RUST RESISTANCE OF OAT VARIETIES. 13 



DISCUSSION OF RESULTS. 



The notes in Table I on the varieties which showed resistance to 

 one or both rusts indicate that rust resistance is very specific and 

 that a particular variety may be entirely susceptible to one rust and 

 somewhat resistant to the attacks of another. 1 



Of the 122 strains tested. 80 unquestionably were susceptible to 

 both rusts in both stages of growth. This does not imply that these 

 varieties are not of great commercial value in other respects and is 

 not sufficient reason for discarding them from cultivation, for at 

 present there are no suitable varieties to substitute for the best of 

 them. It probably does remove them, however, from the list which 

 is to afford promise of rust-resistant varieties. Heavy infections 

 were obtained on practically all of these, and at least some normal 

 uredinia were formed on all. "While such greenhouse tests do not 

 represent field conditions accurately, the optimum conditions for 

 infection provided should make the evidences of resistance which 

 appeared in some varieties all the more valuable. Some of these 

 varieties may show some resistance under field conditions and some 

 of them have properly been recommended as rust-escaping because 

 of their early-ripening habit, as, for instance, the Sixty-Day and 

 Kherson varieties. 



In 80 out of the 122 cases the results at two distinct periods in the 

 life of the host plant have led to identical conclusions as to the sus- 

 ceptibility of the variety. In some of the resistant varieties, also, 

 both seedlings and mature plants gave the same evidences of re- 

 sistance, though the results are not always in agreement. These 

 susceptible varieties need not be discussed in further detail, but the 

 list includes the following commonly grown sorts: American Ban- 

 ner, Big Four. Ligowo, Lincoln, Siberian. Sixty-Day. Swedish 

 Select, and "White Russian. In this list are included also most of 

 the botanical species represented and nearly all of the recently intro- 

 duced foreign varieties. 



In the Avena stenlis group also, where most of the resistance to 

 crown rust is found, several strains are very susceptible to the crown 

 rust, as. for instance. Greenhouse No. 296, Red Algerian, and one 

 strain each of Golden Rustproof, Italian Rustproof. Red Rustproof, 

 and Turkish Rustproof. 



Xot all varieties of the Avena stenlis group show perceptible re- 

 sistance to either rust, and great care should be exercised in recom- 

 mending to farmers these or other varieties as rust resistant. Still 

 greater care is necessary in choosing a strain to use as a parent 



1 The studies of these varieties indicate the necessity for selecting and working from 

 individual plants, for certainly within the same variety, and even within a line supposed 

 to be pure for other characters, differences of a major degree in rust resistance exist. 



