Nov. IS. 1919 Bacterial Blight of Soybean 181 



SEASONAL OCCURRENCE 



The seasonal development of the bacterial blight has been under 

 observation in a number of soybean fields in Wisconsin during the past 

 four years, and a variety of conditions has been found to exist. Some- 

 times the disease will appear with the first leaves and progress steadily 

 throughout the season. In other cases, the first leaves may show 

 infection, then there may be a considerable amount of healthy growth, 

 and later a further development of the disease on newer, younger tissue 

 may occur. Sometimes, also, there has been no apparent development 

 of the lesions until late July or early August, when the spotting might 

 appear in abundance and continue until the plants were mature. 



It seems reasonable to believe that weather conditions, especially 

 those of moisture, have a great influence in determining the nature of 

 the development and progress of the disease. However, since in the 

 vicinity of Madison, Wis., all the above conditions have been observed 

 in different fields during the same season, other factors than weather 

 must have some importance in influencing the amount of disease present 

 in any given locality. Just what these other factors may be is still an 

 open question, since up to this time not enough experimental evidence 

 has been accumulated to warrant making definite statements. The 

 amount of seed infecrion suggests itself at once as having some relation, 

 as do also the possibility of the persistence of the organism in the soil 

 and the degree of exposure of the soybean plants to the blight organism. 

 Moreover, field observations have shown that a real difference in varietal 

 resistance exists. A further discussion of these relations will be given 

 under the subject of control. 



THE ORGANISM 



ISOIyATlON 



Microscopic observations of sections of invaded tissue show the interior 

 of the lesions to be swarming with bacteria. The usual method of isolat- 

 ing the organism has been by the use of poured agar plates. 



In the orignal isolation a portion of freshly invaded tissue was cut out, 

 washed thoroughly through 10 changes of sterile water, and macerated 

 upon a slide under as sterile conditions as possible. This material was 

 introduced into sterile bouillon, further dilutions made, and plates 

 poured, Thaxter's potato hard agar being the medium employed. In 

 three days both yellow and white colonies had appeared on the plates. 

 Characteristic colonies, both yellow and white, were picked and trans- 

 fers made to potato agar slants. Water suspension inoculations with 

 subcultures from several of these strains proved a white organism to be 

 the pathogene. This conclusion was verified by subsequent re-isolation 

 and re-inoculation. In no case did a yellow strain cause infection. 



