Identification, distribution and characterization of pathogenic bacteriaassociated with rice grain discoloration and panicle blight disease in Mazandaran province

In recent years, with the increase in cultivation of improved rice cultivars, grain discoloration and panicle blight disease have prevailed in most paddy fields. Disease symptoms include browning of palea and sterility of seeds on panicles. The causal agents are complex and a variety of bacteria and fungi are associated with the disease. The disease can be observed on local and improved cultivars with different degrees of incidence and severity. In field surveys, improved cultivars, such as Neda, Fajr and Shiroodi, have shown higher infections than Tarom as a local cultivar. In order to study the bacteria associated with the disease comprehensive sampling was conducted in several paddy fields in Mazandaran province for two years. Pathogenic bacteria were isolated from the samples on Pseudomonas agar F and Nutrient Agar mediua. They were identified based on physiological and biochemical tests. There were possible associations between one to three species of pathogenic bacteria with grain discoloration. Pantoea ananas, a dominant species, Pseudomonas syringae, a species similar to Pseudomonas fuscovaginae and Acidovorax avenae subsp. avenae were present in most of the samples. In the pathogenicity test on rice cultivars, improved cultivars were more susceptible than native cultivars. Also, P. syringae and P. fuscovaginae caused more infections than P. ananas on rice. Also, Acidovorax avenae subsp. avenae caused mild grain discoloration and rachis and rachila rot. This is the first report on the isolation and identification of P. ananas and A. avenae subsp. avenae as causal agents of grain discoloration of rice in Iran.