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Druvefors, U. A., Passoth, V. & Schnürer, J. (2003): The role of nutrient competition and ethyl acetate formation in the mode of action of the biocontrol agent Pichia anomala J121. 23rd International Specialised Symposium on Yeasts. 26-29 August 2003
Applying antagonistic yeasts is one of the recent possibilities for controlling postharvest disease caused by blue mould (Penicillium expansum). In this work, antagonistic activity of several Kl. lactisstrains was tested against two strains of P. expansum. Three strains of Kl. lactiswere compared to three biocontrol yeasts: Metschnikowia pulcherrima, Sporobolomyces roseusand Pichia anomala. The investigations were carried out at 25 °C, 15 °C and 5 °C, applying different yeast cell densities and culture media. Statistical analysis showed no significant differences among the three Kl. lactisstrains. The inhibitory effect of the tested yeasts was different according to the applied mould strain temperature, culture medium and cell density. Application of antagonistic yeasts combined with reduced temperature enhanced the inhibitory effect. Direct relationship was observed between increasing cell density and the biocontrol efficiency of Kl. lactis. According to this work, Kl. lactisis a possible biocontrol agent.
Eighteen isolates of fluorescent pseudomonads ad Bacillus spp. were isolated from the Meloidogyne incognita suppressive soils of tomato fields. These isolates were evaluated in the laboratory and green house for the biocontrol of M. incognita . Eight isolates were considered to have potential for the biocontrol of M. incognita on the basis of the antibiotic sensitivity, fluorescence produced by Pseudomonas , inhibitory effect on the hatching and penetration of M. incognita and root colonization of tomato root by these isolates. These 8 isolates (Pa22, Pf25, Pf27, Pa28, B22, B23, B27 and B28) were further tested for their biocontrol potential against M. incognita on tomato in a pot test. Out of 8 isolates, isolate B28 was the best in improving tomato growth of M. incognita inoculated plants. Isolate B28 also caused greater reductions in galling and multiplication of M. incognita on tomato while isolate Pa28 was found best in improving growth of plants without M. incognita .
The antagonistic effect of thirteen Pseudomonas aeruginosa and thirteen strains of other Pseudomonas species was studied on the soil-borne phytopathogenic Rhizoctonia solani and Fusarium solani fungi. The inhibition of pathogen colony growth was tested with two different in vitro techniques using the same type of culture media. In case of the spread slant technique the antagonists induced a significantly stronger inhibition on the growth of pathogens than in case of spot transfer. Among the 26 investigated Pseudomonas strains, P. aeruginosa strains were generally more effective against the fungal pathogens. Rhizoctonia solani proved to be affected to a greater extent by the bacterial strains studied than the Fusarium solani representative. The possibility of in vitro strain selection of biocontrol microbes is being further discussed .
In this study, bacterial biocontrol agents against the phytopathogen Lasiodiplodia theobromae were screened from Thua Nao, a Thai fermented soybean product. A total of 170 bacterial strains were isolated and initially screened for their antagonistic activity by dual culture test. Of these, 39 isolates were able to inhibit the fungal growth showing the percentage of inhibition ranging from 25.0–67.5. Among them, the isolate TN79 was selected as a potential antagonistic strain for further study. For this, the bacterial strain TN79 was cultured on nutrient agar for 2 weeks and its crude extracts were prepared using phosphate buffÍer pH 7.0. The bacterial crude extracts prepared were active and could inhibit all four fungal strains of L. theobromae. The optimum pH for antifungal activity of the extracts was 7. In addition, the extracts were also active when exposed to the UV light (254 nm) up to 1 hour and to proteinase K treatment (1 mg/ml). The bacterial strain TN79 was then characterized in terms of their phenotypic and genotypic properties including morphology, biochemical profiles, and rRNA gene sequence. Based on this analysis, the bacterium TN79 was closely related to Bacillus velezensis.
Six potential isolates of Bacillus and Pseudomonas (out of 20 isolates screened under green house assay) were evaluated under pot and field conditions for the biocontrol of wilt disease complex of pigeonpea caused by Heterodera cajani, Meloidogyne spp. and Fusarium udum . Isolate Pa324 was found best for the biocontrol of wilt disease complex of pigeonpea followed by B18, Pf18, Pa70, Pa116 and B160 under pot condition. Isolate Pa324 caused greater reduction in multiplication of M. incognita and H. cajani and also reduced wilting caused by F. udum . Isolate Pa324 produced greater amount of siderophores followed by Pf18, Pa70 and Pa116. Isolate Pa324 showed greater hydrogen cyanide and indole acetic productions than other isolates. Moreover, seedling growth was higher when seeds were treated with Pf18 followed by Pa324, Pa116, B160 and B18. Isolate Pf18 caused a similar increase in seedling growth as was caused by Pa70. Under field condition too isolate Pa324 was best in reducing wilt disease complex followed by B18. Combined use of Pa324 with B18 provided better biocontrol of wilt disease complex than the use of either of them. Application of these isolates (Pa324 and B18) with Rhizobium sp. caused about 30% increase in yield under field condition and provided substantial protection against wilt disease complex of pigeonpea.
Isolates of Pestalozzia theae Saw. and Trichoderma spp. were collected from Bangladesh Tea Research Institute (BTRI) farm area, Bangladesh. The cultural morphology and antagonistic potentiality of Trichoderma spp. against grey blight pathogen Pestalozzia theae was studied for tea cultivation. The antagonistic potentiality of Trichoderma spp., against Pestalozzia theae showed maximum (inhibition 84.45±0.77%) after 72 hrs of inoculation under in vitro condition followed by 76.02±3.50% after 24 hrs of inoculation. This study revealed that Trichoderma strain was highly effective to control Pestalozzia theae, the causal agent of grey blight disease of tea.
References 1. Brewer , M. T. , Larkin , R. P. ( 2005 ) Efficacy of several potential biocontrol organisms against Rhizoctonia solani on potato . Crop Prot
Elad, Y., Bhardwaj, S., Nitzani, Y., Rav-David, D. (2002): Biocontrol of Sclerotinia sclerotiorum by Trichoderma spp. resistance-inducing isolates as modified by spatial, temporal and host plant factors. Bulletin-OILB/SROP , 25 , 17
preparation and formulation on survival and biocontrol efficiency of Pseudomonas fluorescens F113 Y.J. Appl. Microbiol. 86 :108–116. O’Gara F. Effect of inoculum preparation and
