82 EVA FUCHS 



Also, Manners (1969) postulated the following; If and when a change 

 to a new set of differential-hosts is made, the new set will need to 

 satisfy the following criteria: 



1) It will need to be efficient as defined by Person (1959), i.e., 

 each host variety shall carry only one of the resistance genes. 



2) It shall take into account mature plant as well as seedling 

 reactions, so that the absurdity of having "field races" not integrated 

 with the race determined by the more usual seedling tests made necessary 

 by the present system in some cases, especially in yellow rust, may be 

 avoided. 



3) It should only include hosts that are genetically stable, and 

 whose reactions are not influenced by environmental changes. As far as 

 possible, hosts giving intermediate reactions should be avoided. 



4) It is generally accepted by workers in the field concerned. 



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 Brown, J. F., and E. L. Sharp. 1969. Interactions of minor host genes 



for resistance to Pucoinia striiformis with changing temperature 



regimes. Phytopathology 59: 999-1001. 

 Fuchs, E. 1960. Physiologische Rassen bei Gelbrost {Pucoinia glumarum 



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