TxAG-5, a sclerotinia resistant Spanish germplasm line released jointly by the Texas Agricultural Experiment Station, USDA, and the Oklahoma Agricultural Experiment Station, was crossed in reciprocal to two Spanish lines, Tx851856 and Sn73–30. Parent, F₁, F₂, BC₁F₁, and F₃ populations were evaluated under high natural inoculum for resistance to Sclerotinia minor using a disease rating scale of 1 (no disease) to 5 (severely diseased), and the number of days from first appearance of the fungus until plant death was recorded. F_2:3 families were compared for disease the following year for genotypic assessment of the F₂ parents. F₁ generation plants of the Sn73–30 cross were susceptible, but F₁ plants from Tx851856 were intermediate. Some TxAG-5 succumbed to the disease. F₂ distributions were continuous. F₂ genotypic frequency distributions based on F₃ and BC₁F₃ families were near continuous. Broadsense heritability estimates for disease ratings for TxAG5/Tx851856 and TxAG-5/Sn73–30 were 14 and 23%, respectively. Narrowsense heritabilities based on parent offspring regression of F₃ families on F₂ plants were 11% for Tx851856/TxAG-5 and 1% for Sn73–30/TxAG-5. Selection for resistance among the F₂ plants to increase the frequency of resistant F₃ families would have been ineffective.