Aug. 4,1923 
Resistance in Rye to Leaf Rust 
247 
were various degrees of resistance among these, some having uredinia of 
normal size each surrounded by a large, sharply defined killed area 
(PI. 2, F); others having uredinia much reduced in size but usually 
accompanying each hypersensitive area (PI. 2, G); still others in which 
the hypersensitive areas were numerous and definite but only occasionally 
containing a small uredinium (PI. 2, H); and finally those where the only 
sign of infection was a few more or less indefinite hypersensitive areas, 
no uredinia being produced (PI. 2, I). In all cases where hypersensitive 
areas were present, they were of fairly good size, nothing which might 
be called flecking apparently being produced. 
Vavilov (14) gives a system of classification for the types of suscepti¬ 
bility shown by wheat varieties to the leaf rust of wheat, Puccinia 
triticina , a rust very similar in many ways to the leaf rust of rye. He 
states that this system is a modification of that used by Eriksson, in 
which five degrees are recognized and are designated by numerals, from 
o (no pustules) to 4 (very pronounced susceptibility). Vavilov, besides 
using the number of pustules produced, considers the character of 
development of the fungus of importance, such as the presence of killed 
areas with or without uredinia. A somewhat similar system of classifi¬ 
cation has been used by Stakman and Levine ( 12 ) for the susceptibility 
of wheat varieties to stem rust, P . graminis. In a similar system of 
classification, the types of leaf rust infection of rye should be arranged 
as follows: 
o. No uredinia formed; hypersensitive areas sometimes present and 
definite, sometimes faint or absent. Plate 2, I. 
1. Uredinia few, minute, in the center of definite hypersensitive 
areas; few to many hypersensitive areas without uredinia. Plate 2, 
H, G. 
2. Uredinia fairly abundant, moderate in size but always surrounded 
by hypersensitive areas; hypersensitive areas seldom without uredinia. 
Plate 2, F. 
3. Uredinia abundant, moderate in size, without hypersensitive areas 
but in some cases surrounded by slightly chlorotic tissue. Plate 2, C, B. 
4. Uredinia abundant, very large, hypersensitiveness absent but 
uredinia occasionally in green islands. Plate 2, A, E. 
X. A combination of several of the above types appearing on the 
same leaf, some uredinia large and without hypersensitiveness, others 
small and accompanied by hypersensitive areas. 7 Plate 2, D. 
The manner of inheritance of rust resistance can not be determined 
from the results thus far secured. The results obtained from the 
crosses between the two resistant plants 8 and 9, however, are of interest 
at this time. From the seed obtained as the result of these crosses, 111 
plants were grown. Of these, 2 show r ed a high susceptibility like A, 
Plate II; 7 were like B; 9 like C; 11 like D; 19 like F; 38 like G; 17 like 
H; and 8 like I. In other words, two rye plants showing high resistance, 
when crossed may produce in their offspring almost all degrees of sus¬ 
ceptibility. As shown in Table I, the other crosses and the seJfs furnished 
only 78 kernels altogether. The plants grown therefrom did not furnish 
additional evidence from which definite conclusions could be drawn. 
Studies of the inheritance of susceptibility and resistance are being 
continued with this material. 
1 1 n some cases this mixture of types of infection may indicate a mixture of strains of the rust; but rein¬ 
oculations in a few cases with the large uredinia from such mixed types have continued to give the mixed 
type. These cases, in consequence, would fall into the heterogeneous class X established by Stakman and 
Tevine (ra). 
