Comparative infection and sensitivity studies of Microdochium nivale, Microdochium majus and Zymoseptoria tritici for a better understanding of the field performance of fungicides
In recent years outbreaks of Microdochium leaf blotch have hit wheat farmers in Germany and other European regions unexpectedly. Symptoms were frequently following cool and wet weather periods usually associated with Zymoseptoria tritici and commonly observed on upper leaves of fungicide treated fields. Little is known on the epidemiology of Microdochium leaf blotch, caused by the Microdochium nivale and Microdochium majus. The species are usually associated with pink snow mold and are part of the Fusarium Head blight complex. The leaf symptoms are easily confused with those of Z. tritici. The species M. nivale and M majus typically occur as a complex with a dominance of one or the other and reliable quantification is possible by molecular detection (qPCR).
Since the outbreaks are observed rather in fungicide treated fields than in untreated a first association is with loss of fungicide sensitivity. To untangle the complex of species and their role for symptom development comparative infection studies were carried out with isolates of Z. tritici, M. nivale and M majus. Starting with similar favorable conditions the microscopic studies revealed fundamental differences between Z. tritici and the Microdochium species in in the time for symptom development and considerable differences during early infection between M. nivale and M majus. Different systems for sensitivity testing were established to investigate the role of fungicide resistance for the observed outbreak of Microdochium leaf blotch. The focus was on the two DMI fungicides Prothioconazol and Prochloraz.
In summary, despite differences in fungicide sensitivity the outbreaks in the field rather relate to a different infection biology than fungicide resistance. Still the development of sensitivity towards DMI fungicides must be monitores attentively and the epidemiology M. nivale and M majus and the role of leaf infection in the life cycle needs further investigation.