Identification of pathogenic bacteria rice seedling in nurseries of Mazandaran Prorince.

In the recent years, occurrence and severity of seedling diseases caused by fungi and bacteria have increased in the world. These diseases have caused serious problems in the nurseries especially nursery boxes. In this study, rice nurseries of different regions of Mazandaran province were surveyed at 3-4 leaf stage in 2005- 2006. Samples with seedling stripes, seedling rot and seedling blight syndromes were collected. From these symptomatic tisues 226 strains were isolated on KB, EMB and NA mediums. Based on the biochemical and physiological features and pathogenicity tests on rice seedlings and germinated seeds, five species belong to three genous were identified as Acidovorax avenae subsp. avenae , Dickeya chrysanthemi , Pectobacterium sp., Pseudomonas marginalis and Pseudomonas sp. From seedlings with brown stripe symptom, 96 Acidovorax avenae strains were consistently isolated and identified. Bacterial seedling stripe was widespread among various cultivars especially local varieties. Also, 80 isolates of two soilborne pathogens species, Dickeya chrysanthemi and Pectobacterium sp., were isolated from rotted seedlings. Bacterial seedling rot was widespread among various cultivars especially improved varieties. Pathogenicity of strains of Dickeya chrysanthemi and Pectobacterium sp. were confirmed on corn seedlings which indicates its host range. From Seedling blight syndrome, two species of Pseudomonas sp. (50 isolates) was consistently isolated and identified as Pseudomonas marginalis (21 isolates) and Pseudomonas sp. (29 isolates). Bacterial seedling blight was widespread among various cultivars especially local varieties. In this study, it is confirmed that seed borne and soil borne pathogens caused important diseases in seedlings. For example 3-4 species from the bacterial causal agents were associated with symptomatic seedlings in nurseries. This is the first report of occurrence of rice seedling blight and rice seedling rot diseases caused by Pseudomonas marginalis ,Pseudomonas sp., Pectobacterium sp. and D. chrysanthemi in rice nurseries of Mazandaran province and Iran.