Apr. 21,1923 
Gummosis of Citrus 
205 
The control cuts not inoculated healed without gumming or dying of 
bark. All cuts inoculated with Pythiacystis citrophthora resulted in killing 
of the bark accompanied by exudation of gum. The areas on the branches 
had nearly reached their maximum size when examined on November 25, 
1913, 104 days after inoculation. A slight increase in some of them took 
place previous to the next April, at which time they had ceased to enlarge 
and had become self-limited, as was shown by subsequent records in 
Table V. The fungus apparently died out of these limb lesions, as no 
evidence of it could be found later. 
The inoculation on the orange root resulted in gumming and killing of 
some bark in two weeks and continued gumming for about four months. 
This lesion (PI. 4, C, lower area) became self-limited after an area 14 by 
5 cm. had been killed and later resembled self-limited typical footrot or 
mal di gomma lesions as they often occur naturally on orange trees in 
Florida. 
The diseased area resulting from inoculation on the orange bark 5 cm. 
below the bud union enlarged at about the same rate as that on the root 
for the first two weeks. After it had spread to the lemon bark, however, 
at the bud union, the progress upward was rapid. By May 9, 1914, the 
killed area was 48 by 15 cm. (PI. 4, A, B), only 8 cm. of this extension 
being downward on the orange bark. Of five cultures taken about 10 
months after inoculation from the margin of the invaded area (see chalk 
line on PI. 4, A), three developed Pythiacystis citrophthora. Further 
extension of the area was prevented by cutting out the bark (PI. 4, B) 
and painting the trunk with Bordeaux paste. 
The result of the inoculation made on the lemon bark on the opposite 
side of the same tree a few centimeters above the bud union is shown in 
Plate 4, e, the killed area being at this time (April 9, 1914) 53 by 25 cm. 
with large quantities of gum exuding on the surface. 
COMBINED EFFECTS OF PYTHIACYSTIS CITROPHTHORA AND FUSARIUM SP. 
During the examination of a large number of naturally occurring cases 
of Pythiacystis gummosis it was noticed that a species of Fusarium fre¬ 
quently accompanied and was closely associated with Pythiacystis 
citrophthora in the diseased tissue. The question arose as to whether the 
Fusarium played any part in the development or the severity of the 
disease. 
Fusarium has been mentioned frequently in literature as having some 
possible relation to certain types of gum disease. Briosi (rr) and 
McAlpine {46) concluded that Fusarium limoni Briosi played an impor¬ 
tant part in mal di gomma in Italy and Australia. Earle and Rogers- 
(21), though not able to produce gummosis by inoculation with Fusarium, 
believed that under certain conditions it was probably a factor in a certain, 
type of gum disease in Cuba. The writer had previously also found 
species of Fusarium repeatedly associated with mal di gomma or footrot 
in Florida, but inoculations with them had been negative. 
Cuts, as before, into which bits of pure cultures of Pythiacystis citroph¬ 
thora and Fusarium sp. were placed side by side were now made on lemon 
trees. At the same time inoculations into other similar trees were made 
with P. citrophthora alone and others with Fusarium sp. alone. The 
main results are given in Tables VI and VII. 
