Alginate embedding and subsequent sporulation of in vitro-produced Conidiobolus thromboides hyphae using a pressurised air-extrusion method

Conidiobolus thromboides is an entomophthoralean fungus with potential as a biological control agent of aphids. However, its application in biological control is limited due to its formulation requirements. The objective of this study was to develop and optimise a novel air-extrusion method to embed C. thromboides hyphae at high density in alginate pellets. An orthogonal experimental design was used to investigate selected combinations of parameters known to affect hyphal density within pellets. The diameter of pellets produced, and the calculated density of hyphae within them, ranged from 0.18 ± 0.09 to 3.17 ± 0.06 mm and from 0.02 to 350.56 mg/mm³ respectively. These data were used to predict the optimal parameter combination to deliver the greatest density of hyphae of C. thromboides per pellet: 1% sodium alginate, a 1:2 ratio of hyphae to sodium alginate, an orifice diameter of 0.232 mm and an air pressure of 0.05 MPa. Pellets made under the optimal conditions predicted produced a mean total of 4.3 ± 0.6 × 10⁵ conidia per pellet at 100% relative humidity which was significantly greater than the mean total number of conidia produced from infected aphid cadavers of comparable size (9.35 ± 0.85 × 10⁴) (p < 0.001). In conclusion, air-extrusion embedding appears to be a promising method for formulating in vitro-produced hyphae of C. thromboides for use in biological control.     

Sporulation,storage and infectivity of obligate aphid pathogen Pandora nouryi grown on novel granules of broomcorn millet and polymer gel

Aims: Producing granular cultures of obligate aphid pathogen Pandora nouryi for improved sporulation and storage. Methods and Results: Small millet–gel granules were made of the mixtures of 80–95% millet powder with 5–20% polymer gel (polyacrylamide, polyacrylate or acrylate‐acrylamide copolymer) and inoculated with mycelia at 30 mg biomass g^?1 dry granules plus 87·5% water, followed by static incubation at 20°C for 4–12 days. The fungus grew well on 12 preparations but best on that including 10% copolymer. An 8‐day culture of this preparation discharged maximally 58·5 × 10⁴ conidia mg^?1 granule at 100% RH and was capable of ejecting conidia at the nonsaturated regimes of 86–97% RH. During storage at 6°C, granular cultures with >85% water content had twofold longevity (120 days) and half‐decline period (34–36 days) of those stored at room temperature. The steadily high water content preserved the cultures better than that decreasing at 6°C. However, conidia from 70‐day‐stored granules were less infective to Myzus persicae nymphs than those from fresh ones based on their LC₅₀s. Conclusions: The millet–gel granules had higher sporulation capacity than reported Pandora cultures and a capability of spore discharge at nonsaturated humidity. Significance and Impact of the Study: The granular cultures are more useful for aphid control.     

Efficacy of Beauveria bassiana (Blas.) Vuill. against cabbage aphid Brevicoryne brassicae L. (Hem.: Aphididae) in laboratory condition

In order to replace the conventional chemical pesticides, extensive researches have been done on entomopathogenic fungi. Entomopathogenic fungus Beauveria bassiana is an important biocontrol agent against major economic pests and is being employed in Integrated pest management (IPM) along with synthetic pesticides. Cabbage aphid Brevicoryne brassicae L. is one of the important pests of Brassicaceae family. Therefore, in this research, the virulence isolate of B. brassicae (IRAN 429C) was investigated on adults of cabbage aphid under laboratory conditions. The experiments were conducted at 25 ± 2 °C, 60 ± 10 R. H. and a photoperiod of 16:8 (L: D). After preliminary experiments, the adult aphids were treated with fungal concentrations of 1 × 10³ to 1 × 10⁷ spores/ml. Probit analysis was conducted to calculate LC₅₀ and LC₉₅ values for the isolate. Positive correlation was observed between concentrations and pest mortality. LC₅₀ and LC₉₅ values calculated for IRAN 429C isolate are 2.04 × 10⁵ and 1.82 × 10⁸, respectively. The mortality was counted one day after the treatment and then continued for 14 days. Cumulative mortality for 14 days after treatment varied from 54% for IRAN 429C at low concentration (10³ conidia/ml) to 83% at high concentration (10⁷ conidia/ml). The lowest LT₅₀ was obtained at 7.67 days for IRAN 429C isolate at concentration 1 × 10⁷ spore/ml. According to the insecticidal activity of mentioned fungi on cabbage aphid, it can be used in biocontrol programmes of B. brassicae.     

