1st International Stem Rust Resistance Screening Nursery-2006

							             1st International Stem Rust Resistance
                     Screening Nursery-2006
         270 lines initially identified to carry low to intermediate
          resistance in various nurseries from CIMMYT tested
          during 2005
         These entries tested at UDSA-ARS Cereal Disease Lab
          with Ug99 and other races of stem rust and in Mexico
          with selected races of leaf rust and with molecular
          markers for known genes Sr24, Sr25 and Sr26
         103 selected lines characterized in the field in Kenya
          and Ethiopia for stem rust and in Mexico for leaf and
          stripe rusts at El Batan and Toluca, respectively
         Introduced in the US by Dr. Art Klatt for multiplication
          and distribution

IC A R D A
             1st International Stem Rust Resistance
                     Screening Nursery-2006
             Gene/resistance                Entries (No.)
             Sr24 (White grained)           15 (not effective anymore)
             Sr24 (Red grained)             22 (not effective anymore)
             Sr25 (non-yellow flour)        2
             Sr25 (yellow flour)            17
             SrSha7 (Chinese sources)       7
             SrSynt (Synthetic derived)     4
             Sr1A.1R (Tentative)            2
             SrTmp (Tentative)              1
             Unknown seedling resistance    2
             Adult Plant Resistance (APR)   31



IC A R D A
             1st International Stem Rust Resistance
                     Screening Nursery-2006
         70 out of 103 entries in the nursery carry gene Sr2
          based on pseudo-black chaff phenotype
          characterization
         Sr2 alone not enough (60-70% disease severity)
         APR lines had disease severities ranging between 5-
          30% compared to 100% for the susceptible checks
          (2005 & 2006 Kenya and 2006 Ethiopia)
         Several APR and other lines also carry resistance to leaf
          and yellow rusts and therefore will be better parents for
          breeding



IC A R D A
             2nd International Stem Rust Resistance
                     Screening Nursery-2007
        219 lines selected based on 2006 Kenya stem
         rust data and are under multiplication and
         further field and greenhouse tests
        Seed is already in USDA-ARS Cereal Disease
         Laboratory, St. Paul, MN for seedling stem rust
         characterization
        Several lines in diverse genetic background
         have high yield potential, resistance to leaf and
         stripe rusts and APR to stem rust derived from
         ‘Kiritati’

IC A R D A
        Race-specific genes that confer moderate to high
      levels of resistance in field to race Ug99 and its Sr24-
                          virulent variant
       Sr13, 14, 22, 25, 26, 27, 28, 29, 33, 35, 36, 39, 40, 43, 44, 45, SrTmp,
        Sr1A.1R, SrSha7
       Virulence in other races known for Sr13, 14, 27, 28, 36
       Immediate value: Sr22, 25, 26, 35, Tmp, 1A.1R and Sha7; and to a lesser
        extent Sr13, 14, 24, 36
       Agronomic effects of genes in other translocations need to be
        determined
       Advanced lines with white floured Sr25 and resistance to leaf and stripe
        rusts under yield evaluation at Ciudad Obregon during 2006
       Incorporation of Sr26 in CIMMYT materials underway (most advanced
        materials in F4 generation)
       Breeding strategy should be to achieve combinations of race-specific
        resistance genes to enhance their longevity


IC A R D A
       CIMMYT strategy to breed for minor genes based
      durable resistance (restoring the Sr2- Complex)_1
              Selecting high yielding parents that carry Sr2 gene as
               recurrent parents
              Crossing them with wheat lines identified to carry high
               level of APR
              Producing large (about 500) BC1 plants and grow large
               F2 and further segregating populations
              Selecting plants in BC1-F3/F4 generations for desired
               agronomic characteristics and other traits at site where
               breeding is being done, e.g. Cd. Obregon and Toluca in
               Mexico
              Bulk harvesting selected plants in each generation
               (allows selection and retention of unlimited plants)


IC A R D A
       CIMMYT strategy to breed for minor genes based
      durable resistance (restoring the Sr2- Complex)_2
                Growing large number of densely sown F4/F5 populations at
                 Ug99 shuttle sites under high stem rust pressure, bulk
                 harvesting and selecting plump grains
                Selecting as head row or plants in F5/F6 generation at original
                 breeding site
                Characterizing advanced lines at stem rust shuttle site after
                 final selection at original breeding site and conduct yield
                 evaluations
                 Progress: Most advanced populations are now in F4
                 generation and are being planted in Kenya during 2006-2007
                 off-season



IC A R D A