RaCE differentiation in CEREAL RUSTS 69 



(3) differentiating and useful (a very few) , and 



(4) generally resistant (a few) . 



In groups (2) and (3) only one really new differential variety group has 

 been found during 7 years of testing, i.e., nearly all varieties differ- 

 entiating at all reacted like the already known differentials, although 

 at different intensities. Cappele and Heines Peko in Table 1 are addi- 

 tional differentials. The varieties in Table 2 show a decreasing line of 

 clear infection types (Fuchs , 1966). 



Table 2. Supporting differentials used for race determination 

 based on seedling reaction types 



Variety Race 5/55 Race 54 Race 20A 



Vilmorin 23 IV i-0 



Nord Desprez IV- i-0 



Cappelle Desprez O-IV i-0 i 



Heines Kolben IV II 



Heines Peko i-0 II-IV 



Lee IV 



Reichersberg 42 O-IV 



I have to give an explanation to the note "O-IV", which looks like 

 nonsense. The wheat variety-stripe rust system is sensitive to all kinds 

 of environmental influences. I will discuss this point later. The addi- 

 tional differentials like Cappelle and Heines Kolben don't always give 

 reproducible results. Still they serve in determinations to some extent, 

 since this variability seems to be under genetic control. Sometimes 

 there are different infection types on plants in one test pot, so that 

 the reading "O-IV" means a variation under absolutely equal conditions. 



.An explanation to the type "i-0" is also called for. Very often 

 these supporting differentials show less definite infection types than 

 the main differentials do in the same replication. 



It is up to you to decide if a variety is to be a differential or 

 not, and concurrently how many races you are going to nominate. This 

 process of looking for differentials and reassuring the results never 

 will stop, combined of course with a strong selection of the differential 

 variety seed. But what about practical importance and necessity. The 

 race determination that we do in Europe may be of little value to other 

 areas. Fourteen years ago the Netherlands Grain Center started a 

 European yellow rust trial which still is working for Europe and other 

 areas as well. At Braunschweig, Germany, we try to identify the physio- 

 logic races in the stripe rust samples sent from these trials. Through 



