Observations on the Origins of Septoria nodorum Infection of Winter Wheat

SUMMARY In field experiments with winter wheat in Hertfordshire, seed infection with Septoria nodorum and the incorporation of infected straw into seedbeds were often correlated with reduced seedling establishment and increased seedling infection. Artificially infected straw was a less effective source of inoculum than naturally infected straw, which gave rise to the most severe leaf symptoms in one season when heavy rain favoured the development of an epidemic. In an experiment where a severe epidemic did not develop, organomercury seed treatment was the most important factor increasing seedling emergence and grain yield, also apparently leading to decreased Septoria infection of the flag leaf sheath. Spores from lesions which developed after plots were sprayed with a suspension of pycnidiospores of S. nodorum were not always morphologically typical of that species.