Double-stranded RNA mycoviruses in Fusarium culmorum and Fusarium graminearum isolates

The presence of double-stranded RNA (dsRNA) elements in Fusarium culmorum and F. graminearum isolates of different origin, and the possible effect of these elements on pathogenicity and toxin production of the isolates were examined. Altogether 40 F. culmorum and 38 F. graminearum isolates were involved in this study, together with F. cerealis and F. pseudograminearum strains. Double-stranded RNA elements indicative of mycovirus infection were detected for the first time in 5 F. culmorum isolates. The isolates originated from the United States, The Netherlands, Australia and Israel. The dsRNA nature of the fragments was proved by RNase, DNase and S1 nuclease treatments. The sizes of the dsRNA elements varied between 0.6-3.95 kbp. A dsRNA element of 3.0 kbp in size was also detected in a F. graminearum isolate came from South Africa. None of the Central-European isolates examined were found to carry such elements. We also examined the mycotoxin producing abilities and pathogenicity of the dsRNA infected isolates. Four of the mycovirus infected F. culmorum isolates produced deoxynivalenol and zearalenone (chemotype I), while one of the isolates came from the USA produced nivalenol and fusarenone X (chemotype II). The dsRNA-containing F. graminearum isolate produced deoxynivalenol and zearalenone. In general, dsRNA-containing isolates were found to be as pathogenic to two wheat cultivars as dsRNA free isolates. RAPD analysis and sequence analysis of a putative reductase gene fragment indicated that dsRNA-containing isolates are scattered among dsRNA free isolates. Further work is in progress in our laboratory to characterize these dsRNA elements by sequence analysis.