Pathogenicity of entomopathogenic hyphomycetes, Paecilomyces fumoso-roseus and Nomuraea rileyi, to eggs of noctuids, Mamestra brassicae and Spodoptera littoralis

Bioassays were conducted to determine the susceptibility of egg masses of Mamestra brassicae and Spodoptera littoralis to different spore doses of Paecilomyces fumoso-roseus and Nomuraea rileyi at 20° and 25°C. P. fumoso-roseus was highly virulent against eggs, whereas N. rileyi provoked only a deferred mortality of larvae hatched from treated eggs. Nevertheless, larval mortality of S. littoralis caused by N. rileyi at 25°C was more effective after first-instar larval contamination than after egg mass treatment. The duration of the egg stage could explain differences of susceptibility between the two noctuids at 25°C. Scanning electron microscopical observations suggested two ways of contamination of newly hatched larvae. First, fungal germinations on the chorion surface suggested that newly hatched larvae might be infected by penetration of the egg integument before hatching. Second, conidia on the egg cuticle could be an entomopathogenic inoculum for newly emerging larvae which fed upon chorions. Results showed that pathogenicity of Hyphomycetes to noctuid eggs might be a promising area of investigation for biological control.     

Taka-Amylase A in the Conidia of Aspergillus oryzae RIB40

A study of Taka-amylase A of conidia from Aspergillus oryzae RIB40 was done. During the research, proteins from conidia and germinated conidia were analyzed using SDS–PAGE, 2-D gel electrophoresis, Western blot analysis, MALDI-TOF Mass spectrometry, and native-PAGE combined with activity staining of TAA. The results showed that TAA exists not only in germinated conidia but also in conidia. Some bands representing degraded products of TAA were detected. Conidia, which formed on starch (SCYA), glucose (DCYA), and glycerol (GCYA) plates, contained mature TAA. Only one active band of TAA was detected after native-PAGE activity staining. In addition, TAA activity was detected in cell extracts of conidia using 0.5 M acetate buffer, pH 5.2, as extraction buffer, but was not detected in whole conidia or cell debris. The results indicate that TAA exists in conidia in active form even when starch, glucose, or glycerol is used as carbon source. TAA might belong to a set of basal proteins inside conidia, which helps in imbibition and germination of conidia.     

Fungal conidia distribution on chrysanthemum: varying spray parameters

The conidial deposition of BotaniGard® 22WP on chrysanthemum plants was assessed. Assessments were conducted on stationary and moving applications using different spray nozzles, application angles and tank pressures. In addition, the spray time and distance from the target plant were included. Conidial deposition was greater on the upper canopy of the plants and the upper sides of the leaves. The nozzle type, spray angle, and distance from the target plant had the most significant effects on conidial distribution. The optimal spray nozzles were found to be HC-22 and FAN-1, which provided the best coverage of both the plants in general, and on the lower surfaces of the leaves.     

Control of Bemisia tabaci by entomopathogenic fungi isolated from arid soils in Argentina

Entomopathogenic Hypocreales were isolated from arid soils in Argentina using Tenebrio molitor as bait and tested for their biological performance at 30°C and 45–65% RH. Conidial germination was tested in three vegetable oils (sunflower, olive and maize) at two concentrations (1% and 10%) to evaluate their compatibility for further liquid formulations. According to radial growth and germination results, we selected four isolates to test their pathogenicity against second instar B. tabaci nymphs with the selected oil formulations at 30°C. CEP381 and CEP401 showed the highest radial growth. Isolates CEP381, CEP401, CEP413 and CEP409 (Metarhizium spp.) had similar germination percentages as compared with water control when germinated on either sunflower, olive or maize oils at 10% v/v. The highest mortality of B. tabaci was observed for the isolates CEP381 in sunflower oil and CEP401 in olive oil. Molecular identification of isolates was performed using ITS4–5 primers. All isolates belong to the Metarhizium core group. Tested isolates could grow and infect B. tabaci nymphs at 30°C in some of the vegetable oils as carriers, providing new possibilities for integrated pest management of Bemisia tabaci.     

Autoregulation of Conidium Germination in Micromycetes of the genus Trichoderma

The amount of germinated conidia of micromycetes belonging to the genus Trichoderma considerably decreased with an increase in the population density. Strains exhibited different ecological strategies. The maximum number of germinated conidia (30–70%) was recorded when the average distance between conidia was 50 m.     

