Lettuce root rot caused by Pythium aphanidermatum and other Pythium species is the main disease in hydroponic systems in Brazil. The present work aimed to evaluate the behavior of four commercial lettuce cultivars as to their sensitivity to root rot caused by P. aphanidermatum in hydroponic systems. Experiments were conducted in Petri dishes containing water-agar medium and seedlings of the crisp head lettuce cultivars (Vera and Verônica) and leafy lettuce cultivars (Regina and Elisa), infested or not with the pathogen. With the same cultivars, four other experiments were carried out in hydroponic systems (Nutrient Film Technique), two in a shaded greenhouse and the other two in a conventional greenhouse. Seedlings infected or not with P. aphanidermatum were transplanted to hydroponic systems infested or not with the pathogen. The disease severity and the plant development were evaluated. All cultivars were susceptible to root rot in both in vitro and in vivo experiments. The shading did not reduce root rot in the lettuce cultivars in hydroponic system. The cultivar Regina showed higher shoot and root dry mass in the presence or absence of the pathogen, constituting thus the most suitable cultivar for hydroponic systems during the hottest period of the year.
Lactuca sativa; Pythium; root rot; hydroponic system
