Detection of variants of wheat stem rust race Ug99 (Puccinia graminis f. sp. tritici) in Zimbabwe and Mozambique.
During surveys of wheat fields for Ug99 in Zimbabwe and Mozambique in August and September 2010, high stem rust severities were found at Chiredzi, Chisumbanje, and Birchenough in Zimbabwe and at Rotanda in Mozambique. In Mozambique, stem rust was only observed at Rotanda (sample Moz1001). Collections from Chiredzi (samples Zim1004 and Zim 1005), Chisumbanje (Zim1006), and Birchenough (Zim1009 and Zim1010) yielded viable urediniospores for infection studies. Using 8 selected SSR primer combinations, all 6 isolates clustered within the Ug99 lineage. Isolates Zim1005, Zim1006, Zim1009, Zim1010, and Moz1001 and the stem rust control races TTKSF, TTKSK, and PTKST grouped into 2 main clusters, with Zim1009 and Zim1010 clustering together and sharing 88% similarity with the rest of the isolates. Zim1005 and Zim1006 were identical to TTKSF and TTKSK, respectively. Zim1004 shared 96% genetic similarity with the TTKSP control, with these 2 sharing 74% genetic similarity with the remaining isolates. The confirmation of Sr31 virulence in race PTKST in Zimbabwe is important because it provides new geographical records for an Ug99-related race and puts Southern African cultivars with 1B.1R resistance at risk.