50 



J. C. ZADOKS 



RESISTANCE 



1 CV 



Figure 5. The "one race - one cultivar" interaction, with resis- 

 tance nearly complete. 



RESISTANCE 1 RACE 



I 2 3 U 5 CULTIVARS 



Figure 6. The "one race - many cultivars" interaction showing the 

 "infection spectrum" (Zadoks, 1966) that indicates differential 

 virulence. 



RESISTANCE 1 CV 



Figure 7. The "one cultivar - many races" interaction showing 

 the "resistance spectrum" (Zadoks, 1966) typical for differen 

 tial resistance. 



