RUST RESISTANCE OF OAT VARIETIES. 15 



crown or leaf rust, Puccinia lolii amenae McAlpine. The stem rust is 

 more common in the North, while the crown rust, though practically 

 always present, seems to be most abundant and serious in the South. 



(2) Greenhouse studies are of value in determining varietal re- 

 sistance under optimum conditions for infection. These studies, how- 

 ever, should always be supplemented by rust nursery and field trials. 



(3) Plants of more than 120 strains of oats were inoculated at two 

 different periods of growth (the seedling stage and the heading stage) 

 and their reaction to both rusts determined. 



(4) The inoculations made on these varieties were as follows : Stem 

 rust. — Seedlings, 1,256 ; headed plants, 260. Crown rust.— Seedlings, 

 1,480 ; headed plants, 260. Total, 3,256. 



(5) Of more than 120 strains tested, 80 were found to be entirely 

 susceptible to both rusts at both stages of growth. Unquestionable 

 resistance to stem rust was present in only two varieties, White Tar- 

 tarian and Ruakura Rustproof. Several varieties of the red-oat 

 group (Avena sterilis), including certain strains of Burt, Cook, 

 Appier, Italian Rustproof, Red Rustproof, and Turkish Rustproof, 

 are very resistant to the crown rust. Ruakura Rustproof and certain 

 recently introduced species of Avena also gave indications of resist- 

 ance to crown rust. 



(6) Rust resistance is shown to be specific, for many of the varie- 

 ties which are resistant to crown rust are thoroughly susceptible to 

 the stem rust under identical conditions. The evidences of resistance 

 described for wheat are shown to apply also to resistant oat varie- 

 ties. In addition, the early production of telia on seedling leaves 

 has been observed and is believed to be an indication of resistance. 



(7) Further search must be made for varieties resistant to stem 

 rust. 



(8) Varieties of the A vena sterilis group which are really resistant 

 to the crown rust, if found to be high in yield, should replace other 

 " rustproof " varieties now being grown in the Southern States. 

 None of the varieties of this group which have been tested will with- 

 stand the attacks of stem rust. 



(9) A basis is now offered for making selections and crosses to 

 produce improved oat varieties resistant to crown rust and suitable 

 for culture in the several oat-growing areas of the United States. 



