Browning and rishitin accumulation in tubers, whether inoculated with an incompatible race of Phytophthora infestans or treated with sonicates of the fungus, were markedly reduced at 25 C or 30 C as compared with 19 C.  Browning and rishitin accumulation were not evident at 14 or 37 C.  Germination of zoospores and growth of the germ tubes were not affected by incubation at 25 C or 30 C for 12 hours.  The accumulation of fungitoxic steroid glycoalkaloids, characteristic of the wound response, was increased by incubation at 25 C or 30 C and decreased markedly at 37 C compared with 19 C.  It appears that incubation at 25 C and 30 C accentuates the wound response, but inhibits browning and rishitin accumulation which are associated with the hypersensitive response to incompatible races of P. infestans.

Additional key words: control of phytoalexin synthesis.