Ethylene production from cultures of Cylindrocladium and from Cylindrocladium-infected azalea leaves Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/b8515q88w

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  • Ethylene was produced by Cylindrocladium floridanum and C. scoparium in culture. Production was methionine dependent and maximal during the active growth phase of the fungus, beginning shortly after spore germination. More ethylene was produced sooner by C. floridanum than C. scoparium. Ethylene was produced by Cylindrocladium both from active mycelium (direct) and non-enzymically from culture filtrates (indirect). Both direct and indirect systems were light mediated, and appeared to involve a fungal metabolite, a flavin-like compound (FLC), either contained in the mycelium or secreted into the medium. The FLC in culture filtrates exhibited light absorbing properties similar to flavin mononucleotide, a known cofactor in at least one reported ethylene biosynthetic pathway. Another possible system (either direct or indirect) of ethylene production by Cylindrocladium cultures occurred in the dark, exhibited a production lag, and produced less ethylene than the light-mediated system. Ethylene production by detached Cylindrocladium-infected azalea leaves was first detectable 17-21 hours after inoculation and increased sharply with the onset of lesion formation (22-26 hours). Ethylene production ceased when leaves were completely colonized, possibly indicating that ethylene originated from host tissue. Lesion formation and ethylene production were enhanced by incubating inoculated leaves in the dark rather than the light. In addition, the ethylene produced/unit lesion area was greater in the dark than in the light. These results suggest that dark treatment may enhance host susceptibility and/or pathogen virulence as well as make available a stimulator for ethylene biosynthesis. Lesion area seemed to be unrelated to ethylene production, both in the light and dark, 48-72 hours after inoculation, suggesting that ethylene may only be produced by the host tissue at or ahead of the advancing margins of the lesion. Additional evidence that ethylene production during disease development originated from host tissue include the observation that light incubation greatly enhanced ethylene production by Cylindrocladium cultures, whereas dark incubation greatly enhanced ethylene production by Cylindrocladium-infected azalea leaves. Furthermore, the ability to produce ethylene in culture does not appear to relate to the virulence of C. floridanum or C. scoparium.
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