Nov. 1, 1925 
Ophiobolus graminis and Take-All of Wheat 
811 
extremely acid and alkaline cultures, thus indicating that the concen¬ 
trations necessary for inhibition lay slightly beyond the hydrogen-ion 
concentrations used in the experiment, which were P H 4.8 to P H 10.0 + 
for nutrient-broth growth and P H 4.6 to P H 10.0+ for Czapek’s 
solution. In nutrient broth growth was best in cultures with an 
initial hydrogen-ion concentration of P H 6.6. In Czapek’s solution the 
greatest growth also occurred near this point. However, there was 
no striking optimum in the case of this medium. Final hydrogen-ion 
determinations of the media showed that all of the cultures involving 
Czapek’s full nutrient solution became more acid with the growth of 
the fungus. The acid and slightly alkaline cultures of the nutrient 
broth shifted their reactions to greater alkalinity, while the most 
alkaline cultures tended to become slightly less alkaline. Unfortu¬ 
nately, no final determinations were made on the checks, so that it is 
impossible to say whether or not the latter changes were due to the 
growth of the organism or merely to changes in the reactions on 
standing. 
Table III. — Influence of hydrogen-ion concentration of nutrient broth and Czapek’s 
solution on the growth of the mycelium, of the Oregon strain of Ophiobolus graminis 
Nutrient broth 
Czapek’s solution 
Initial 
Final 
Average 
Initial 
Final 
Growth 
Average 
Ph 
Ph 
vjrrow tn 
growth 
Ph 
Ph 
VXIU VY bll 
growth 
Gm 
Gm. 
Gm. 
Gm. 
4.8 
5.4 
0.033 
4.6 
4.2 
0.018 
4.8 
6.4 
.045 
0.039 
4.6 
4.2 
.020 
0.019 
5.0 
8.4 
.100 
6.0 
5.4 
.007 
5.0 
8.4 
.105 
.102 
6.0 
5.4 
.010 
.0085 
5.4 
8.4 
.090 
6.4 
5.8 
.025 
5.4 
.090 
6.4 
5.8 
.020 
.0225 
6.6 
8.6 
.120 
6.4 
6.0 
.030 
6.6 
8.6 
.120 
.120 
6.4 
6.0 
.035 
.0325+ 
6.8 
8.8 
.095 
6.4 
6.2 
.025 
6.8 
8.6 
.105 
.100+ 
6.4 
6.2 
.035 
.030 
8.0 
8.8 
.085 
7.8 
7.6 
.020 
8.0 
8.8 
.095 
.090 
7.8 
7.8 
.020 
.020 
10.0 
8.8 
.040 
9.4 
8.0 
.020 
10.0 
8.8 
.055 
.0475 
9.4 
8.0 
.025 
.0225 
10+ 
8.8 
.050 
10+ 
6.4 
.020 
10+ 
8.8 
.070 
.060 
10+ 
6.0 
.015 
.0175 
10+-J-O 
9.2 
.025 
10 1 
8.2 
.015 
10++ 
9.2 
. 035 
.030 
10++ 
8.2 
.020 
.0175 
• In the alkaline range, more NaOH was added to each succeeding flask; therefore, as one reads these 
figures, each 10+ had more chemical added than the previous one. 
Although there are certain variations in the results in Table III, 
a few general conclusions may be drawn. The ranges of hydrogen-ion 
concentration in which Ophiobolus graminis will grow favorably are 
about the same for potato-dextrose agar, nutrient broth, and Czapek’s 
solution. Growth took place in all cases where cultures possessed 
an alkaline reaction of or greater than P H 10.0+ , but it was very 
slight. This value, then, could be stated as approximately the most 
alkaline reaction in which vegetative growth of Ophiobolus graminis 
occurred. On the other hand, the most acid reaction permitting 
growth varied from P H 3.0 and P H 3.8, depending on the strain of the 
Fungus. In these experiments the optimum hydrogen-ion con¬ 
centration for the different strains varied too much to draw definite 
conclusions, except that if an average were taken it would occur on 
the acid side of neutrality. 
