June, 1955 
Table 21.—Per cent of mats of Endoconid- 
iophora fagacearum with perithecia, average 
number of perithecia on a 6-mm. square area 
of mat surface, and average per cent ger- 
mination of ascospores (465 mat samplings in 
five condition classes*). 
Curt: Oak Witt INOcCULA 
NuMBER 
Patan (2° PErR- PER 
ae aa tans sy gp ON ae 
-MM ERMI- 
cae ee SQuaRE |NATION OF 
BASS ea AREA OF Asco- 
Trees Mar SPORES 
SuRFACE 
@lass Ty... .. 0 (0) 0) 
Glassell... 21 23 16 
Class III. 36 45 33 
Class IV.. 33 32 17 
Class V... 6 16 11 
* Condition class I, immature; II, mature; III, aging; 
IV, declining; V, deteriorating. 
Table 22—Numbers and per cents of posi- 
tive cultures obtained by mass transfers of 
pad cells from mycelial mats of Endoconidio- 
phora fagacearum in five condition classes* 
over the 10-month period October, 1952, 
through July, 1953. 
NumBerR |Per Centr 
alae Seen GIVING GIVING 
Cpass eet Positive | Posirive 
Cuttures | CuLTuRES 
Class Ls 26... 68 56 82 
Class II..... 57 24 42 
Class III..:.. 64 16 25 
Class IV..... 112 0 0) 
Class V...... 122 0 0 
* Condition class I, immature; II, mature; III, aging; 
IV, declining; V, deteriorating. 
and many old mats had masses of asco- 
spores infested by nematodes, bacteria, and 
spores of fungi other than Endoconidio- 
phora fagacearum. In neither of these 
types of mats were ascospore germination 
tests possible. 
The average number of perithecia per 
mat sample and the average percentage 
of ascospores germinating in four mat 
classes are treated graphically by months 
in fig. 22. Perithecia were found in all 
months except July; the largest average 
number per mat sample, 44, was found in 
May. However, germination of asco- 
spores was obtained only in October, No- 
vember, April, May, and June. The best 
average germination rate was 49 per cent, 
obtained with ascospores collected in 
317 
April; 32 per cent germination was ob- 
tained with ascospores collected in May. 
In some cases, as high as 83 per cent of 
the ascospores germinated. 
Like conidia, perithecia and ascospores 
were strikingly influenced by the extent 
of mat development or decline, table 21. 
Of 465 mat samplings in all areas and all 
months of the study period, class III, 
aging mats, had the highest percentage 
with perithecia, 36 per cent. Mats of 
this class contained the greatest number 
of perithecia, an average of 45 on a 6 mm. 
square area of mat surface, and they had 
the highest rate of germinating asco- 
spores, 33 per cent. Mats frequently had 
as many as 90 perithecia on a sample 6 
mm. square. 
Mycelial Pads 
A potential source of oak wilt inoculum 
which should not be overlooked is that 
afforded by the highly germinable cells 
that comprise the central pads of mycelial 
mats. The ability of these cells to ger- 
minate and produce large numbers of 
conidia was shown in laboratory studies. 
From October, 1952, through July, 
1953, 423 mycelial pads on mats of all 
five condition classes were sampled in the 
field. The results of mass transfers from 
the interiors of these pads to potato dex- 
trose agar are given in table 22. Eighty- 
two per cent of the pads from class I 
mats, 42 per cent of the pads from class 
II mats, and 25 per cent of the pads from 
class III mats gave positive cultures of 
Endoconidiophora fagacearum. The living 
fungus was never isolated from pads of 
class IV and class V mats. 
DISCUSSION 
The present study has shown that three 
potential oak wilt inocula are present in 
nature in Illinois. These are conidia, 
ascospores, and mycelial pad cells, all of 
which are furnished by the macroscopic 
subcortical fruiting mats of Endoconidio- 
phora fagacearum on wilt-killed oaks. 
The mats on which conidia and perithe- 
cia form develop readily on both standing 
diseased trees and trees felled after symp- 
toms have appeared. Additional conidium 
inoculum may be created by the forma- 
tion of padless mycelial mats adjacent to 
