Antibacterial Effects of Some Plant Extracts against Tomato Bacterial Speck Disease Caused by Pseudomonas syringae pv. tomato

Bacterial speck disease caused by Pseudomonas syringae pv. tomato (Pst) is the most important seed-borne bacterial diseases of tomato. In this study, the antibacterial activities of aqueous twenty-nine plant extracts were investigated in vitro and in vivo conditions. In in vitro experiments, extracts of Allium sativum, Coriandrum sativum, Eucalyptus camaldulensis inhibited Pst growth with the inhibition zones 3 mm, 13 mm and 13.6 mm, respectively. Minimum Inhibition Concentrations (MIC) values against Pst determination were Eucalyptus camaldulensis 3.75 μl/ml, Allium sativum 4.25 μl/ml, and Origanum onites >128 μl/ml. The effects of Allium sativum, Coriandrum sativum, Eucalyptus camaldulensis, Origanum 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 Allium sativum and Origanum onites extracts. Additionally, no negative effect on seed germination and emergence were recorded for the tested plant extracts as seed treatments. In pot experiments, foliar spraying of Allium sativum, Eucalyptus camaldulensis, Origanum onites, Zingiber officinale extracts were reduced the disease incidence from 96% to 99% ratios, whereas the disease incidence was inhibited as 80-100% ratios by root dipping. Root dipping applications of Allium sativum extract were toxic on tomato plants in both experiments for Pst. As a result, plant extracts are promising for the development of new pesticides in the control of bacterial diseases of tomatoes