BUST RESISTANCE OF OAT VARIETIES. 15 
crown or leaf rust, Puccinia lolii avenae 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 Avena sterilis group which are realty 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. 
