Abstract
The studies on the biocontrol potential of pink pigmented facultative methylotrophic (PPFM) bacteria other than the genus Methylobacterium are scarce. In the present study, we report three facultative methylotrophic isolates; PPO-1, PPT-1, and PPB-1, respectively, identified as Delftia lacustris, Bacillus subtilis, and Bacillus cereus by 16S rRNA gene sequence analysis. Hemolytic activity was tested to investigate the potential pathogenicity of isolates to plants and humans, the results indicates that the isolates PPO-1, PPT-1, and PPB-1 are not pathogenic strains. Under in vitro conditions, D. lacustris PPO-1, B. subtilis PPT-1, and B. cereus PPB-1 showed direct antagonistic effect by inhibiting the mycelial growth of fungal pathogens; Fusarium oxysporum f. sp. lycopersici (2.15, 2.05, and 1.95 cm), Sclerotium rolfsii (2.14, 2.04, and 1.94 cm), Pythium ultimum (2.12, 2.02, and 1.92 cm), and Rhizoctonia solani (2.18, 2.08, and 1.98 cm) and also produced volatile inhibitory compounds. Under plant growth chamber condition methylotrophic bacterial isolates; D. lacustris PPO-1, B. subtilis PPT-1, and B. cereus PPB-1 significantly reduced the disease incidence of tomato. Under greenhouse condition, D. lacustris PPO-1, B. subtilis PPT-1, and B. cereus PPB-1 inoculated tomato plants, when challenged with F. oxysporum f. sp. lycopersici, S. rolfsii, P. ultimum, and R. solani, increased the pathogenesis related proteins (β-1,3-glucanase and chitinase) and defense enzymes (phenylalanine ammonia lyase, peroxidase, polyphenol oxidase, and catalase) on day 5 after inoculation. In the current study, we first report the facultative methylotrophy in pink pigmented D. lacustris, B. subtilis, and B. cereus and their antagonistic potential against fungal pathogens. Direct antagonistic and ISR effects of these isolates against fungal pathogens of tomato evidenced their possible use as a biocontrol agent.
Highlights
Tomato (Lycopersicon esculentum) is one of the most popular commercial vegetable crops
Twenty pink pigmented facultative methylotrophic (PPFM) bacteria were isolated from phylloplane of various crop plants (Table S1)
The isolates PPO-1, PPT-1, and PPB-1 exhibited mycelial growth inhibition of Fusarium oxysporum f. sp. lycopersici (2.15, 2.05, and 1.95 cm), S. rolfsii (2.14, 2.04, and 1.94 cm), P. ultimum (2.12, 2.02, and 1.92 cm), R. solani (2.18, 2.08, and 1.98 cm), respectively, in a dual plate assay on day 5 (Table 1)
Summary
Tomato (Lycopersicon esculentum) is one of the most popular commercial vegetable crops. Among the pathogens that affect the tomato crop, soil borne fungal pathogens, including Fusarium, Pythium, Rhizoctonia, and Verticillium causing the root rot or dampingoff and wilt affect the quality with yield reduction (Lucas et al, 1997). In the present study, we have tested the possibility of using facultative methylotrophic bacteria which is ubiquitously occurring with intimate association with plants, as a biocontrol agent in controlling wilt and root rot pathogens of tomato
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