Metarhizium rileyi biopesticide to control Spodoptera frugiperda: Stability and insecticidal activity under glasshouse conditions

The insect-pathogenic fungus Metarhizium rileyi is highly sensitive to nutritional and environmental conditions which makes it difficult to produce as a stable biopesticide. In this study, a Colombian isolate of this fungus was produced in bulk, and conidia were formulated as an emulsifiable concentrate (EC). The stability of formulated conidia was studied. Conidial viability was maintained at >85 % viability for 12 m under refrigeration and for >three months at 18 °C. The pH values were stable, while contaminant content was significantly reduced. The efficacy of the EC to control Spodoptera frugiperda (Smith) was correlated with the storage time using different mathematical models, and conservative values of six and 12 months at 8 °C and 18 °C respectively, were established. Finally, the EC was evaluated in maize plants under glasshouse conditions. The LC₅₀ and LC₉₀ were estimated to be 1.17 × 10⁴ and 4.03 × 10⁶ conidia/mL respectively and a 57 % reduction in recent damage of plants was achieved. This study demonstrated the potential of M. rileyi formulated as EC to control S. frugiperda in maize. Therefore, it is necessary to continue developing this biopesticide, in order to deliver a new tool to be integrated in pest management programs.     

Stability of the intra- and extracellular toxins of Prymnesium parvum using a microalgal bioassay

Prymnesium parvum produces a variety of toxic compounds, which affect other algae, grazers and organisms at higher trophic levels. Here we provide the method for development of a sensitive algal bioassay using a microalgal target, Teleaulax acuta, to measure strain variability in P. parvum toxicity, as well as the temporal stability of both the intracellular and the extracellular lytic compounds of P. parvum. We show high strain variation in toxicities after 3 h incubation with LC₅₀s ranging from 24 to 223 × 10³ cells ml⁻¹. Most importantly we prove the necessity of testing physico-chemical properties of P. parvum toxins before attempting to isolate and characterize them. The extracellular toxin in the supernatant is highly unstable, and it loses significant lytic effects after 3 days despite storage at −20 °C and after only 24 h stored at 4 °C. However, when stored at −80 °C, lytic activity is more easily maintained. Reducing oxidation by storing the supernatant with no headspace in the vials significantly slowed loss of activity when stored at 4 °C. We show that the lytic activity of the intracellular toxins, when released by sonication, is not as high as the extracellular toxins, however the stability of the intracellular toxins when kept as a cell pellet at −20 °C is excellent, which proves this is a sufficient storage method for less than 3 months. Our results provide an ecologically appropriate algal bioassay to quantify lytic activity of P. parvum toxins and we have advanced our knowledge of how to handle and store the toxins from P. parvum so as to maintain biologically relevant toxicity.     

Identification and virulence characterization of entomopathogenic fungus <Emphasis Type="BoldItalic">Lecanicillium attenuatum</Emphasis> against the pea aphid <Emphasis Type="BoldItalic">Acyrthosiphon pisum</Emphasis> (Hemiptera: Aphididae)

