Investigation of antimicrobial effects of plant extracts on bacterial disease agents of tomato

Bacterial speck disease caused by Pseudomonas syringae pv. tomato (Pst) and bacterial wilt and cancer disease caused by Clavibacter michiganensis subsp. michiganensis (Cmm) are the most important seed-borne bacterial diseases of tomato. In the study, the antibacterial activities of aqueous twenty-nine plant extracts were investigated in vitro and in vivo conditions. In in vitro experiments, A. sativum, C. sativum, E. camaldulensis extracts have shown inhibitiory effect on Pst whereas A. sativum and M. communis extracts were effective on Cmm. The effects of A. sativum, C. sativum, E. camaldulensis, O. onites, Origanum vulgare subs. hirtum and Zingiber officinale extracts on disease incidence and severity caused by Pst recorded 8.8-100% ratios as seed treatments. The most successful seed treatments were A. sativum and O. onites extracts. Additionally, no negative effect on seed germination and emergence were recorded for the tested plant extracts as seed treatments. In pot experiments, A. sativum, E. camaldulensis, O. onites, Z. officinale extracts by spraying were reduced the disease incidence caused by Pst as 96-99% ratios whereas the disease incidence was inhibited as 80-100% ratios by root dipping. The extracts were reduced the disease caused by Cmm as 40-67% and 63-89% ratios by spraying and root dipping, respectively. Root dipping applications of A. sativum extract were toxic on tomato plants in both experiments for Pst and Cmm. As a result, plant extracts are promising for the development of new pesticides in the control of bacterial diseases of tomatoes. Keyword: Tomato, Plant Extracts, Antibacterial Effect, Seed Treatments, Foliage Applications