The effect of powdery mildew on the cell structure and cell wall composition of red clover

We aim to reveal the cytological mechanisms of interactions between red clover and the powdery mildew causal pathogen and provide a foundation for forage disease resistance breeding, prevention and control. In this study, we characterized powdery mildew resistance in an F2 generation segregating population of a hybrid between a powdery mildew susceptible variety (Minshan red clover) and a resistant variety (“Gannon RPM1” red clover), and determined the changes in cellular structure and cell wall composition of the different populations after infection with powdery mildew. The results showed that disease-resistant red clover increased plant defence against powdery mildew infection by increasing wax production, enlarging upper epidermal cells, promoting cell stratification of palisade cells tissues, compressing palisade cells tissue cell gaps, and increasing leaf thickness. Infestation with powdery mildew increased hemicellulose, cellulose and lignin content while decreasing soluble pectin content. The lignin and hemicellulose content increased gradually with time since inoculation, with disease-resistant material showing the largest increase. Soluble pectin levels in disease susceptible material were significantly lower. The powdery mildew infestation induced physical defence in red clovers, and all components contributed to red clover resistance to powdery mildew.