Abstract

In recent years, similar symptoms to sheath rot complex (SH C) and grain discoloration (GD) has been observed in paddy fields in the north of Iran. To survey the etiology of this complex disease, 207 samples of rice plants showing wide range of sheath and grain discoloration were collected during 2002-2005 at booting and ripening stages from various geographical locations in Mazandaran province. Pathogenic strains were often isolated from samples with the symptom of longitudinal brown to reddish brown necrosis 5 mm wide extending the entire length of flag leaf sheath. Over 800 strains were isolated from collected samples and tested for pathogenicity on rice and/or hypersensitivity on tobacco or pelargonium. Pathogenic strains were isolated from 20.28% samples which contained only 5.3%of total strains. Eighty two strains comprising 72 strains from plants showing symptoms of sheath rot and grain discoloration, five strains from diseased seedling and fivestandard strains were analyzed for phenotypic studies. Pseudomonas-specific primers were used to confirm identification of the genus.On the basis of phenotypic characters and genus specific primers, the strains belonged to genera Acidovoraxand Pseudomonas. Cluster analysis of 67 biochemical characters grouped 70 selected strains into seven distinct cluster and six groups with one member. The results confirmed that pathogenic strains associated with SH C and GD in Iran (Mazandaran province) belong to Acidovorax avenae subsp avenae (2.32%),Pseudomonas putida (2.32%), Pseudomonas marginalis (6.65%), Pseudomonas syringae (76.7%) and two unidentified species of Pseudomonas (13.95%). Accordingly, the P. syringae  was revealed that is the major causal agent of SH C and GD in north of Iran.

Key words: Oryza sativa L., bacterial flag leaf sheath rot, Pseudomonas.