An entomopathogenic fungal strain was originally isolated on artificial medium from the corpse of a pea aphid (Acyrthosiphon pisum Harris) collected at Jingzhou, China (N30°21′18.15″, E112°08′41.63″). Based on tests of the morphological, physiological and biochemical characteristics and analysis of internal transcribed spacer (ITS) sequences, it was considered to be a strain of Lecanicillium attenuatum Zare & W. Gams. Therefore, the strain was designated L. attenuatum YZU 151121. The activity of the biological agents under study was determined at 26 °C and 90% relative humidity. The number of A. pisum killed was increased by increasing the concentration of L. attenuatum. The results demonstrated that L. attenuatum YZU 151121 showed a high efficacy against 3rd-instar nymphs (LC₅₀ = 2.91 ± 0.365 × 10⁵ conidia/ml) and adults (LC₅₀ = 3.12 ± 0.398 × 10⁶ conidia/ml) after 6 days of exposure. Crude extract from this strain was tested for contact toxicity and showed high activity in 3rd-instar nymphs and adults, with LC₅₀ values of 251.34 ± 49.54 and 315.46 ± 87.66 mg/l, respectively. In addition, crude extract at a concentration of 200 mg/l could significantly reduce fecundity in adults. These results revealed that the strain YZU 151121 may be useful in biopesticides for controlling pea aphid.     

Method To Enhance Growth and Sporulation of Pelletized Biocontrol Fungi

The biocontrol fungi Trichoderma harzianum, used to control soilborne plant pathogens, and Beauveria bassiana, used to control insect pests, were formulated as mycelial biomass in alginate pellets with wheat bran added. After drying for 0, 4, or 16 h, pellets were placed in water or in aqueous solutions of polyethylene glycol (PEG) 8000 for 4 to 24 h and then allowed to continue drying. PEG-treated pellets containing T. harzianum showed significantly greater proliferation of hyphae in soil than untreated pellets or pellets treated with water. Production of conidia of T. harzianum from PEG-treated pellets was lower than production from untreated pellets after 4 days, although rates were equivalent after 7 days. In contrast, production of conidia of B. bassiana was significantly more rapid from PEG-treated pellets than from untreated pellets. Biocontrol of soilborne plant pathogens or insect pests may be enhanced by rapid hyphal growth of T. harzianum in soil or rapid sporulation of B. bassiana on foliage, respectively. Therefore, PEG treatment may improve the efficacy of these biocontrol agents.     

Combination of the fungus Beauveria bassiana and pheromone in an attract‐and‐kill strategy against the banana weevil,Cosmopolites sordidus

An attract‐and‐kill approach based on pellets from soybean or palm stearin fats blended with the entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. sensu lato and the aggregation pheromone sordidin (Cosmolure^®) was tested against the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae). The viability of B. bassiana conidia, blended with hydrogenated oil and exposed for up to 150 min to heating at 50 °C, was not affected and the aggregation pheromone did not undergo any decomposition. Conidial viability in pellets decreased by 50% after an average of 15.1 and 9.1 days at 25 and 40 °C, respectively, when packaged in polypropylene bags. Active packaging (hermetic bag + O₂/moisture‐absorbing sachet) increased the shelf lives almost 10 and 6 times at 25 and 40 °C, respectively. In olfactometer bioassays, fat pellets amended with pheromone (sordidin, 1% wt/vol) were highly attractive to C. sordidus adults for up to 15 days, after which the pheromone release rate had decreased by about 90% and pellets were no longer attractive. Pellets with pheromone and conidia were as attractive to C. sordidus as banana rhizomes, and considerably more attractive than pieces of pseudostem. In no‐choice experiments conducted in boxes, survival of insects exposed to fungus‐impregnated pellets was affected by fat type (soybean fat vs. palm stearin) and bioassay temperature (25 vs. 30 °C), with results favoring soybean fat pellets at the higher temperature (96.9% of mortality after 18 days and ST₅₀ of 7.7 days). However, mortality levels were low (21.7% for soybean fat pellets) or very low (1–5% for palm stearin pellets) in choice experiments carried out at 25 °C when fungus‐impregnated pellets were applied before or after exposure of pseudostem residues to insects, respectively. The potential of this delivery system to manage C. sordidus populations and other insect pests (including those with cryptic habits) is discussed.     

