Fusarium graminearum, a known producer of trichothecene mycotoxins in cereal hosts, has been recently documented as a cause of dry rot of potato tubers in the United States. Due to the uncertainty of trichothecene production in these tubers, a study was conducted to determine the accumulation and diffusion of trichothecenes in potato tubers affected with dry rot caused by F. graminearum. Potato tubers of cv. Russet Burbank were inoculated with 14 F. graminearum isolates from potato, sugar beet, and wheat and incubated at 10 to 12 degrees C for 5 weeks to determine accumulation of trichothecenes in potato tubers during storage. Twelve of the isolates were classified as deoxynivalenol (DON) genotype and two isolates were as nivalenol (NIV) genotype. Trichothecenes were detected only in rotted tissue. DON was detected in all F. graminearum DON genotype isolates up to 39.68 microg/ml in rotted potato tissue. Similarly, both NIV genotype isolates accumulated NIV in rotted potato tissue up to 18.28 microg/ml. Interestingly, isolates classified as genotype DON accumulated both DON and NIV in the dry rot lesion. Potato tubers were then inoculated with two isolates of F. graminearum chemotype DON and incubated up to 7 weeks at 10 to 12 degrees C and assayed for DON diffusion. F. graminearum was recovered from >53% of the isolations from inoculated tubers at 3 cm distal to the rotted tissue after 7 weeks of incubation but DON was not detected in the surrounding tissue. Based in this data, the accumulation of trichothecenes in the asymptomatic tissue surrounding dry rot lesions caused by F. graminearum is minimal in cv. Russet Burbank potato tubers stored for 7 weeks at customary processing storage temperatures.