Selection of bacterial antagonists for the biological control of Botrytis cinerea in apple (Malus domestica) and in comparison with application of thiabendazole.

In this study fifteen strains of identified Pseudomonas fluorescens and Bacillus subtilis were investigated for biological control activity against Botrytis cinerea. P. fluorescens P-35 and B. subtilis B-16 showed the most inhibitory zone in dual culture assay against B. cinerea, In vitro. After ten days, P. fluorescens P-5 and B. subtilis B-3 showed the considerable results against B. cinerea on apple fruits and could reduce the grey mould from 100% to less than 35%. After twenty days, P. fluorescens P-5 and 8. subtilis B-16 decreased the disease from 100% to less than 65%. Also, application of thiabendazol at 1500 mg/litre was more effective and could reduce the disease from 100% to 30% and 60%, after 10 and 20 days respectively. Results indicated that there is no significant difference among the treatments (thiabendazol and bacterial strains). So, bacterial strains could not only control the disease but also be a reliable replacement instead of Thiabendazol.

Screening of Pseudomonas and Bacillus isolates for potential biocontrol of the damping-off of bean (Phaseolus coccineus).

In this study fifteen isolates of identified Pseudomonas fluorescens and Bacillus subtilis were investigated for control of bean damping-off disease caused by Rhizoctonia solani. In vitro, P. fluorescens P-6 and B. subtilis B-3 showed the most inhibitory zone in dual culture assay against R. solani. The growth of P-6 (4.5 x 10(8) cfu/ml) was significantly higher than in the other treatments. In greenhouse condition, all of the isolates effectively controlled damping-off on bean. P. fluorescens P-5 and P-6 showed the considerable results against R. solani and could reduce the damping-off disease from 100% to less than 30%. P-5, P-6 (P. fluorescens) and 8-16 (8. subtilis) strains had the highest effect on fresh weight of bean.

Effect of essential oils in control of plant diseases.

In this study, antifungal activity of some essential oils, extracted from Syzygium aromoticum, Foeniculum vulgare, Cuminum cyminum and Mentha piperita were investigated against grey mould of apple. The essential oils of S. aromaticum and F. vulgare showed considerable antifungal activities on PDA medium against Botrytis cinerea. Results indicated that the increasing of dosage of the essential oils caused to the more antifungal activity against B. cinerea in vitro condition. After 10 days, results showed that the essential oil of F. vulgare in both of the concentrations (750 and 1000 microL/L) was more effective than the essential oil of S. aromaticum against grey mould of apple and decrease the disease up to 15.5% in comparison with the check treatment (100%). After 20 days, biocontrol potential of the essential oils of S. aromaticum and F. vulgare at 1000 microL/L were more effective than the other treatments and the percentage of disease was evaluated 41.6% and 50.8%, respectively, in comparison with the check treatment (100%).

Interaction of media on production and biocontrol efficacy of Pseudomonas fluorescens and Bacillus subtilis against grey mould of apple.

The medium has a profound effect on biocontrol agents, including ability to grow and effectiveness in disease control. In this study, growth and antagonistic efficacy of strains P-5 and P-35 (P. fluorescens), B-3 and B-16 (B. subtilis) were evaluated in combinations of two carbon (sucrose and molasses) and two nitrogen (urea and yeast extract) sources to optimize control of Botrytis cinerea on apple. All of the strains were grown in different liquid media (pH = 6.9) including: sucrose + yeast extract, molasses of sugar beet + yeast extract in 2:1 and 1:1 w/w ratios, molasses of sugar beet + urea, molasses, malt extract and nutrient broth. Apples (Golden Delicious) were inoculated by a 25-microl suspension of 10(6) spores of B. cinerea per ml, wounding each fruit (in two sites separately). Then a 25-microl suspension of each strain, containing 2 x 10(8) cfu ml(-1) grown in each of the above culture media, was applied to each wound. Results indicated that Molasses + Yeast extract (1:1 w/w) medium supported rapid growth in all of the strains. The final growth of B. subtilis B-16 in Molasses + Yeast extract (1:1 w/w) medium was 5 x 10(9) cfu ml(-1). After ten days, all of the strains significantly inhibited pathogenicity of B. cinerea on apples. The biocontrol efficacy of B. subtilis B-3 in Molasses + Yeast extract (1:1 w/w) medium reduced the severity of grey mould from 100% (inoculated control) to less than 26.9%. After 20 days, Strain B-3 showed a considerable biocontrol efficacy in Molasses medium and reduced the severity of grey mould from 100% (inoculated control) to less than 38.2%. The results obtained in this study could be used to provide a reliable basis for the increase of population of biocontrol agents in fermentation process.

Effect of carbon and nitrogen sources on growth and biological efficacy of Pseudomonas fluorescens and Bacillus subtilis against Rhizoctonia solani, the causal agent of bean damping-off.

One of the most important environmental factors that regulate the growth and antagonistic efficacy of biocontrol agents is the medium. The aim of this paper was to find the nitrogen and carbon sources that provide maximum biomass production of strains P-5 and P-6 (Pseudomonas fluorescens), B-3 and B-16 (Bacillus subtilis) and minimum cost of media, whilst maintaining biocontrol efficacy. All of the strains were grown in seven liquid media (pH=6.9) including: sucrose + yeast extract, molasses of sugar beet + yeast extract in 2:1 and 1:1 w/w ratios, molasses of sugar beet + urea, nutrient broth, molasses and malt extract, at an initial inoculation of 1 x 10(5) CFU ml(-1). Cells from over night cultures used to inoculate soil at 1 x 10(9) CFU cm(-3) soil. At the same time, fungal inoculum (infected millet seed with Rhizoctonia solani) was added to soil at the rate of 2 g kg(-1) soil. Results indicated that growth of P-6, B-3 and B-16 in molasses + yeast extract (1:1 w/w) medium was significantly higher than in the other media. Molasses + yeast extract (1:1 and 2:1 w/w) media supported rapid growth and high cell yields in P-5. In greenhouse condition, results indicated that the influence of the media on the biocontrol efficacy of P-5, P-6, B-3 and B-16 was the same and Pseudomonas fluorescens P-5 in molasses and malt extract media reduced the severity of disease up to 72.8 percent. On the other hand, there were observed significant differences on bean growth after one month in greenhouse. P-5 in molasses + yeast extract (1:1 w/w) medium had the most effects on bean growth promotion. In this study molasses media showed good yield efficacy in all of the strains. The high sucrose concentration in molasses justifies the high biomass in all of the strains. Also, the low cost of molasses allows its concentration to be increased in media. On the other hand, yeast extract was the best organic nitrogen source for antagonist bacteria but it is expensive for an industrial process. So it should be replaced by another industrial product instead of yeast extract, which confirm by an economic and technological study. The results obtained in this study could be used to provide a reliable basis to increase the population of biocontrol agents in fermentation process.