AMERICAN 
JOURNAL OF BOTANY 
Vol. 9 April, 1922 No. 4 
HYDROGEN-ION CONCENTRATION IN ITS RELATION TO 
WHEAT SCARi 
E. F. Hopkins 
(Received for publication July 9, 192 1 ) 
That the reaction of the soil affects the severity of certain soil-borne 
plant diseases such as potato scab and the club-root of cabbage has been 
known for many years. That the hydrogen-ion concentration of the soil 
solution, however, is the controlling factor was not appreciated until Gillespie 
(i, 2) demonstrated that the soil solution has a definite hydrogen-ion con- 
centration which can be easily determined, and Gillespie and Hurst (3, 4) 
showed that the hydrogen-ion concentration of the soil solution is apparently 
the controlling factor in the incidence of potato scab. The demonstration 
of the close relation between hydrogen-ion concentration and this soil- 
borne disease suggests that a complete and thorough investigation should 
be made of the relation of hydrogen-ion concentration to the development 
of other pathogenic organisms carried in the soil and to their ability to 
infect the host. In the present paper, a study is presented of the relation 
of hydrogen-ion concentration to the growth of Gihherella Saubinetii, the 
causal organism of wheat scab, and to the ability of this organism to pro- 
duce seedling infection in wheat. 
The Effect of Hydrogen-ion Concentration on the Growth of 
GiBBERELLA SaUBINETII (MoNT.) SaCC. 
Comparatively little work has been done on the relation of hydrogen-ion 
concentration to the growth of pathogenic or non-pathogenic fungi. Clark 
and Lubs (5) grew Aspergillus niger on a mineral nutrient solution plus 
sucrose and found that the hydrogen-ion concentration on the seventh day 
was 2 X io~^ (ph = i-7o)- E)uggar, Severy, and Schmitz (6), in studying 
certain fungi in plant decoctions, found that in all solutions they used except 
sugar-beet and cornmeal decoctions, Aspergillus niger caused a shift towards 
the acid side equivalent to a hydrogen-ion concentration of about io~^ 
(Ph = 3-o)> while Macrosporium commune and Glomerella Gossypii generally 
evidenced a pronounced change in the other direction. With these latter 
two organisms the reactions of turnip, beet, and potato decoctions were 
changed from io~^ to io~^ (pn = 6.0 to 8.0). The authors state that 
^ Published by permission of the Director of the Missouri Agricultural Experiment 
Station. 
[The Journal for March (9: 93-157) was issued April 24, 1922] 
159 
