Preliminary Studies on Induced Resistance of Cucumber to Downy Mildew

摘要

1 mL of sporangial suspensions (5×10~5 xpporangia per millilitcr) of Pseudoperonospora cubensis was droplet-inoculated on the surface of the second leaf of the plant grown in greenhouse (inducing inoculatoin), then the lower surfaces of the third, the forth and the fifth leaves were uniformly sprayed with inoculum of the same fungi (5×10~4 sporangia per milliliter, about 5 mL per plant) every 3 days interval (challenge inoculation). Plants were moistened at 18-22 C for 18 h, then kept at room temperature (24-～28 C) and supplemented with cool-white fluorescent lights. All three challenge leaves were collected after 7 days of challenge to measure the amount of sporulation and area of necrosis. Plants prior inoculated with P. cubensis were protected38% (based on the area of necrosis) against disaesc caused by subsequent foliar challenge with the pathogen. Protective action was about 12% after 3 days, and maintained this level until 9 days, suddenly reached 34% after 12 days, and came to a maximumafter 15 days, then dropped down slowly.