470 
Fusarium vasinfectum Atk., cultures that 
exhibited abundant aerial mycelium and 
grew rapidly were in the highly path- 
ogenic group, but that variation from this 
cultural type may or may not be paralleled 
by decrease in pathogenicity. Wellman & 
Blaisdell (1941), in a study of pathogenic 
and cultural variation among single-spore 
isolates from strains of the tomato-wilt F'u- 
sarium, reported that the raised form is 
the most highly pathogenic, the appressed 
is mildest, and intermediate cultural types 
are intermediate in pathogenicity. In a 
later study, Wellman (1942) reported 
that these pathogenically and culturally 
variable strains of the tomato-wilt Fu- 
sarium also could be distinguished by dif- 
ferences in pH relations. 
Many studies have been made on 
changes occurring in laboratory cultures 
of Fusarium. Burkholder (1925) re- 
ported that an isolate of Fusarium mar tii 
phaseoli Burkh. lost some of its virulence 
during its 5 years in culture. He noted 
changes in morphology and_ physiology, 
also. When first isolated, the pathogen 
produced on most media a blue-green slimy 
growth. At the end of 6 years the growth 
was white and fluffy. Armstrong, Mac- 
Lachlan, & Weindling (1940) reported 
that variations of the cotton-wilt Fusarium 
were chiefly in two directions: decrease in 
abundance of aerial mycelium and de- 
crease in the rate of radial growth. No 
changes occurred in the opposite direction. 
Isolates that had long been retained in cul- 
ture were weakly pathogenic. Their cul- 
tural characteristics indicated that they 
were variants which had arisen in culture. 
These same authors reported that a cul- 
tural variant may or may not be less path- 
ogenic than the isolate from which it has 
arisen. 
McCulloch (1944) noted that varia- 
tions and changes in pathogenicity oc- 
curred in isolates of the organism she 
called Fusarium orthoceras App. et Wr. 
var. gladioli. She observed that patho- 
genicity of this vascular Fusarium was re- 
duced by long periods of culture in arti- 
ficial media but she kept no extensive rec- 
ords of the changes. She also found that 
the isolates varied in their ability to infect 
different gladiolus varieties. Although she 
observed that some isolates produced dense 
Ittinois NaturAL History SuRVEY BULLETIN 
Vol. 26, Art. 6— 
aerial mycelium and others were of the 
appressed type, she made no attempt to as- 
sociate these characters with differences in 
pathogenicity. 
Several investigators have reported 
cases of physiologic specialization in cer- 
tain species of Fusarium.  Broadfoot 
(1926) reported that at least nine physio- 
logic forms of F’. lini Bolley can be distin-— 
guished by their parasitism on four varie-— 
ties of flax. Armstrong & Armstrong 
(1950) wrote that there are definitely two 
Table 10—Growth forms of isolates of the 
gladiolus Fusarium when originally cultured 
on potato dextrose agar and when grown on 
Wellman’s agar, August, 1953. a 
——————— 
GrowrH Form 
OF ORIGINAL GrowTH FoRM ON 
IsoLvaTe | ISOLATES ON WELLMAN’s AGAR, 
Porato Dex- 1953 
TROSE AGAR 
45-73...| Not recorded | Raised 
45-80...| Not recorded | Intermediate-appressed 
46-3....| Not recorded | Appressed é 
46-5....| Intermediate | Intermediate-appressed — 
46-9....| Intermediate | Intermediate-raised 
46-14...| Not recorded | Intermediate-raised 
47-6....| Raised Intermediate-raised 
47-10...) Raised Intermediate-raised 
49-4....| Intermediate | Raised "7 
49-15...| Raised Appressed 
49 -23...| Raised Raised 
49 -30...| Raised Intermediate-raised 
49-31...| Intermediate | Appressed 
50-6....| Not recorded | Intermediate-raised 
50-24...| Not recorded | Intermediate-raised 
50-27...| Not recorded | Raised 
50-28...| Not recorded | Intermediate-raised 
45-8....| Raised Raised 
45-74...| Not recorded | Appressed 
45-75...) Not recorded | Intermediate-raised 
45-78...| Not recorded | Intermediate-appressed 
46-4....| Appressed Intermediate-raised 
46-12...| Intermediate | Intermediate-raised 
47-1....| Appressed Raised a 
47-8....| Appressed Intermediate-appressed 
47-12...| Not recorded | Raised 
47-19...| Appressed Intermediate-raised 
47 -32...| Raised Raised 
49-1....| Intermediate | Appressed 
49-17...) Appressed Appressed 
49-19...| Intermediate | Intermediate-raised 
50-7....| Not recorded | Intermediate-appressed 
50-22...| Not recorded | Intermediate-raised 
50-25...| Not recorded | Intermediate-raised 
47-2....| Appressed Intermediate-raised 
47-3....| Appressed Raised 
49-8....| Raised Intermediate-raised 
49-20...| Intermediate | Intermediate-appressed 
50-23...}| Not recorded | Raised 
50-26...| Not recorded | Raised 
