Biocontrol performance of two isolates of Pseudomonas fluorescens in modified soil atmospheres

The incidence of tomato wilt caused by Pseudomonas solanacearum, and the biocontrol performance of two isolates of Pseudomonas fluorescens (M29 and M40) against P. solanacearum were measured under four soil atmospheres containing O-2/CO2 concentrations of 210:0.3 (210 and 0.3 mi of O-2 and CO2 per liter, respectively, ambient concentrations), 180:30, 150:60, or 120:90. Altering the O-2 and CO2 concentrations of the soil atmosphere did not cause a statistically significant (P less than or equal to 0.05) change in disease incidence. However, suppression of wilt by M29 and M40 was significantly (P less than or equal to 0.05) decreased when roots were exposed to atmospheres containing lower than ambient levels of O-2 and higher than ambient levels of CO2. Isolate M29 significantly (P less than or equal to 0.05) reduced incidence of tomato wilt only under the ambient atmosphere and not under any of the three modified atmospheres tested. Isolate M40 reduced disease incidence significantly (P less than or equal to 0.05) only under the ambient atmosphere and one of the modified atmospheres containing O-2/CO2 concentrations of 180:30 ml/liter.