Feb. 9, 1924 
Effect of Fertilizers on Stem Rust of Wheat 
349 
EXPERIMENTS IN THE GREENHOUSE IN 1914-15 
As there was no observable effect of the different fertilizers on the 
amount of stem rust in the field during the summer of 1914, experiments 
were made in the greenhouse during the winter to determine whether 
an effect could be brought about under controlled conditions. 
Wheat, oats, barley, and rye were sown in ordinary greenhouse soil, 
made up of sand, leaf mold, and black loam in 4-inch pots, where the 
plants were grown to maturity. Fertilizers were added to some and 
others were left as controls. 
Wheat plants- were inoculated with Puccinia graminis tritici and be¬ 
came quite uniformly infected with rust. The lightest infection was on 
plants which had been fertilized with acid phosphate. It was evident, 
however, that too much fertilizer had been used, since the plants were 
subnormal in vigor and size. Even when so much acid phosphate was 
used, however, that the plants were injured, the development of stem 
rust was not greatly inhibited. 
Several pots of barley were fertilized with sodium nitrate and others 
with potassium chlorid. About 20 plants were inoculated in each 
series. Practically 100 per cent became infected. The uredinia, how¬ 
ever, on the plants which had been fertilized with sodium nitrate were 
larger than were those on plants which had been fertilized with potassium 
chlorid. As there seemed to be some effect of fertilizers on the develop¬ 
ment of rust on plants growing in the greenhouse, an attempt was made 
to ascertain whether fertilizers would influence the development of 
stem rust on a semicongenial host. 
Rye was inoculated with Puccinia graminis tritici , to which it is highly 
resistant. Some of the plants were grown in soil that had been heavily 
fertilized with sodium nitrate and others were grown in unfertilized 
soil. Two of the 13 plants which had been fertilized with nitrogen 
became infected, and one of the 19 grown in ordinary soil also developed 
uredinia. There were very few uredinia on any of the plants, but the 
individual uredinia were slightly larger on the plants which had been 
fertilized with sodium nitrate. 
In order to get further data on the effects of fertilizers on the develop¬ 
ment of rust on a very highly resistant host, 58 barley plants growing 
in soil which had been heavily fertilized with sodium nitrate, and 40 
growing in soil which had been heavily fertilized with potassium chlorid, 
were inoculated with Puccinia graminis avenae . Barley is almost immune 
from this form of stem rust although minute uredinia, usually smaller 
than a pinhead, sometimes are formed. One plant in the nitrate series 
became infected, and; two of those in the potassium series developed 
uredinia. All of the uredinia were extremely small. The resistance of 
the barley plants to Puccinia graminis avenae certainly was not broken 
down by excessive fertilization with nitrogen, nor did the resistance 
seem to be increased by heavy fertilization with potassium chlorid. 
In order to get still more information regarding the effect of stem rust 
on a congenial host, experiments were made with Puccinia graminis 
avenae on oats. Acid phosphate was added to the soil in some of the 
pots, while no fertilizer was added to others. So much acid phosphate 
was added that the tips of the leaves burned slightly. The degree of 
infection was about equal in both series. However, sometime after the 
plants had become infected, the uredinia seemed to be larger on the plants 
