Feb. 9, 1924 
Effect of Fertilizers on Stem Rust of Wheat 
343 
Hiltner (12), in 1914, noted that excessive use of Chile saltpeter greatly 
increased the amount of rusts on fall-sown wheat, but excessive amounts of 
ammonium sulphate did not increase them as much. 
In 1915, Stranak (33), in his investigation of the effect of fertilizers 
on infection of wheat by P. glumarum, observed the greatest injury 
when the soil fertilization was unbalanced. Wheat grown on insuffi¬ 
ciently fertilized soil suffered the greatest damage. But wheat over¬ 
fertilized with nitrogen, especially when there was an insufficient supply 
of potash or phosphates, also was nearly always severely rusted. 
Molz and Muller ( 21 ) in 1914 and 1916 concluded that potassium and 
phosphate fertilizers increased the resistance of wheat to stripe rust, and 
that the effect of nitrogen was uncertain. 
Stakman (31) in 1913 made experiments on the effect of nutrient salts 
on the development of P. graminis on wheat plants in soil and sand 
cultures and found that excessive amounts of such fertilizers as nitrogen 
and phosphorus salts had no direct effect on the immunity or suscepti¬ 
bility of wheats. He considered temperature conditions and atmospheric 
humidity probably more important than soil conditions. 
Armstrong (2), in 1922, pointed out that wheat fertilized with sodium 
nitrate was delayed and opportunity for the development of P. glumarum 
was increased. He attributed the effect of nitrogen to a lengthening of 
the growing period rather than to an actual increase of susceptibility. 
Gassner (jo), investigating the effect of fertilizers on the development 
of rusts of wheat, oats, barley, rye, and maize, in Uruguay, found that 
an apparent effect of fertilizers on the development of P. graminis was 
due to the effect on maturity of the host plants rather than to a change 
in the actual resistance. 
Vavilov (36, p. 60-61) concluded that the apparent increased sus¬ 
ceptibility of wheat to Puccinia triticina , when grown in soil fertilized 
with nitrogen, was due to increased development of leaf surface rather 
than to any change in real resistance. He grew 30 pure-line selections 
of spring wheat, of varying degrees of resistance to P. triticina, in un¬ 
fertilized soil and also in soil heavily fertilized with potassium nitrate. 
There were only slight differences in the amount of rust on the plants in 
different plats, and resistant varieties remained resistant under all 
conditions. 
Raines ( 23 ) studied the factors governing the virulence of P. coronata 
Cda., P. secalina Grove, P. triticina Erikss., and P. sorghi Schw. He was 
of the opinion that “ a more catholic point of view in pathologic thought, 
recognizing that, for longer or shorter phases in the course of a disease, 
the relation between host and parasite may be highly mutualistic, would 
be of material value as a working concept in the study of diseases and in 
defining the practical problem of disease prevention and control.” 
This conclusion, in general, corroborates the evidence given by Ward 
(39), Arthur (3), Sheldon (27), Gibson (jj), Stakman (31), Fromme 
(9), Mains (17), and others that the vigor of various rust parasites is 
likely to be directly proportional to the vegetative vigor of the host. 
The observations of Zavitz (41) on the effect of spacing also may be ex¬ 
plained on the basis of greater vegetative vigor. Butler ( 6 , p. 473-474 ) 
gives some evidence, however, that well nourished coffee bushes can 
withstand attacks by coffee rust, Hemileia vastatrix B. and Br., better 
than those which are growing under less favorable conditions. 
It is apparent that the general consensus of opinion is that nitroge¬ 
nous fertilizers increase the susceptibility of cereals to rusts, while potas- 
