September, 1955 FORSBERG: 
Table 11.—Changes in growth form of iso- 
lates of the gladiolus Fusarium after being 
grown for various periods of time on labora- 
tory media. 
DrrecrTion or CHance | NumBeror Iso.ates 
MeMGMANeen = Pe be Soe, 
Raised to intermediate. ... 
Raised to appressed...... . 
Intermediate to raised... . 
Intermediate to appressed. 
Appressed to intermediate. 
Appressed to raised....... 
NmPNRe KH Pwo 
changes were classified, with the two in- 
termediate forms included in a single 
group, the results shown in table 11 were 
obtained. 
Records show that variation in these 
cultures took place in both directions. Of 
the 14 isolates in which change in culture 
type was observed, 7 changed from raised 
to or toward appressed and 7 changed in 
the opposite direction. 
pH Studies.—Wellman (1942) re- 
ported that raised (virulent) and ap- 
pressed (mild) strains of the tomato-wilt 
Fusarium produced characteristic progres- 
sive pH changes in a liquid culture me- 
dium. Immediately after either of the 
strains began growing, acidity increased in 
the liquids for the first 5 days and became 
most intense in cultures of the appressed 
organism. The pH readings then gradually 
rose, but not at the same rate, until a maxi- 
mum pH of about 8.7 was reached. With 
the raised strains, neutrality was reached 
at about the twelfth day, but with the ap- 
pressed strains it was not reached until 
about the twenty-fifth day. By this time 
the pH of raised strains had nearly reached 
the maximum. ‘The appressed strains did 
not reach the same point until after the 
fortieth day. 
The 40 isolates of gladiolus Fusarium 
cultured in the studies reported here were 
grown in Tochinai liquid of the following 
composition: proteose peptone 10.0 grams, 
dihydrogen potassium phosphate 0.50 gram, 
magnesium sulfate 0.25 gram, maltose 20.0 
grams, water 1,000.0 milliliters. The orig- 
inal pH of the medium was 6.21. Each 
isolate was grown in 100 milliliters of the 
culture medium in a 250-milliliter Erlen- 
meyer flask. Uniform disks of inoculum 
FuUSARIUM DiIsEASE oF GLADIOLUS 473 
were cut from agar plate cultures with a 
sterile metal tube 9 millimeters in diam- 
eter. Each flask was inoculated with a sin- 
gle disk of inoculum. The flasks were 
shaken immediately and then left on the 
laboratory table. Small samples of liquid 
were removed from the flasks for pH de- 
termination after 3, 5, 8, 12, 15, 23, 28, 
34, 41, 50, and 58 days. All pH deter- 
minations were made with a Beckman pH 
meter, standardized at frequent intervals 
against known buffer solutions. 
The pH readings for 38 isolates are 
shown in table 12. As isolates 49-15 and 
50-27 became contaminated early in the 
experiment they are not included in the 
table. 
The progressive changes in pH _ pro- 
duced by 16 of the isolates are shown in 
figs. 15, 16, 17, and 18. Pairs of isolates 
which had shown apparent differences in 
pathogenicity were selected from each dis- 
ease form for comparison in pH reactions. 
The more virulent isolate of each pair, as 
determined by inoculation tests, is repre- 
sented by the solid line in the graphs, and 
the milder isolate is represented by the 
broken line. 
The figures show curves of the same 
general type as that obtained by Wellman 
for the tomato Fusarium. The liquid me- 
dium became more acid through the period 
of the first 5 days; then it gradually be- 
came less acid and more alkaline until a 
maximum of about pH 8.5 was reached. 
In fig. 154, vascular isolates 49-4 and 
49-23 are compared. Both isolates were 
of the raised type on Wellman’s agar, fig. 
13. Isolate 49-4 was much more virulent 
than isolate +9-23 in pathogenicity tests in 
the greenhouse. Also, isolate 49-4 caused 
rot on corms inoculated in the laboratory ; 
isolate 49-23 did not. The progressive pH 
changes produced by these two isolates 
were quite similar. 
In fig. 158, vascular isolates 50-24 and 
50-28 are compared. Both isolates were 
of the intermediate-raised type on Well- 
man’s agar. In pathogenicity tests, isolate 
50-28 was the more virulent under both 
greenhouse and laboratory conditions. Iso- 
late 50-28 reached a lower pH reading 
than isolate 50-24 and also required a 
longer time to reach maximum alkalinity. 
In these two isolates the relation between 
