Infective Propagules Research Articles

Comparing the differing effects of host species richness on metrics of disease

AbstractChanges in host species richness can alter infection risk and disease levels in multi‐host communities. I review theoretical predictions for direct and environmental transmission pathogens about the effects of host additions (or removals) on three commonly used disease metrics: the pathogen community reproduction number and infection prevalence and infected density in a focal host. To extend this prior work and explain why predictions differ between metrics, I analyze Susceptible Infected‐Recovered‐type models of an environmentally transmitted pathogen and multiple host species that compete for resources. Using local sensitivity analysis, I show how trait‐mediated and density‐mediated indirect effects drive each metric's response to variation in an added host's ability to transmit a pathogen, the added host's density, and the pathogen transmission mechanism. For each disease metric, the responses are typically predicted by the added host's ability to transmit the pathogen when interspecific competition is weak whereas the responses can be altered by shifts in host densities when interspecific competition is strong. In addition, the three metrics often respond in the same direction. However, the metrics can respond in different directions for three reasons: (1) differences between the ability of exposed individuals to transmit the pathogen over the length of time the individuals are infected (i.e., host competence) and a host population's instantaneous net rate of production of infectious propagules; (2) strong density‐mediated feedbacks driven by disease‐induced mortality; and (3) host additions or removals cause large changes in focal host density via competition or disease‐induced mortality. This study extends and unifies prior theoretical studies, and helps identify the rules governing the context‐dependent relationships between host species richness and the three metrics of disease.

Phenotypic characterization of HAM1, a novel mating regulator of the fungal pathogen Cryptococcus neoformans.

Fungal mating is a vital part of the lifecycle of the pathogenic yeast Cryptococcus neoformans. More than just ensuring the propagation of the species, mating allows for sexual reproduction to occur and generates genetic diversity as well as infectious propagules that can invade mammalian hosts. Despite its importance in the biology of this pathogen, we still do not know all of the major players regulating the mating process and if they are involved or impact its pathogenesis. Here, we identified a novel negative regulator of mating that also affects certain cellular characteristics known to be important for virulence. This gene, which we call HAM1, is widely conserved across the cryptococcal family as well as in many pathogenic fungal species. This study will open new avenues of exploration regarding the function of uncharacterized but conserved genes in a variety of pathogenic fungal species and specifically in serotype A of C. neoformans.

Divergent Aspergillus flavus corn population is composed of prolific conidium producers: Implications for saprophytic disease cycle

ABSTRACT The ascomycete fungus Aspergillus flavus infects and contaminates corn, peanuts, cottonseed, and tree nuts with toxic and carcinogenic aflatoxins. Subdivision between soil and host plant populations suggests that certain A. flavus strains are specialized to infect peanut, cotton, and corn despite having a broad host range. In this study, the ability of strains isolated from corn and/or soil in 11 Louisiana fields to produce conidia (field inoculum and male gamete) and sclerotia (resting bodies and female gamete) was assessed and compared with genotypic single-nucleotide polymorphism (SNP) differences between whole genomes. Corn strains produced upward of 47× more conidia than strains restricted to soil. Conversely, corn strains produced as much as 3000× fewer sclerotia than soil strains. Aspergillus flavus strains, typified by sclerotium diameter (small S-strains, <400 μm; large L-strains, >400 μm), belonged to separate clades. Several strains produced a mixture (M) of S and L sclerotia, and an intermediate number of conidia and sclerotia, compared with typical S-strains (minimal conidia, copious sclerotia) and L-strains (copious conidia, minimal sclerotia). They also belonged to a unique phylogenetic mixed (M) clade. Migration from soil to corn positively correlated with conidium production and negatively correlated with sclerotium production. Genetic differences correlated with differences in conidium and sclerotium production. Opposite skews in female (sclerotia) or male (conidia) gametic production by soil or corn strains, respectively, resulted in reduced effective breeding population sizes when comparing male:female gamete ratio with mating type distribution. Combining both soil and corn populations increased the effective breeding population, presumably due to contribution of male gametes from corn, which fertilize sclerotia on the soil surface. Incongruencies between aflatoxin clusters, strain morphotype designation, and whole genome phylogenies suggest a history of sexual reproduction within this Louisiana population, demonstrating the importance of conidium production, as infectious propagules and as fertilizers of the A. flavus soil population.

