INFLUENCE OF CARBOHYDRATES ON THE INDUCTION OF HAUSTORIA OF THE COWPEA RUST FUNGUS INVITRO

Rust fungi are obligate plant parasites whose successful parasitism appears to depend on the formation of haustoria within living plant cells. To test the hypothesis that the lack of haustorium formation in the absence of a living cell reflects a need for a simple "signal" released during attempted invasion, various carbohydrates were applied toin vitro-formed infection structures ofUromyces vignae just prior to haustorial mother cell (HMC) formation. Up to 6% of HMCs formed haustoria after treatment with arabinose, mannose, xylose, sucrose, or xylan. Other monosaccharides, oligosaccharides, and polysaccharides were less or not effective. Sugar mixtures induced haustorium frequencies of up to 10%. Timing of the application of inducing chemicals was critical. The data indicate that haustorium formation does not require the presence of a living plant cell and may be triggered by plant products at the time of penetration peg development. © 1990 Academic Press, Inc.