24 



THE RUSTS OF GRAINS IN THE UNITED STATES. 



to determine whether or not this rust goes more easily to the other 

 cereals after having been grown on barley, as is the case with the 

 stem rust of wheat. Carleton (30, p. 20) reports negative results 

 with Puccinia rubigo-vera tritici in inoculations on oats, barley, and 

 rye. This indicates either that the strain of rust which he used for 

 his inoculations may have been slightly different from the strains 

 used in our inoculations, or that the conditions were not as favorable 

 for infection. Such a difference in strains, perhaps, may exist in 

 the same species of rust gathered from different localities even in 

 the same country. 



Diagram 18 presents a summary of inoculation experiments with 

 Puccinia simplex (leaf rust) from barley. 



Diagram 18. — Summary of inoculation experiments with leaf rust from barley. 



»■? 



'37 



44 

 46 







•so' 



These experiments indicate that the leaf rust of barley is closely 

 confined to the one host, barley, as no infection took place on either 

 wheat, rye, or oats in a large number of inoculations on each. In 

 this particular it is very different from the stem rust of barley, which 

 may be transferred to the other three cereals. 



Diagram 19 presents a summary of inoculation experiments with 

 Puccinia rubigo-vera secalis (leaf rust) from rye. 



Diagram 19. — Summary of inoculation experiments with leaf rust from, rye. 



o 



Wt. (most leaves flecked). 



R 35 





 B Hq (many leaves flecked 



The leaf rust of rye is also highly specialized and in numerous 

 inoculations did not transfer to the other cereals. Carleton's results 

 (30, p. 43) in numerous trials are identical. The flecking of the 

 wheat and barley showed that they were infected with the rust, but 

 that extensive development of the rust mycelium did not take place. 

 The rye stem rust, on the other hand, easily transfers from rye to 

 barley. * 



Diagram 20 presents a summary of inoculation experiments with 

 Puccinia coronata (leaf rust) from oats. 



216 



