Agrochemicals are important tools for safeguarding plants from invasive pathogens, insects, mites, and weeds. How they may affect the plant microbiome, a critical component of crop health and production, was poorly understood.
One hundred eighty four strains of Ralstonia solanacearum isolated in 2007 and 2008 from 11 tobacco fields in North Carolina were evaluated for genotypic diversity and aggressiveness. All strains were race 1, biovar 1, and belonged to phylotype II. Genetic diversity of the strains was assessed with the use of repetitive sequence-based polymerase chain reaction. DNA primers (REP, ERIC, and BOX) were used to generate genomic fingerprints. Both REP and BOX revealed 3 patterns: A r , C r , and D r and A b , C b , and D b , respectively. Five patterns were identified with ERIC-PCR. Pattern A e was found in 80% of the strains collected. Pattern B e was in 4%, pattern C e in 13%, pattern D e in 2%, and pattern E e in 1% of the strains collected. Cluster analyses showed that the strains were 88% similar and constitute a rather homogeneous group. Aggressiveness of strains was evaluated on 3 tobacco cultivars with different levels of resistance to bacterial wilt. Overall, aggressiveness depended on the field from which the strains were collected. Within a field there was a significant difference (P , 0.0001) in aggressiveness among strains. Differences in aggressiveness were significantly associated (P , 0.0001) to genotypic patterns. In fields where patterns A and C were found, strains of pattern A were the most aggressive, whereas in fields with patterns B, C, and E, strains of pattern E were the most aggressive.
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