Microscopic and Transcriptomic Comparison of Powdery Mildew Resistance in the Progenies of × .

Powdery mildew is a widespread disease in rapeseed due to a lack of resistant germplasm. We compared the foliar epidermal features and transcriptomic responses between the resistant (R) and susceptible (S) plants among the two parents and progenies of × . The amount of cuticular wax and callose deposition on the R plants was much lower than that on the S plants; hence, these chemicals are not all essential to pre-penetration resistance, although the cuticular wax on the R plants had more needle-like crystals. A total of 1049 genes involved in various defense responses were expressed differentially among the R/S plants. The expression levels of two well-known susceptibility genes, and , were much lower in the R plant, indicating an important role in PM resistance. A set of genes related to wax biosynthesis (, , and ), cell wall modification (, , , and ), chloroplast function (, , , and ), receptor kinase activity (, , , , , , , and ), , , and were highly expressed in the R plants. In the S plants, most highly expressed genes were involved in later defense responses, including , , , , , , and and the genes involved in salicylic acid-dependent systemic acquired resistance and hypersensitive responses, indicating the occurrence of severe fungal infection. The results indicate that some uncertain pre-penetration defenses are pivotal for high resistance, while post-penetration defenses are more important for the S plant survival.