Abstract:

The cytology of interactions between poplar cultivars and leaf rust (Melampsora larici-populina Kleb.)with different compatibilities were observed using electron microscopy at various times after inoculation. The results are as follows:(1) In non-compatible combination, the infection structure of the hypha was restrained in different ways. In medium resistant species or hybrids with the hypha were slightly restrained, and the extending area was relatively large. As compared with susceptible species, there were more vacuoles and lipid body in the hypha, and the hypha became more the electron dense. Species or hybrids with a high ability of resistant were similar to the medium resistant ones, but the number of hypha was smaller with more hypha deformity, darker in electron dense. Compare with resistant species, hypha deformity in near immune species or hybrids was more serious, and the cell wall of hypha were thicker, hypha became darker, the vacuole was larger, some of the organelles disintegrated, and hypha cells were dead or near dead.(2) The restrain and death of haustorium in all incompatible combination were similar. All the haustoria showed deformity and darken, with irregular form and with more black grains on the plasmallemma. (3) The reaction of host cells to pathogen was different in different compatible combinations. When rust hypha grew in the intercellular spalls between cells or along the cell wall, the cells of mesophyll maintained in normal state within the susceptible species. In the resistant combination, the cell wall became thicker when contacted with hypha, and papilla formed to restrain the infection. There were some black deposit between cell wall and membrane. Nucleus, mitochondria, and golgiosome gathered around the haustorium. Chloroplast deformed, starch grain became smaller and disappeared. The tonoplast membrane broke and some dark grains deposited on it, and all other organelles disintegrated, granulated or vacuolized, and then died. Cells adjacent to the infected cells were normal in medium resistant species, cell disintegration and death were common in resistant and immune species, and cells adjacent to the infected cells disintegrated or died to different level. (4) The death of haustorium was earlier than the death of host cell. When haustorium deforming or in necrosis, organelles in the host cell were still normal. With the developing of infection, the necrosis occurred to haustorium and host cells. The host hypersensitive necrotic reaction was similar to other rust fungi.

Key words: Melampsora larici-populina, Poplar, Resistance, Ultrastructure, Cytology