VIEW ARTICLE

Resistance

Rust Resistance of Wild Helianthus Species of the North Central United States. D. E. Zimmer, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, North Dakota State University, Fargo 58102; Dale Rehder, Graduate Research Assistant, Department of Plant Pathology, North Dakota State University, Fargo 58102. Phytopathology 66:208-211. Accepted for publication 16 August 1975. DOI: 10.1094/Phyto-66-208.

Plants free of rust, Puccinia helianthi, were observed in 190 of 200 populations of wild annual and perennial Helianthus spp. in the North Central United States. Seed were collected from 100 randomly selected plants of each population, and P. helianthi was obtained from 27 populations. Rust from H. annuus belonged to races 1, 2, and 3, whereas only race 1 was recovered from H. petiolaris. Rust of the perennial species H. grosseserratus, H. maximiliani, H. nuttallii, H. rigidus, and H. tuberosus, with the exception of one collection from H. tuberosus, were avirulent on H. annuus ‘S-37-388’, the “universal suscept.” Cross-inoculation studies revealed that P. helianthi comprised many pathogenic races with considerable, but not restrictive, specificity to the annual or perennial group, and to the species from which it was collected. Collectively, all rust collections had one of more common hosts that allowed exchange of virulence genes, which made it difficult to postulate the existence of biologic forms. Wild Helianthus spp. contained a multiplicity of rust resistances. Plants resistant to all races were identified. Resistance to rust was more prevalent in wild annual sunflower populations collected from Nebraska and Kansas, than from northern states. Wild sunflowers of the North Central United States offer unexplored sources of rust resistance, as well as a breeding sanctuary for P. helianthi in the absence of susceptible domestic cultivars.