Description:
The SAM-2 sunflower population was developed after three cycles of recurrent selection for resistance to Alternaria leaf blight (Alternaria helianthi), Septoria leaf blight (Septoria helianthi), and powdery mildew (Erysiphe cichoracearum). The most resistant 8-12% of the plants were retained during each selection cycle and allowed to intercross, starting from an original pool of 512 plants representing 32 wild H.annuus accessions. Line of descent was recorded to identify accessions that contributed the female parent plants. Resistance to Alternaria and Septoria leaf blights was characterized by hypersensitive flecks on leaves or by small leaf spots (ratings of 1 or 2 on a 1-4 scale) with little of the extensive yellowing, leaf necrosis, and defoliation observed on susceptible plants. The hypersensitive response to A. helianthi is similar to that found in H. tuberosus. Plants were concurrently selected for resistance to natural infection by powdery mildew, caused by E. cichoracearum. Equal numbers of seed from 81 plants in the final (C3) population were bulked to form SAM-2. The resistance in SAM-2 may be of particular value in humid or higher rainfall regions where leaf blights can limit sunflower production.