The bacterium Pseudomonas fluorescens can be used as a biocontrol agent, protecting plants against soilborne pathogenic fungi. A strain of the bacterium named CHA0 has been successfully used to suppress diseases caused by other microbial agents including Thielaviopsis basicola. P. fluorescens when introduced as a soil or seed innoculant becomes an aggressive root colonizer making up to half of the culturable rhizosphere microbiota. This rapid growth in the primarily the older parts of the root is being used with the advances in immunofluorescent microscopy (IF) in order to determine its interaction with the target fungal pathogen.

The CHA0 strain of P. fluorescens was grown in nutrient-yeast extract broth and King's agar while the T. basicola was grown on malt agar. The tobacco plants in the research were grown aseptically for 5 weeks before being used. The soils used was from a sandy-loam surface horizon and was autoclaved twice before usage. The soil was then inoculated with a small amount of P. fluorescens CHA0 strain followed by an inoculation of T. basicola a few days later. After about a week the aseptically grown tobacco plants in the four leaf stage were transplanted into the soil. After 12 days the plants were uprooted washed and root samples were sectioned for observation using IF. The sectioning process was quite in depth using multiple chemicals to polymerize the roots samples in order to minimize damage during sectioning the microtome. For each inoculation a total of 20 plants were used with 5 root samples being taken from each.

The results of the experiment indicate that the CHA0 strain was successful in disease suppression of ailments brought on by the pathogen T. basicola. The CHA0 strain delayed colonization of the pathogen into the interior of the tobacco roots. Thus, the chlamydospores, (otherwise known as black root rot) that form on the roots of the plants were significantly inhibited in their growth. The results of this experiment suggest that the CHA0 strain of P. fluorescens can be commercially used as a biocontrol agent in suppressing the devastating affects of disease in soil-borne plant pathogenic fungi such as T. basicola