specific timing of early spring spore dispersal in the sensitive fern. While hygroscopic movement is common in seed-free plants, it mostly occurs in small structures that are either one or a few cells in size, such as the leptosporangium. Given its multicellular structure and integration across many cells and tissues, the movement and construction of the sensitive fern pinnules are more similar to structures in seed plants. The evolution of this complex trait in the sensitive fern efficiently regulates the timing of spore release, leading to early spring dispersal. This phenology likely gives gametophytes and subsequent sporophytes an advantage with early germination and growth.

Temporal and spatial dispersal of Thekopsora areolata basidiospores, aeciospores, and urediniospores

AbstractCherry spruce rust causes huge yield losses in Norway spruce seed production in Fennoscandia. The causal agent, Thekopsora areolata, has three types of spores that disperse during spring: basidiospores are produced on basidia that grow out from teliospores in overwintered bird cherry leaf litter to infect new pistillate spruce cones, aeciospores are released from old diseased spruce cones to infect bird cherry leaves, and urediniospores are produced from new bird cherry leaves for reinfection. No study has examined the dispersal of T. areolata spores, including the basidiospores that cause primary infection in spruce cones. In this study, teliospores of T. areolata were germinated in the laboratory and the morphology of basidiospores was described. T. areolata spores were sampled in Ultuna, Sweden and Joutsa, Finland with 21 spore traps at each site. Peaks in aeciospores were observed from 11 to 25 May and from 2 to 8 June at the Finnish site, and from 4 to 18 May at the Swedish site. Urediniospores were first observed 2–3 weeks after the peaks in aeciospores and they were mainly distributed within 10 m from the bird cherry trees. Peaks of 1–2 weeks in basidiospore detection coincided with multiple rain events. The basidiospore peak overlapped with the spruce pollen peak in Finland but not in Sweden. The quantities of basidiospores from different spore traps within 100 m from the spore source had no gradient. Information on spatial and temporal spore release is important for making decisions on disease management strategies.

Meteorological factors associated with the timing and abundance of Hymenoscyphus fraxineus spore release

The ascomycete Hymenoscyphus fraxineus has spread across most of the host range of European ash with a high level of mortality, causing important economic, cultural and environmental effects. We present a novel method combining a Monte-Carlo approach with a generalised additive model that confirms the importance of meteorology to the magnitude and timing of H. fraxineus spore emissions. The variability in model selection and the relative degree to which our models are over- or under-fitting the data has been quantified. We find that both the daily magnitude and timing of spore emissions are affected by meteorology during and prior to the spore emission diurnal peak. We found the daily emission magnitude has the strongest associations to weekly average net radiation and leaf moisture before the emission, soil temperature during the day before emission and net radiation during the spore emission. The timing of the daily peak in spore emissions has the strongest associations to net radiation both during spore emission and in the day preceding the emission. The seasonal peak in spore emissions has a near-exponential increase/decrease, and the mean daily emission peak is approximately Gaussian.