Interaction of virus-infected celery and Septoria apiicola

Inoculation of celery plants with viruses CV036 (celery mosaic) and CV506 (parsnip yellow fleck) decreased blight on leaves inoculated later with Septoria apiicola by 17–39% and 54–91%, respectively. There was a significant negative correlation between the amount of blight and the furanocoumarin content of the celery petioles. The antifungal activity of these furanocoumarins was demonstrated by their in vitro inhibition of the germination of spores of S. apiicola and Botrytis cinerea . Scanning electron microscopy of virus-infected leaves sprayed with spores of S. apiicola also showed slight but significant reductions in percentage germination and in germ-tube length, and considerable reductions in the proportion of germ-tubes which produced an appressorium, compared with spores on virus-free leaves.