Powdery mildew is a typical fungal infection in crop plants and only the regular application of fungicides prevent huge yield losses in agriculture. Some crops, however, hold a natural resistance against powdery mildew like cultivars of the European barley with a mutation in the Mlo gene. Scientists from the Max Planck Institute for Plant Breeding Research (MPIZ) in Cologne have collaborated with colleagues from Great Britain, France and Denmark to solve the mystery of the resistance mechanism and to highlight the cultural history of plant breeding (nature, 19.08.2004, cover story).
Plants have - similar to animals and humans - a sophisticated multi-level immune system which enables them to identify parasites and destroy them. The detection of parasites is based on an armada of plant receptors - a plant radar system which signalizes pathogen invasion. To circumvent the immune system, a parasite has to either slip through the plant radar system or affect the cellular immune response following its detection. The mildew chose the latter strategy and therefore manipulates the so called MLO protein in the cell membrane of Barley cultivars that is encoded by the corresponding Mlo-gene in the genome. Although laboratory experiments with mutated mlo-genes confirmed a correlation to the resistance, the detailed genetic analysis revealed no causal differences between the DNA sequence of the mlo gene from resistant and susceptible plants. Thus, the precise mechanism behind this resistance remained unknown.
A specific mlo-resistance-gene recovered from a natural habitat was originally retrieved from Ethiopian landraces, primitive forms of Barley cultivars. They were collected during an expedition in 1937. Nowadays this mutation plays a crucial role in mildew resistance; it was introduced by traditional plant breeding methods into
Contact: Claudia Lorenz