Apr. a, 1917 
A New Bacterial Citrus Disease 
7 
EFFECT OF PHYSICAL CONDITIONS 
SENSITIVENESS TO DESICCATION 
Drops of 24-hour cultures in +15 peptone-beef bouillon were placed 
upon sterile cover glasses in sterile petri dishes and kept in a dry dark¬ 
room. The organism was not killed after 12, 24, or 36 hours; but no 
growth was obtained after seven days of drying. On the other hand, 
although susceptible to drying in the air, old Citrus-blast material which 
had been kept for four months in the laboratory was found to yield the 
pathogenic organism. Under this condition, then, the organism is 
apparently able at least to live over the dry summer months. 
SENSITIVENESS TO SUNLIGHT 
The Citrus-blast organism is rather sensitive to direct sunlight. Thinly 
sown agar plates from io-day-old cultures in Uschinsky’s solution and 
from 24-hour bouillon cultures were exposed bottom up to sunlight in 
September for 5, 10, 15, 30, 45, and 60 minutes. One-half of each plate 
was protected from the light by black paper, and in each case the plates 
were protected from heat by being placed upon ice. 
Plates exposed for 30, 45, and 60 minutes showed no growth upon the 
parts exposed to the sunlight. Plates exposed for 15 minutes showed 
that 82 per cent were killed by the exposure, and those which survived 
grew more slowly than those unexposed. Plates exposed for 5 and 10 
minutes showed colonies growing uniformly on the exposed as well as the 
unexposed sides. 
TEMPERATURE RELATIONS 
The best growth obtained was at temperatures between 25 0 and 28° C. 
Scanty growth was observed at 16 0 and at 37 0 C. 
The thermal death point determined by exposing newly inoculated 
peptone beef-bouillon cultures for 10 minutes to definite temperatures 
was found to be 50° C. In this case transfers were made from a 24-hour- 
old culture in peptone-beef bouillon to the bouillon tubes to be tested. 
ECONOMIC IMPORTANCE OF CITRUS BLAST 
The chief injury caused by Citrus blast is in the killing of the young 
wood which should bear the blossoms and later the crop. Damage also 
results from defoliation and a consequent loss of leaf area for the whole 
tree. The whole result is a decrease in the ability of the tree to produce 
crops. The disease has also been observed in nurseries, and, although 
there is no means of knowing the actual loss suffered by this industry, 
the idea of dissemination by nursery stock immediately suggests itself. 
As yet the disease has not caused any widespread damage, but the 
possibility of its becoming distributed throughout the State and perhaps 
other Citrus-growing regions is not to be disregarded. 
