Mayis, I930 Halo-Blight of Oats 171 



Another method of seed treatment is being developed at Wisconsin 

 which in 191 8 entirely controlled halo-blight. The treated seed was 

 heated in a gas oven at 100° C. for 30 hours. The plot from this treated 

 seed did not show a single halo lesion even during the time when other 

 oats were most severely attacked. The plot from untreated seed of 

 the same variety showed primary infections on 10 per cent of the plants 

 and 100 per cent secondary infections on the lower leaves during May 

 and the first two weeks in June. While oats in good condition success- 

 fully withstand this treatment of 30 hours at 100° C, a similar treatment 

 for a shorter period would perhaps be just as effective. The commercial 

 application of this treatment has not as yet been worked out. 



SUMMARY 



A bacterial disease known as halo-bUght was unusually severe in its 

 attack on oats throughout Wisconsin during the 191 8 season, and reports 

 of a similar disease were received from southern Minnesota, Iowa, north- 

 ern Illinois, and Indiana. Such epidemics occur under particularly 

 favorable weather conditions, disappearing v/ith the advent of weather 

 conditions more favorable to the development of the host plant. 



Typical lesions of halo-blight are characterized by halolike margins 

 of chlorotic tissue about a center of dead tissue. 



Isolations from these lesions have constantly given a typical white 

 organism. Yellow organisms also appear from isolations when the surf- 

 ace of the tissue has not been sterilized. 



Inoculation experiments have shown conclusively that the white organ- 

 ism alone is responsible for the production of typical lesions. The yellow 

 organism is evidently a surface saprophyte. 



Since few if any organisms are found outside the central infection area, 

 the halo is thought to be due to a diffusible substance, probably am- 

 monia. 



The organisms live over winter on the seed, producing primary lesions 

 on the first leaves of seedlings. From these lesions the organisms are 

 carried to other leaves by wind and rain. 



It seems probable that the percentage of blasting on oat panicles 

 varies with the severity of the halo-blight from season to season. This 

 blasting seems to be due to the same unfavorable weather conditions 

 which favor the development of the bacterial blight rather than to the 

 disease itself. 



Halo-blight lesions from natural infections have never been observed 

 on any hosts except oats and rye. Artificial inoculations show that the 

 halo organism may be slightly pathogenic on wheat, rye, and barley. 



When the halo-blight is not too severe, different varieties of oats show 

 differences in susceptibility to the disease. 

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