Mayis, I920 Halo-Blight of Oats 167 



The primary yellowing sooner or later changes to a mottled red or brown. 

 In another place he says: 



The preliminary effects of this disease 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 blade. Occasionally it begins at the tips and 

 works back into the ctdm; again the upper leaves often break down through a weak- 

 ened condition of the plant from defoliation below. 



When lesions work back from the leaves to the culm a general yel- 

 lowing and collapse of all the foliage may result. In 1909 — 



the disease in the majority of infected leaves began as small yellow spots on different 

 parts of the blades. When these points of infection were numerous, the infected areas 

 quickly became confluent, and the collapsed leaf showed a brownish mottled appear- 

 ance. 



These brief statements are the only references in the bulletin (exclu- 

 sive of PI. XIII) to anything at all corresponding to the lesions char- 

 acteristic of the blight here described, and there is much that is contra- 

 dictory. His colored figures as well as most of his text indicate an entirely 

 different disease, but his Plate XIII shows that this halo-disease formed 

 at least a part of the phenomenon under consideration. The distinct 

 reddening v;hich he describes and which he illustrates in Plates X and 

 XI was not observed anywhere in V/isconsin even in the worst blight 

 year, 191 8. A distinct reddening of oat leaves was observed in our 

 plots but was not due to the halo-blight. Two unsuccessful attempts 

 were made by the writer to isolate bacteria from these reddened leaves. 

 Manns attributes the severity of the outbreak in 1907 to the abnormally 

 low temperatures of April, May, June, and July and to the unusual 

 amount of rainfall during those months and gives convincing climato- 

 logical data in support of his conclusion. He states that the results 

 of artificial inoculation in the greenhouse also support this theory that 

 cool, humid weather conditions favor the disease. 



Through isolation and inoculation experiments Manns came to the 

 conclusion that the blade-blight of oats was due to two species of bacteria 

 living in symbiotic relations within the host tissue (Psevdomonas avenae 

 Manns and Bacillus avenae Manns). His isolations were made by ster- 

 ilizing the blades in 2 to 1,000 mercuric chlorid solutions for i to i^ 

 minutes and following this by four washings in sterile water. He states 

 that in practically all isolations from diseased oats these two bacteria 

 were found to be more or less abundant, and when occurring together 

 they could be plainly seen on the agar poured plates in from 2 to 3 days. 

 The yellow organism (Bacillus avenae Manns) always appeared first. 

 As a rule, the white organism predominated. 



Inoculations were made by Manns in several ways: (i) Directly 

 from crushed leaves; (2) by hypodermic injecrion, using separate pure 

 cultures of the white and the yellow organism; (3) by hypodermic in- 

 jection, using the two cultures mixed {3, PI. X); (4) by spraying mixed 



