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A recombinant Bacillus subtilis strain containing a plasmid encoding a luxAB fusion, which gave bioluminescence upon addition of an exogenous long-chain aldehyde as substrate for the endogenous luciferase enzyme, was used as test organism. Its populations were treated with 300 MPa for 20 min, or 600 MPa for 20 min at around room temperature, and this treatment is foreseen as a quality-friendly, non-thermal pasteurisation of foods. Besides the estimation of viable cell counts, the extent of pressure-induced germination and post-process development were investigated by phase-contrast microscopy, turbidimetry and luminometry. Increased heat sensitivity of pressurized spore populations was observed both by viable cell counting during a linearly programmed elevation of temperature and a simultaneous differential scanning calorimetry. This was related to pressure-induced germination of spores, although a small fraction remained ungerminated. The luciferase pool built into the spores during their formation seemed to have withstood pressurization. Spore germination was accompanied by the emergence of bioluminescence which also indicated sensitively the characteristic changes of metabolic activity running parallel with the development of untreated cell populations and that of the survivors of the hydrostatic pressure treatments when the cells were incubated in a nutrient broth.

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Colletotrichum falcatum Went, the causal agent of red rot of sugarcane produces a specialized infection structure called appressorium, for penetrating the host. Environmental cues like surface hydrophobicity and hardness tend to break the dormancy of the conidia and initiate conidial germination. Conidial attachment is generally stronger on hydrophobic surfaces, while hydrophilic surfaces do not permit conidial attachment of C. falcatum. In vitro studies on conidial germination and appressorium development were made to examine whether the Ca2+/calmodulin dependent pathways are involved in appressorium formation in C. falcatum. Effects of calcium chelator (EGTA), calcium channel blocker (methoxy verampamil), calmodulin antagonists (chloropromazine, phenoxy benzamine and W-7) and phospholipase C inhibitor (neomycin) were also examined to see whether they can impair conidial germination and appressorium development. All these chemicals were found to inhibit conidial germination and or appressorium formation in C. falcatum. Chloropromazine and W-7 specifically inhibited appressorium formation at the µM level. Exogenous addition of Ca2+ was found to restore the inhibition of conidial germination and appressorium development by EGTA. These results suggest that the Ca2+/calmodulin signal transduction pathway play an important role in the conidial morphogenesis and appressorium development in C. falcatum.

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The crude protein extract from the leaves of Andrographis paniculata was found to inhibit the spore germination of two major pathogens Aspergillus flavus and Macrophomina phaseolina. The antifungal protein component was further purified from the crude extract and the molecular mass of toxic protein was estimated to be 39.5 KDa.

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Spores of four Frankia strains, the nitrogen-fixing actinomycete, were exposed to short wavelength UV-C radiation of 254 nm at 1 lux cm2 (0.24 mw cm2 of energy) for 10 min. The used strains were HFP020203, UGL020604, UGL020602q and ORS021001. Exposure to UV was followed by reactivation with visible white light at 327.4 lux cm2 for the same period of time. Spore germination percentage, spore protein content, and cell growth were damaged by this treatment. The lower and higher percentages of reduction in spore germination were 32 and 63% and, for the same strains, the recovery by white light was 7.2 and 37%. The lower percentages of UV damage and subsequent low recovery were recorded for strain ORS021001 that is considered more resistant to UV than the other strains. The higher percentages were recorded for strain HFP020203 that is more sensitive to UV but having more efficient repairing mechanisms. All the tested strains showed repairing activity induced by white light as indicated from the increase in their spore germination, protein content and almost restoring the normal shape of Frankia hyphae, after being damaged, as revealed by scanning electron microscope. This is the first evidence that photo-repairing systems are present in Frankia strains although there are variations in their response to both UV-C and photoreactivation by white light.

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Fphog1 , a HOG-type mitogen-activated protein kinase (MAPK) encoding gene of Fusarium proliferatum was constitutively expressed in all types of fungal cells. Δ Fphog1 mutants grew normally on artificial media; sporulation and spore germination were also normal. The mating capability of M24, a representative strain of the Δ Fphog1 mutants, showed no detectable decline, indicating that this HOG-type MAPK gene is dispensable for growth and reproduction under optimal culture conditions. Strain M24 had increased tolerance to vinclozoline and fludioxonil fungicides. Invasive growth of the wild type and three Δ Fphog1 gene replacement mutants (M21, M24, M36) were assessed on tomato fruits. All strains behaved similarly, i.e. they produced visible symptoms on the second day after infection, and produced ∼3 cm lesion, overgrown by fungal mycelium after six days of incubation. These data suggest that the HOG-type MAPK pathway is not required for the invasive growth of this fungus.

