Diseases of tobacco caused by Pythium spp. can start as damping-off of seedlings, evolve as root and stem rot of young plants, and finally cause root decay of field plants. Root and stem rot of tobacco reduces stands more than 20% in some fields, and results in stunted, yellowing and death of tobacco. In Southern Brazil, Burley tobacco has shown to be highly susceptible to this pathogen complex, which includes different species of Pythium . Universal Leaf Tabacos Breeding Program developed a set of lines of Burley tobacco in the past years, and new protocols including isolation of the main Pythium species were developed. Once the isolates were identified, sequenced in the ITS region, and an accurate zoospore inoculation method was developed, these breeding lines were challenged with this pathogen under controlled conditions. The studies included P. deliense , P. ultimum , and P. dissotocum . Besides that, field evaluations in specific nurseries for this soil born disease have been performed in the past three years. With the results from controlled inoculations and field selections, ULT Brazil was able to develop a set of lines that show consistent high level of resistance to root decay.