Biological Control of soft rot bacteria of onion in Bangladesh

An investigation was conducted to search antagonistic bacteria as biological control agents of soft rotting bacterial pathogen of onion (Allium cepa L.) in vitro and in storage. Antibacterial activity of previously isolated 91 bacterial isolates was tested in vitro against onion soft rot bacteria Burkholderia cepacia O-15. Two isolates namely, R-15 and E-37 were found antagonistic against onion soft rot bacteria. Isolate R-15 was identified as the genus Bacillus and the isolate E-37 to Lactobacillus sp. Isolate R-15 proved to be a strong antagonist against onion soft rot bacteria was selected for bio-control of onion in storage. That was also effectively reduces the soft rot disease of onion in storage condition. Percentage of disease reduction (PDR) due to treatment with antagonistic bacteria was 72.4% compared to untreated control. It is therefore suggested that this isolate could be exploited as biocontrol agent for onion soft rot in Bangladesh. Bangladesh J. Sci. Ind. Res.56(4), 231-240, 2021

Potential Antagonistic Bacteria against Verticillium dahliae Isolated from Artificially Infested Nursery

As an ecofriendly biocontrol agent, antagonistic bacteria are a crucial class of highly efficient fungicides in the field against Verticillium dahliae, the most virulent pathogen for cotton and other crops. Toward identifying urgently needed bacterial candidates, we screened bacteria isolated from the cotton rhizosphere soil for antagonisitic activity against V. dahliae in an artificially infested nursery. In preliminary tests of antagonistic candidates to characterize the mechanism of action of on culture medium, 88 strains that mainly belonged to Bacillus strongly inhibited the colony diameter of V. dahliae, with inhibiting efficacy up to 50% in 9 strains. Among the most-effective bacterial strains, Bacillus sp. ABLF-18, and ABLF-50 and Paenibacillus sp. ABLF-90 significantly reduced the disease index and fungal biomass of cotton to 40–70% that of the control. In further tests to elucidate the biocontrol mechanism (s), the strains secreted extracellular enzymes cellulase, glucanase, and protease, which can degrade the mycelium, and antimicrobial lipopeptides such as surfactin and iturin homologues. The expression of PAL, MAPK and PR10, genes related to disease resistance, was also elicited in cotton plants. Our results clearly show that three candidate bacterial strains can enhance cotton defense responses against V. dahliae; the secretion of fungal cell-wall-degrading enzymes, synthesis of nonribosomal antimicrobial peptides and induction of systemic resistance shows that the strains have great potential as biocontrol fungicides.

Are there bacterial bioprotectants besides Bacillus and Pseudomonas species?

This chapter discusses the taxonomy of non-Bacillus and Pseudomonas (NBP) bioprotectant strains, including enterobacteria, actinomycetes, Sphingomonas, Methylobacterium, Agrobacterium-Rhizobium and Lactobacillus. The chapter reviews their mechanisms of action against plant pathogens. Sources of isolates and methods of isolation are discussed in building strain collections. The chapter then reviews procedures for screening antagonistic bacteria candidates as bioprotectants using biochemical and molecular markers, including the example of lactic acid bacteria. The chapter then covers strain improvement to increase fitness and efficacy in the field through physiological and genetic manipulation. Since they are essential for commercial development, biosafety issues are discussed, followed by an overview of patented substances and commercialized products. The chapter concludes with a summary and future trends in research on non-Bacillus and Pseudomonas species.

