962 MICROBIAL DISEASES OF PLANTS 



i : 1000 solution of mercuric chlorid. All diseased wood must be collected 

 and burned. 



STREAK DISEASE or SWEET PEAS AND CLOVERS 

 Bacillus lathyri Manns and Taubenhaus 



HISTORY. The first recorded observations of this disease were made 

 by Diggs on sweet peas in Dublin, Ireland, in 1904. The trouble was 

 known locally as "Streak" disease of the sweet pea, and various 

 parasitic fungi were assigned as the cause. One investigator even 

 ventured the assertion that the malady was of a physiological nature. 

 In 1912, Taubenhaus isolated a bacillus from clovers and sweet peas 

 collected in the vicinity of Newark, Delaware, and which bore lesions 

 similar to those described for "Streak." Subsequent inoculations 

 with pure cultures proved the disease to be of bacterial origin and 

 identical with that observed in England and Ireland. 



SYMPTOMS. The disease makes its appearance during the season of 

 heavy dew and is characterized by light reddish-brown to dark brown 

 spots and streaks, almost purple when old, along the stems. They 

 usually originate near the ground, which seems to indicate distri- 

 bution by spattering rain and infection through the stomata. The 

 disease is quickly distributed over the more mature stems, and ulti- 

 mately the cambium and deeper structures are destroyed in con- 

 tinuous areas resulting in the premature death of the plant. Occa- 

 sionally the petioles and leaves show the infection; the latter exhibit 

 the water-soaked. areas common to bacterial stomatal infections such 

 as are met with in alfalfa blight and bacteriosis of beans. 



CAUSAL ORGANISM. Manns and Taubenhaus have described the organism 

 which is responsible for the disease as a new species under the name Bacillus lathyri. 

 It is a small rod, motile by means of 8-12 short, peritrichiate flagella; it grows lux- 

 uriantly upon all of the common nutrient media, especially if sugars are present, 

 producing a yellow pigment; on glucose agar, colonies appear in twenty-four to 

 thirty-six hours, showing a tendency to become stellate or auriculate. 



PATHOGENESIS. Bacillus lathyri, n. sp. has been isolated from 

 specific lesions on the following hosts: Sweet pea, Lathyrus spp., 

 red, alsike and mammoth clovers, soy beans, garden beans, cow peas 

 and alfalfa. 



METHOD OF INFECTION. Infection appears to take place through 

 the stomata, the organism being spattered on the plants from the 

 soil_duringrrains. 



