Modelling the effect of temperature on the development of Polymyxa betae

Polymyxa betae is the fungal vector of beet necrotic yellow vein virus (BNYVV), which is the causal agent of the sugar beet disease rhizomania. The within-season dynamics of the fungus are a crucial factor in the occurrence and severity of rhizomania. Late infection of the host by viruliferous fungi enables host resistance to the virus to develop and hence limits crop damage. A previously published mechanistic model for the dynamics of Polymyxa betae is extended in this paper to incorporate the effect of temperature on the germination of resting spores, and on the latent periods between infection and the production of secondary zoospores and new resting spores. It is shown that, for UK temperature conditions, the effect of sowing date on infection is greater than that of year-to-year variations in temperature associated with a single representative sowing date. The variation in inoculum build-up predicted when temperature data from a range of soil types were used in the model agreed with field observations, where higher levels of infection are observed on sandy soils than on black fen peat soils. The difference was most distinct when daily maximum soil temperature values were used to drive the model rather than rolling 24-hour average values.