First Report of Bacterial Stalk Rot of Maize Caused by Dickeya zeae in Mexico

A bacterial disease of maize, bacterial stalk and top rot, was found in the state of Morelos in February 2011, and in the state of Puebla in July 2013, Mexico. In both cases, the incidence of diseased plants was lower than 0.5%. The typical symptoms were a soft rot and darkening of the tissues affecting the stalk and the top of the plant, causing breaking of the stalk. The lesions progressed from the top to below nodes, leaf sheaths and blades, and rotten tissues emitted an unpleasant odor. Eleven diseased plants were collected, and bacterial colonies were isolated from fragments detached from the edges of symptomatic tissues after sterilization with a 0.5% solution of NaClO for 30 s, rinsing three times in sterile water. The sterilized fragments were macerated in drops of distilled sterile water for 10 min and the extract was streaked on King's medium B (agar 15 g, distilled water 1,000 ml, proteose peptone 20 g, K2HPO4 1.5 g, MgSO4·7H2O 1.5 g, glycerol 10 ml). Eight representative strains from Morelos a...