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agent Trichoderma harzianum in soil as influenced by certain herbicides. Indian Journal of Weed Science , 32 , 116–117. Radhakrishnan N. V. Survival of the biocontrol
Five isolates of Trichoderma viride, Pseudomonas fluorescens and four isolates of Bacillus subtilis were evaluated for their ability to control Rhizoctonia solani, the causal agent of stem and stolon rot of peppermint (Mentha piperita Lin.). Of the various isolates of T. viride, P. fluorescens and B. subtilis tested, TVUV10, PFMMP and BSG3 showed the maximum inhibition of mycelial growth of R. solani. Among these isolates, P. fluorescens, PFMMP recorded the highest inhibition zone against R. solani in vitro and was very effective in reducing disease incidence in greenhouse condition. The effective isolates were evaluated for their ability to induce defense related enzymes and chemicals in plants. Increased activity of phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenoloxidase (PPO) and total phenolics were recorded in the biocontrol agents pretreated peppermint plants challenged with R. solani. P. fluorescens isolate PFMMP recorded early and increased synthesis of all defense related enzymes and total phenol. Thus, the present study shows that application of biocontrol agents; induce defense related enzymes involved in phenyl propanoid pathway in addition to direct antagonism which collectively contribute for enhanced resistance against invasion of R. solani in M. piperita.
Fusarium wilt of tomato is one of the most prevalent and economically important diseases of tomato worldwide especially in tropical regions. The aims of the present study were to isolate and characterize Bacillus bacteria from tomato rhizospheric soil of various regions in Iran and determine the isolates that exhibit high levels of antagonistic efficiency against tomato Fusarium wilt pathogen, Fusarium oxysporum f. sp. lycopersici (Fol) and growth promotion activity. In this study, 303 Bacillus isolates were obtained from tomato rhizospheric soil. Dual culture and volatile metabolite tests were used to screen for antagonism of Bacillus isolates against Fol. Among them, 20 isolates were found to inhibit pathogen growth by 67.77% and 33.33% in dual culture and volatile metabolite tests, respectively. Based on the results of physiological tests and 16S rRNA and gyrA gene sequence analysis of 20 effective isolates, 11, seven and two isolates were identified as B. subtilis, B. velezensis and B. cereus, respectively. The results of greenhouse assessment showed that KR1-2, KR2-7 and A2-9 isolates which were characterized as Bacillus subtilis, reduced the disease index to 16.67% and promoted the plant growth by 80%. These isolates may serve as potential promising biocontrol agents against Fusarium wilt of tomato.
Biological control of die-back of bottle brush (Callistemon citrinus) caused by Botryodiplodia theobrome was made with the application of antagonistic agents like Trichoderma viride, T. lignorum, T. harzianum, Aspergillus niger and Penicillium citrinum. The effect of volatile and non-volatile antibiotics of Trichoderma origin on growth inhibition of the die-back pathogen was studied. T. harzianum showed maximum growth inhibition (75.33%) of the pathogen through mycoparasitism and the non-volatiles produced by the same agent exhibited its excellent antagonism to the growth of the pathogen (91.11%) under in vitro condition and that the effect was also proved to be durable.
Downy mildew of maize caused by Peronosclerospora sorghi was significantly controlled by seed treatment and foliar sprays of a talc-based formulation of a Pseudomonas fluorescens strain under greenhouse and field conditions. Leaf extracts of Prosophis chilensis and Azadirachta indica were found to be equally effective as P. fluorescens in controlling maize downy mildew, although the extracts were not as effective at inhibiting conidial germination as the pseudomonad or as metalaxyl. These treatments also suppressed sporulation of P. sorghi on diseased foliage. Enhanced induction of defense enzymes, chitinase and β-1,3-glucanase appeared to be associated with control mechanism and metalaxyl did not show such induction. The reduction in disease incidence under field condition resulted in increased yield. The inhibitory effect of P. fluorescens and extracts of P. chilensis or A. indica make them potential alternatives to metalaxyl for control of maize downy mildew, although their efficacy, practical application and cost needs to be explored in greater detail before they can be incorporated into an integrated pest management programme.
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
Sharma, K., Mishra, A.K., Misra, R.S. 2009. Morphological, biochemical and molecular characterization of Trichoderma harzianum isolates for their efficacy as biocontrol agents. J. Phytopathol. 157 :51–56. Misra
Agricultural use of chemical pesticides has polluted the environment and resulted in resistance among the target organisms. The chemical strategies of pest control are dangerous to both the nontarget organisms in natural habitats and human health. Biological control is an attractive less dangerous possibility for controlling plant pathogens.Some methods of biological control are becoming now commercially available against plant parasitic fungi, nematods and insects. Among filamentous fungi many candidates with biocontrol potential can be found. Fungal biocontrol agents are less effective and reliable than the synthetic pesticides therefore their use in the agricultural practice requires genetic improvement.
Chaetomium globosum Kunze Ex. Fries has been identified as a potential antagonist of Bipolaris sorokiniana and Ascochyta rabiei. Nine isolates of this biocontrol agent were characterized based on RAPD technique using 40 random primers of OPB and OPM series, out of which 24 primers gave a total of 356 amplification products, showing 91% polymorphism. RAPD analysis revealed that C. globosum isolates taken under study formed genetically two distinct clusters, with isolates Cg2, Cg3 and Cg4 in one cluster and the remaining isolates in another cluster, which in turn was grouped separately into two subclusters separating isolates Cg6 and Cg8 from Cg1, Cg5, Cg7 and Cg9. Similarity matrix indicated that Cg1 and Cg2 were genetically distinct as they showed only 29.4% similarity followed by Cg2 and Cg7 showing 31.1% similarity, while isolates Cg7 and Cg9 were found to be genetically similar with 68.9% similarity index.
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.
