1st International Stem Rust Resistance Screening Nursery2006

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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

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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

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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

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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

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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

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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)

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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