4 BULLETIN 1058, IT. S. DEPAETMEISTT OF AGRICULTURE. 



It is quite evident, however, that considerable sterility occurs on 

 oat panicles which have not come in contact with diseased leaves or 

 sheaths, and even in fields where there has been little or no bacterial 

 blight; also there is evidence that in years of severe bacterial blight 

 early in the season the yield per acre has not been reduced, but some- 

 times has been greater than when there was less blight. 



In order to learn more about the relationship of the halo blight 

 to the sterility of oats the observations and experiments described 

 in the following pages were made. 



EXPERIMENTS OF 1918. 



During the season of 1918, 11 varieties of oats were used for 

 inoculation experiments. In each variety bundles containing about 

 a dozen plants were sprayed with water suspensions of the halo- 

 blight organism and covered with glassine bags for two or three days. 

 One bundle was sprayed without being injured in any way and another 

 after the plants had been drawn between the fingers to rub off the 

 bloom. The plants of a third bundle of each variety were injured 

 by needle pricks or were cut with a scalpel before spraying. Check 

 bundles of each variety, injured and uninjured, were sprayed with 

 sterile water and also covered with bags. In some cases water 

 suspensions of the organism were sprayed into unopened sheaths 

 and sterile water into similar plants as checks. (Pis. I to IV.) 



In most of the varieties the sheaths were about ready to open or 

 were already partly open. In Wisconsin Pedigree 7 the heads were 

 entirely out of the sheaths and were inoculated to learn whether 

 or not the spikelets themselves were susceptible to infection with the 

 halo-blight organism and what the effect of infection would be. 

 In the oat panicle the uppermost spikelets develop first and at the 

 time when the sheath is about ready to open are usually fully grown, 

 while those at the base are still only partly developed. The difference 

 in the stage of development of the spikelets on the panicle influences, 

 of course, the results of the experiments where inoculations are made 

 upon panicles about to emerge from the sheath. The almost fully 

 developed spikelets at the top are less influenced by the inoculum 

 than the partly developed ones at the base. 



When these inoculated and check plants were mature and were 

 collected for recording the results, a bundle of untreated plants of 

 each variety was also collected in order to compare the proportion 

 of sterility with that of treated plants. The results of this set of 

 inoculations, together with the amount of sterility found on untreated 

 plants, are shown in Table I, and a brief summary of the same is 

 presented in Table II. 



