Genetic and virulence diversity of Puccinia graminis f. sp. Tritici populations in Ethiopia and stem rust resistance genes in wheat

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As a result of a recent spread of a new and highly virulent race of Puccinia graminis f. sp.
tritici called Ug99, stem rust is becoming a serious threat to wheat production in Ethiopia and
other east African countries. Therefore, there is an urgent need to analyse the virulence
spectrum of Pgt populations in Ethiopia. Wheat stem rust samples were collected in 2006 and
2007 in Arsi, Bale, Shewa and the Northwest regions of Ethiopia to determine the virulence
diversity and race distribution in P. graminis f. sp. tritici populations. Stem rust incidence was
high in Arsi, Bale and East Shewa. In Northwest Ethiopia, and North and West Shewa, stem
rust was prevalent at low levels. A total of 152 isolates was analyzed and 22 races were
identified. Races TTKSR (Ug99), TTHSR and RRTTR were predominant with frequencies of
26.6, 17.7 and 11.1%, respectively. These races were also detected in all regions. It turned out
that the highly virulent race designated as Ug99 was present throughout the country and
dominated in all regions except Northwest Ethiopia. A variant of Ug99, which is virulent
against Sr24 was not detected in this study. Four stem rust resistance genes (Sr13, Sr30, Sr36
and SrTmp) were found to confer resistance to most of the races prevalent in Ethiopia. With
the exception of Sr30, which is not effective to Ug99, the other three genes can be used in
breeding for resistance to stem rust in Ethiopia.