Pythium species are responsible for root rot in hydroponically grown, being the aims of this study to evaluate the Pythium aphanidermatum and P. dissotocum pathogenicity, in lettuce. Petri dishes contained water-agar and the mycelium of the isolates were incubated at 15 to 45 ºC to verify the optimum temperature of growth, which were 31 ºC for P. aphanidermatum and 26 ºC for P. dissotocum. It was evaluated the pathogenicity of the isolates in the optimum temperatures, and 20 ºC ideal to lettuce, placing the seeds in water-agar and the mycelium in the center of the dishes. Petri dishes contained only the seeds in media as controls. It was evaluated the hypocotyl and primary root length and the percentage of survivors seedlings, selecting P. aphanidermatum as more pathogenic; Vera and Tainá varieties as less susceptible and Elisa most susceptible.
hydroponic system; Pythiales; root infection
