Abstract
In the last 20 years, stem rust caused by the fungusPuccinia graminisf. sp.tritici(Pgt), has re-emerged as a major threat to wheat and barley production in Africa and Europe. In contrast to wheat with 82 designated stem rust (Sr) resistance genes, barley's genetic variation for stem rust resistance is very narrow with only ten resistance genes genetically identified. Of these, only one complex locus consisting of three genes is effective against TTKSK, a widely virulentPgtrace of the Ug99 tribe which emerged in Uganda in 1999 and has since spread to much of East Africa and parts of the Middle East. The objective of this study was to assess the functionality, in barley, of cloned wheatSrgenes effective against race TTKSK.Sr22,Sr33,Sr35andSr45were transformed into barley cv. Golden Promise usingAgrobacterium-mediated transformation. All four genes were found to confer effective stem rust resistance. The barley transgenics remained susceptible to the barley leaf rust pathogenPuccinia hordei, indicating that the resistance conferred by these wheatSrgenes was specific forPgt. Furthermore, these transgenic plants did not display significant adverse agronomic effects in the absence of disease. ClonedSrgenes from wheat are therefore a potential source of resistance against wheat stem rust in barley.