ObjectivesPlant growth promoting rhizobacteria (PGPR) can promote plant growth, control disease and improve the crop yield, and have some advantages with environmental compatibility, no-resistance, lasting stability, and so on. Screening efficient multi-functional bacteria, researching on the mechanism of disease control and promoting growth have very important theoretical and realistic significance for development prevention and control microbial technology for garlic soil borne disease and the garlic industry of " high-yield, high-quality, high efficiency, ecology, safe”.

Methods In this study, seventy bacteria of prophase isolated from the rhizosphere of garlic in Jinxiang county of Shandong province were tested to screen bacteria with the ability of inhibiting the pathogenic fungi (Fusarium sporotrichioides) ACCC37402 and (Alternaria sp.) D14011-1. Bacteria were identified by 16S rDNA sequence analysis. The antagonistic characterizations were studied by measuring the sensitivity to antibiotic, the capability to hydrolyze proteins, the production of siderophore and hydrogen cyanide (HCN). The promoting characterizations was studied by measuring the ability to fix nitrogen and solubilize phosphate, and the production of indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The greenhouse pot experiments were set up to study how the multi-functional bacteria and axenic fermentation extracts effect on the garlic seedling growth and disease resistance.

ResultsThe bacterium DD3 was screened for antagonistic activity against the pathogenic fungi ACCC37402 (Fusarium sporotrichioides) and (Alternaria sp.) D14011-1, it showed antifungal index value of 45% inhibition to both pathogenic fungi. This strain was identified as Bacillus sp. based on 16S rDNA sequence analysis. Other functional characterizations’ results showed that the strain Bacillus sp. DD3 had the ability to proteolysis, the production of hydrogen cyanide (HCN) and siderophore, nitrogenase activity, and phosphate solubilizing ability. But, the strain DD3 did not present the sensitivity to ampicillin sodium, kanamycin sulfate and other eleven kinds of antibiotics. It produced the indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. In greenhouse experiments, 80% garlic plants inoculated with strain Bacillus sp. DD3 showed positive effect of prevention and control of root rot. Inoculation with both bacterial suspension and axenic fermentation of strain Bacillus sp. DD3 liquid promoted the growth of garlic seedlings, and the inoculation of strain Bacillus sp. DD3 suspension provided the optimum result.

Conclusions Bacillus sp. DD3 with multifunctional characterizations showed antagonistic effects to garlic root rot and growth promoting of garlic seedlings. Therefore, Bacillus sp. DD3 has the potential to be developed as microbial fertilizer.