Hay IS, 1920 



Halo-Blight of Oats 



159 



discolorations on the glumes. A week after inoculation every spikelet 

 of these panicles showed distinct typical halo lesions. Many halo lesions 

 also appeared on the uninjured spikelets. Injured and uninjured con- 

 trols sprayed with sterile water and treated in a similar way showed 

 no halo lesions. 



Early in July natural infections on the spikelets of Wisconsin No. 14 

 oats were observed. Flag leaves w^ere found which showed either 

 scattered halos or yellow halo tissue the length of the blade and sheath. 

 Where sheaths surrounding the heads were badly haloed, every spikelet 

 in the panicle showed infection. If there is one single lesion on a glume 

 it appears as a typical light green to yellow halo about the point of infec- 

 tion. When the whole glume is infected the tissue becomes yellow and 

 translucent between the veins. Only a few such complete infections of 

 panicles were found. Further observations showed that infections 

 on a small percentage of the spikelets in a panicle were not uncommon 

 even when there were no lesions on the sheaths below. Wind and rain 

 might easily spread the infection directly from lower leaves to panicles. 

 Isolations from the glumes showing these lesions and from the parts 

 inside the glumes gave typical halo organisms. Table I, which records 

 the counts on 42 panicles in one corner of a Wisconsin No. 14 plot, will 

 give some idea of the percentage of blighted spikelets. 



Table I. — Number of blighted and blasted spikelets on oats naturally infected with 



halo-blight 



Panicle No. 



I 



2 



3 

 4 

 5 

 6 



7 

 8 



9 

 10 

 II 

 12 



13 

 14 

 15 

 16 



17 

 18 



19 

 20 

 21 

 32 

 23 



Panicle No. 



24. 



25- 

 26. 

 27. 

 28. 

 29. 

 30- 

 31- 

 32- 

 33- 

 34- 

 35- 

 36. 

 37- 

 38. 



39- 



40. 



41- 

 42. 



Number 



of 

 spikelets 



per 

 panicle. 



67 



33 

 80 



65 



45 

 72 



85 

 46 



50 

 55 

 45 

 71 

 65 

 109 



52 

 69 

 66 

 60 



Total 2,387 



Average 59+ 



Per cent 



Number Number 



of of 



blighted | blasted 



spikelets 



per 

 panicle. 



4 

 o 

 o 



12 

 O 



25 



29 



o 



5 

 o 



165 

 4 



6-f 



spikelets 



per 

 r)anicle. 



17 



8 



12 



14 



7 



o 



47 

 8 



7 

 4 



14 

 6 

 o 

 8 

 6 



13 



587 

 14+ 

 24+ 



