Spore dispersal of yellow rust (Puccinia striiformis) on winter wheat at early growth stages.

Karsten Dalsgaard Bjerre, The Royal Veterinary and Agricultural University, Denmark.

e-mail: kdb@kvl.dk

The short range dispersal of yellow rust spores was investigated in field experiments at three locations. Spore sources consisted of wheat plants in pots with sporulating lesions. These were placed centrally in field plots grown with wheat and spores were allowed to disperse for 6-14 days. The resulting infection patterns in the field crop were observed as lesion counts within grid cells.

The dispersal from point sources was modeled by simple models assuming radial symmetry and by diffusion models describing two-dimensional dispersal (Stockmarr, 2002). As climatic conditions and wind did vary within the periods of spore dispersal a number of combined models was made. Among others, these could describe effects of two dominant wind directions and effects of (unknown) background spore sources.

It was found that grid-cell infections counts were over-dispersed relative to a Poisson distribution. A number of processes potentially leading to over-dispersion are discussed.