Institut National de la Recherche Agronomique, Unité de recherches intégrées en grandes cultures, Le Rheu cedex, France

Tapesia yallundae and Tapesia acuformis are the causal agents of eyespot\ the major foot disease of cereals[ Many authors have suggested that the two species di}er in epi! demiological behaviour\ based on the later appearance of lesions with T[ acuformis than with T[ yallundae[ How! ever\ the reasons for this di}erence in natural conditions are unclear in the absence of a method to distinguish the two species in the plant before the symptoms appear[ Methods of detection visual assessment\ enzyme!linked immunosorbent assay\ polymerase chain reaction "PCR# test and characterization "isolation on arti_cial mediumPCR test# were used to investigate the behaviour of Tapesia spp[ in the _eld under various epidemiological conditions[ The PCR test was used to determine infection dates and to identify the species involved early\ in order to demonstrate that infection occurred at the same time for T[ yallundae and T[ acuformis[ Symptoms of T[ acuformis infection occurred later because the pathogen developed more slowly in the tissues[ A triticonazole seed treatment was used to evaluate the e}ectiveness of the PCR test for estimating fungicidal e}ects[ This molecular tool for determining the period of activity of the chemical and changes in the proportions of the two species of Tapesia involved in the disease was demonstrated to be accurate[ The PCR test either had advantages over or was complementary to the other methods tested[