Erwinia Chrysanthemi - Management

Management

D. dadantii is member within the genus that is able to produce the pigment indigoidine, also known as indigo carmine. Rapid identification of this species utilizes this water insoluble blue pigment appearing in the bacterial colonies as a chemotaxonomic trait. The presence of a soft rot may be an indication of a bacterial disease. However many other organisms and plant disorders may appear as various soft rot or black lesions. Proper identification is important for treatment and control measures. Thus a differential media is used to culture Dickeya species and isolate or identify D. dadantii. Researchers at Fu Jen Catholic University in Taiwan developed a medium that differentiates D. dadantii from other species. This NGM media contains nutrient agar (NA) and glycerol medium supplemented with MnCl₂ :4H₂O. To make this media mix 23g of nutrient agar, 10ml glycerol (1% v/v), and 0.4g MnCl₂:4H₂O (2mM) to 1.0 liter of water. Note the pH of this media is 6.5 and it has a light brown base color. The proper temperature for culturing D. dadantii is 28 degrees Celsius. A positive result occurs when a bacterial streak produces a brownish blue color on the agar plate. Further isolation and extraction of the indigoidine pigment is possible using the methods described by Chatterejee and Brown.

Currently there are no effective chemical controls for D. dadantii. The most important practices involve lowering the prevelance of disease by proper sanitation of materials, exclusion of infected materials, and avoiding environments condusive to disease. Most important to disease management is exclusion because D. dadantii can move through vegetatively propogated tissues asymptomatically. Therefore, it is important to have certified disease free stock. Some promising biological control research is being done for orchid species. D. dadantii has been studied in commercially valuable Phalaenopsis orchids. Soft rot diseases caused by Dickeya spp is one of the most devastating diseases in orchid production. Orchid growers have used environmental controls to provide the optimum growth conditions for the plants while minimizing the cultivation of the pathogens. Proper control of humidity and air movement combined with clean, high quality water, in a temperature and light regulated facility are the most commonly employed methods for disease prevention. Other biological controls of D. dadantii include symbiotic fungi known as mycorrhiza and possibly transgenic proteins. Transfer of sweet pepper genes coding for ferredoxin like protein and defensin was shown to reduce D. dadantii disease in Phalaenopsis orchids under cultivation. Under controlled conditions, plants with mycorrhizal fungi such as Rhizoctonia solani and Ceratobasidium sp demonstrated resistance to D. dadantii.