312 Diseases of Economic Plants 



in the extreme South. The evidence is also to the effect that 

 such rust as does overwinter in the South does not pass to the 

 North, but that the main source of infection in the North is 

 from the barberry. 



Some durum wheats are highly resistant to rust, and 

 recently, by selection, the Kansas Agricultural Experiment 

 Station produced a bread wheat of the Crimean group 

 that under Kansas conditions was highly rust-resistant. 

 Before the rust problem can be solved by breeding resistant 

 plants, much fundamental knowledge must be gained re- 

 garding the biologic races of the parasites and their host 

 ranges. Many wild grasses propagate and spread the rust 

 and, especially if they are exposed to infection from the 

 barberry, may bridge the way to a wheat field. Prominent 

 among those grasses are wild barley, slender-wheat-grass, 

 western-wheat-grass, and wild rye grasses. Obviously they 

 should be kept down as much as possible. 



Orange-leaf- rust (Piiccinia triiicina Eriks.). — This rust 

 of wheat and possibly of several wild grasses is the most 

 common and widely distributed of all rusts of the United 

 States and is especially injurious in the southern states. It is 

 said by Carleton that it is not only never absent from the 

 wheat fields throughout the year, but that it is sometimes 

 abundant even in dry seasons. Notwithstanding its preva- 

 lence its inroads upon the crop are not usually serious, and 

 in no case on record has it caused shriveling of the grain such 

 as is common from the black-stem-rust. 



The most conspicuous character of this rust is the presence 

 of many orange-colored sori upon the leaves, especially upon 

 their lower surfaces. The grayish black telia are neither 

 so prominent nor so profuse as in the black-stem-rust. Both 

 of these rusts possess the uredinial stage, and it is difficult 

 to distinguish them apart in this condition except by the 

 microscope. 



As with the rye orange-leaf -rust, this fungus also can winter 

 in its live uredinial mycelium and continue to bear uredinio- 

 spores throughout the year, spending its entire existence, if 



