LAUSR

Abstract Bacillus velezensis XT1 is a halotolerant bacterium isolated from a saline habitat in Spain. The objective of this work was to evaluate its plant growth promotion capacity on horticultural crops and its in vitro antifungal activity. The biochemical properties related to both of these characteristics were identified. When applied directly in the soil, strain XT1 significantly increased aerial fresh weight of tomato, pepper, pumpkin and cucumber plants by 53%, 63.6%, 129.2% and 100.8%, respectively, as compared to the control. Plant height, number of flowers and number of fruits increased more significantly in tomato plants treated with strain XT1. Under sterile conditions, strain XT1 significantly increased shoot and root biomass, height and number of leaves of tomato plants showing that its plant growth-promoting properties were independent of soil microbiota. In greenhouse and field experiments, addition of strain XT1 increased aerial biomass between 37 and 43.8% and height of tomato plants by 20.1 and 22.2%, respectively. Metabolic features associated with the properties of strain XT1 included nitrogen-fixing capacity; organic and inorganic phosphate solubilization; siderophore production, enzymes (e.g. urease and 1-aminocyclopropane-1-carboxylate deaminase) and volatile metabolites (such as acetoin and 2,3-butanediol). It produced endospores, had a high motility, synthesized high yields of exopolysacharides and formed biofilms. Strain XT1 displayed in vitro antifungal activity (over 40% of mycelium inhibition) against the phytopathogens Alternaria alternata, Fusarium oxysporum, Monilinia fructicola, Magnaporthe oryzae, Thanatephorus cucumeris and Sclerotinia sclerotiorum. All the characteristics described above showed a high potential of Bacillus velezensis XT1 to be used in agriculture.