Potential effect of Beauveria bassiana (Hypocreales: Clavicipitaceae) on Anthonomus signatus (Coleoptera: Curculionidae) in strawberries

The strawberry bud weevil, Anthonomus signatus (Say) (Coleoptera: Curculionidae) is a serious pest of strawberry crops in Canada. The results of previous laboratory screening and bioassay experiments showed that A. signatus adults were susceptible to several isolates of Beauveria bassiana (Balsmo) Vuillemin. Based on these results, the INRS-IP and INRS-CFL isolates were selected for field trails. Using a randomized block design with four replicates, three applications of the INRS-IP and INRS-CFL isolates were applied at a rate of 1×10¹³ conidia/ha at 7-day intervals. The multiple applications of B. bassiana triggered a significant reduction of A. signatus adult populations in strawberries. Twenty-four days after the first application, a significant difference was observed between the mean numbers of surviving adults in all B. bassiana-treated plots compared to control plots. During the field experiment, the persistence of insecticidal activity and the viability of B. bassiana conidia were also monitored. Results showed the presence of viable and infective conidia on strawberry foliage up to 6 days after each application. Moreover, the multiple applications of B. bassiana at a rate of 1×10¹³ conidia/ha resulted in a significant reduction of damaged strawberry fruits compared with control plots, where fruit loss was caused by A. signatus feeding and egg laying.     

The polyene antimycotics nystatin and filipin disrupt the plasma membrane, whereas natamycin inhibits endocytosis in germinating conidia of Penicillium discolor

Aims:  To investigate the differences in membrane permeability and the effect on endocytosis of the polyene antimycotics nystatin, filipin and natamycin on germinating fungal conidia.
Methods and Results:  The model system was Penicillium discolor , a food spoilage fungus. Filipin resulted in permeabilization of germinating conidia for the fluorescent probes TOTO-1 and FM4-64, but not for ferricyanide ions. Nystatin caused influx of all these compounds while natamycin did not. Untreated germinating conidia internalize the endocytic marker FM4-64. Pretreatment of germinating conidia with natamycin showed a dose and time dependent inhibition of endocytosis as judged by the lack of formation of early endosomal compartments.
Conclusions:  The results obtained from this study indicated that, unlike nystatin and filipin, natamycin is unable to permeabilize germinating conidia, but interferes with endocytosis in a dose and time dependent manner.
Significance and Impact of the Study:  Natamycin acts via a different mode of action than other polyene antimycotics. These results offer useful information for new strategies to prevent fungal spoilage on food products and infection on agricultural crops. For laboratory use, natamycin can be used as a specific inhibitor of early endocytosis in fungal cells.     

Peculiarities of Exogenous Dormancy of Aspergillus nigerConidia

Aspergillus nigerconidia are characterized by exogenous dormancy: the first stage of their germination is accomplished in twice-distilled water. However, germ tube formation requires the availability of carbon and nitrogen sources. Exogenous dormancy in A. nigerconidia exhibits the following peculiar features: (i) nitrogen-containing substances are active stimulators of germination; (ii) temperature-dependent changes in the lipid bilayer and in the neutral lipid composition of conidia are virtually identical to those occurring in growing mycelium under temperature stress; and (iii) the spore viability threshold does not exceed 45°C; i.e., the spores are more heat-resistant than the mycelium, but they are less heat-resistant than the spores that are in the state of endogenous dormancy. According to the current classification of the types of cell metabolism arrest, the exogenous dormancy of A. nigerconidia resembles the pattern of metabolism characteristic of vegetative cells during the idiophase.     

Differential susceptibility of Amblyomma maculatum and Amblyomma americanum (Acari:Ixodidea) to the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae

Nymph and adult ticks from Ambylomma americanum and Ambylomma maculatum were treated with conidia and blastospores of the entomopathogenic fungi Beauveria bassiana (90517) and Metarhizium anisopliae (20500). Fungal suspensions of conidia harvested from potato dextrose plates containing 10⁸ conidia/ml caused greater than 90% mortality in adult A. maculatum but less than 10% mortality in adult A. americanum over a 28 day time course. Similarly, infection with M. anisopliae (10⁸ conidia/ml) resulted in 60 and 15% mortality in A. maculatum and A. americanum, respectively. Nymphs of both tick species were more susceptible to fungal infection reaching mortality rates of almost 100% for A. maculatum and over 35% for A. americanum. Scanning electron microscopy of infected ticks showed rapid attachment, germination, and proliferation of fungal spores on A. maculatum cuticles, and to a much lesser extent on A. americanum cuticles. Pentane extracts of A. americanum cuticle hydrocarbons inhibited germination and hyphal growth of B. bassiana conidia, whereas no inhibition was observed using A. maculatum extracts. Significant mortality towards A. americanum was observed (>60%, 28 days) only when the ticks were treated with B. bassiana directly from the growth medium (10⁷ blastospores/ml, grown for 3–4 days in Sabouraud dextrose + 0.5% yeast extract liquid media). These results indicate tick species display differential susceptibility to the entomopathogenic fungi B. bassiana and M. anisopliae, and that the ability to overcome fungistatic compounds present in the tick epicuticle may determine the likelihood of successful infection and virulence.     

