The reaction of Chrysanthemum cultivars to Puccinia horiana and the inheritance of resistance

Summary Four types of reaction of Chrysanthemum morifolium to infection by Puccinia horiana are described. (1) Resistant plants show no macroscopic lesions. Cultivars classified as resistant carry a single dominant gene mostly in a simplex, sometimes in a duplex condition. (2). Incomplete resistance provides good protection but under extreme test conditions some pustules develop slowly. (3) Necrosis inhibits spore formation to a large extent. The progenies of crosses between necrotic and susceptible cultivars are mostly susceptible. (4) Susceptible plants sporulate abundantly.The merits of the three types of resistance are discussed.