Reactions of Argentine and Australian Sunflower Rust Differentials to Four North American Cultures of Puccinia helianthi from North Dakota. Shaw- Ming Yang, Research Plant Pathologist, USDA-ARS, Conservation and Production Research Laboratory, Bushland, TX 79012. E. F. Antonelli, INTA Castelar, Buenos Aires, Argentina; and A. Luciano and N. D. Luciani, Gualeguay, 446, 3100 Parana, Entre Rios, Argentina. Plant Dis. 70:883-886. Accepted for publication 14 March 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/PD-70-883.

Four North American (NA) cultures (1, 2, 3, and 4) of Puccinia helianthi were tested on 12 Argentine (six from Antonelli [A] and six from Luciano and Luciani [LL] and three Australian (from Kochman and Goulter [KG]) rust differential cultivars and lines of sunflower (Helianthus annuus). Impira INTA NAL (LL) and Guayacan INTA NAL (LL) were susceptible to all four NA rust cultures; Morden 307-1 (A,LL) and 29-3-1-3-21 (KG) were susceptible to NA cultures 2 and 4; Guayacan INTA sel. Castelar (A) and F164A (LL) were susceptible to NA cultures 3 and 4; Pergamino 71/538 (A) was susceptible to culture 2 but resistant to 4; Impira INTA sel. 11 Castelar was susceptible to culture 3 but resistant to culture 4; F164A × Morden 307-1 (LL), 953-88-3-1-54 (KG), and 953-102-1-1-41 (KG) were susceptible to culture 4. INTA sel. 5 Castelar (A), Pergamino 78 / 287 (A), Saenz Peņa 74-1-2 (A), and P386 (LL) were resistant to the four NA cultures. We hypothesize that the genes that condition rust resistance in Antonelli's Impira INTA sel. 5 Castelar, Impira INTA sel. 11 Castelar, Pergamino 71 / 538, Pergamino 78 / 287, Saenz Peņa 74-1-2, and Luciano and Luciani's P94A and P386 are different from the genes R₁ and R₂ that were found in CM 90R R (or Guayacan INTA sel. Castelar or F164A) and CM 29-3 (or 29-3-1-3-21 or Morden 307-1), respectively. We propose using the term "cultures" instead of "races" in studies on the genetic relations of sunflower rust systems. A list of sunflower rust differentials is suggested for documenting the corresponding gene pairs in the sunflower rust systems and pathogenicity formulas are proposed for describing the cultures of P. helianthi.