Predicting airborne ascospores of Sclerotinia sclerotiorum through machine learning and statistical methods

AbstractA main biological constraint of dry bean (Phaseolus vulgaris) production in Canada is white mould, caused by the fungal pathogen Sclerotinia sclerotiorum. The primary infectious propagules of S. sclerotiorum are airborne ascospores and monitoring the air for inoculum levels could help predict the severity of white mould in bean fields. Daily air samples were collected in commercial dry bean fields in Alberta, Manitoba and Ontario and ascospores were quantified using quantitative PCR. Daily weather data was obtained from in‐field weather stations. The number of ascospores on a given day was modelled using 63 different environmental variables and several modelling methods, both regression and classification approaches, were implemented with machine learning (ML) (random forests, logistic regression and support vector machines) and statistical (generalized linear models) approaches. Across all years and provinces, ascospores were most highly correlated with ascospore release from the previous day (r ranged from 0.15 to 0.6). This variable was also the only variable included in all models and had the greatest weight in all models. Models without this variable had much poorer performance than those with it. Correlations of ascospores with other environmental variables varied by province and sometimes by year. A comparison of ML and statistical models revealed that they both performed similarly, but that the statistical models were easier to interpret. However, the precise relationship between airborne ascospore levels and in‐field disease severity remains unclear, and spore sampling methods will require further development before they can be deployed as a disease management tool.

Morphology, Development, and Pigment Production of Talaromyces marneffei are Diversely Modulated Under Physiologically Relevant Growth Conditions.

Talaromyces marneffei is an opportunistic pathogenic fungus that mainly affects HIV-positive individuals endemic to Southeast Asia and China. Increasing efforts have been made in the pathogenic mechanism and host interactions understanding of this pathogen in the last two decades; however, there are still no conclusions on how T. marneffei was transmitted from the donor bamboo rats to humans. A perception that the failure of fungus isolation from soil was attributed to the low salt tolerance of T. marneffei. Therefore, the effect of environmental fluctuations in fungal growth and development is fundamental for the characterization of its origin and fungal biology understanding. Herein, we characterized high osmolarity, pH, metal ions, nutrients, and oxidative stress have versatile effects on T. marneffei hyphal or yeast growth, conidia generation, and pigment production. Among these, high pH, low glucose amounts, and the inorganic nitrogen ammonium tartrate stimulated the red pigment production, whereas high osmolarity, high pH, and the inorganic nitrogen sodium nitrate could significantly accelerate the conidia generation. Specifically, zinc starvation repressed conidia generation and prevented the wrinkled yeast colony formation, indicating the function of zinc regulators in pathogenicity regulation. Since conidia are recognized as the infectious propagules, the effects characterization of different environmental factors in T. marneffei morphology in this work will not only expand the growth and pathogenic biology understanding of the fungus but also provide more clues for the T. marneffei infection transmission origin investigation.

Biogenesis, germination, and pathogenesis of Cryptococcus spores.

SUMMARYSpores are primary infectious propagules for the majority of human fungal pathogens; however, relatively little is known about their fundamental biology. One strategy to address this deficiency has been to develop the basidiospores of Cryptococcus into a model for pathogenic spore biology. Here, we provide an update on the state of the field with a comprehensive review of the data generated from the study of Cryptococcus basidiospores from their formation (sporulation) and differentiation (germination) to their roles in pathogenesis. Importantly, we provide support for the presence of basidiospores in nature, define the key characteristics that distinguish basidiospores from yeast cells, and clarify their likely roles as infectious particles. This review is intended to demonstrate the importance of basidiospores in the field of Cryptococcus research and provide a solid foundation from which researchers who wish to study sexual spores in any fungal system can launch their studies.

Ergosterol Is Critical for Sporogenesis in Cryptococcus neoformans.

