Upon establishing contact, germ tubes and hyphae of Phytophthora megasperma f.sp. glycinea either penetrate soybean protoplasts (2-4% of cases), grow along their surface (12-17% of cases) or continue their growth after contact with no directional change. No appressoria are formed prior to penetration, and during penetration the pathogen is always surrounded by a continuously expanding host plasma membrane. Contact between protoplast and pathogen frequently triggers the production of finely fibrillar material at the contact sites which stains positively with the fluorescing dye "diethanol", indicative of polysaccharides. The material is probably produced by the host protoplast and may be similar to material formed at points of apposition in the wall during infection of the intact tissue. It is not primarily responsible for the observed physical adhesion of hyphae to protoplasts. No differences in the reaction pattern were observed between two near-isolines differing mainly in their resistance against the fungal pathovar used. However, production of the wall-like material was much less frequently observed in non-host combinations (P. infestans on soybean, P. megasperma f.sp. glycinea on barley). © 1988.
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