220 
Journal of Agricultural Research 
Vol. XXIV, No. j 
SCLI^ROTINIA GUMMING, DU^ TO SCUKROTINIA LIBERTIANA 
This disease, usually of minor importance, occasionally has been found 
associated with rapid dying of bark on the roots and trunks of Citrus trees 
growing in damp, cool situations, especially after periods of severe frost. 
The bark is at first soft, as if from an attack by Botrytis cinerea. Though 
the fungus usually advances more rapidly than Botrytis, it is soon checked,^ 
and callus begins to form as soon as gum accumulates. Later, as the bark 
dries, it is left in shreds and large black sclerotia are found within and 
under this bark. Its effect on Citrus twigs has been described by C. O. 
Smith (54), who refers to the gumming usually accompanying its attack. 
It appears to infect the young growth, usually at the blossoming period 
and frequently extends back into larger branches. 
When found on the trunk or roots, observations have indicated that 
previous injury of the bark was usually necessary for the entrance of the 
fungus. It has frequently been found on young trees following frost 
injuries, apparently advancing from frost-injured tissue into tissue not 
killed by frost. It has been observed on a 20-year-old lemon tree where 
all the roots had been infected, probably from injuries made in digging 
about them and placing vetch straw near the crown in damp, cool weather. 
An old seedling orange tree was also observed with the bark on one side 
of the trunk killed by the fungus, which had apparently gained entrance 
through a slight sunburned area and had advanced into the live bark for 
some distance. 
In order to obtain some idea of the ability of Sclerotinia libertiana to- 
break down sound bark and induce gumming, several inoculations with 
pure cultures were made on healthy lemon trees, of which the following 
examples may be given: 
On February 20, 1913, a bit of mycelium from a pure culture was 
inserted into a vertical cut in the bark of an 18-year-old Lisbon lemon 
tree. A similar cut to serve as a control was made on the opposite side 
of the same tree. These were then covered with oiled paper. The cut 
not inoculated healed normally, but the bark adjacent to the inoculation 
was soft on one side within 4 weeks. In 8 weeks there was a dead, soft 
area 15 by 8 cm., which had increased to 22 by 9 cm. in ii weeks with a 
white mycelium conspicuous over a smaller area of 13 by 5 cm. About 
4 months after inoculation (June 27,1913) the area of dead bark measured 
30 by 14 cm. and increased to 45 by 15 cm. by July 28, 1913, after which 
it soon ceased enlarging and became self-limited. The gum began to- 
appear in 6 weeks; its rate of formation increased rapidly and reached a 
maximum about 3 months after inoculation. It ceased to increase about 
5 months after inoculation. The sclerotia were seen to have formed in 
flat plates under and within the bark in 4 months and appeared to be 
alive for at least 2 years, but no subsequent activity was apparent in this 
lesion for a period of at least 3 years. The killed bark showed the charac¬ 
teristic shredded appearance. Without treatment, there was a complete 
stoppage of further invasion by the fungus. 
A 2-year-old lemon tree was similarly inoculated i inch above the bud 
union on February 25, 1913. By May 7, 1913, the tree was girdled and 
showed gumming, the bark being killed 6 inches upward and i inch 
downward to the bud union. The invasion did not advance into the sour- 
orange tissue of the stock. The foliage at this time showed no effect, but 
by June 27, 1913, the leaves were wilted. In both these cases similar 
