Mayxs. I930 Halo-BUght of Oats i6i 



neighboring untreated plots, one of which was only 3 feet away. On May 

 24 and 25 there were more driving rains, and on the twenty-eighth the 

 effects of these storms were evident. Secondary lesions in the untreated 

 plots were so abundant that no attempt was made to count them. Many 

 of the first leaves were completely yellowed and dead, and lesions on sec- 

 ond and third leaves were so numerous that tips, margins, and even whole 

 leaves were becoming yellowed. On varieties where infections were not 

 so abundant the second leaves showed only scattered lesions. On the 

 treated plot the primary lesions were still few, and there was here very 

 striking evidence of the way in which the organism spreads about a center 

 of infection. More or less circular spots of infected plants could be dis- 

 tinguished with the more heavily spotted plants in the center. The 

 amount of infection in this treated plot gradually increased until most of 

 the first and second leaves showed some spotting, but in none of the vari- 

 eties was there more than half as much blighting as in the untreated plots. 

 In the third treated plot, Wisconsin No. 8 showed only scattered lesions 

 on the lower leaves and none on the upper. In the untreated plot of this 

 variety the lower leaves were practically destroyed and the upper so 

 badly spotted that they showed a yellow-brown color at a distance. 

 There were similar but less marked differences in other varieties. Through 

 June there was very little rain. The amount of blight gradually de- 

 creased until at heading time, about the first of July, very few halo lesions 

 could be found, and the upper leaves were practically unspotted. 



No halo lesions were observed on the fourth plot from Wisconsin No. 

 14 treated seed until about the twenty-fifth of the month, when two or 

 three centers of infection began to appear as small yellow spots. These 

 spread rapidly after each rain until one of them stood out as a distinct 

 yellow spot irregularly 5 by 10 feet in diameter. The plants in this spot at 

 heading time were 4 or 5 inches shorter than the more normal plants 

 about them and headed out about a week later. Subsequently scattered 

 lesions occurred on lower leaves throughout the plot and undoubtedly 

 came either from the first infections observed or from the neighboring 

 plots. If these primary infections had been produced by soil organisms 

 they would probably have been much more general. Either sterilization 

 of seed was not complete or else the infection came from the neighbor- 

 ing plots. 



An experiment with hot-air treatment of seed gave additional proof 

 that the organism is seed-borne. A plot from Graber oats heated to 

 100° C. for 30 hours showed no lesions throughout the season. There 

 was not a single spot. The plot from untreated Graber oats showed an 

 abundance of halo lesions through May and June. On every plant there 

 was some spotting and many lower leaves were yellowed and dead. 



This early appearance of lesions on seedlings grown on new soil, the 

 appearance of typical halo lesions on the glumes and lemmas of the 



