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Race diversity of Puccinia helianthi (sunflower rust) in the Northern Great Plains in 2011.
A. FRISKOP (1), T. Gulya (2), M. Acevedo (1), R. Harveson (3), R. Humann (1), S. Markell (1). (1) North Dakota State University, Fargo, ND, U.S.A.; (2) USDA-ARS, Sunflower Research Unit, Fargo, ND, U.S.A.; (3) University of Nebraska, Scottsbluff, NE, U.S.A.

Sunflower rust, caused by the macrocyclic heteroecious pathogen <i>Puccinia helianthi</i>, is an economically important disease in the Northern Great Plains, particularly in North Dakota, where approximately 40 – 50% of the U.S. crop is produced. In 2008, the first documented sexual recombination event in the Northern Great Plains occurred, which coincided with localized epidemics and subsequent yield loss. Race determination is essential for breeding for resistance, and no race assessment of single pustule isolates in North Dakota has been done. The objective of this study is to determine the races of single pustule isolates collected in the Northern Great Plains. In 2011, a minimum of two single-pustule isolates were collected from 37 discrete locations in ND. In addition, a limited number of single-pustule derived isolates were created from bulk samples collected in other Northern Great Plains states. To determine races, single-pustule isolates were increased on a susceptible hybrid, fresh urediniospores were inoculated onto the standard set of nine sunflower differentials and infection types were evaluated 13-15 days later. Nine races were identified from 100 isolates with races 300 and 304 comprising ~80% of tested isolates. The most virulent race detected was 776, which is virulent on the resistance genes in eight of the nine differentials. The differential lines CM29 and HAR3 conferred resistance to ~98% of the races identified. Races identified in other Plains states were similar to those in North Dakota. Results from this survey will be used to aid resistance breeding efforts in the future.<p><p>Keywords: Fungus

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