Pathogenicity of entomopathogenic fungus,Metarhizium anisopliae MET-GRA4 isolate on dengue vectors,Aedes albopictus and Aedes aegypti mosquito larvae (Diptera: Culicidae)

Considering the rapid transmission of the dengue virus, substantial efforts need to be conducted to ward-off the epidemics of dengue viruses. The control effort is depending on chemical insecticides and had aroused undesirable conflicts of insecticide resistance. Here, we study the entomopathogenic fungus, Metarhizium anisopliae as a promising new biological control agent for vector control. The pathogenicity effects of Metarhizium anisopliae against field and laboratory strains of Aedes albopictus and Aedes aegypti larvae were tested using the larvicidal bioassay technique. The results demonstrate that the treatments using M. anisopliae isolate MET-GRA4 were highly effective and able to kill 100% of both Ae. albopictus and Ae. aegypti mosquito larvae at a conidia concentration of 1 × 10?/ml within 7 days of the treatment period. The fungus displayed high larvicidal activity against laboratory and field strain of Ae. aegypti larvae with LC₅₀ values (9.6 × 10³/ml, 1.3 × 10³/ml) and LC₉₅ values (1.2 × 10?/ml, 5.5 × 10⁵/ml) respectively. For Ae. albopictus, LC₅₀ values for laboratory and field strains were (1.7 × 10⁴/ml, 2.7 × 10⁴/ml) and the LC₉₅ values were (2.1 × 10?/ml, 7.0 × 10⁵/ml) respectively. Interestingly, the susceptibility of field strain towards M. anisopliae was higher as compared to the laboratory strain Aedes larvae. In which, the causative agents of all the dead larvae were verified by the virulence of M. anisopliae and caused morphological deformities on larval body. The findings from this study identify this isolate could be an effective potential biocontrol agent for vector mosquitoes in Malaysia.     

Effect of temperature on germination,growth, and infectivity of the mosquito pathogen Tolypocladium cylindrosporum (deuteromycotina; hyphomycetes)

The mosquito pathogen Tolypocladium cylindrosporum was examined with regard to its response to temperature. Similar temperature ranges were found for growth, germination, and infectivity of blastospores and conidia. Germination occurred at 8° and 33°C but not at 6° and 35°C. Optimal germination and growth was noted between 24° and 27°C for both spore types. Infectivity of blastospores and conidia at different temperatures was examined by exposing L₂Aedes sierrensis larvae to concentrations of 5 × 10⁵ blastospores/ml or 5 × 10⁶ conidia/ml. Larvae were incubated at 12°, 15°, 25°, and 30°C. Infection occurred at all temperatures tested with LT₅₀ values ranging from 22.7 days (12°C) to 5.6 (25°C) days for conidia and 4.7 days (12°C) to 0.6 day (25°C) for blastospores. These results confirmed earlier findings that blastospores infected and killed host larvae more rapidly than conidia and suggested that this difference is largely due to the more rapid germination rate of blastospores. These experiments demonstrated that T. cylindrosporum can be active against mosquito larvae over a broad range of temperatures encompassing both the cold-water habitat of certain temperate mosquito species as well as the habitat of tropical vector species.     

Soil microbial biomass influence on growth and biocontrol efficacy of Trichoderma harzianum

Hyphal growth and biocontrol efficacy of Trichoderma harzianum may depend on its interactions with biotic components of the soil environment. Effects of soil microbial biomass on growth and biocontrol efficacy of the green fluorescent protein transformant T. harzianum ThzID1-M3 were investigated using different levels of soil microbial biomass (153, 328, or 517 μg biomass carbon/g of dry soil). Hyphal growth of T. harzianum was significantly inhibited in soil containing 328 or 517 μg biomass carbon/g of dry soil compared with soil containing 153 μg biomass carbon/g. However, when ThzID1-M3 was added to soil as an alginate pellet formulation, recoverable populations of ThzID1-M3 varied, with the highest populations in soil containing 517 μg biomass carbon/g. When sclerotia of Sclerotinia sclerotiorum were added to soils (10 sclerotia per 150 g soil) with ThzID1-M3 (20 pellets per 150 g soil), colonization of sclerotia by ThzID1-M3 was significantly lower in the soil containing the highest level of biomass. Addition of alginate pellets of ThzID1-M3 to soils (10 pellets per 50 g) resulted in increased indigenous microbial populations (total fungi, bacteria, fluorescent Pseudomonas spp., and actinomycetes). Our results suggest that higher levels of microbial soil biomass result in increased interactions between introduced T. harzianum and soil microorganisms, and further that microbial competition in soil favors a shift from hyphal growth to sporulation in T. harzianum, potentially reducing its biocontrol efficacy.     

