Control of Potato Bacterial Soft Rot Disease Caused by Erwinia carotovora subsp. carotovora with Streptomyces sioyaensis and Cinnamon Oil

SOFT rot of potato is one of the most important diseases caused by Erwinia carotovora subsp. carotovora. Possibilities of its biological control were investigated by the use of some actinomycetes antagonists for controlling E. carotovora subsp. carotovora. A total of 40 different actinomycetes strains were isolated from the rhizosphere soil of healthy potato plants collected from different localities of Dakahlyia Province, Egypt. These were then tested, in vitro, for their antibacterial activity against E. carotovora subsp. carotovora using an agar disc method. Eight isolates were active against E. carotovora subsp. carotovora and the most active isolate was selected for further tests and characterized by conventional methods. Morphological, physiological and cultural characterization of the most active isolate established that it was closely related to Streptomyces sioyaensis.
On the other hand, 28 commercial plant essential oils were screened, in vitro, to evaluate their inhibitory activities against E. carotovora subsp. carotovora. Nine out of 28 oils exhibited considerable inhibitory activities and the oil of Cinnamomum zeylanicum (cinnamon oil) was the most active.
Controlled bacterial soft rot of potatoes were carried out with S. sioyaensis and cinnamon oil in greenhouse experiments. Treatment of potato tubers with S. sioyaensis or cinnamon oil either individually or in combination, caused significant decrease in the percentage of soft rot disease at harvest time and after storage compared with control treatment. Different formula of S. sioyaensis (powder, suspension and granules) showed different effects on reducing disease incidence. Powder formulation of S. sioyaensis showed the highest reduction in disease incidence at harvest time and after storage. Increasing dose of S. sioyaensis in granules formula enhanced its efficacy in reducing disease incidence of potato tubers.