[newton] wheat stem RUST 183 



Attention should be drawn to two other rather striking facts, 

 evident in the diagrams. It will be seen that Khapli, an emmer from 

 India, is resistant to every form of rust found, while Little Club is 

 completely susceptible in all cases. From the standpoint of the 

 plant breeder, it is unfortunate that Khapli is very difificult to hybridize 

 successfully with the bread wheats. 



Importance of Forms Isolated 



The factors which determine the importance of- a biologic form 

 are its varietal range and virulence, and its distribution and frequency 

 of occurrence. 



Varietal Range and Virulence. 



A glance at Table III will show that rusts from different localities 

 vary greatly in their parasitic behaviour to wheat varieties. Marquis, 

 a wheat quite susceptible to practically all forms of rust in Western 

 Canada, is highly resistant to a form found at Indian Head. Four 

 distinct biologic forms were found at Saskatoon ; one of these infected 

 White Spring emmer very heavily, while another scarcely infected it 

 at all. In the same way, Kanred showed heavy normal infection at 

 Brandon, Yorkton, Moose Jaw, and Edmonton, and complete im- 

 munity at Winnipeg, Prince Albert, and Lacombe. One of the forms, 

 XV, was very virulent on all but one of the varieties inoculated, 

 while another, III, was so weak that it could attack only a few 

 varieties successfully. Several forms differed from one another only 

 in their action on one or two varieties, but these differences were 

 always definite and consistent. 



Usually more than one biologic form was found on the same 

 variety, sometimes even on the same plant. From one rusted plant 

 collected at Rosthern, Saskatchewan, were isolated three distinct 

 forms. III, IX, and XVII. On the other hand, the same form was 

 present on a great variety of hosts and apparently was not changed 

 in any way by association with this host. One form collected on 

 barley, emmer, club wheat, and various other varieties of spring and 

 winter wheats, as well as on wild grasses, gave the same reaction in all 

 cases, whether taken from the wild glasses of northern Alberta or 

 from the hard spring wheats of southern Manitoba. This constancy 

 of behaviour will be more fully discussed in a later section of this 

 paper. 



