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Title: Diversity in Puccinia triticina detected on wheat from 2008 to 2010 and the impact of new races on South African wheat germplasm

Author
item TEREFE, T - Agricultural Research Council Of South Africa
item VISSER, BOTMA - University Of The Free State
item PRINS, R - University Of The Free State
item NEGUSSIE, T - University Of The Free State
item Kolmer, James
item PRETORIUS, Z - University Of The Free State

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2013
Publication Date: 1/7/2014
Citation: Terefe, T.G., Visser, B., Prins, R., Negussie, T., Kolmer, J.A., Pretorius, Z.A. 2014. Diversity in Puccinia triticina detected on wheat from 2008 to 2010 and the impact of new races on South African wheat germplasm. European Journal of Plant Pathology. 139:95-105.

Interpretive Summary: Wheat is attacked by a fungus called Puccinia triticina, that causes the disease leaf rust. This disease occurs in the U.S. and around the world including South Africa causing regular yield losses in wheat. The purpose of this study was to genetically characterize the P. triticina population in South Africa using DNA based molecular markers and by testing the P. triticina isolates for their ability to attack different resistance genes in wheat. Eight different types or races of leaf rust were found in South Africa. Based on results with the DNA markers, two of the races were likely new introductions to South Africa from other continents, possibly Europe. The DNA patterns of isolates from South Africa will be compared to P. triticina populations from the U.S. and other regions to determine how this fungus migrates and to determine the origin of any new biotypes that may be found in the U.S.

Technical Abstract: Samples of wheat and triticale infected with leaf rust were collected from 2008 to 2010 in South Africa to identify Puccinia triticina races. Races were identified based on their virulence profile on standard differential lines. Eight races were identified from 362 isolates. The dominant races were 3SA133 (syn. PDRS) in 2008 (78%) and 2009 (34%), and 3SA145 (47%) in 2010. Race 3SA145 (CCPS) identified in 2009 was a new race in South Africa with virulence for the adult plant resistance gene Lr37. Another new race, 3SA146 (MCDS), was identified in 2010. Race 3SA146 is also virulent for Lr37 but unlike 3SA145, it is virulent for Lr1 and Lr23 and avirulent for Lr3ka and Lr30. Microsatellite analysis showed that 3SA145 and 3SA146 shared 70% genetic similarity with each other, but only 30% similarity with other races in South Africa, suggesting that both represent foreign introductions. In seedling tests of 98 South African winter and spring cultivars and advanced breeding lines, 27% were susceptible to 3SA145 and 3SA146 but resistant to 3SA133. In greenhouse studies of 59 spring wheat adult plants, 19% of breeding lines and 46% of cultivars were susceptible to 3SA145, whereas 29% of the lines and 53% of cultivars were susceptible to 3SA146. The cssfr6 gene-specific DNA marker confirmed the presence of Lr34 gene for leaf rust resistance in a homozygous condition in 28 wheat entries. Five entries were heterogeneous for Lr34. Several entries which were susceptible as seedlings to the new races carried Lr34. These lines are expected to show lower levels of leaf rust as adult plants. Results of these studies indicate a continued vulnerability of South African wheat cultivars to new races and emphasise the importance of regular rust monitoring and the need to incorporate genes for durable resistance.