Annual Report 2006/07 - ETH - North-South Centre North-South ...

Research Fellow Partnership ProgrammeResearch fellowPeter Njoroge Njau,University of ZurichSupervisorsBeat Keller, University of Zurich /Ravi P. Singh, CIMMYT, MexicoCollaboratorMacharia Gethi, Kenya AgriculturalResearch Institute (KARI), KenyaDurationJanuary 2007 – December 2009Comprehensive analysis and initial exploitationof resistance to wheat stem rust race Ug99A young crop in the nursery showing the layout of the experiment: Note the twodouble rows and the spreader row planted perpendicular to the plotsA stem rust-infested plot at a trial site in Njoro, Kenya with rapidly growing pustuleson the stems and leavesThis study aims at identifying new sources of resistance tothe new race of stem rust (Puccinia graminis f. sp tritici) Ug99and initial reconstruction of the Sr2 complex gene for durableresistance using molecular techniques. One hundred linesselected from international screening nurseries in 2005 and2006 were planted in Njoro, Kenya, in 1 m double-row plots.To facilitate inoculum build-up and uniform disseminationwithin the nursery, a continuous row of stem rust spreaderwas planted perpendicular to all entries in the nursery. Theresults show that the levels of resistance ranged from TR to20MR 1 . We have very good lines showing adult plant resistance.There are those with pseudo black chaff characteristicsof Sr2. Also some synthetics and advanced lines whereChinese cultivars are used as parents were identified to beresistant. The Avocet/Pavon mapping population wasinitially developed for the evaluation of slow-rusting leaf rustand yellow rust resistance in Pavon 76. Pavon 76 is also knownto be carrying the Sr2 complex. It was found appropriate touse this F5 derived F6 populations to (i) estimate the numberof minor genes that constitute the Sr2 complex, and (ii) identifyQTLs for these genes. A population of 285 recombinantinbred lines (RIL) was planted in Njoro in 1 m double-rowplots with a spreader row as described earlier. Initial resultsshow that there could be three minor genes operating inPavon 76. In 2007/08, we will do the final screening of the 100lines in the field in Njoro and finalise the analysis of the parentsfor the genetic studies. In 2007/08, the selected parentswill be planted in CIMMYT Mexico for the development of themapping population. The same parents will be planted inNjoro for the initiation of the transfer of resistant genes tothe Kenyan commercial varieties. A third field evaluation ofthe Avocet/Pavon population will be carried out in Njorowhile more screening of the international materials will bedone to identify any new sources of resistance.581 TR means traces of the disease, while 20MR stands for 20 % disease severity and crop reaction to the disease, i. e. it was moderately resistant (MR)