49 



Studies on Expcrtnicnlally Produced Physiologic Races of tJie 



Oat Siiiiits 



Dr. L. Gordon Utter has continued his infection studies with 

 13 new races which resulted from his hybridization experiments 

 between tlie loose and covered smuts of oats. These races were 

 selected on the basis of their sym])toms, morjjhology and patho- 

 genicity on differential host varieties over a four year period. 

 Eight races of the covered smut and 5 of the loose smut were 

 obtained on Gothland, Rossman, Monarch Selection, Seizure and 

 Monarch oat varieties. The covered smut types gave a range of 

 infection up to 100 ])er cent, on Gothland and other varieties. 

 Monarch showed full resistance to all but one race, and then with 

 only 40 ]:)er cent, infection. Infections with the loose smut races 

 ranged from 63 to 100 ])cr cent, on Monarch, while Gothland was 

 fully resistant to three races. Both Monarcli and Gothland were 

 100 per cent, infected by one race. Since Gothland is normally 

 resistant to the covered smut but susceptible to the loose smut, 

 and Monarch is resistant to the loose smut but susceptible to the 

 covered, the new races selected show recombinations for symptoms, 

 morphology and pathogenicity which make tlicm distinctive. 



Smut spores from these races were used to inoculate the varie- 

 ties cited and also Early Chamjjion, during the past season. The 

 results generally indicated that the same degree of infection was 

 maintained by these races toward Monarch and Gothland. Fur- 

 ther, identical percentages of smut were frequently obtained on 

 the same variety from which the race was selected. A few races, 

 however, showed either higher or lower infections. 



Tests were also made with smut collections from other oat 

 varieties which occurred in the same original series with the 

 selected new races. The ol)ject was to determine wliether such 

 collections corresponded in infection behavior to the designated 

 race from a given series. The results indicated that slight to 

 decided diiTerences in infection of the oat varieties occurred with 

 these collections and in only one instance was the percentage of 

 smut comparable with that of the race. 



The variability of smut percentages shown by the collections 

 would suggest that they are still undergoing segregation for 

 pathogenicity since their symptoms and morphology remain un- 



