Induced systemic resistance and growth promotion in tomato by an indole-3-acetic acid-producing strain ofPaenibacillus polymyxa

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Paenibacillus polymyxa strain CF05, a plant-growth-promoting rhizobacterium (PGPR) showed inhibitory effect on Fusarium oxysporum f. sp. lycoersici in vitro, causal agent of Fusarium-wilt of tomato. In the greenhouse experiments, tomatoes inoculated with strain CF05 promoted the significant growth. Meanwhile, strain CF05 suppressed the Fusarium-wilt with 78.24% in control efficiency, which was similar to the carbendazim treatment. The bacterial culture supernatant was found to have the presence of indole-3-acetic acid (IAA), which could be accumulated throughout the growth. Furthermore, strain CF05 could greatly stimulate the activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) and superoxide dismutase (SOD) in either the absence or the presence of fungal pathogen, and the stimulation stayed throughout the entire experimental assessment. Activities of POD and SOD reached the maximum amount at the second day post-inoculation (dpi) after inoculation while activities of PAL and PPO reached the maximum amount at the third dpi and the fourth dpi, respectively. Moreover, strain CF05 could stimulate the H2O2 and phenol contents in the initial phase after pathogen inoculation. These results suggest that the sustained and timely induction of defence enzymes and accumulation of H2O2 and phenolics treated with P. polymyxa might have contributed to restriction of invasion of fungal pathogen in tomato roots. In summary, P. polymyxa strain CF05, which elicited both plant growth promotion and induction of defence response, could be potential agent to improve the yield of tomato and manage Fusarium-wilt disease.

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