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.
Highlights
Sheath rot complex and grain discoloration of rice (Oryza sativa L.) generally describes t disease which involves brown discoloration or the flag leaf sheath rot and grain discoloration
Pathogenic strains were often isolated from samples with symptoms that include longitudinal brown to reddish brown necrosis 5 mm wide extending the entire length of flag leaf sheath
Eight hundred bacterial stains were collected from rice plants with the sheath rot complex and grain discoloration, of which only 5.3% (43 strains) were pathogenic and majority of this bacteria were saprophytic
Summary
Sheath rot complex and grain discoloration of rice (Oryza sativa L.) generally describes t disease which involves brown discoloration or the flag leaf sheath rot and grain discoloration. The symptoms apparently caused by these agents are similar, preventing reliable diagnosis only based on symptomology (Duveiller et al., 1998; Cottyn et al, 1996a; Zeigler and Alvarez, 1990) This disease is widespread in temperate (Joana et al, 2007) and tropical areas (Cottyn et al, 1996a; Jaunet et al, 1996) and more prevalent in areas where low temperature (and humidity) occur during the rice booting and heading stages (Jaunet et al, 1996) and the disease is especially apparent during the rainy season and the intensity of infection varies from mild to severe
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