Microbes, both bacteria and fungi, produce spores to survive stressful conditions. Spores produced by the environmental fungal pathogen Cryptococcus neoformans serve as both surviving and infectious propagules. Because of their importance in disease transmission and pathogenesis, factors necessary for cryptococcal spore germination are being actively investigated. However, little is known about nutrients critical for sporogenesis in this pathogen. Here, we found that ergosterol, the main sterol in fungal membranes, is enriched in spores relative to yeasts and hyphae. In C. neoformans, the ergosterol biosynthesis pathway (EBP) is upregulated by the transcription factor Sre1 in response to conditions that demand elevated ergosterol biosynthesis. Although the deletion of SRE1 enhances the production of mating hyphae, the sre1Δ strain is deficient at producing spores even when crossed with a wild-type partner. We found that the defect of the sre1Δ strain is specific to sporogenesis, not meiosis or basidium maturation preceding sporulation. Consistent with the idea that sporulation demands heightened ergosterol biosynthesis, EBP mutants are also defective in sporulation. We discovered that the overexpression of some EBP genes can largely rescue the sporulation defect of the sre1Δ strain. Collectively, we demonstrate that ergosterol is a critical component in cryptococcal preparation for sporulation.

Plant Stomata: An Unrealized Possibility in Plant Defense against Invading Pathogens and Stress Tolerance.

Stomata are crucial structures in plants that play a primary role in the infection process during a pathogen's attack, as they act as points of access for invading pathogens to enter host tissues. Recent evidence has revealed that stomata are integral to the plant defense system and can actively impede invading pathogens by triggering plant defense responses. Stomata interact with diverse pathogen virulence factors, granting them the capacity to influence plant susceptibility and resistance. Moreover, recent studies focusing on the environmental and microbial regulation of stomatal closure and opening have shed light on the epidemiology of bacterial diseases in plants. Bacteria and fungi can induce stomatal closure using pathogen-associated molecular patterns (PAMPs), effectively preventing entry through these openings and positioning stomata as a critical component of the plant's innate immune system; however, despite this defense mechanism, some microorganisms have evolved strategies to overcome stomatal protection. Interestingly, recent research supports the hypothesis that stomatal closure caused by PAMPs may function as a more robust barrier against pathogen infection than previously believed. On the other hand, plant stomatal closure is also regulated by factors such as abscisic acid and Ca2+-permeable channels, which will also be discussed in this review. Therefore, this review aims to discuss various roles of stomata during biotic and abiotic stress, such as insects and water stress, and with specific context to pathogens and their strategies for evading stomatal defense, subverting plant resistance, and overcoming challenges faced by infectious propagules. These pathogens must navigate specific plant tissues and counteract various constitutive and inducible resistance mechanisms, making the role of stomata in plant defense an essential area of study.

Structure of glyceraldehyde-3-phosphate dehydrogenase from Paracoccidioides lutzii in complex with an aldonic sugar acid

The pathogen Paracoccidioides lutzii (Pb01) is found in South America countries Colombia, Ecuador, Venezuela and Brazil, especially in the central, west, and north regions of the latter. It belongs to the Ajellomycetaceae family, Onygenales order, and is typically thermodimorphic, presenting yeast cells when it grows in animal tissues, but mycelia when in the environment, where it produces the infectious propagule. This fungus is one of the etiologic agents of Paracoccidioidomycosis (PCM), the most important endemic fungal infection in Latin America. Investigations on its genome have contributed to a better understanding about its metabolism and revealed the complexity of several metabolic glycolytic pathways. Glyceraldehyde-3-Phosphate Dehydrogenase from Paracoccidioides lutzii (PlGAPDH) is considered a moonlighting protein and participates in several biological processes of this pathogen. The enzyme was expressed and purified, as seen in SDS-PAGE gel, crystallized and had its three dimensional structure (3D) determined in complex with NAD+, a sulphate ion and d-galactonic acid, therefore, a type of ‘GAA site’. It is the first GAPDH structure to show this chemical type in this site and how this protein can bind an acid derived from oxidation of a linear hexose.

Impact of long-term application of paclobutrazol in communities of arbuscular mycorrhizal fungi and their efficiency in the development of Helianthus annuus L.

