Effect of light on hormonal regulation of sexual reproduction in Phytophthora parasitica

Abstract

A1 and A2 isolates of Phytophthora parasitica were exposed to light at different stages of sexual development to study the mode of action of light on sexual reproduction. Exposure to light during the process of sexual reproduction reduced the number of oospores produced to about 7% of that produced in darkness. Light was inhibitory to production of α hormones but not receptors of these hormones by both A1 and A2 isolates of P. parasitica. However, after being produced, α hormones were stable under light. The number of oospores produced was greatly reduced when A1 and A2 cultures were exposed to light during hormone induction of sexual reproduction but was not affected when the cultures were exposed to light during oospore formation after hormone induction. The results suggest that the effect of light on sexual reproduction in P. parasitica was mainly through inhibition of hormone production and hormone induction of sexual reproduction. Key words: Phytophthora parasitica, light effect, hormonal regulation.