Visual disease and PCR assessment of stem base diseases in winter wheat

Stem base disease (eyespot, sharp eyespot and brown foot rot) was assessed visually and by the polymerase chain reaction (PCR) technique on single pla nts sampled at four-week intervals in two crops of winter wheat grown in th e UK in 1992-3. PCR assays were conducted for Fusarium avenaceum, F. culmor um, both varieties of Microdochium nivale, both eyespot-causing species of Tapesia and Rhizoctonia cerealis. PCR diagnoses were compared with visual d iagnoses at each time point. Eyespot was caused principally by T. acuformis (R-type) and developed rapidly late in the season. Visual diagnoses of eye spot were largely confirmed by PCR but T. acuformis was detected in many pl ants lacking eyespot symptoms. R. cerealis was detected at relatively low i ncidences on both sites, and sharp eyespot visual diagnoses did not correla te with the incidence of any of the pathogens assayed by PCR. Brown foot ro t, caused principally by Microdochium nivale var. majus, accumulated earlie r in the season than eyespot. Overall, visual diagnoses of stem base diseas e coincided poorly with PCR data until after growth stage (GS) 30.