Gums induced in tulip (Tulipa gesneriana L.) bulbs by Fusarium oxysporum f. sp. tulipae elicit bikaverin in the mycelium of the pathogen

The Fusarium oxysporum fungus under some stress conditions produce secondary metabolites including naphthoquinone pigments. One of such stressors/elicitors are tulip gums. It is interesting to mention that tulip gums induced red pigment synthesis by Fusarium oxysporum pathogenic for tulip bulbs but did not elicit the red pigment formation through mycelium of F. oxysporum f. sp. callistephi, F. oxysporum f. sp. dianthi and F. oxysporum f. sp. narcissi. The purpose of this study was to determine the chemical structure of the red coloured pigments occurring in F. oxysporum f. sp. tulipae elicited by tulip gums. In present research the red colour pigment was analysed and its composition was confirmed by UV and mass spectrometry to include bikaverin and norbikaverin as predominant components. Concentration of total bikaverin and norbikaverin was quite high and was increasing during the incubation period from 3.58 mg after 7 days of incubation up to 5.64 mg per 100 mg of mycelium dry matter after 15 days cultured on tulip gum solution. Due to the interest in naphthoquinone pigment application in pharmaceutical drug development, industrial application and agriculture, this finding may be the base for development of alternative processes of bikaverin synthesis. On the other hand, since this mechanism was observed only for Fusarium oxysporum pathogenic to tulips physiological role of these compounds in tulips would be of great interest.