Modelling the effect of temperature on the development of Polymyxa betae

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