Nutrient Solution Temperature Affects Pythium Root Rot of Tobacco in Greenhouse Float Systems.

Float nutrient solution, soilless media, and ambient temperatures were monitored in two tobacco greenhouses with different heating regimes. Water temperatures at seeding were 11°C in an unheated greenhouse and 17°C in a heated greenhouse. Water temperature differences between greenhouses continued over the duration of seedling production. Media and air temperatures varied diurnally, but not float solution. In a greenhouse float system where water temperatures were constant at 15, 20, 25, or 30°C, seedling disease caused by Pythium myriotylum was correlated with float-water temperature and could be described by quadratic equations (R = 0.99) with the lowest level of root necrosis at 15°C. Pythium spp.-infected and noninfected seedlings grown in controlled-temperature water baths were transplanted to the field and evaluated for disease development. Previous infection with P. myriotylum, regardless of float-temperature regime, failed to alter yield, leaf quality, or root necrosis (P = 0.05) in field-grown tobacco.