INFECTION OF WHEAT SEEDLINGS BY ASCOSPORES OF TAPESIA-YALLUNDAE - MORPHOLOGY OF THE INFECTION PROCESS AND EVIDENCE FOR RECOMBINATION

The infectivity to wheat seedlings of ascospores from apothecia of Tapesia yallundae grown in vitro was demonstrated for the first time. The infection process from spore adhesion to lesion formation was monitored using low-temperature scanning electron microscopy and was similar to that observed for conidia of the anamorph, Pseudocercosporeila herpotrichoides. Mycelium isolated from lesions was characterized using randomly amplified polymorphic DNA (RAPD) markers and was compared to DNA amplification patterns obtained for parental isolates from which the teleomorph was induced. Recombination was demonstrated in all but one lesion from which mycelium was successfully reisolated. A high proportion of reisolates had unique RAPD profiles, indicative of novel genotypes. The implications for pathogenic variation and the development of fungicide resistance in the field are discussed.