EFFECT OF LIGHT ON HORMONAL-REGULATION OF SEXUAL REPRODUCTION IN PHYTOPHTHORA-PARASITICA

A(1) and A(2) isolates of Phytophthora parasitica were exposed to ligh t at different stages of sexual development to study the mode of actio n of light on sexual reproduction. Exposure to light during the proces s of sexual reproduction reduced the number of oospores produced to ab out 7% of that produced in darkness. Light was inhibitory to productio n of cc hormones but not receptors of these hormones by both A(1) and A(2) isolates of P. parasitica. However, after being produced, a hormo nes were stable under light. The number of oospores produced was great ly reduced when A(1) and A(2) cultures were exposed to light during ho rmone induction of sexual reproduction but was not affected when the c ultures were exposed to light during oospore formation after hormone i nduction. The results suggest that the effect of light on sexual repro duction in P. parasitica was mainly through inhibition of hormone prod uction and hormone induction of sexual reproduction.