Biocontrol of Pseudomonas syringae pv. syringae affecting citrus orchards in Tunisia by using indigenous Bacillus spp. and garlic extract

Citrus blast and black pit that became increasingly important bacterial diseases are caused by Pseudomonas syringae pv. syringae . This study aimed to evaluate the antibacterial potential of Bacillus species strains and garlic extracts against two P . syringae isolates (BAT13 and DAPP-PG115). The Bacillus species strains were isolated from symptomless citrus leaves. Under in vitro conditions, 21 Bacillus species strains and garlic extract displayed antibacterial activity against the pathogen. Under greenhouse conditions, antagonistic bacteria, garlic extract, and copper sulfate confirmed their antimicrobial effect on P . syringae and reduced significantly the extend of stem necrosis 10 weeks after inoculation by BAT13 up to 60.55, 56.11, and 45.83%, and by DAPP-PG115 up to 70.83, 62.5, and 46.52%, in respect to relevant treatments. Garlic extract was the most effective treatment in our hands, and it suggests that Allium sativum extract could be used to control and prevent infection by the pathogen.