May 17, 2010: Ug99 Lineage Race PTKST (virulent to Sr31 and Sr24) confirmed in South Africa

A stem rust sample collected from near Greytown, KwaZulu-Natal, South Africa in Nov. 2009 has been confirmed to be Ug99 lineage race PTKST. Samples from another site – Cedara, KwaZulu-Natal, collected in Dec. 2009 showed similar virulence profiles. The confirmed findings have just been published in Plant Disease by Pretorius et al (2010). Race PTKST was only previously known from Kenya, where it was detected in 2008. Race PTKST is notable in that it carries combined virulence for resistance genes Sr24 and Sr31. The published avirulence/virulence profile of race PTKST is:

Avirulent: Sr13, 14, 21, 22, 25, 26, 27, 29, 32, 33, 35, 36, 37, 39, 42, 43, 44, Em, Tmp, and Satu

Virulent: Sr5, 6, 7b, 8a, 8b, 9a, 9b, 9d, 9e, 9g, 10, 11, 16, 17, 24, 30, 31, 34, 38, 41, and McN.

In seedling tests, 59 out of 103 South African cultivars tested were susceptible to race PTKST. It is believed that PTKST may be an exotic introduction into South Africa rather than a single –step mutation from local stem rust races.

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