Cytological observations of infection on Alfalfa leaves of Pseudopeziza medicaginis
苜蓿假盘菌侵染苜蓿叶片的细胞学研究

The infection process of Pseudopeziza medicaginis on leaves of Medicago sativa was observed by using of differential interference phase contrast microscope, and scanning and transmission electron microscope. The results showed that ascospores began to germinate and form germ tube four hours after inoculation. The germ tubes penetrated the host epidermal cells directly and formed infection mycelium in 12h. The infection mycelium reached to nearby epidermal cells, penetrated into mesophyll cells and showed intracellular growth in 24h. The infection mycelium formed initial colony in mesophyll tissue under the epidermal cell in 72h. The mycelium extended within the host tissues in 5 days and gathered to form stroma tissue, from which apothecium and asci were then developed. At earlier stage of infection, the mycelium did not penetrate the host protoplast membranes and cytoplasm. With mycelial extension in host tissues, a series of alterations occurred in host tissues, including swelling of mesophyll cells, degeneration of cytoplasm, disintegration of organelles such as chloroplasts and collapse of host cells, resulting in appearance of brown necrotic spots on the infected host leaves.