Evaluation of essential oils as seed treatment for the control of xanthomonas spp. associated with the bacterial leaf spot of tomato in Tanzania
Journal of Plant Pathology
Danish Seed Health Centre for Developing Countries, Department of Agriculture and Ecology, University of Copenhagen, Hoejbakkegaard, Allé 13, 2630 Taastrup, Denmark; African Seed Health Centre, Department of Crop Science and Production, Sokoine University of Agriculture, P.O.BOX 3005, Morogoro, Tanzania
Bacterial leaf spot (BLS) caused by Xanthomonas spp. is a serious and a major constraint to tomato production worldwide. The seed-borne nature of BLS, the complex nature of the disease, which is caused by different bacterial species and the current ineffective control measures have made the evaluation of alternative control compounds for seed treatment necessary. Therefore, the efficacy of 11 essential oils applied as seed treatments to control Xanthomonas perforans in tomato and the effect on seed germination and seedling growth was evaluated. Seed treatment with oils of eucalyptus (Eucalyptus globules Labill.), rosemary (Rosmarinus of-ficinalis L.) and niaouli (Melaleuca viridiflora Sol. ex Gaertn.) at 2% concentration inhibited the growth of X. perforans in the in vitro assays and consistently reduced the incidence and severity of BLS in planta tests. Negative effects on seed germination and seedling growth were not observed when tomato seeds were treated with the essential oils of eucalyptus and rosemary. Therefore, eucalyptus and rosemary oils can be used for seed treatment to control BLS in tomato. Further investigation is required on the shelf life of these oils, mode of action and their effects on other seed-borne pathogens of tomato and in other crop systems in Tanzania.