Arguments for a low risk of establishment of Karnal bunt disease of wheat in Europe

Abstract

Tilletia indica, which causes Karnal bunt of wheat, has been perceived as a pathogen that has a high risk of establishment in the UK and other countries in Europe. This viewpoint is challenged with arguments for the risk of establishment being much lower. The present distribution of the pathogen and its likely widespread dissemination with consignments of germplasm and wheat seed from Mexico over a 20 year period without establishment outside the hot arid and semi-arid zones strongly suggests that T. indica is unsuited to environments other than those similar to where it is now found. A critical density of teliospores needs to remain viable and ungerminated between periods of wheat anthesis and then germinate during a narrow window of opportunity to ensure infection and establishment. Despite the results of outdoor teliospore longevity experiments, it is by no means certain that this can occur under European conditions. Generally cooler conditions and more frequent periods of rain in Europe are likely to trigger teliospore germination at times unsuitable for infection making establishment much more unlikely. A model based on year-round soil conditions, especially moisture content, is seen as appropriate to predict teliospore survival and germination potential. It is only after areas where teliospores can survive and germinate in sufficient numbers to guarantee regular infection cycles have been defined can another model, based on temperature, rainfall and/or humidity prior to anthesis, be applied to determine if environmental conditions are suitable for infection.