Paclobutrazol (PBZ) is a phytoregulator known for inhibiting plant vegetative growth and promoting flowering in mango crop (Mangifera indica L.). PBZ belongs to the triazole family, a group recognized by its fungicide capacity, and its application to the soil can directly influence microbial communities, however, little is known about its effects on arbuscular mycorrhizal fungi (AMF). The objectives of this work were to evaluate the impact of long-term application of PBZ on the AMF communities and to verify whether the management time affects the functionality of these communities in promoting the development of ornamental sunflower Helianthus annuus L. (var. Dwarf Double Sungold). Sampling was carried out in mango cultivation areas with a history of PBZ application that varied from no application to application for up to 15 years. For the analysis of the AMF community, the quantification of most probable number (MPN) of infective AMF propagules, abundance of glomerospores, richness, diversity, Simpson dominance, and Pielou's evenness were evaluated. The analysis of the functionality of the AMF community was based on the analysis of the variables of growth and mycorrhizal colonization. Soils with a prolonged history of PBZ application (>nine years) presented distinct AMF communities with lower abundance of glomerospores in relation to areas without PBZ application and with native Caatinga vegetation. However, the soil-inoculum of this AMF community has greater efficiency in promoting sunflower development and mycorrhizal colonization, suggesting greater functionality. It is concluded that the time of application and performance of PBZ in the soil influence the composition of the AMF community. Even with reduction of richness and diversity of AMF species in soils with a prolonged history of PBZ application, there are functional AMF communities in these soils that promoted sunflower plant growth, selecting more efficient and resistant species.

A healthy but depleted herd: Predators decrease prey disease and density.

The healthy herds hypothesis proposes that predators can reduce parasite prevalence and thereby increase the density of their prey. However, evidence for such predator-driven reductions in the prevalence of prey remains mixed. Furthermore, even less evidence supports increases in prey density during epidemics. Here, we used a planktonic predator-prey-parasite system to experimentally test the healthy herds hypothesis. We manipulated density of a predator (the phantom midge, Chaoborus punctipennis) and parasitism (the virulent fungus Metschnikowia bicuspidata) in experimental assemblages. Because we know natural populations of the prey (Daphnia dentifera) vary in susceptibility to both predator and parasite, we stocked experimental populations with nine genotypes spanning a broad range of susceptibility to both enemies. Predation significantly reduced infection prevalence, eliminating infection at the highest predation level. However, lower parasitism did not increase densities of prey; instead, prey density decreased substantially at the highest predation levels (a major density cost of healthy herds predation). This density result was predicted by a model parameterized for this system. The model specifies three conditions for predation to increase prey density during epidemics: (i) predators selectively feed on infected prey, (ii) consumed infected prey release fewer infectious propagules than unconsumed prey, and (iii) sufficiently low infection prevalence. While the system satisfied the first two conditions, prevalence remained too high to see an increase in prey density with predation. Low prey densities caused by high predation drove increases in algal resources of the prey, fueling greater reproduction, indicating that consumer-resource interactions can complicate predator-prey-parasite dynamics. Overall, in our experiment, predation reduced the prevalence of a virulent parasite but, at the highest levels, also reduced prey density. Hence, while healthy herds predation is possible under some conditions, our empirical results make it clear that the manipulation of predators to reduce parasite prevalence may harm prey density.

Comparative efficacy of zirconium dioxide nanoparticles and AM fungus against wilt disease complex of bottle gourd and upregulation of biochemical and physiological processes

ABSTRACT The disease complex affecting bottle gourd [Lagenaria siceraria (Mol.) Standl.] caused by Meloidogyne incognita and Fusarium oxysporum results in high yield loss and there is a need for their management. Nanoparticles (NPs) and arbuscular mycorrhizae have potential in disease management. The impacts of 0.10 g.L−1 zirconium dioxide nanoparticles (ZrO2 NPs) (applied as foliar spray or seed priming) and AM fungus Rhizophagus irregularis were determined when applied alone, or in combination, on the disease complex of bottle gourd. Use of ZrO2 NPs as seed priming and foliar application increased plant growth and photosynthetic pigments and reduced disease indices, galling and population of M. incognita. Foliar application of ZrO2 NPs increased plant growth and photosynthetic pigments and reduce disease indices, galling, and population of M. incognita than did seed priming. Use of R. irregularis alone resulted in lessened plant growth and photosynthetic pigments than NPs foliar application alone. Use of R. irragularis with NPs foliar application was best for management of disease complex of bottle gourd than its use as seed priming. Wilt disease indices were rated 1–5. Use of R. irregularis/NPs reduced disease incidence, and disease indices were reduced to 1 in treatment where R. irragularis was used with ZrO2 NPs. Root colonization by R. irragularis was similar when used alone or with NPs. Inoculation of pathogens reduced colonization by R. irregularis. Management of the disease complex of bottle gourd may be achieved by use of 500 infective propagules of R. irragularis with 0.10 g.L−1 ZrO2 NPs foliar application.

