Resistance analysis and improvement of rice varieties by gene pyramiding APPLICATION OF MARKER-ASSISTED SELECTION IN RICE BREEDING Pyramiding Wheat Powdery Mildew Resistance Genes Pm2, Pm4a and Pm21 by Molecular Marker-assisted Selection Comparison of Pathogenicity of Pyricularia oryzae under Different Genetic Backgrounds Resistance of Slow Mildewing Genes to Stripe Rust and Leaf Rust in Common Wheat