192 Journal of Agricultural Research voi. xviii, no. 4 



almost completely destroyed by the bacterial blight. In fact, very often 

 the leaves of the two plants were in actual contact and yet this difference 

 in susceptibility to the disease persisted throughout the season. Inocu- 

 lation experiments in the greenhouse have strengthened the belief that 

 certain varieties of soybeans are immune to the attacks of the blight 

 organism (PL 18), and organized experimental work is now under way 

 at the University of Wisconsin on this phase of the problem. It seems 

 very probable from evidence at hand that the bacterial blight might at 

 present be greatly mitigated if not satisfactorily controlled by the 

 intelligent selection of disease-resistant varieties from among those 

 already in use. If it appears that the ideal combination of disease 

 resistance with other desirable characters does not occur in the standard 

 varieties now preferred, it should be possible to combine these by prop- 

 erly directed breeding efforts. 



SUMMARY 



(i) The blight of soybean described in this paper has been observed 

 in the University of Wisconsin plots for several years. A disease, 

 undoubtedly the same, has been reported from various parts of the 

 United States. 



(2) It is characterized on the leaves, where it is most conspicuous, by 

 small, angular spots, either isolated or confluent. The lesions are light- 

 colored and translucent in early stages and very dark-colored in late 

 stages. In late stages, also, the diseased tissue may become dry and 

 drop out, giving the leaves a ragged appearance. Bacterial exudate 

 occurs on the leaf spots as droplets but is not very evident except 

 under favorable moisture conditions. It is pale in color and dries as 

 inconspicuous granules or scales. 



(3) Petiole, stem, and pod lesions accompany the disease on the 

 leaves. Exudation has been observed on petioles and pods. 



(4) The blight is caused by Bacterium glycineum, n. sp., which is able 

 to make entrance into the tissues without wounds. The organism is a 

 medium-sized rod, motile by means of from one to several polar flagella. 

 In culture its color is creamy white tinged with brown. 



(5) Isolation of the organism has been accomplished repeatedly by 

 macerating a thoroughly washed lesion upon a slide under sterile condi- 

 tions and using this material for dilutions from which agar plates were 

 poured. Cultures made by transferring from characteristic colonies or 

 from fresh exudate droplets to agar slants have furnished the material 

 used in the inoculation work. 



(6) Simply spraying water suspensions of the organism upon soy- 

 bean plants is sufficient to produce infection. It is advisable, however, 

 to rub the tissue gently between thumb and finger to insure contact 

 between inoculum and plant surface. 



