VIEW ARTICLE

Cytology and Histology

Infection of Alfalfa Pollen by Verticillium albo-atrum. H. C. Huang, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1; E. G. Kokko, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1. Phytopathology 75:859-865. Accepted for publication 21 March 1985. Copyright 1985 Department of Agriculture, Government of Canada. DOI: 10.1094/Phyto-75-859.

Light microscopy and scanning and electron transmission microscopy revealed that alfalfa pollen is susceptible to in vitro infection by Verticillium albo-atrum, the causal organism of Verticillium wilt of alfalfa. Infection occurred after pollen grains were mixed with spores of V. albo-atrum and incubated for 24 hr on potato-dextrose agar media. Hyphae of V. albo-atrum penetrated the exine wall layer with a thin penetration peg without forming appressoria. Penetration occurred more readily through the germinative pores than through other parts of the host wall. During the early stage of hyphal invasion, the pollen showed plasmolysis, breakage of cytoplasmic membranes, and formation of large vacuoles in the cytoplasm. The invading hyphae filled the entire cell lumen by rapid hyphal proliferation. Eventually, the infected pollen ruptured, leaving a cluster of compact hyphal cells encircled by remnants of the pollen cell walls.