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Breeding for Resistance

Breeding for Resistance. Control important crop diseases and pests Must have genetic variability Consider both genetic variability in the plant and in the pest Sources: Fehr, ch. 21 Slusarenko, Fraser, and van Loon, 2000. Types of Genetic Resistance. Qualitative Resistance

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Breeding for Resistance

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  1. Breeding for Resistance Control important crop diseases and pests Must have genetic variability Consider both genetic variability in the plant and in the pest Sources: • Fehr, ch. 21 • Slusarenko, Fraser, and van Loon, 2000

  2. Types of Genetic Resistance Qualitative Resistance Distinct classes of resistance and susceptible plants Controlled by one or a few genes Also called “Vertical” resistance Quantitative Resistance Continuous variation among genotypes Many loci Also called “Horizontal” resistance

  3. Qualitative Resistance • Controlled by major genes (one or two) • Genes are readily transferred from one genotype to another • Presence of genes can be determined by exposing plants to particular races

  4. Qualitative Resistance Advantages • Easier screenings • Easier transfer of genes “all or nothing” Disadvantages • Vulnerability to new races • Continuous use of particular cultivar may lead to development of new race or shift in pest population (shift from race 1 to race 2)

  5. Qualitative Resistance Examples: Leaf Rust Resistance in Wheat

  6. Quantitative Resistance Controlled by many genes each with minor effects Advantages • Can control a broad range of races due to the fact that many loci are involved Disadvantages • Difficult to transfer resistance from one genotype to another • Individual genes harder to identify

  7. Quantitative Resistance Examples: Fusarium Head Blight in Wheat

  8. Sources of Resistance Primary Gene Pool Other breeding programs Landraces Germplasm collections (GRIN) Wild Relatives Tomato: Lycopersicon genus Wheat: Agropyron genus Aegilops tauschii, Triticum monococum Mutant Transformations: powdery mildew in Barley

  9. Vertical vs Horizontal Resistance Resistance Susceptibility Vertical Resistance to Races 2, 5, and 6

  10. Vertical vs Horizontal Resistance Resistance Susceptibility Horizontal Resistance to all Races

  11. Hypersensitive Response • Stem Rust of Wheat • Programmed cell death • A lot of black boxes • Pathogen recognition, signaling proteins, transcription factors,

  12. Gene-for-Gene Hypothesis Proposed by Flor (1956)-study on flax rust “For each resistance gene in the plant there is a gene in the pathogen that determines if the pathogen will be able to injure the plant.”

  13. Gene combinations and Disease Reaction Types in the Gene for Gene concept

  14. Complementary Interaction of Two Host Genes For Resistance and the Corresponding Two Pathogen Genes for Virulence Virulence a or Avirulence A genes In the pathogen

  15. Races of Pests • Genetic variability within the pathogen population • Different isolates cause different responses among host genotypes • Example: Soybean Cyst Nematode Races

  16. Minimizing Changes in Races • Alternation of Resistant and Susceptible Cultivars (soybean cyst nematode) • Mixtures of Resistant and Susceptible Genotypes • Prevention of New Races

  17. Resistance vs Tolerance Resistance: no establishment of the pathogen in/on the host, or a limited establishment Tolerance: the host develops, continues to grow, and produces well despite the pathogen’s presence

  18. Breeding for Specific Resistance Individual Major Genes Multilines Pyramiding

  19. Breeding for Specific Resistance Individual Major Genes • Breed cultivars with major genes that control the prevalent pest races • Select progeny from a segregating population or … • Transfer major genes from other sources • Example: Black Shank Tobacco Varieties • Advantages and Disadvantages

  20. Breeding for Specific Resistance Multilines • Develop many individual lines each with individual major resistance genes and then … • Mix the seed of these lines together to get … • Protection against a broad spectrum of races • Example: wheat cultivar Miramer 63 • Advantages and Disadvantages

  21. Breeding for Specific Resistance Pyramiding • Put all known major genes into one line • Advantages and Disadvantages • Example: Leaf Rust in Wheat

  22. Comparative structural analysis of the Lr10 homologous regions from diploid wheat, rice 5 (japonica), indica rice and rice 1 (japonica). Lr10

  23. QTL and Resistance • Quantitative Trait Loci • Identify QTL that control variation in resistance observed in genotypes • Use markers to screen genotypes (throw out the susceptibles) • Applications in Marker Assisted Selection (MAS)

  24. QTL and Resistance Wheat chromosome 1A Leaf rust gene ‘Lr10’ Source: J.C. Nelson et al. 1997 Crop Science 37:1928-1935

  25. QTL for Fusarium Head Blight Resistance in Wheat Ning 7840/Clark population 11 AFLP markers associated with resistance 1 marker explained 53% of the variation Bai, Kolb, Shaner, and Domier. Phytopathology 89:343-348. Sumai 3/Stoa population -- used RFLP markers 5 genomic regions were associated with resistance (3 from Sumai 3, 2 from Stoa) Waldron, Moreno-Sevilla, Anderson, Stack, Frohberg. Crop Sci 39:805-811.

  26. Example of Quantitative Genetics • 3 F2:3 populations, 40 families, 3 reps, 13 individual observations per rep • Separated variance into two parts • Among families • Within families • Narrow sense heritabilities were estimated

  27. ANOVA

  28. Example from Population 2 Estimate from 2555

  29. Genetic Parameters and h2 of FHB Severity

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