Airborne inoculum as a major source of Septoria tritici ( Mycosphaerella graminicola ) infections in winter wheat crops in the UK

The pattern and extent of primary infection by Septoria tritici were compared over a period of 3 years in winter wheat grown at sites with differing histories and from seed stocks obtained in different countries, in the open, under airtight cover and in sterilized soil. Only the airtight cover altered the number of lesions found, substantially reducing it. Lesions were evenly distributed. Lesions were found throughout the autumn and occasionally in the winter and spring on wheat seedlings exposed in trays to the open air for periods of 1 week, then given good conditions for infection to occur. This was true even at a site 0.4 km distant from wheat residues. The results show that the main source of primary infection of winter wheat in these experiments was evenly dispersed and airborne. It probably consisted mainly of ascospores of Mycosphaerella graminicola.