Detection of Double-Stranded RNA inCeratocystis ulmi

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Abstract
Double-stranded RNA (dsRNA) was detected in USA isolates of C. ulmi [the Dutch elm disease pathogen] by serology and polyacrylamide gel electrophoresis. Molecular weight of dsRNA segments ranged from .apprx. 0.4 to 2.0 .times. 106 daltons. dsRNA segments were present in both more aggressive and less aggressive isolates; however, less aggressive isolates generally possessed more segments. The dsRNA segments that were unique to less aggressive isolates may contribute to diminished pathogenicity, although other unknown factors apparently influence pathogenicity as well. Single-conidial isolates from 1 less aggressive strain were 3 types based on their dsRNA content and cultural characteristics. One segregant type, which contained all 7 segments present in the parent strain, was less pathogenic than a 2nd type containing only 1 segment or a 3rd type having no dsRNA. Whether the dsRNA is of viral origin was not determined. Attempts to detect viruslike particles in semipurified preparations failed.