48 



J. C. ZADOKS 



MICROFIELD 



O O OO O 



O O O O O 



OOIOO 



o o o o o 



o o o o o 



polycyclic test 

 < ► 1 m 



O test hill 



• inoculated hill 



I 



Figure 3. Design of a field experiment for polycyclic testing 

 estimate cumulative effects of partial resistance. A single 

 Puooinia veoondita isolate, inoculated on the central among 

 25 clumps of a single wheat cultivar, spreads over the popula- 

 tion of host plants in successive infection cycles. Clump 

 spacing as in Fig. 2. 



RUBIS 

 RUBIS 



FLAMINGO 



HEINES VII 





150 160 170 



DAYS FROM JANUARY 1 



Figure 4. Demonstration of "slow rusting" in polycyclic tests. 

 Four plots were established and inoculated as in Fig. 3, two of 

 the plots containing the susceptible (control) cultivar Rubis , 

 and the other two the widely-grown, slow rusting cultivars 

 Heines VII and Flamingo. Differential rates of rust epidemic 

 build-up are reflected in the differential slopes of the curves. 



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