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REPORTS ON RESEARCH FOR 1929 

 Plant Pathology 



By Geokc]'. M. Reed 

 Physiologic spccializalion of flic oat siintts 



In 1924 we ])ul)lishe(l our first data, givius^- definite evidence 

 of the existence of specialized races of both loose (UstUago 

 avcnac) and covered {U. Icvis) smut. The data were obtained 

 from two collections of both of the smuts, and each collection 

 showed well marked dififerences in its capacity to infect varieties 

 of oats. A second paper dealing with the same problem was 

 published in 1927. and contained the account of the demonstration 

 of specialized races characterized l)y their capacity for infecting- 

 the cultivated varieties of ]^ed ( )ats, wdiich are grown more or 

 less extensively in the southern ])art of the United States. In 

 tliese experiments tw^o distinct races were differentiated, one of 

 which proved cai)able of infecting Fulghum and related varieties, 

 while the other seemed to 1)e largely confined to the Red Rust- 

 proof types. 



During- the ])ast few years several additional collections of both 

 loose and covered smut have been obtained from various sources. 

 Many of these have lieen secured in the United States, while others 

 have come from various parts of Europe, and one from China. 

 These collections have been used to inoculate definite strains or 

 selections of oats in order to determine whether they showed dif- 

 ferences in tbeir capacity for infection. Relatively few varieties 

 of oats have been used in all of these experiments, but they have 

 served to difl'erentiate distinct races of smut. Altogether, twenty- 

 eight varieties l)eloni;ing to seven different species have been grown. 



Adequate data on fifteen collections of the loose smut have been 

 secured, and eleven distinct races have been found. Nine col- 

 lections of the covered smut have also been used, and there is 

 definite evidence of five distinct specialized races. 



Some of the more important ]:)oints in the behavior of the oat 

 varieties may be mentioned. The wild oat (Avcna barbata) 

 seems to be perfectly susceptible to every race of loose and cov- 