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Acta Alimentaria
Authors:
M.Y. Jiang
,
Z.R. Wang
,
K.W. Chen
,
J.Q. Kan
,
K.T. Wang
,
Zs. Zalán
,
F. Hegyi
,
K. Takács
, and
M.Y. Du

After suffering from mechanical injury and fungal infection, grapes are perishable. Botrytis cinerea, the causal agent of gray mould, is a critical pathogen for grapes. In this study, the inhibitory effect of Pseudomonas fluorescens on the formation of gray mould on grapes during the postharvest storage was investigated on “Kyoho” grape. The results suggest that a living cell suspension of P. fluorescens significantly inhibited spore germination of B. cinerea, and significantly reduced the incidence of grape gray mould. Moreover, compared with the control, the fruit inoculated with P. fluorescens had elevated activities of polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT), phenylalanine ammonia-lyase (PAL), chitinase (CHI), and β-1,3-glucanase (GLU). Increase in enzyme activity correlated with enhanced host resistance. In addition, there was little difference in storage quality between the treated group and control group, indicating no adverse effects of the induced defence response on fruit quality.

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A strain of Clonostachys rosea , ACM941 (ATCC #74447) was evaluated for its antibiosis to G. zeae in vitro and for controlling of fusarium head blight (FHB) under both greenhouse and field conditions, in comparison to the registered fungicide Folicur (tebuconazole). ACM941 reduced the mycelial growth of the pathogen by 53% in dual culture and completely suppressed the macroconidium germination of G. zeae in coculture for 6 hours. ACM941 reduced the perithecium production by more than 99% in leaf disc assay, 23–57% on debris, and 36–70% on infested kernels. When sprayed onto wheat heads prior to inoculation with G. zeae , ACM941 significantly reduced infected spikelets (IS) by 58–71% and fusarium damaged kernels (FDK) by 59-73% compared to the untreated disease control. Under the simulated natural epidemic conditions during 2005–2007, ACM941 reduced IS by 44–51%, FDK by 33–68%, and deoxynivalenol (DON) in grains by 10–28%. ACM941 was similar to Folicur in reducing the mycelial growth, spore germination, and perithecium production of G. zeae , but was less effective than Folicur in reducing IS, FDK, and DON in the field. Results of this research suggest that ACM941 is an effective antagonist against G. zeae and may be used as an alternative of chemical fungicides in an integrated FHB management program.

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Long-term storage of Rhynchosporium secalis cultures is a challenge for any lab managing a working collection of isolates. In this work, the viability and pathogenicity of R. secalis stock cultures were tested after four years of storage at −20 °C in different concentrations of glycerol. Germinability were measured after each storage by collecting spores by coverslips and placing them on water agar in closed Petri dishes at 20–22 °C in the dark and allowed to germinate for 24 h. Additionally, at the end of each storage treatment, conidia were collected by coverslips from sporulated leaf lesions of symptomatic barley leaves and placed under similar conditions as non-stored controls.

Cultures of all stored isolates were viable with a spore germination rate of 72.28% (Rs22) after four years of storage at −20 °C in 60% glycerol. Low viability and contamination were observed when spores were stored in sterile distilled water and in Lima bean agar. All isolates continued to infect barley leaves after 4 years of storage. However, the pathogenicity was significantly (P <0.05) reduced in isolates stored in glycerol as compared with controls.

This work helps to preserve R. secalis for a long term period at −20 °C without any contamination; therefore, due to the low costs our results could be applicable for laboratories that have limited resources.

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Acta Alimentaria
Authors:
A. Taczman-Brückner
,
Cs. Mohácsi-Farkas
,
Cs. Balla
, and
G. Kiskó

. (1987): Effect of organic volatiles from Saccharomyces on the spore germination of fungi. Acta microbiol. Hung. , 34 (3-4), 255-257. Effect of organic volatiles from Saccharomyces on the spore germination of fungi

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value according to the method of L ivak and S chmittgen (2001). The relative expression of defense-related enzymes and PR genes were calibrated with the values for the day 0 fruit being set as 1. 1.6 Effect of EBR on spore germination of R

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