244 
Journal of Agricultural Research 
Vol. XXV, No. 5 
early springs with cool nights and heavy dews, the rust develops to a 
conspicuous extent in the principal rye-growing districts, so that by head¬ 
ing time the plants have a reddish appearance from the development of 
the uredinia of the rust. The rye plant, however, is not killed by the 
disease, and shriveling of the kernels by this rust has never been noted. 
Loss in yield is difficult to estimate, since the general prevalence of the 
rust does not permit any basis for comparison. On the other hand, it 
is hardly probable that heavy infections do not cause loss, for such infec¬ 
tions destroy much photosynthetic tissue, draw heavily on the plant’s 
supply of food material in the development of the rust and especially in 
its large spore production, and increase evaporation through the ruptur¬ 
ing of the epidermis of the rye leaves. All these are factors which vary 
with the amount of infection, the vigor of the host plant, the condition 
of the soil, and the temperature and humidity of the atmosphere. As a 
result, opinions vary as to the amount of damage which may be pro¬ 
duced. That the aggregate loss, however, may be considerable, is 
shown by the estimate made by the Plant Disease Survey of the United 
States Department of Agriculture * * * 4 for the year 1919. This is based upon 
reports from the various pathologists throughout the United States, and, 
therefore, should be a fairly accurate average. According to this estimate, 
the loss due to the leaf rust of rye in the United States for 1919 was 
placed at 538,000 bushels, a third of the estimated reduction of yield of 
rye from all diseases in that year. 
As with other rusts of the small grains, there is no feasible method of 
controlling leaf rust of rye by fungicides. Because of rather general 
winter survival of the rust in this country, elimination of the alternate 
host would be of little benefit, even if the latter occurred to any extent. 
Consequently, the discovery or development of a resistant strain of rye 
apparently offers the only promise of control of this disease. While the 
investigations of a number of workers have determined the susceptibility 
of rye as a species to specialized races of Puccinia graminis Pers. and 
Erysiphe graminis DC., as found on the other cereals and grasses, appar¬ 
ently no study has been made to determine whether varietal or individual 
differences exist in rye as to suceptibility to diseases which are specific 
to it. A few general field observations have been recorded. Sorauer 
(11) lists eight rye varieties as susceptible to “rust” in Germany and nine 
varieties as resistant. Vavilov (15) states that opinions vary as to the 
resistance of rye to P. dispersa f but that Jaczewski holds Champagne 
and the ordinary “bushy” variety to be resistant and Noviko notes 
resistance to leaf rust in Zealand, Danish Kampin, Probst, and Petkus 
rye. 5 Eriksson (<?), in the case of the snow-mold disease, states that 
Petkus rye is resistant, while Zealand is susceptible. 
As Vavilov ( 1 5) and others have pointed out, rye is a cross-pollinated 
plant with no sharply defined botanical varieties, the commercial varie¬ 
ties differing in being constituted of somewhat different complexes. 
Under such conditions, sharp varietal differences as to rust resistance are 
hardly to be expected, and the detection of resistant strains in such 
complexes is difficult, especially under field conditions, where the plants 
are intermingled so that individuals are not easily distinguished. The 
4 U. S. Department op Agriculture, Bureau op Plant Industry. Plant Disease Survey. 
Crop losses prom plant diseases in the united states in 1919. In U. S. Dept Agr., Bur. Plant 
Indus., Plant Disease Bui. Sup. 12, p. 307-332. 1920. 
4 The writers wish to acknowledge the kindness of Mr. M. N. Devine, Assistant Pathologist, Office of 
Cereal Investigations, Bureau of Plant Industry, United States Department of Agriculture, in translating 
from the Russian Vavilov's statements concerning rust resistance in rye. 
