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The effect of double-stranded (DS) RNA on Monosporascus cannonballus culture morphology and virulence
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Attempts to eliminate double-stranded (ds) RNA elements in Monosporascus cannonballus by subculturing on PDA amended with various concentrations of cycloheximide (O to 15 pg/ml) and incubating at elevated temperatures were partially effective. Elevated incubation temperature (37'C), but not cycloheximide, resulted in a change of dsRNA banding profiles in one isolate (TX 93-449') of M. cannonballus. Some of the subcultures lost all dsRNA fragments, while others lost or gained specific fragments. The dsRNA-cured subcultures were used for comparison in their culture morphology and virulence on muskmelon (Cucumis melo) with a dsRNA-free, wild type M.cannonballus isolate. The dsRNA-cured subculture reverted to a dsRNA-free, wild type phenotype both in culture morphology and virulence. Typically, dsRNA' isolates exhibit a degenerated culture morphology, manifested as an uneven and retarded growth rate, reduced number of perithecia, and the development of a specific yellow to brown pigment. However, the dsRNA-cured subculture grew equally fast, produced a normal number of perithecia, and did not develop any pigment, which is similar to behavior of the dsRNA-free, wild type M cannonballus isolate. Also, pathogenicity tests conducted under greenhouse conditions revealed thatthe dsRNA-cured subcultures were equally virulent on muskmelon as the dsRNA-free, wild type isolate. In addition to the elimination of dsRNA from one isolate, dsRNA from a dsRNAcontaining isolate was transferred to a dsRNA-free, wild type isolate via hyphal anastomosis. Random amplified polymorphic DNA (RAPD) markers were developed for each strain and were used to confirm the transfer. The new dsRNA-containing isolates (TX 90-25 +44') resulted in the development of typical degenerated culture morphology and hypovirulence to muskmelon. The occurrence of two different mycelium interactions among isolates of M. cannonballus was observed. In a macroscopic study, one interaction was considered as vegetatively compatible and was characterized by lack of a distinctive mycelium interaction zone. The other reaction was considered as vegetatively incompatible and was characterized by the presence of a dense mycelium interaction zone. However, in the microscopic study, no difference was detected among the different interactions as anastomosis apparently occurred in both compatible and incompatible interactions.
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Includes bibliographical references: p. 88-94.
Issued also on microfiche from Lange Micrographics.
Park, Yunjung (1996). The effect of double-stranded (DS) RNA on Monosporascus cannonballus culture morphology and virulence. Master's thesis, Texas A&M University. Available electronically from
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