Effect on Host Hypersensitivity of Suppressors Released During the Germination ofPhytophthora infestansCystospores

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Abstract
Germinating cystospores of P. infestans released substances into the germination fluid which suppressed the hypersensitive reaction of potato tuber tissue to an incompatible race of the fungus. The suppressors were partially characterized as water-soluble glucans containing .beta.(1 .fwdarw. 3) linkages. A nonanionic glucan isolated from germination fluid of compatible P. infestans race 1,2,3,4 suppressed hypersensitive cell death and the accumulation of rishitin in potato tuber tissue (Kennebec, R1-resistance gene) infected with incompatible race 4. The nonanionic glucan from race 4 was a less active suppressor. The amount of nonanionic and anionic glucans in the germination fluids from both races increased equally during the germination of the cystospores. Possible roles for the glucans as determinants of specificity in the potato-P. infestans interaction are discussed.