Investigation on the insecticidal efficacy of novel pellet formulation against Callosobruchus maculatus (F.) (Col.: Bruchidae) in three different heights and compared with phosphine

Applying essential oils, fumigant toxicity in stored products pests control has sharpened recently. Since these products have low penetration power and vapour pressure, their use in crop depth is restricted. The aim of this work was using controlled release technology to solve this problem. In this research, 1,8-cineole-based pellets were prepared by dry mixing method and physical load of 1,8-cineole on strach, which followed by pressing the mixture, using pellet maker apparatus, to form pellets. Insecticidal efficacy of produced pellets was investigated against adults (1–3?days old) Callosobruchus maculatus F. (Col.: Bruchidae) compared with phostoxin under 28?±?2?°C and darkness in laboratory condition. LC₅₀ and LC₉₅ of pellets against C. maculatus in 24?h were 0/017 and 0/050?ml active ingredient per L air, respectively. LC₅₀ and LC₉₅ of phosphine pellets against C. maculatus in 24?h were 0/124 and 1/852?ml active ingredient per L air, respectively.     

Shelf-life of a Biocontrol Pseudomonas putida Applied to Sugar Beet Seeds Using Commercial Coatings

Pseudomonas putida 40RNF is a putative biological control agent (BCA) of Pythium damping-off of sugar beet. The survival of 40RNF during commercial seed treatment and its subsequent shelf-life (i.e. long-term viability and biocontrol activity) were assessed. Two methods were used to apply 40RNF to sugar beet seeds: incorporation into film-coats sprayed on to pre-pelleted seeds and incorporation into the pellet material prior to pelleting. Only 7.1% of applied 40RNF survived film-coating, but an initial concentration of 7 × 10⁸ ensured that 83.3% of a pre-determined target rate of 6 × 10⁷ |pellet was achieved. After 52 weeks of storage at 4°C,the numbers of 40RNF had declined by one to two orders of magnitude, with a decrease of approximately 50% in disease control. After 52 weeks at 18-20°C, 40RNF was below detectable limits (< 100|pellet), yet the biocontrol activity of the seed treatments was not reduced. The survival of 40RNF during incorporation into the pellet material was poor (< 0.2% of those applied, i.e. 5 × 10⁵ pellet). However, bacterial viability and biocontrol efficacy were maintained at 100% of the control value for 24 weeks when stored at 18-20°C. The results indicate that commercial seed treatments and the storage of pellets at ambient temperatures has potential for the introduction of bacterial BCAs into the spermosphere.     

Thermal response and horizontal transmission of cameroonian isolates of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae – Candidates for microbial controls of the banana root borer Cosmopolites sordidus

Beauveria bassiana and Metarhizium anisopliae are two promising microbial agents for biopesticides development against the banana root borer Cosmopolites sordidus. In this study, germination, mycelial growth, and sporulation of six local Cameroonian isolates of those two species were assessed under seven different thermal conditions (13, 15, 20, 25, 29 33, and 37 °C) to select thermo-tolerant isolates. The Transmission potential of the thermo-tolerant isolates was determined at 25 ± 1 °C by dipping adult weevils in conidial suspensions (3.2 × 10⁸) conidia/ml and mixing these with uninoculated weevils in different proportions (0, 10, 30 and 50%), in groups of 30, and assessing the spread of the mycosis within the group over 35 d of co-incubation. Incubation temperature and isolates significantly affected germination, mycelial growth and conidial production. All isolates had large thermal tolerance ranges (13–33 °C) except MIITAC6.4.2 (20–29 °C). Horizontal transmission resulted in mortality of non-inoculated weevils from 4.63 ± 1.77 to 53.3 ± 11.9%. The isolate BIITAC6.2.2 exhibited high auto-dissemination potential and high conidia yield in cadavers. These results demonstrate the potential use of these isolates for biopesticides development against C. sordidus in Central Africa.     