Partitioning of ochratoxin A in mycelium and conidia of Aspergillus carbonarius and the impact on toxin contamination of grapes and wine

AIMS: Aspergillus carbonarius is an important ochratoxin A (OTA)-producing fungus which is responsible for toxin contamination of grapes and wine. The objectives of this study were to examine the partitioning of OTA in mycelium and conidia of a range of A. carbonarius strains on artificial grape juice and defined media, to determine the excretion patterns of OTA from these spores, and the effect of organic acids used in wine production on OTA excretion from conidia. METHODS AND RESULTS: The results showed that 60-70% of the OTA was accumulated in the conidia of a number of different isolates of A. carbonarius. Calculations showed that on different defined media, an amount of 0.011- to 0.1-pg OTA was present per conidium. The OTA in spores was found to be rapidly excreted into the medium during the initial few hours after conidial germination leading to an increase of OTA in must during maceration for wine production. The presence of tartaric acid inhibited OTA production, but malic acid enhanced this production during mycelial growth. These acids were also shown to affect the time course of germination and the rate of OTA excretion from conidia during germination. CONCLUSIONS: This study is the first to examine and show the partitioning of OTA into spores of strains of A. carbonarius and that rapid excretion of OTA from spores could be a reason for OTA accumulation in musts during wine production. SIGNIFICANCE AND IMPACT OF THE STUDY: Conidia of A. carbonarius could be a major source of OTA contamination of grapes used in wine production. This information could help in the development of effective prevention strategies to minimize wine contamination with this important mycotoxin.     

Seasonal changes in primary and secondary inoculum during epidemics of leaf blotch (Rhynchosporium secalis) on winter barley

Seasonal changes in numbers of conidia of Rhynchosporium secalis on debris from previous barley crops infected with leaf blotch (primary inoculum) were monitored in 1985–86 and 1986–87. In 1986–87, changes in numbers of conidia on leaves of plants in the new winter barley crop (secondary inoculum) were also recorded. The greatest increases in production of primary inoculum were in early spring after rain, when temperatures were increasing after periods of sub-zero temperatures when there was little conidial production. Subsequently, more conidia were recovered from this debris after cycles of drying and rewetting than when it remained wet. After January 1987, amounts of secondary inoculum produced on the crop were much greater than amounts of primary inoculum on debris. Most spores were produced on the basal leaves and more spores were present on the September-sown than on the November-sown crop. Thus, while primary inoculum was a source of disease when plants were emerging, secondary inoculum on basal leaves was the main source of disease at stem extension, especially on early-sown crops.     

The effect of selected allelochemicals on germination of conidia and blastospores and mycelial growth of the entomopathogenic fungus,Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes)

Selected allelochemicals that protect plants from invasion by plant pathogenic fungi were investigated for their activity against the entomopathogenic fungus, Paecilomyces fumosoroseus. The alkaloids tomatine, solanine, and camptothecin; the furanocoumarin, xanthotoxin; and the phenolic, tannic acid were tested for their effects on germination of conidia and blastospores and growth of mycelia. The LC50 values (corresponding to 50% inhibition of germination) for tomatine, solanine, camptothecin, xanthotoxin and tannic acid were 51.6, 95.9, 55.9, 83.0 and 72.8 mg/l respectively. When blastospores were placed on media containing a concentration of the individual allelochemicals that inhibit germination in approximately 50% of conidia, all but blastospores on tomatine had significantly less germination than did aerial conidia. Growth rates of mycelia were slowest in the camptothecin medium, followed by those of tomatine and xanthotoxin and were not significantly different from controls in the media containing solanine and tannic acid. A multitude of biotic and abiotic factors are responsible for specificity and degree of pathogenicity of entomopathogens. The effect of crop plant chemistry on the efficacy of entomopathogens should be quantified further in order to maximize their potential when used concomitantly with resistant plant varieties. This revised version was published online in June 2006 with corrections to the Cover Date.     

Compatibility of OMRI-certified surfactants with three entomopathogenic fungi

The Organic Materials Review Institute (OMRI) is a non-profit organisation providing an independent review of products intended for use in organic production systems to certify compliance with US national organic standards. Since all adjuvants to be used in organic agriculture production are required to meet these standards, OMRI's certified list of products is a convenient starting point when developing organic pest control formulations. In the current study, six OMRI-certified surfactants are tested for their compatibility with three common entomopathogens: Beauveria bassiana, Metarhizium brunneum and Isaria fumosorosea. The fungi were evaluated in two common propagule forms, solid-state produced conidia and liquid-media produced blastospores. The results show that most of the surfactants are compatible with the fungi at a high surfactant concentration (2% w/v). In general, the conidia showed a higher susceptibility (greater reduction in spore germination) to the surfactants than the blastospores under these conditions. In addition, the surface tension and foaming properties of the surfactants were determined.