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Biological Control of Chili Damping-Off Disease, Caused by Pythium myriotylum.

ABSTRACT: Pythium myriotylum is a notorious soil-borne oomycete that causes post-emergence damping-off in chili pepper. Of various disease management strategies, utilization of plant growth promoting rhizobacteria (PGPR) in disease suppression and plant growth promotion is an interesting strategy. The present study was performed to isolate and characterize PGPR indigenous to the chili rhizosphere in Pakistan, and to test the potential to suppress the damping-off and plant growth promotion in chili. Out of a total of 28 antagonists, eight bacterial isolates (4a2, JHL-8, JHL-12, 1C2, RH-24, 1D, 5C, and RH-87) significantly suppressed the colony growth of P. myriotylum in a dual culture experiment. All the tested bacterial isolates were characterized for biochemical attributes, and 16S rRNA sequence based phylogenetic analysis identified these isolates as Flavobacterium spp., Bacillus megaterium, Pseudomonas putida, Bacillus cereus, and Pseudomonas libanensis. All the tested bacterial isolates showed positive test results for ammonia production, starch hydrolase (except 4a2), and hydrogen cyanide production (except 4a2 and 1D). All the tested antagonists produced indole-3-acetic acid (13.4-39.0 μg mL^-1), solubilized inorganic phosphate (75-103 μg mL^-1), and produced siderophores (17.1-23.7%) in vitro. All the tested bacterial isolates showed varying levels of susceptibility and resistance response against different antibiotics and all these bacterial isolates were found to be non-pathogenic to chili seeds and notably enhanced percentage seed germination, plumule, redical length, and vigor index over un-inoculated control. Additionally, under pathogen pressure, bacterization increased the defense related enzymes such as Peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) activates. Moreover, the treatment of chili seeds with these bacterial isolates significantly suppressed the damping-off caused by P. myriotylum and improved PGP traits compared to the control. In addition, a positive correlation was noticed between shoot, root length, and dry shoot and root weight, and there was a negative correlation between dry shoot, root weight, and seedling percentage mortality. These results showed that native PGPR possesses multiple traits beneficial to the chili plants and can be used to develop eco-friendly and effective seed treatment formulation as an alternative to synthetic chemical fungicides.

SUBMITTER: Hyder S

PROVIDER: S-EPMC8155717 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The in vitro and in vivo efficacy of three biocontrol agents, Trichoderma viride, Pseudomonas fluorescence, and Bacillus subtilis, were tested against Rhizoctonia solani (AG-4) infection compared to two conventional fungicides (Rizolex-T 50%wettable powder and Amistar 25%). Antifungal enzyme activity was assayed in the culture filtrate of the biocontrol agents. The impact of the tested biocontrol agents on the induction of the coriander immune system was investigated against R. solani by assessing the resistance-related enzymes and compounds in biocontrol agent-treated plants compared with the control. The obtained results revealed that all tested biocontrol agents significantly reduced the linear growth of R. solani, and T. viride recorded the highest inhibition percentage. This could be linked to the ability of T. viride to produce higher activities of antimicrobial enzymes, i.e., cellulase, chitinase, and protease, compared to P. fluorescence and B. subtilis. Applying the tested biocontrol agents significantly alleviated pre- and post-emergence damping-off and root rot/wilt diseases of infected coriander compared with untreated plants. The tested biocontrol agents exhibited significantly higher germination percentage and vigor index of the coriander than the tested fungicides. The tested biocontrol agents significantly minimized the reduction of photosynthetic pigments induced by R. solani. In addition, the results showed a significant increase in enzymes/molecules (i.e., phenylalanine, catalase, peroxidase, catalase, superoxide dismutase, phenylalanine ammonia-lyase, phenolics, ascorbic acids, and salicylic acid) involved directly and indirectly in coriander resistance to R. solani. The principal component analysis of the recorded data recommended the role of the high accumulation of oxidative parameters (hydrogen peroxide and lipid peroxidation) and the inhibition of phenolic compounds in the downregulation of coriander resistance against R. solani. The heatmap analysis results revealed that biocontrol agents, especially Trichoderma, enhanced the resistance against R. solani via the stimulation of salicylic acid, phenolics, and antioxidant enzymes. Overall, the data recommended the efficacy of biocontrol agents, especially T. viride, against R. solani infecting coriander plants, which could be an efficient and a safer alternative to conventional fungicides.

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Biological Control of Chili Damping-Off Disease, Caused by Pythium myriotylum.

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