Sept. 1, 1924 
Bacterial Pustule of Soybean 
249 
TRANSMISSION OF SOYBEAN 
PUSTULE 
Very little is known regarding the 
transmission of the disease. Circum¬ 
stantial evidence points to seed and 
perhaps insect transmission, although 
there is little experimental evidence. 
Seed transmission. —In the spring 
of 1919 some very badly diseased seed 
was received from Arkansas. Bacteria 
were found in some of the blackened 
spots, but all attempts at isolation 
failed, the plates being quickly over¬ 
grown by a spreading green fluorescent 
organism. Some of the seeds were then 
germinated and in 10 days 7 out of the 
12 seedlings were badly diseased. The 
stems were water-soaked and full of 
bacteria, and 11 seedlings were broken 
over. Bad. phaseoli sojense was iso¬ 
lated and proved to be very infectious 
to Lima and bush string bean. There 
were many secondary infections also as 
new leaves unfolded on the diseased 
plants. No infection was obtained on 
Ito San soybean, however, although 
this is a very susceptible variety, and 
the plants inoculated ranged from seed¬ 
lings l}/2 inches high with no leaves to 
plants 8 or 9 inches high with leaves in 
3,11 stages of development. Both spray 
3nd prick inoculations were made (in¬ 
oculations of June 18 and 26, 1919). 
Insect transmission. —Inasmuch as 
the disease was observed on 40 varieties 
of soybean growing in close proximity 
3 t Arlington Farm, Va., 1921, and 
raised from seed from widely sep¬ 
arated regions, 18 it seemed reasonable 
to suppose that some of the seed at 
least was sound and that the plants be¬ 
came infected from their neighbors di¬ 
rectly or indirectly. In the Dismal 
8wamp in 1917 the spotted cucumber 
beetle ( Diabrotica duodecimpundata) 
had been found on the diseased plants 
and a series of experiments was planned 
in an attempt to discover whether this 
insect might be a carrier of the in¬ 
fection. The results * were negative. 
In the first experiments the beetles 
were fed on diseased leaves but they 
seemed to avoid the infected areas, 
which were rather hard and dry at this 
stage. Other beetles were fed on leaves 
smeared with Bad. phaseoli sojense and 
on potato cultures of it, which they 
seemed to relish, then transferred to 
healthy soybean plants. Although they 
fed on the leaves of the healthy plants, 
no infection resulted. It may be that 
temperature and moisture conditions 
were not favorable. The plants were 
in insect cages in the hothouse and no 
attempt was made to keep them in a 
moist atmosphere at any time during 
the experiments (carried on in October 
and November). 
Other means of transmission.— 
There is a possibility, of course, that 
the organism is spread by the rain and 
that it lives over on soybean refuse in 
the soil, but no observations have been 
made to support this theory. 
SUMMARY 
1. This paper describes a leaf spot 
of soybean ( Glycine hispida) produced 
by Bad. phaseoli sojense Hedges and 
characterized in the early stages by 
minute pustules and later by irregular 
reddish-brown spots, sometimes accom¬ 
panied by yellowing. 
2. Bad. phaseoli sojense is a short, 
1-to 2-polar flagellate rod, very closely 
resembling Bad. phaseoli EFS. in most 
respects, but its colonies are commonly 
characterized by certain very striking 
internal markings, which are almost 
wholly absent from colonies of Bad. 
18 There were 177 different lots of seed, 124 of them having been received in 1921 and hence grown for the 
first time at Arlington. The seed had been obtained from Arkansas, Delaware, Georgia, Illinois, Indiana, 
Iowa, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, North 
"Carolina, New York, Ohio, Pennsylvania, South Dakota, Tennessee, Virginia, West Virginia, Wisconsin, 
China, Java (some seed received from each of the foregoing localities in 1921), Japan, and Manchuria. 
EXPLANATORY LEGEND FOR PLATE 7 
Bacterium phaseoli EFS. (Photographs by James F. Brewer) 
Colonies on beef agar plates; inoculations on Lima bean pods and soybean seedlings. 
A to D.—Colonies 10 days old. (X10, except C, which is X5.) First two are in same poured plate and 
descended from a colony like type A. 
E to H.—Lima bean pods six weeks after inoculation with colonies A to D, respectively. XI. 
I to M.—Rarer types, except J, which is frequent. (J is 6 days old.) L has depressed center. All except 
K and M, tested and found pathogenic. X5-10. 
N and O — Germinating soybean seed sprayed in damp chamber with Bad. phaseoli EFS. Sown in damp 
chamber November 24, 1920, inoculated November 26, 1920, and photographed eight days later; water 
soaking and bacterial ooze on cotyledons; organism reisolated. X3 ca. 
P—Browned and curled leaf tip from soybean seedling No. 27 grown from seed germinated in damp 
chamber (sown November 24, 1920), transferred to Sachs’ solution December 1, sprayed in greenhouse 
December 2, with Bad. phaseoli EFS.; organism reisolated from similar leaves. Photographed eight 
days after inoculation. X2. 
