1 62 



Journal of Agricultural Research 



Vol. XIX, No. 4 



developing spikelets from which the halo organism was isolated, and 

 finally, the absence of the disease on plants from sufficiently treated seed 

 all lead to the conclusion that this is a seed-borne disease. 



HOSTS OTHER THAN OATS 



Field observations and artificial inoculation experiments indicate that 

 the halo-blight organism of oats does not readily infect other hosts. No 

 halo lesions similar to those appearing on oats have been observed in 

 the field on wheat, barley, corn, or timothy. In Jefferson and Dodge 

 Counties, Wis., fields of oats and barley were planted so close together 

 that the plants were intermingled at the margins. In both places the oat 

 plants were heavily spotted with halo lesions, but even where these spotted 

 oat leaves came in contact with the barley leaves not a halo could be 

 found on barley. At Arlington Farm, Va., one halo lesion was found on 

 a rye plant growing among infected oat plants, but no plates were made. 

 The field was half oats and half rye, and although practically all the oat 

 plants were spotted no other lesions could be found on rye. 



Six different sets of inoculation experiments were carried on in the 

 greenhouse during the winter of 1917-18 to test the pathogenicity of 

 the halo-blight organism on wheat, rye, barley, and com. The methods 

 of inoculation were the same as those described above. The organisms 

 used were stock and No. 36. The results are given in Table 11. 



Table II. — Inoculations on other plants with halo-blight from oats 



Host. 



Experi- 

 ment I, 

 stock. 



Experi- 

 ment II, 

 stock. 



Experi- 

 ment III, 

 stock. 



Experi- 

 ment IV, 

 stock. 



Experi- 

 ment V, 

 stock. 



Exjjeri- 



ment VI, 



No. 36. 



Wheat 



Rye 



Barley 



Spelt 



Com 



Oats, Wisconsin 14 . 

 Controls 



+ + + 

 + 



+ 

 + 



+ 



+ + 



+ 



++ 



- + + 



+ + + 



+ + + 



+ + + 



+ + + 



+ + + 



+ Slight infection. 

 -1-4- Moderate infection. 



-1-4- -I- Heavy infection. 

 — No infection. 



Halo lesions were obtained on wheat in two different experiments, in 

 the second of which the halo lesions were not so large but almost as 

 numerous as on oats. 



In three out of six experiments halo lesions were produced on rye. In 

 the first, infection was so heavy that there was a general wilting of the 

 leaves. Typical white organisms were isolated from these leaves which 

 on reinoculation produced halo lesions on oats but not on rye. 



Halos on barley were obtained in three out of six inoculation experi- 

 ments. There were eight halos in the first experiment and two in the 

 second. In the third experiment, six leaves had one or more halos. 



