2007 Annual Report 1a.Objectives (from AD-416) 1. To identify sunflower wild species with resistance to Sclerotinia; 2. Develop Sclerotinia resistance germplasm by incorporating resistant genes from wild species into cultivated background. 1b.Approach (from AD-416) Twenty wild sunflower accessions of H. maximiliani and H. nuttallii previously identified as having Sclerotinia resistance will be reevaluated, and the resistant accessions crossed with cultivated inbred lines. Embryo rescue will be utilized to establish all the F1 hybrids. Seedlings will be treated with colchicine to induce chromosome doubling and to produce amphiploids. Amphiploids will be evaluated for Sclerotinia head rot resistance by artificial inoculation with ascospores and growth under mist irrigation to optimize environmental conditions. Similar procedures will be followed for the stalk rot resistance gene transfer. Evaluations will be made with inoculum consisting of Sclerotinia mycelium grown on millet grains, which are then deposited in the soil beside each plant in the field, and below the plant roots for greenhouse pots. 3.Progress Report This report documents research conducted under a Specific Cooperative Agreement between ARS and North Dakota State University, Department of Plant Sciences. Additional details of research can be found in the report for the in-house associated project 5442-21000-027-00D, Enhancement of Sunflower Germplasm Diversity Through the Use of Wild Species and Genome Characterization. Stem rot resistant wild perennial diploids Helianthus maximiliani, H. giganteus, and H. grosseserratus were crossed with NMS HA 89 and the F1 plants were established. Stem-rot resistant hexaploids H. schweinitzii and H. californicus have been crossed with tolerant HA 410, and backcrossed with HA 410 three times. The chromosome numbers are now approaching the desired number of 34. When the chromosome numbers reach 34, the lines will be ready for crossing with cultivated sunflower for introduction of new sources of resistance to Sclerotinia stem rot. Two years of stem and head rot resistance evaluation were completed in the field and greenhouse for interspecific amphiploids, which retain the complete set of chromosomes of both parental species. The resistant plants were established in the greenhouse and crossed with stem rot and head rot tolerant lines HA 410 and HA 441, respectively, in order to pyramid new stem and head rot resistance genes into lines that already have some tolerance. A total of 18 diploid perennial accessions of H. maximiliani and H. nuttallii highly resistant to head rot were crossed first with NMS HA 89, and then backcrossed with HA 441. BC1F2 plants with 34 chromosomes were self-pollinated to produce BC1F3 seeds for replicated field evaluation. Plants that show good resistance to Sclerotinia head rot will be potential sources of new genes for introduction into cultivated sunflower. The ADODR monitors research progress by quarterly meetings with the Cooperator’s personnel and by site visits to field plot locations.