Factors Affecting Disease Development by Rhynchosporium alismatis in Starfruit (Damasonium minus), a Weed of Rice

The fungal pathogen Rhynchosporium alismatis is being developed for biological control of starfruit (Damasonium minus), an important aquatic weed in Australian rice fields. The development of R. alismatis in starfruit differs between juvenile and adult plants. Juvenile starfruit plants are stunted as a result of fungal infection, while in adult plants, the main effect is necrosis and chlorosis of floating leaves. A conidial concentration of 1×10⁴ conidia mL^-1 was adequate to cause disease symptoms on floating leaves, but the stunting effect on juveniles was caused by concentrations of at least 1×10⁵ conidia mL^-1. To successfully inoculate juvenile plants, the water must be drained before inoculation to expose plants to the inoculum. The artificial addition of dew periods did not enhance disease development in plants. The stunting of juvenile starfruit plants caused by the infection of R. alismatis may give rice plants a competitive advantage over the weed at the seedling stage     

Betaine-homocysteine methyltransferase in the fungus Aspergillus nidulans.

A betaine:homocysteine methyltransferase activity was demonstrated in the cell-free extracts from the fungus $\text{Aspergillus}\text{nidulans}$. Among methionine-requiring mutants which do not grow on homocysteine one class responds to betaine indicating that this compound can serve as a methyl donor in methionine synthesis $\text{in vivo}$. Mutants of the second class which grow only on methionine were shown to have betaine: homocysteine — and methyltetrahydrofolate: homocysteine methyltransferases simultaneously impaired.     

Aspergillus fumigatus exoβ(1‐3)glucanases family GH55 are essential for conidial cell wall morphogenesis

The cell wall of Aspergillus fumigatus is predominantly composed of polysaccharides. The central fibrillar core of the cell wall is composed of a branched β(1‐3)glucan, to which the chitin and the galactomannan are covalently bound. Softening of the cell wall is an essential event during fungal morphogenesis, wherein rigid cell wall structures are cleaved by glycosyl hydrolases. In this study, we characterised the role of the glycosyl hydrolase GH55 members in A. fumigatus fungal morphogenesis. We showed that deletion of the six genes of the GH55 family stopped conidial cell wall maturation at the beginning of the development process, leading to abrogation of conidial separation: the shape of conidia became ovoid, and germination was delayed. In conclusion, the reorganisation and structuring of the conidial cell wall mediated by members of the GH55 family is essential for their maturation, normal dissemination, and germination.     

几种诱导黑麦草Loliump erenneL.内生真菌产孢的方法

从黑麦草Lolium perenne5个栽培品种中分离、纯化得到6株形态稳定的内生真菌,它们在常规培养条件下均不产生分生孢子。通过在PDA和MEA培养基上进行预培养、扫刷营养体、近紫外光照射以及在菌丝体上放置宿主植物等诱导方法,使其中5株真菌不同程度产生了分生孢子,通过分生孢子的形态成功鉴定了黑麦草内生真菌。实验证明通过诱导内生真菌产孢的方法并借助形态学依据来鉴定无性的内生真菌是可行的。     

The hyphomycete Sorosporetta — Syngliocladium from mole cricket,Scapteriscus vicinus

The hyphomycete Sorosporella sp. was isolated from the mole cricket, Scapteriscus vicinus collected in Alachua Co., Florida. Scanning (SEM) and/or transmission (TEM) electron microscopy were used to study the chlamydospores characteristic of this genus and the conidial production in the alternate state, Syngliocladium. Brick-red chlamydospores, which occur in clusters in insect cadavers, have a fibrous cell wall as revealed by TEM. Pores often occur between walls of adjacent cells. Lipids, including a large central lipid droplet and smaller droplets along the periphery of the cell, are abundant in the cytoplasm. Most organelles were difficult to distinguish due to the density of the cytoplasmic material. Chlamydospores germinate on water or media. On Sabouraud maltose agar, germinating chlamydospores produce a white mycelial mat; synnematous-type growth was sometimes observed. Mycelia may bear conidiophores and ellipsoid conidia.Florida Agricultural Experiment Station Journal Series No. 7789.