Nutrient solution temperature affects Pythium root rot of tobacco in greenhouse float systems

Float nutrient solution, soilless media, and ambient temperatures were moni tored in two tobacco greenhouses with different heating regimes. Water temp eratures at seeding were 11 degrees C in an unheated greenhouse and 17 degr ees C in a heated greenhouse. Water temperature differences between greenho uses continued over the duration of seedling production. Media and air temp eratures varied diurnally, but not float solution. In a greenhouse float sy stem where water temperatures were constant at 15, 20, 25, or 30 degrees C, seedling disease caused by Pythium myriotylum was correlated with float-wa ter temperature and could be described by quadratic equations (R-2 = 0.99) with the lowest level of root necrosis at 15 degrees C Pythium spp.-infecte d and noninfected seedlings grown in controlled-temperature water baths wer e transplanted to the field and evaluated for disease development. Previous infection with Fl myriotylum, regardless of float-temperature regime, fail ed to alter yield, leaf quality, or root necrosis (P = 0.05) in field-grown tobacco.