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Bacterial fruit blotch (BFB) was a serious threat to cucurbitaceae crops. It was caused by the gram-negative bacterium Acidovorax avenae subsp. citrulli . Two hundred strains, which have the potential in controlling plant diseases in our laboratory's biocontrol strain library, were employed to this research to screen some antagonistic bacteria, which can efficiently control bacterial fruit blotch disease. Based on the results of antagonistic activity experiments, greenhouse tests and field trials, 5 of the test strains have high abilities to control BFB. One of the 5 bacteria strains has the highest potential to control BFB named 54. The biocontrol efficacy of 54 was up to 60%. To characterize the strain, we used series of methods to evaluate the bacterium, including morphology analysis, physiological biochemical test and biomolecular assay. We found that the bacterium 54 belongs to the species Bacillus amyloliquefaciens. The colonization test results showed that 54 had the highest colonization levels, and the density of the strain on leaves was up 10 5 colony forming units (CFU) per gram of leaf tissue. Our recent results show that B. amyloliquefaciens 54 can promote the plant growth due to raised the contents of available N, P, K and the leaf chlorophyll. The antagonistic bacterium 54 can significantly control the BF B by increasing the expression level of defense-related gene PR1 and the accumulation the hydrogen peroxide in the plant. The results of trail experiment was also verified this efficient results of bacterium. This is also the first report of B. amyloliquefaciens strain that is able to control BFB. [ABSTRACT FROM AUTHOR]

Drought stress is a major obstacle to agriculture. Although many studies have reported on plant drought tolerance achieved via genetic modification, application of plant growth-promoting rhizobacteria (PGPR) to achieve tolerance has rarely been studied. In this study, the ability of three isolates, including Bacillus amyloliquefaciens 54, from 30 potential PGPR to induce drought tolerance in tomato plants was examined via greenhouse screening. The results indicated that B. amyloliquefaciens 54 significantly enhanced drought tolerance by increasing survival rate, relative water content and root vigor. Coordinated changes were also observed in cellular defense responses, including decreased concentration of malondialdehyde and elevated concentration of antioxidant enzyme activities. Moreover, expression levels of stress-responsive genes, such as lea, tdi65, and ltpg2, increased in B. amyloliquefaciens 54-treated plants. In addition, B. amyloliquefaciens 54 induced stomatal closure through an abscisic acid-regulated pathway. Furthermore, we constructed biofilm formation mutants and determined the role of biofilm formation in B. amyloliquefaciens 54-induced drought tolerance. The results showed that biofilm-forming ability was positively correlated with plant root colonization. Moreover, plants inoculated with hyper-robust biofilm (ΔabrB and ΔywcC) mutants were better able to resist drought stress, while defective biofilm (ΔepsA-O and ΔtasA) mutants were more vulnerable to drought stress. Taken altogether, these results suggest that biofilm formation is crucial to B. amyloliquefaciens 54 root colonization and drought tolerance in tomato plants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bacillus amyloliquefaciens HSSN09 with antagonistic effect on FON was isolated. • B. amyloliquefaciens HSSN09 could effectively control watermelon Fusarium wilt and promote the growth of watermelon seedlings. • Tacrolimus has a very obvious antifungal effect and can be used to control watermelon Fusarium wilt. • Tacrolimus was also able to stimulate the growth of watermelon seedlings. • Tacrolimus or its analogs may play a role as a pleiotropic factor in B. amyloliquefaciens HSSN09 biological control. Watermelon Fusarium wilt caused by Fusarium oxysporum f. sp. niveum (FON) is one of the most devastating diseases in watermelon production. Biological control approaches are efficient and environmentally-friendly, thus have aroused broad interest. However, only a few biocontrol factors/molecules have been characterized due to varied genomes and diversified secreted secondary metabolites of biocontrol microorganisms. We report the screen and identification of a Bacillus amyloliquefaciens strain HSSN09 with high antagonism to FON and watermelon growth promotion capacity. B. amyloliquefaciens HSSN09 and its secondary metabolites showed inhibition on FON mycelial growth, spore formation and spore germination. Metabolomes of the highly antagonistic strain B. amyloliquefaciens HSSN09, medium antagonistic strain B. amyloliquefaciens FGW53, weakly antagonistic strain B. subtilis JC03 and non-antagonistic strain B. cereus FGW109 were compared with LC-MS/MS. By antagonistic assay, tacrolimus was screened out among the 531 molecules that appeared in the sequencing results of HSSN09 metabolome but not in that of the non-antagonistic strain without significant inhibition on the growth of FON. Among the four tested Bacillus strains, tacrolimus analogue was only observed in the supernatant of HSSN09 by HPLC and MALDI-TOF-MS. We further confirmed the ability of tacrolimus to suppress FON and promote watermelon seedling growth. [ABSTRACT FROM AUTHOR]