Role of inoculum sources in Rhynchosporium population dynamics and epidemics on barley

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Rhynchosporium leaf blotch of barley, caused by the fungus Rhynchosporium secalis, is of increasing importance in world agriculture. It is the most serious disease on winter and spring barley in the UK, causing substantial losses nationally, despite expenditure of £50M per year on fungicides. The disease is difficult to control with fungicides, as the fungus can exist for a long period in the crop without causing symptoms. A severe epidemic may then emerge without warning. The sources of infection responsible for such epidemics are not well understood. We have recently discovered, for instance, that contaminated seed may be an important primary source of the disease. This project aims to clarify the origin and early dynamics of epidemics using molecular techniques (quantitative PCR) that can detect and quantify the DNA of the pathogen in barley plants before symptoms occur. The same techniques can also detect genetic characteristics of the fungus, such as mating type, virulence, and genes responsible for resistance to fungicides. Each season, epidemics will be monitored on both winter (October-sown) and spring (March-sown) barley. Work will also be done on historical spring barley samples archived at Rothamsted over 150 years, and on samples from current crops from at least 10 sites in England, Scotland and Ireland. We aim to study short-term and long-term changes in the pathogen population. Knowledge from this project will be combined with new information from related projects being funded by BBSRC LINK, Defra, HGCA and SEERAD (at ADAS, and in Scotland, SAC and SCRI) to develop guidelines for crop husbandry and agronomic practices to reduce R. secalis population size and genetic variation to achieve sustainable control of rhynchosporium disease of barley.