Effect of mycorrhizae on phosphate fertilization efficiency and maize growth under field conditions

Phosphorus (P) is a plant macronutrient that is indispensable for maize (Zea mays L.) production. However, P is difficult to manage in weathered soils, and its fertilization practice has low efficiency because it becomes unavailable for absorption by plant roots. Symbiosis of plants with arbuscular mycorrhizal fungi increases plant growth and enhances P uptake from the soil that is not directly available to the roots. Thus, the objective of this study was to determine how inoculation with Rhizophagus intraradices and phosphate fertilization interacts and influences the development and productivity of second-crop maize. The experiment was conducted in Selvíria, Mato Grosso do Sul, Brazil, in 2019 and 2020, both in a Typic Haplorthox. A randomized block design in subdivided plots was used for the phosphate application during crop sowing (0, 25, 50, 75, and 100% concentrations of the recommended level), and the secondary treatments were the doses of mycorrhizal inoculant (0, 60, 120 and 180 g ha−1) applied to the seed using a dry powder inoculant containing 20,800 infectious propagules per gram of the arbuscular mycorrhizal fungus R. intraradices. Only in the first year of the experiment, inoculation and phosphate fertilization promoted benefits to the maize crop, indicating potential to increase yield.

Formulation of Metarhizium pinghaense and Metarhizium robertsii and the infection potential of the formulations against Pseudococcus viburni (Hemiptera: Pseudococcidae), after storage

Formulation of entomopathogens refers to the mixing of various inert ingredients, like clays and mineral oils, with the active ingredients which are the entomopathogens. Successful formulation enhances the survival of the entomopathogen and also eases their transportation, storage, preparation and application. The aim of this study was to develop a formulation to maintain the longevity and pathogenicity of the mass-produced conidia of local Metarhizium pinghaense and M. robertsii, for above-ground future commercial field application against Pseudococcus viburni. The objectives were to develop a cost-effective protocol for formulation of infective propagules and to test their effectiveness under laboratory conditions. The conidia of both isolates were formulated using four different oils (liquid paraffin, coconut, canola and olive oils) as liquid carriers, and diatomaceous earth as a mineral carrier. Conidial viability and pathogenicity were assessed over a period of eight weeks. In the study, it was observed that the conidia formulated in oil carriers maintained a high conidial viability and survival rate of &gt;95 % over a period of eight weeks for both isolates, relative to when formulated in mineral carriers, or when stored as dry conidial powder. The conidia in all the oil formulations were also observed to induce high mortality, ranging between 60 % and 90 % for M. pinghaense, and between 70 % and 90 % for M. robertsii, when used against P. viburni. The ability of conidia of both isolates to maintain viability and pathogenicity, following storage in the oil formulations, increased the likelihood of the local isolates being successfully integrated as biological control agents for management of P. viburni under field conditions.

Isolation and evaluation of indigenous endophytic entomopathogenic fungus, Beauveria bassiana UHSB-END1 (Hypocreales: Cordycipitaceae), against Spodoptera litura Fabricius

BackgroundMicrobial biological control agents are gaining worldwide attention to manage insect pests as an alternative to synthetic insecticides. Entomopathogenic fungi (EPF) meet eco-friendly pest management’s demand since mere contact of infective propagules is sufficient to cause disease in insect pests, unlike other entomopathogens. However, epiphytic fungal isolates encounter multiple challenges including direct exposure of conidia to sunlight and UV light, high temperature, and low moisture content that reduce their efficacy at the field level. Therefore, utilization of endophytic EPF is becoming more popular because they get protection from adverse conditions compared to the epiphytic EPF as they reside inside the host tissue. In addition, the endophytic EPF also give protection against crop diseases and promote plant growth, degradation of heavy metals, and tolerance to abiotic stress.ResultsThe increased mortality of Spodoptera litura (Fab.) (Noctuidae: Lepidoptera) was achieved through endophytic colonization of indigenous Beauveria bassiana UHSB-END-1 (OM131742). The bioassay proved the highest mortality 2nd instar larvae of S. litura at 40 dpi, both in vivo and in planta experiment. Further, larvae fed with fungal colonized leaves of tomato plant ended with abnormal growth and developmental process. The recovery of B. bassiana from different plant parts (stem, leaves, and roots) was the highest (100%) in all the methods of colonization at 14, 40, 60, 80 dpi, and it was decreased at 120 dpi (80%). The colonization rate was again increased in the next-generation seeds and seedlings (25 days old). This isolate gets vertically transmitted to their progenies via seeds, and it is the first report in tomato crop.ConclusionAfter ensuring the safeness of this isolate against non-target organisms, it can be one of the constitutes in sustainable cost-effective strategy for management of pests affecting tomato as one of the components in integrated pests management. Inoculation of endophytic EPF into seed/seedling reduces environmental impacts and also easy, economical, and sustainable approach for pest management in horticulture crops which are often consumed as raw. Although field studies are required to support the present finding, this appears to be an interesting tool that should be considered for pest biocontrol.

