Sept. 22, 1923 
Bacterial Leafspot of Clovers 
487 
WISCONSIN CI»OVER BACTERIA. 
Growth grayish white and not en¬ 
tirely opaque on agar. 
Growth butyrous on beef media. 
Fluorescent in beef media. 
Milk coagulated. Becomes translu¬ 
cent and brownish. 
Slight to no reduction of litmus in 
milk. 
Congo red in media containing dex¬ 
trose changed to dark purple-brown 
(acid reaction). 
Potato agar, usually contoured growth. 
Potato cylinders, abundant growth. 
In Uschinsky’s solution, pellicles and 
sediment not viscid, moderate 
flourescence. 
Casein digested. 
Approximate alkali limit, Ph 9.0 to 
9 - 5 * 
TECHNICAL DESCRIPTION 
Bacterium trifoliorum, n. sp. 10 
Cylindrical rods rounded at ends, solitary or in short chains; cells 1.2 to 3.0 n bif 0.4 
to 1.0 /a, with an average length of 1.7 /z and a width of 0.7 u> motile by means of one 
to four unipolar flagella; aerobic, Gram negative, no spores; not conspicuously 
capsulated. 
Colonies on nutrient agar grayish white, glistening, margins entire, convex or 
slightly umbonate. 
Gelatin not liquefied, nitrates not reduced, digests starch very feebly, acid formed 
from dextrose and saccharose, no gas produced in various carbohydrate media. 
Group number 212.2322023, following the descriptive chart of 1917 of the Society of 
American Bacteriologists. 
Type collected at Madison, Wisconsin, on Trifolium pratense L. • 
The type strain from Wisconsin has proved pathogenicity only on the red clovers 
(Trifolium pratense L. and T. medium L.); the strains from North Carolina and the 
vicinity of Washington, D. C., otherwise scarcely distinguishable, have been proved 
pathogenic also on T. repens L., T. hybridum , L., T. incarnatum L-, T, pannonicum L., 
and T . alexandrinum L. Lesions occur on leaves, stems, petioles, stipules, and flowers. 
Distribution apparently widespread in the northern Mississippi Valley on the red 
clovers T. pratense and T. medium , and the same organism, at least on the Atlantic 
seaboard, occurs on T. repens , T. hybridum , T. incarnatum , T. pannonicum and T. 
alexandrinum . 
Specimens on all these hosts showing both natural and artificial infections have been 
deposited in the herbaria of the department of plant pathology, University of Wis¬ 
consin, and the Bureau of Plant Industry, United States Department of Agriculture. 
RELATION OF PARASITE TO HOST TISSUE 
Infection apparently occurs through the stomates. This has been 
evidenced by noting that lesions first appear on the lower leaf sur¬ 
face, the one occupied by the breathing pores. Then, too, young 
lesions have been fixed in alcohol, embedded, sectioned, and stained 
with methylene blue. The intercellular spaces of the mesophyll imme¬ 
diately subjacent to the stomates in such sections are seen to be densely 
packed with bacteria. In older lesions in which the host cells have 
collapsed, the parasite may invade the cell cavities. 
VIRGINIA CI.OV3R BACTERIA. 
1. Growth pure white and opaque on 
agar. 
2. Growth extremely viscid on beef 
media. 
3. No fluorescence in beef media. 
4. Milk not coagulated. Remains opaque 
and cream color. 
5. Strong reduction of litmus in milk. 
6. Congo red in media containing dex¬ 
trose is unchanged. 
7. Potato agar, smooth growth. 
8. Potato cylinders, slight growth. 
9. In Uschinsky’s solution, viscid pelli¬ 
cles and sediment and very slight 
fluorescence. 
10. Casein not digested. 
11. Approximate alkali limit, P H 8.2 to 
8 . 6 . 
10. 
11. 
10 According to the classification of Migula and the recent report of the committee of the Society 0 / 
American Bacteriologists the name of this clover organism would be Pseudomonas trifoliorum, n. sp. 
60097—23 - 2 