Turning up the heat on subzero fish: thermal dependence of sustained swimming in an Antarctic notothenioid

We determined the maximum sustained swimming speed (U_crit), and resting and maximum ventilation rates of the Antarctic fish Pagothenia borchgrevinki at five temperatures between −1°C and 8°C. We also determined resting metabolic rate (VO₂) at −1°C, 2°C, and 4°C. U_crit of P. borchgrevinki was highest at −1°C (2.7±0.1 BL s⁻¹) and rapidly decreased with temperature, representing a thermal performance breadth of only 5°C. This narrow thermal performance supports our prediction that specialisation to the subzero Antarctic marine environment is associated with a physiological trade-off in performance at high temperatures. Resting oxygen consumption and ventilation rate increased by more than 200% across the temperature range, which most likely contribute to the decrease in aerobic swimming capabilities at higher temperatures.     

Potential of Metarhizium anisopliae and Beauveria bassiana to control Dinoderus porcellus (Coleoptera: Bostrychidae) infesting yam chips

The beetle Dinoderus porcellus Lesne is a serious storage insect pest that causes important losses by destroying stocks of yam chips. In the aim to found an alternative control method to the use of synthetic insecticides for its management, the virulence of the entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin (isolate Bb115) and Metarhizium anisopliae (Metschnikoff) Sorokin (isolate Met 31) against adults of D. porcellus was evaluated under laboratory conditions (25 ± 2 °C and 70 ± 5% RH). Then, the effectiveness of the most virulent entomopathogenic fungus as biological agent against D. porcellus was assessed under farmer storage conditions. For each entomopathogenic fungus isolate, four conidial concentration (0, 10⁵, 10⁷, and 10⁹ conidia/mL) at the dose of 1 µL were inoculated topically on D. porcellus adults (3–5 days old). Observations focused on insect mortality, cadaver sporulation and weight loss of yam chips. Lethal dose and lethal time values were estimated using probit analysis. Both fungal isolates at all conidial dose caused more than 50% mortality on day 7, with the highest mortality (94.44%) achieved using B. bassiana at the 10⁹ conidia/mL. LT₅₀ values for B. bassiana and M. anisopliae isolates were 2.63 and 3.35 days, respectively, while their LT₉₀ values were 6.15 and 9.87 days, respectively. Yielding the lower LD₉₀ values and the highest rates of cadaver sporulation, B. bassiana isolate appeared as the most virulent against D. porcellus. After 3 months of storage, comparatively to the control, the B. bassiana isolate at the highest conidial dose (10⁹ conidia/mL) significantly reduced D. porcellus populations, and weight loss of yam chips. This study revealed the potential of B. bassiana and M. anisoplae isolates as biological control agent against D. porcellus for yam chips protection.     

Laboratory and semi-field evaluation of Beauveria bassiana (Ascomycota: Hypocreales) against the lettuce aphid,Nasonovia ribisnigri (Hemiptera: Aphididae)

The lettuce aphid, Nasonovia ribisnigri (Mosley), is an economically important pest of lettuce worldwide. The entomopathogenic fungus Beauveria bassiana strain GHA has recently been reported as a potential biocontrol candidate for use against the lettuce aphid. This study provides information on the mortality inflicted by B. bassiana when applied against different life stages of the lettuce aphid under laboratory conditions and how fungus infection affects the aphid fecundity. In addition, temporal changes in persistence of fungus inoculum applied to foliage of young lettuce plants under semi-field conditions was analysed. Immature life stages were generally the least susceptible to fungal infection and the susceptibility of all stages was dose-dependent, with the highest mortality occurring at the highest dose. B. bassiana significantly affected the rate of nymph production by the lettuce aphid, with the highest effect seen when the alatoid fourth instar of N. ribisnigri was inoculated with B. bassiana. The persistence of B. bassiana conidia on lettuce foliage was not influenced by leaf position. Within 5 days, the cumulative percentage decline in the conidial population was 38% which declined further to 92% and 99% on day 11 and 20 post-spraying, respectively. In accordance, the infectivity to second instar lettuce aphid nymphs of B. bassiana conidia deposited on leaves declined according to an exponential decay model predicting an intercept of 0.59 ± 0.03 (S.E), a reduction in aphid mortality at a rate of 11% with each increasing day after fungal application and a fungus half-life of 6.34 ± 0.69 days.     

