Most plants are non-hosts for most pathogens; however, when a host:pathogen relationship exists, susceptibility is more

1. Most plants are non-hosts for most pathogens; however, when a host:pathogen relationship exists, susceptibility is more common than resistance.

2. In 1940s, Harold Flor (NDSU) was researching flax rust by studying both the inheritance of resistance in flax and the inheritance of virulence in Melampsora lini. [Flor 1946 JAgrRes 73:335; Flor 1947 JAgrRes 74:241; Flor 1955 Phytopath 45:680; Flor ARPP 1971 9:275]

3. Gene-for-gene: Dominant Alleles for Resistance in Plant; Recessive alleles for virulence in pathogen

4. Eventually became the Gene-for-Gene (GFG) concept: • Flax plants contain single, dominant resistance genes (R) that specifically recognize flax rust races that contain complementary avirulence genes (AVR). • Avirulence genes – Genes in the pathogen that encode a protein product that is conditionally recognized directly or indirectly only by those plants that contain the complementary R gene. • Specific recognition results in the induction of the defense gene expression and the inhibition of pathogen growth.

5. Practical Interpretations of the GFG Interaction: Resistance (incompatibility between host and pathogen) is the consequence of interaction between the products of at least one host resistance gene and at least one corresponding pathogen avirulence gene. When more than one interacting gene pair are involved, the level of incompatibility is as low as, or lower than , the level produced by the most incompatible interacting gene pair acting alone. Breeding Implications: Resistance will not remain effective if the pathogen acquires the corresponding virulence by losing the avirulence allele that elicits resistance (either by deletion or genetic recombination; avirulence genes lacking, nonfunctioning or malfunctioning). However – Resistance genes can be combined together and the pathogen must evade the effect of each gene by a change at a specific corresponding locus. The pathogen must accumulate the necessary changes to allow for virulence.

6. Practical Genetics and Inheritance of Disease Resistance - Useful information: dominant or recessive; one or a few genes vs. many genes; is variation for the resistance expressed continuously or discontinuously - Durability of resistance

7. Development of TAM 302 hard red winter wheat  Pedigree: Probrand 812/Caldwell//TX86D1310 Jan 85 - Made cross Probrand 812/Caldwell (WX85D006) [Lr16/AP] Apr 85 - Harvested F1 seed May 85 - Vernalized F1 seed June-Aug 85 - Grew F1 plants in Ghse to produce F2 seed Sep 85 - Vernalized F2 seed Oct85-Apr86 - Grew F2 plants in Ghse & selected for LR resistance, harvested F3 seed Fall86-Spr87 - F3 lines (F2:3) grown as rows in field & selected for LR resistance, harvested F4 seed Fall 87 - F4 lines (F3:4) grown in Ghse; crossed WX85D006-2-17/TX86D1310 Spr 88 - Harvested F1 seed; vernalized & grew F1 plants in Ghse Fall 88-Spr 89 - Grew F2 in field & selected for LR and other characteristics Fall 89-Spr 90 - Grew selected F3 lines (F2:3) as rows in field & selected for LR, etc.

8. Development of TAM 302 hard red winter wheat (continued) Fall 90-Spr 91 - Grew selected F4 lines (F3:4) as plots in field; Plots harvested for yield Fall 91-Spr 92 - Grew F5 lines (F3:5) in field; One line, TX91D6913, was highest yielding Fall 92-Spr 93 - Tested TX91D6913 (F3:6) in replicated, multiple location trials; seed increased Fall 93-Spr 94 - Tested TX91D6913 (F3:7); seed increased Fall 94-Spr 95 - Tested TX91D6913 (F3:8); seed increased Fall 95-Spr 96 - Tested TX91D6913 (F3:9);Released to seedsmen as TAM 302

9. Singh, William, Huerta-Espino, Rosewarne. 2004. Wheat rust in Asia: Meeting the challenges with old and new technologies. 4th Int Crop Sci Congress, Brisbane, Australia

10. Singh, William, Huerta-Espino, Rosewarne. 2004. Wheat rust in Asia: Meeting the challenges with old and new technologies. 4th Int Crop Sci Congress, Brisbane, Australia