Identification of antagonistic bacterium Pseudomonas aeruginosa K5 against watermelon fusarium wilt and its role in disease suppression and plant growth promotion

【Objective】Watermelon fusarium wilt, caused by Fusarium oxysporum f. sp. niveum (Fon- 1), is a serious disease that causes significant yield loss and threatens the development of watermelon industry. Effectiveness of chemical pesticides in control of watermelon fusarium wilt is currently not satisfactory. Thus, there is an urgent demand to explore other effective strategies. This study aimed to screen out effective antagonistic strains for biocontrol of watermelon wilt disease.【Methods】Antagonistic bacterial strains were isolated from watermelon rhizosphere soil. The antagonistic effect of the isolated strains on Fon and other pathogenic fungi was detected using a plate confrontation test. Pot experimentswere conducted to investigate the biocontrol capacity of the bacterial strains against watermelon wilt disease. Growth- promoting activity of the antagonistic strains was also explored in terms of plant height, leaf number, dry and fresh weights of both aboveground and underground parts of the plant. The obtained antagonistic bacterial strains were identified using molecular tools and biochemical assays. 【Results】The strain K5 had a significant impact on hyphae in dish, and the inhibition rate of Fon-1 was 75.31%. K5 had a significant inhibitory effect on seven other watermelon and melon crop pathogens in dish. The potted experiments showed that the K5 had a good antagonistic effect on Fon, with a control effect of 78.95%. The pot experiment showed that K5 had a 78.95% control effect on Fon-1, and had a significant growth- promoting effect. The plant heights, leaf numbers, aboveground and underground dry weights, root lengths, and aboveground and underground fresh weights increased significantly, while there was no difference in stem thickness. Analysis of phylogenetic trees showed that the strain K5 was Pseudomonas aeruginosa based on the 16S rDNA and rpob gene sequences. Biological characteristics analysis revealed that K5 produced siderophores and hydrogen cyanide. It also had enzymatic activities such as cellulase, chitinase, and β-1-3 glucanase. Moreover, the genes related to hydrogen cyanide, phenazine-1-carboxamide, and nitropyrrolin were amplified from the K5 genome.【Conclusion】 In summary, K5 had a good control effect on watermelon wilt disease and promoted the growth of watermelon seedlings. It will be a highly potential strain for developing a biocontrol agent.