Exploring How a Generalist Pathogen and Within-Host Priority Effects Alter the Risk of Being Infected by a Specialist Pathogen.

AbstractIn multihost-multipathogen communities, a focal host's risk of being infected by a particular pathogen can be influenced by the presence of other host and pathogen species. We explore how indirect interactions between pathogens at the within-host level (through coinfecting the same individual) and the between-host level (through altered susceptible host densities) affect the focal host's risk of infection. We use an SI-type epidemiological model of two host species and two environmentally transmitted pathogens where one pathogen is a specialist on the focal host and the other pathogen is a generalist. We show that monotonic, unimodal, and U-shaped relationships between the specialist and generalist infectious propagule densities (proxies of the focal host's risk of infection) are driven by the way within-host priority effects alter the production of specialist infectious propagules by infected focal host individuals. Interestingly, within-host priority effects can also lead to overcompensation in density wherein increased infected host mortality results in greater specialist infectious propagule density. We interpret these results in terms of how the focal host's risk of being infected by a specialist pathogen is affected by the presence of a generalist pathogen, its alternative host, and within-host priority effects.

Effects of Dual Symbiotic Interactions Performed by the Exotic Tree Golden Wreath Wattle (Acacia cyanophylla Lindl.) on Soil Fertility in a Costal Sand Dune Ecosystem

The present study aims to evaluate the effects of the exotic shrub Acacia cyanophylla Lindl. on soil fertility by studying 1) its ability to modify the soil physicochemical composition, 2) its contribution to the soil mycorrhizal potential and its impact on the richness and diversity of the arbuscular mycorrhizal fungi (AMF) community in the rhizospheric soil (RS), and finally 3) its atmospheric nitrogen fixation potential. The physicochemical analysis of the RS has shown that soil invasion by A. cyanophylla has a beneficial effect on its fertility; this advantage is demonstrated by the increase of the organic matter and the nutrient contents (N, P, K, Na, Ca) in the RS. Furthermore, the roots of this shrub exhibited broad AMF colonization, which confirms its high mycotrophic aspect. Four differentiated morphotypes of mycorrhizal spores were isolated from the RS of A. cyanophylla by use of the wet sieving method. In addition, the most probable number method showed that A. cyanophylla was capable of dramatically increasing the mycorrhizal potential of the soil. Indeed, more than 1,213 infectious propagules per one hundred grams of soil were detected in the RS of A. cyanophylla. Moreover, A. cyanophylla roots showed a significant presence of nodules indicating an active atmospheric nitrogen fixation. Counting revealed the presence of at least 130 nodules in the root fragments contained in 1 kg of soil. In conclusion, the biological invasion of sand dunes by the exotic shrub A. cyanophylla exhibited beneficial effects on the soil’s chemical composition and functioning, the activity of rhizobacteria in fixing atmospheric nitrogen, and phosphate bioavailability under the action of the native AMF community.

Production of Microsclerotia by Metarhizium sp., and Factors Affecting Their Survival, Germination, and Conidial Yield.

Microsclerotia (MS) produced by some species of Metarhizium can be used as active ingredients in mycoinsecticides for the control of soil-dwelling stages of geophilic pests. In this study, the MS production potential of two Metarhizium brunneum strains and one M. robertsii strain was evaluated. The three strains were able to produce MS in liquid fermentation, yielding between 4.0 × 106 (M. robertsii EAMa 01/158-Su strain) and 1.0 × 107 (M. brunneum EAMa 01/58-Su strain) infective propagules (CFU) per gram of MS. The EAMa 01/58-Su strain was selected for further investigation into the effects of key abiotic factors on their survival and conidial yield. The MS were demonstrated to be stable at different storage temperatures (−80, −18, and 4 °C), with a shelf-life up to one year. The best temperature for MS storage was −80 °C, ensuring good viability of MS for up to one year (4.9 × 1010 CFU/g MS). Moreover, soil texture significantly affected CFU production by MS; sandy soils were the best driver of infective propagule production. Finally, the best combination of soil temperature and humidity for MS germination was 22.7 °C and 7.3% (wt./wt.), with no significant effect of UV-B exposure time on MS viability. These results provide key insights into the handling and storage of MS, and for decision making on MS dosage and timing of application.

