496 MICROBIAL DISEASES OF PLANTS. 



On potato, spreading, glistening, smooth, white to dirty white, shiny, medium grayed, 

 slight action on starch. Gelatin stab, filiform, no liquefaction. Beef broth, pellicle, 

 strong clouding. Milk, no coagulation, rendered alkaline, becomes clear by solution of 

 fat and casein, litmus not reduced. No growth or scant in Cohn's solution. Uschinsky's 

 solution, copious, pellicle, not viscid, fluid bluish-fluorescent color. No gas from dex- 

 trose, saccharose, etc. Aerobic. No indol or slight. Nitrates not reduced. Thermal 

 death-point 51.5; does not grow at 37. 



BLADE BLIGHT OF OATS. 

 Pseudomonas avena Manns and Bacillus avena Manns. 



HISTORY AND DISTRIBUTION. A specific bacterial disease of oats 

 has been described by Manns* in 1909. What appears to have been a 

 similar trouble, extending from the Atlantic coast west to Indiana, and 

 from the Great Lakes to the Gulf States, was observed as early as 1890 

 by Galloway and Southworth. 



SYMPTOMS. In the early stages of the disease there is " a yellowing, 

 beginning either as small round lesions on the blade, or as long, streak 

 lesions extending throughout the blade or even the whole length of the 

 culm and blades. In the advanced stages, the affected blades take on 

 a mottled to almost red color, which has been called 'rust' and 

 'blight.'" 



CAUSE or THE DISEASE. The disease is produced by the symbiotic 

 growth of two bacteria whose activity is favored by rainy, humid, and 

 cloudy weather. One of these organisms, Ps. avencz, alone, is said to be 

 capable of effecting the blight in a mild form, while the other, B. avencz, 

 is nonpathogenic; but a mixture of the two germs results in an 

 aggravated attack. 



METHOD OF INFECTION. Infection takes place through the stomata, 

 the organisms being spattered on the leaves from the soil by rains. 

 Grain insects are also responsible for spreading the disease. 



CONTROL. It is believed that the control of the disease lies in the 

 selection of resistant strains. 



PEAR BLIGHT. 

 Bacillus amylovorus (Burrill) De Toni. 



HISTORY AND DISTRIBUTION. As early as 1780, William Denning, 

 a fruit grower, who lived on the Highlands of the Hudson River, observed 

 pear blight in the trees of his neighborhood. It is very probable that 



* Manns, " The Blade Blight of Oats, A Bacterial Disease," Bull. 210, Ohio Exp. Sta., 1909. 



