The photosensitization of the plant pathogen Fusarium culmorum by phenylheptatriyne from Bidens pilosa

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Abstract
The photosensitization of the cereal pathogen F. culmorum by phenylheptatriyne (PHT), a naturally occurring acetylene of B. pilosa L. (Asteraceae), was investigated. PHT strongly inhibited germination of macroconidia (mean effective concentration (EC50) = 1.7 ppm) and growth of mycelia (EC50 = 5.6 ppm) of F. culmorum in the presence of near-UV radiation. Photosensitization of macroconidia was found to be fungicidal and was not reversed after repeated washings in PHT-free media. Photosensitization was less apparent in germ tube elongation in liquid media. However, nonphotosensitizing growth inhibition was observed in these trials. Endogenous levels of PHT in B. pilosa were highest (up to 450 .mu.g/g fresh weight) in all plant parts during the seedling stage ad declined during vegetative growth. The concept that PHT acts as a preinfectional inhibitor to F. culmorum is discussed.