DIFFERENTIAL TROPISM TO LIVING AND DEAD CEREAL ROOT HAIRS BY THE BIOCONTROL FUNGUS IDRIELLA-BOLLEYI

Video microscopy was used to study the orientation of spore germination and germ-tube growth on root hairs of aseptic cereal seedlings. Germ-tubes of Idriella (Microdochium) bolleyi emerged away and grew away from living wheat and oat root hairs, but towards dead root hairs which were rapidly overgrown and penetrated. I. bolleyi also germinated away from adjacent glass fibres, cotton fibres and touching spores of itself, Gliocladium roseum or Clyindrocarpon sp. On wheat, Fusarium oxysporum f. sp. lycopersici, Gliocladium roseum and Geotrichum candidum showed lesser and contrasting responses compared with I. bolleyi: F. oxysporum orientated slightly towards living and away from dead root hairs, G. candidum orientated slightly towards both living and dead hairs, and G. roseum showed no significant orientation. Also, these fungi did not proliferate on dead root hairs. The tropic responses of I. bolleyi are consistent with its role as a weak parasite of cereals and its ability to control cereal root pathogens by competitive exclusion from naturally senescing host tissues. © 1992.