214 
Journal of Agricultural Research 
Vol. XXIV, No. 
PART II.—GUMMOSIS DUE TO BOTRYTIS CINEREA AND OTHER- 
FUNGI 
botrytis gummosis 
INTRODUCTION 
Botrytis gummosis differs from Pythiacystis gummosis, discussed im 
Part I of this paper, in that it causes softening of the invaded bark in the 
early stages and produces conidiophores and spores in damp, cool weather.- 
In the later stages the outer layer of bark is killed and becomes dry and 
hard much in advance of the inner layer, while there is a greater tendency^ 
than in Pythiacystis gummosis for the tree to renew the bark undemeatk 
the dead hard layer and there is usually also a less copious flow of gum. 
Botrytis gummosis is confined in California almost exclusively to lemon- 
trees growing in the coastal regions and is usually seen on trees more than 
lo years of age. This disease should not be confused with a desquamated- 
bark (shellbark) condition in which the outer bark on old lemon trees dies,, 
cracks, and breaks away in longitudinal strips, a condition which is. 
somewhat similar to that frequently brought about in the later stages of 
Botrytis gummosis. Neither disease should be confused with psorosisv 
(scaly-bark) of sweet-orange trees. 
The causal fungus, Botrytis cinerea Lk., depends to a much greater 
extent than does Pythiacystis citrophthora Sm. and Sm. on wounds or 
other conditions predisposing the bark to attack. 
Hie writer’s attention was first called to this type of gummosis early im 
February, 1912. After a period of moist, cool weather, patches of bark 
15 to 30 cm. long and half as wide presented the gray furry appearance- 
characteristic of the fruiting bodies of Botrytis cinerea. In a later survey* 
of the Citrus districts of &Iifomia, Botrytis cinerea was usually found 
associated with this type of gummosis and was isolated from a large- 
nuinb^ of diseased lesions. Penicillium roseum Link,^^ Fusarium sp.,, 
and several other fungi were also frequently conspicuous. 
The important question at once arose, whether any of these fungr 
might break, down sound tissue and initiate conditions leading to disease- 
and gum formation or whether gumming and associated death of the- 
bark might result primarily from injuries or other contributing condi¬ 
tions, the fungi pla3dng only a minor or secondary part, as had previously* 
been assumed. It seemed advisable, therefore, to attempt to answer 
this| question experimentally, 
INOCULATION EXPERIMENTS 
Preliminary Tests 
On March 7, 1912, at Santa Paula, a preliminary set of rough inoc¬ 
ulations was made with diseased tissue and with fungi taken directly- 
from the surface of the bark. 
Sixteen Lisbon lemon trees 18 years old, on sweet-orange stocks, were- 
used for the inoculation. The portion of the bark to be inoculated was. 
washed first with water and then with alcohol, and the flame of an alcohol 
lamp was quickly passed over the surface. A cut about 3 cm. long was. 
made through the bark with a heavy sterilized knife. Into these cuts the 
materials for inoculation were inserted. The cuts were made at varying: 
Detennination of this species was kindly made by Dr. Charles Thom. 