Ocimum basilicum L. associated bacteria with antifungal activity

The presence of pathogens, like fungi, is one of the most important causes of basil crop loss around the world; however, many microorganisms have a crucial role on plant development including protection against pathogenic ones. In the present study, basil associated bacteria were isolated, quantified and preserved. Characterization of isolated bacteria showed 165 Gram positive strains, 152 with bacillary and 13 with coccoid morphology. Later, in vitro antagonism assays were performed, first against Aspergillus spp. and then against Neoscytalidium dimidiatum, Alternaria spp. and Aspergillus spp. Finally, the effect of the isolated bacteria on basil seed germination and first stages of development were carried out. Sampled basil plants, produced around La Paz, Baja California Sur, Mexico, were colonized by known antagonistic bacteria of the Bacillus genus. Bacillus amyloliquefaciens strains were the prevailing species with antifungal activity. Moreover, strains ALMH42, ALMR73 and ALAH91 did not show any deleterious effect on basil seedling development. Biotechnological potential exploration of these isolated strains from healthy basil plants is of great interest for future applications on this and other crops.

The Effect of Salt-Tolerant Antagonistic Bacteria CZ-6 on the Rhizosphere Microbial Community of Winter Jujube (Ziziphus jujuba Mill. “Dongzao”) in Saline-Alkali Land

As the main economic crop cultivated in the Yellow River Delta, winter jujube contains various nutrients. However, soil salinization and fungal diseases have affected the yield and quality of winter jujube. In order to use plant growth-promoting rhizobacteria (PGPR) to reduce these damages, the antagonistic bacteria CZ-6 isolated from the rhizosphere of wheat in saline soil was selected for experiment. Gene sequencing analysis identified CZ-6 as Bacillus amyloliquefaciens. In order to understand the salt tolerant and disease-resistant effects of CZ-6 strain, determination of related indicators of salt tolerance, pathogen antagonistic tests, and anti-fungal mechanism analyses was carried out. A pot experiment was conducted to evaluate the effect of CZ-6 inoculation on the rhizosphere microbial community of winter jujube. The salt tolerance test showed that CZ-6 strain can survive in a medium with a NaCl concentration of 10% and produces indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase. Studies on the inhibition mechanism of pathogenic fungi show that CZ-6 can secrete cellulase, protease, and xylanase. Gas chromatography-mass spectrometry (GC-MS) analysis showed that CZ-6 can release volatile organic compounds (VOCs), including 2-heptanone and 2-nonanone. In addition, the strain can colonize the rhizosphere and migrate to the roots, stems, and leaves of winter jujube, which is essential for plant growth or defense against pathogens. Illumina MiSeq sequencing data indicated that, compared to the control, the abundance of salt-tolerant bacteria Tausonia in the CZ-6 strain treatment group was significantly increased, while the richness of Chaetomium and Gibberella pathogens was significantly reduced. Our research shows that CZ-6 has the potential as a biological control agent in saline soil. Plant damage and economic losses caused by pathogenic fungi and salt stress are expected to be alleviated by the addition of salt-tolerant antagonistic bacteria.

Integrated biocontrol of tobacco bacterial wilt by antagonistic bacteria and marigold

Tobacco bacterial wilt (TBW) is seriously damages the growth of tobacco. There is an urgent need to find a safer and more effective measure to control TBW. In this study, B. amyloliquefaciens ZM9 and marigold powder were applied to the tobacco roots alone or in combination, and the potential inhibition of TBW was assessed. On the other hand, the effects of these treatments on soil physicochemical properties, rhizosphere microbial community and soil metabolites were also evaluated. The results showed that the application of B. amyloliquefaciens ZM9 or marigold powder alone significantly reduced the abundance of R. solanacearum in rhizosphere soil, while the integrated treatment showed the strongest inhibitory effect. Moreover, the integrated treatment can inhibit the secretion of chemoattractants, and affect the change of rhizosphere soil microbial composition. In conclusion, the combination of antagonistic bacteria agent B. amyloliquefaciens ZM9 with marigold powder can enhance the suppression of TBW. Furthermore, B. amyloliquefaciens ZM9 and marigold have synergistic effects on suppressing TBW by regulation soil physicochemical properties, soil metabolites and microbial structure. This study provide a promising strategy for TBW control by integrated applying of B. amyloliquefaciens ZM9 and marigold powder.