Reaction of <Emphasis Type="Italic">Bipolaris euphorbiae</Emphasis> to environmental factors and its tolerance to solar and ultraviolet radiation

The determination of the ideal cultivation conditions and the knowledge of solar radiation tolerance are important aspects that must be investigated for the use of Bipolaris euphorbiae Muchovej and Carvalho as a biocontrol agent. The present study was done to assess the growth rate, sporulation and viability of the fungus cultivated under different conditions of the initial pH value of the growth medium, temperature and photoperiod. The tolerance of this fungus’ conidia to light from a source simulating solar and ultraviolet radiation was also assessed. B. euphorbiae was affected by different pH values of the growth medium being 6.0 the adequate pH for fungus cultivation. Incubation of the fungus under temperatures of 22, 25 and 28°C enhanced mycelium growth, while sporulation and viability of conidia were better at 22 and 16°C. Different regimens of exposure to light of fungal cultures only affect sporulation. Conidia exposed to solar and ultraviolet radiation for 8 h and 90 min, respectively, presented viabilities higher than 92%, indicating high tolerance levels to radiation exposure.     

Myrothecium verrucaria strain X-16, a novel parasitic fungus to Meloidogyne hapla

Options for control of northern root-knot nematode (NRKN, Meloidogyne hapla) on vegetables are very limited currently. In this study, we characterized the parasitism of Myrothecium verrucaria strain X-16, a new nematophagous fungus, on NRKN at the stages of eggs, J2, and adult females and evaluated its biocontrol efficacy in the greenhouse. Strain X-16 produced conidia that geminated and invaded in 80 h after in contact with eggs, causing the shrinkage and depression of egg shell and blastocolysis of the embryo. The strain also attacked 2nd-stage juveniles by producing developing surface networks of hyphae on the nematode body wall. Strain X-16 attacked adult females by producing dense networks of hyphae on the nematode body wall in 120 h. Strain X-16 had lethal effects (22–71% mortality) against NRKN J2 at the concentration as low as 3.1 × 10⁷ conidia/ml and with the incubation treatment time as short as 24 h. The lethal effects linearly increased with the increase of conidial concentration, with the estimated LC₅₀ values as low as 1.0 × 10⁸ conidia/ml. Soil treatments with strain X-16 at 1%, 2% or 4% (wt/wt) induced significant reductions in J2 nematode counts in 100 g of dry soil, Pf/Pi ratios and root-know index in cucumber in the greenhouse evaluations. These studies are the first to demonstrate that M. verrucaria is able to parasitize NRKN and strain X-16 can be a potential biocontrol agent for management of NRKN.     

The Influence of Water Activity and Temperature on Germination,Growth and Sporulation of <Emphasis Type="Italic">Stachybotrys chartarum</Emphasis> Strains

The objectives were to determine the influence of water activity (a_w, 0.997–0.92) and temperature (10–37°C) and their interactions on conidial germination, mycelial growth and sporulation of two strains of Stachybotrys chartarum in vitro on a potato dextrose medium. Studies were carried out by modifying the medium with glycerol and either spread plating with conidia to evaluate germination and germ tube extension or centrally inoculating treatment media for measuring mycelial growth rates and harvesting whole colonies for determining sporulation. Overall, germination of conidia was significantly influenced by a_w and temperature and was fastest at 0.997–0.98 a_w between 15 and 30°C with complete germination within 24 h. Germ tube extension was found to be most rapid at similar a_w levels and 25–30°C. Mycelial growth rates of both strains were optimal at 0.997 a_w between 25 and 30°C, with very little growth at 37°C. Sporulation was optimum at 30°C at 0.997 a_w. However, under drier conditions, this was optimum at 25°C. This shows that there are differences in the ranges of a_w x temperature for germination and growth and for sporulation. This may help in understanding the role of this fungal species in damp buildings and conditions under which immune-compromised patients may be at risk when exposed to such contaminants in the indoor air environment.