Bacillus isolates as potential biocontrol agents of Fusarium clove rot of garlic

Clove rot caused by Fusarium spp. is a very important disease of common garlic (Allium sativum L.) occuring in many areas of the world. However, there is a lack of data about biocontrol of these pathogens. Bacillus species are attractive for research due to their potential use in the biological control of fungal diseases. The aim of this study was to select effective biocontrol agents from a series of indigenous Bacillus spp. isolated from soil. Bacterial isolates positive for hydrolytic enzymes production were screened for antifungal activity against Fusarium spp. isolated from infected garlic cloves. Polymerase chain reaction (PCR) analyses were used for molecular identification of bacterial (16S rDNA gene) and fungal (EF-1 alpha gene) isolates, and detection of biosynthetic genes for antimicrobial lipopeptides (surfactin, iturin, bacillomycin D and fengycin) in Bacillus spp. The obtained results confirmed the presence of Fusarium tricinctum, F. oxysporum f. sp. cepae, F. proliferatum, F. acuminatum and F. verticillioides as the causal agents of garlic clove rot. Four bacterial isolates identified as Bacillus subtilis exhibited the highest antagonistic effect during in vitro testing of antifungal activity (up to 71% reduction in fungal growth), and caused a significant suppression of garlic clove infection (up to 58% reduction in rot symptoms) in situ. Analysis of the antifungal compounds involved in the antagonistic activity of the examined isolates revealed their ability to produce the antibiotic lipopeptide surfactin. The most effective isolates of B. subtilis could be used as potential biocontrol agents of garlic clove rot