Red-light treatment induces resistance in pepper and pumpkin plants to Phytophthora capsici

Phytophthora capsici infects more than 50 species in 15 plant families. Peppers and cucurbits are major hosts of this pathogen, as it causes up to 100% crop losses in the commercial fields. This study was conducted to evaluate the effectiveness of red-light treatment for managing P. capsici in pepper and pumpkin production. Seeds of bell pepper (Capsicum annuum) and pumpkin (Cucurbita moschata) were sown in 10-cm diameter plastic pots containing steamed soil mix and plants were grown in a greenhouse under continuous red-light irradiation (600-700 nm) from fluorescent tubes, with light intensity of 287 µW cm^-2. Control seedlings were kept under either white-light fluorescent tubes or natural daylight in the same greenhouse. Four-week-old pepper seedlings, and three-week-old pumpkin seedlings were transferred from under red light to natural daylight. Plants were inoculated with a zoospore suspension of P. capsici (2×10⁵ zoospores mL^-1 water). Four days after inoculation, seedlings were evaluated for defoliation and damping-off symptoms every day for 20 successive days. Red-light treatment of seedlings reduced Phytophthora damping-off by up to 79%. Only 21 to 36% of red light treated pumpkin and pepper seedlings, respectively, became infected with P. capsici, whereas 78-100% of the control seedlings (grown under either white light or natural daylight) died. The results indicated that the red-light treatment induces resistance in pepper and pumpkin seedlings against P. capsica.