Mass Production of Entomopathogenic Fungi, Metarhizium robertsii and Metarhizium pinghaense, for Commercial Application Against Insect Pests.

Entomopathogenic fungi of the Metarhizium anisopliae species complex have gained importance as the biological control agents of agricultural insect pests. The increase in pest resistance to chemical insecticides, the growing concerns regarding the negative effects of insecticides on human health, and the environmental pollution from pesticides have led to a global drive to find novel sustainable strategies for crop protection and pest control. Previously, attempts to mass culture such entomopathogenic fungi (EPF) species as Beauveria bassiana have been conducted. However, only limited attempts have been conducted to mass culture Metarhizium robertsii and M. pinghaense for use against insect pests. This study aimed to mass-produce a sufficient number of resilient infective propagules of South African isolates of M. robertsii and M. pinghaense for commercial application. Three agricultural grain products, flaked oats, flaked barley, and rice, were used as the EPF solid fermentation substrates. Two inoculation methods, conidial suspensions and the liquid fungal culture of blastospores were used to inoculate the solid substrates. Inoculation using conidial suspensions was observed to be relatively less effective, as increased levels of contamination were observed on the solid substrates relative to when using the blastospore inoculation method. Flaked oats were found not to be a suitable growth substrate for both M. robertsii and M. pinghaense, as no dry conidia were harvested from the substrate. Flaked barley was found to favor the production of M. robertsii conidia over that of M. pinghaense, and an average of 1.83 g ± 1.47 g of dry M. robertsii conidia and zero grams of M. pinghaense conidia was harvested from the substrate. Rice grains were found to favor the conidial mass production of both M. pinghaense and M. robertsii isolates, with an average of 8.2 g ± 4.38 g and 6 g ± 2 g harvested from the substrate, respectively.

PM10 and Other Climatic Variables Are Important Predictors of Seasonal Variability of Coccidioidomycosis in Arizona.

ABSTRACTCoccidioidomycosis (Valley fever) is a disease caused by the fungal pathogens Coccidioides immitis and Coccidioides posadasii that are endemic to the southwestern United States and parts of Mexico and South America. Throughout the range where the pathogens are endemic, there are seasonal patterns of infection rates that are associated with certain climatic variables. Previous studies that looked at annual and monthly relationships of coccidioidomycosis and climate suggest that infection numbers are linked with precipitation and temperature fluctuations; however, these analytic methods may miss important nonlinear, nonmonotonic seasonal relationships between the response (Valley fever cases) and explanatory variables (climate) influencing disease outbreaks. To improve our current knowledge and to retest relationships, we used case data from three counties of high endemicity in southern Arizona paired with climate data to construct a generalized additive statistical model that explores which meteorological parameters are most useful in predicting Valley fever incidence throughout the year. We then use our model to forecast the pattern of Valley fever cases by month. Our model shows that maximum monthly temperature, average PM10, and total precipitation 1 month prior to reported cases (lagged model) were all significant in predicting Valley fever cases. Our model fits Valley fever case data in the region of endemicity of southern Arizona and captures the seasonal relationships that predict when the public is at higher risk of being infected. This study builds on and retests relationships described by previous studies regarding climate variables that are important for predicting risk of infection and understanding this fungal pathogen.IMPORTANCE The inhalation of environmental infectious propagules from the fungal pathogens Coccidioides immitis and Coccidioides posadasii by susceptible mammals can result in coccidioidomycosis (Valley fever). Arizona is known to be a region where the pathogen is hyperendemic, and reported cases are increasing throughout the western United States. Coccidioides spp. are naturally occurring fungi in arid soils. Little is known about ecological factors that influence the growth of these fungi, and a higher environmental burden may result in increases in human exposure and therefore case rates. By examining case and climate data from Arizona and using generalized additive statistical models, we were able to examine the relationship between disease outbreaks and climatic variables and predict seasonal time points of increased infection risk.