ABSTRACT

Anexperimental investigation was carried out to evaluate the biocontrol efficacyof two Trichoderma species on pathogenic fungi isolated from therhizospheric soil. Experiments revealed the beneficial interactions between thetest biocontrol agents against the isolated pathogenic fungi. Two Trichodermaspecies viz. T. harzianum, and T. virens were assessed fortheir biological control efficiency against ten different pathogenic fungi viz.Alternaria alternata, Chaetomium cochliodes, Cladosporium cladosporoides,Colletotrichum fructicola, Curvularia lunata, Fusarium oxysporum, F.ventrichosum, F. proliferatum, F. solani and Mucor hiemalis. T.harzianum exhibited the highest mycelial growth inhibition against F.solani (71%), followed by C. cochliodes and C. lunata (70%), F.ventrichosum (69%), and C. fructicola (68%). Moderate inhibition wasrecorded against F. oxysporum, A. alternata, C. cladosporioides,and F. proliferatum (58–65%), while the lowest inhibition (44%) wasobserved against M. hiemalis. Similarly, T. virens showed maximummycelial growth inhibition against C. fructicola (80%), followed by F.oxysporum (75%), C. cochliodes and C. lunata (72%), and F.proliferatum (70%). Inhibition against F. solani, A. alternata,F. ventrichosum and C. cladosporoides ranged from 59–68%, whilethe lowest inhibition was observed against M. hiemalis (54%). The studyalso assessed parameters such as the time to colony contact, overgrowth, andplate coverage by the biocontrol agent, pathogen radial growth, resistance, andPakdaman’s Biological Control Index (PBCI). These attributes collectively also revealedthe significant biocontrol efficacy of T. virens and T. harzianumagainst the tested soil-borne fungal pathogens.

Keywords: Dual culture; confrontation; Trichoderma; growth inhibition; pathogenresistance

ABSTRACT

A total of 178 microbial cultures were isolated fromrhizospheric soil, of which 45 cultures were identified as actinomycetes basedon morphology. After primary and secondary screening, the actinomycete GK-121was found to be a potent biocontrol agent for the rice blast pathogen Pyriculariaoryzae. The culture was identified using conventional microscopy, ScanningElectron Microscope (SEM) and molecular characterization of the 16S rRNAsequence, and showed 99% similarity with Streptomyces maritimus, whichwas further confirmed by phylogenetic analysis. The cultureexhibited a 45 mm zone of inhibition during in vitro screening against P. oryzae. The greenhouse experimentfurther proved the effectiveness of the isolate, as the seeds treated with S.maritimus showed very low disease incidence in plants inoculated with thepathogen P. oryzae, whereas untreated seeds showed high diseaseincidence. This is the first report to suggest thatS. maritimus is effective in controlling the rice blast pathogen, P.oryzae, in vitro and in vivo.

Keywords: Rhizosphere,Actinomycetes, Antiphytopathogenic activity, Molecular characterization,Biocontrol

ABSTRACT

An in vitro experiment was conducted during 2018–2020 atBARI, Bangladesh, Gazipur to screen the antagonistic effects of nine fungaland five bacterial antagonists against Sclerotinia sclerotiorum (Lib.) de Bary.White mold disease of mustard is one of the most important diseases of mustard causedby the phytopathogen S. sclerotiorum. Among the fungal antagonist tested, Aspergillusniger 2, A. niger 3, Penicilium sp, Trichodermaharzianum, T. viride and T.             virens were mosteffective in inhibiting 89.35% to 100% mycelial growth of S.sclerotiorum in the dual culture method on PDA medium.Among these antagonist fungi, Aspergillus niger 2, A. niger 3, T.harzianum, T. viride and T.virens were capable of completely stopping the sclerotia formation of S.sclerotiorum. The Culture filtrates of Trichoderma species viz., T.harzianum, T. viride, T. virens completely(100%) inhibited the radial growth of the test pathogen. The highest inhibition ofradial growth of S. sclerotiorum observed with the volatilemetabolites of Trichoderma viride (90%) followed by T. harzianum (89.39%)and T. virens (89.35%). More than 90% ofmycelial growth was inhibited by Pseudomonas sp. and Bacillussubtilis strain B20 in dual culture on PDA medium and alsoeffective in stopping sclerotia formation. In the volatile method, all thetested antagonistic bacteria showed moderate antagonistic effects against S. sclerotiorum. Further study isrequired to develop effective formulation of those biocontrol agents for controllingthis alarming pathogen in field condition in an eco-friendly manner.

Keywords: White mould, Sclerotinia sclerotiorum, Antagonism, Biological control

ABSTRACT

Streptomyces scabieiis a gram-positive soil dwelling actinobacteria, that causes the scab diseasein many plants, especially in potatoes. This causes black blotcheson the tuber that negatively impacts the economic and market worth of potatoes. Plantspecies like Chromolaena odorata andneem are known for their antibacterial potential againstcommon human microflora and agricultural pathogens. Aiming to find naturalsolutions to plant pathogens, the current study analyzes, the antimicrobialeffect of these plant extracts at different concentrations using welldiffusion, MIC and MBC. Combination study was also performed to test thesynergistic antimicrobial effect against Streptomycesscabiei. In addition, another soil dwelling bacteria, Paenibacillus polymyxa, known for its plant growth promotingpotential was also tested against the plant pathogen to understand microbe-microbe interactions through cross streakassay. Both plant extracts showed promising antimicrobial effect against Streptomycesscabiei, however, they showed very less antimicrobial potential against theplant growth promoting bacterium. Moreover, cross streak assay showed that both the bacteriumcoexisted together. Hence, further studies canbe conducted to formulate a biofertilizer containing the two-plantextract in optimum concentrations and Paenibacilluspolymyxa to prevent scab disease and also enhance plant growth.

Keywords: Well diffusion, MIC, MBC, Phytochemical analysis, FTIR analysis, GC-MS analysis.

ABSTRACT

This study was carried out to screen indigenousrhizospheric fungal and bacterial antagonists for their capacity to antagonizecotton root rot pathogen Macrophomina phaseolina (Tassi) Goid. Five fungal strains and seven bacterial strains wereisolated and assessed for their ability to inhibit the growth of M.phaseolina, under in vitro condition. Among them, the isolate fiveof Trichoderma and isolate five of Bacillus have been identifiedas potent antagonistic agents. Best performing isolates were molecularlyidentified as Trichoderma longibrachiatum Accession No. PP800312 and Bacilluscereus Accession No. PP800283.