88 journal of Agricultural Research voi. xxn. No. a 



INOCULATION OF HEALTHY STEMS IN THE GREENHOUSE 



The stems of four young healthy potato plants were inoculated with 

 24-hour-old broth cultures of the three western strains of the bacillus 

 injected by means of a hypodermic needle. A severe decay with an 

 accompanying blackening resulted in all cases. 



FIELD EXPERIMENTS 



These experiments were conducted for two successive years at Arling- 

 ton Farm, Va. In 1 9 19 Netted Gems and Irish Cobblers were used. The 

 tubers were inoculated with the western strains of the blackleg organism 

 a few days before planting. Six whole tubers and 20 halves of the first 

 variety and 9 whole and 19 halves of the second variety were planted. 

 In addition a number of uninoculated pieces of each variety were planted 

 for controls. Planting was done on May 5. One half-tuber seed piece 

 of each variety decayed in the ground. On July i one hill from the cut 

 seed of Irish Cobblers was noted to show secondary symptoms character- 

 istic of blackleg — ^namely, yellowing and rolling of the leaves. There 

 was no blackening of the stem above ground. The underground portions, 

 however, showed brown lesions and a brown rot of the stem at the point 

 of attachment to the seed piece and somewhat above it. None of the 

 remaining plants showed symptoms of the disease. At digging time, on 

 September 15, no decay of the tubers was found, with the exception of 

 one very small tuber of the Netted Gem variety which showed a soft bac- 

 terial decay at the stem end. The progress of the decay, however, was 

 checked, and the affected portion fell off, leaving only the sound part, 

 so that the recovery of the causal organism was not possible. 



Since the hot weather after May 5 might have had something to do 

 with the slight progress of the disease in 19 19, two sets of plantings were 

 made on another piece of ground on the same farm in 1920 — one on 

 April 8 and the other on May 6. Only Irish Cobblers were used this time. 

 Twelve tubers were cut in halves through the inoculated wound so as to 

 make 24 seed pieces for each of the two series. Inoculations were made 

 a few days before planting. Eight tubers were inoculated with the three 

 western strains of the blackleg organism and 4 with the "B. sol." strain 

 received from Dr. Morse. Up to July 20 four hills out of 16 inoculated 

 with the western strains in the earlier planting and 2 out of 8 inoculated 

 with " B. sol." in the same series showed typical field symptoms of black- 

 leg, including an intense blackening of the base of the stem. On the 

 other hand, no hill of the series inoculated with the same organisms and 

 on the same plan, but planted one month later, showed any signs of 

 infection. At harvesting time, on July 20, a number of tubers in the 

 planting of April 8 showed blackleg-rot, and in the later planting only 

 2 tubers were found showing the same decay. It appears, therefore, 

 that the earlier planting, when the soil and the air temperatures were 



