Apr. is, 1921 
Bacterial Spot of Tomato 
139 
development at 35 was not much better than at 15 0 . The most vigorous 
development occurred at 22 0 , 25 0 , and 30°; and although there was very 
little noticeable difference, the optimum temperature seems to lie between 
25 0 and 30°. High temperatures in the greenhouse noticeably shorten 
the incubation period. 
An interesting correlation between temperature and pigmentation was 
noted. In the cooler temperatures the yellow color was more intense 
than in the higher temperatures, ranging from a barium yellow at io° C. 
to a naphthaline yellow at 22 0 and a marguerite yellow at 30° and 35°. 
At 35 0 the colonies soon became almost colorless and translucent. 
In determining the thermal death point, water suspensions from agar 
slant cultures were subjected to 10-minute exposures to a series of tem¬ 
peratures in a water bath and tested by loop transfers to agar slants. 
As a result of two trials it was determined that the thermal death point 
lies between 49 0 and 50° C. 
EFFECT OF SUNUGHT 
The organism was found to be very susceptible to sunlight. Practi¬ 
cally complete sterilization of the unshaded portions of agar poured plates 
was obtained by 20, 30, and 40 minute exposures to morning sunlight. 
When a black background was used, colonies developed in the shaded 
portions of the plates, but when a white background was used, colonies 
failed to develop even in the shaded portions of plates exposed 40 and 60 
minutes. This indicates that the organisms are killed by reflected white 
light as well as by direct sunlight. 
resistance to desiccation 
The organism is very resistant to desiccation. When dried on sterile 
cover glasses it was found alive after 25 days. In this test a loopful 
of a water suspension of the bacteria from an agar culture was allowed to 
dry on each cover glass. Tests were made by inserting the cover slips 
into tubes of slanted agar. 
To determine the resistance to desiccation on tomato seed, a water 
suspension of the bacteria was poured over sterilized seed in Petri dishes 
and allowed to dry. This seed was tested at intervals by planting in 
agar plates. In a test as yet unfinished the organism was still viable 
after 11 months' desiccation. As will be discussed later, it has already 
been proved that the organism lives over winter on the seed. 
susceptibility to germicides 
In a water suspension of the bacteria, complete sterilization was 
obtained by 5-minute exposures to mercuric chlorid in concentrations of 
1 to 1,000, 1 to 2,000, and 1 to 4,000, and by 5-minute exposures to 10 
per cent, 5 per cent, and 2 per cent commercial formaldehyde. 
