24 BULLETIN 1029, U. S. DEPAETMEXT OF AGEICULTIJEE. 



This was brought very forcibly to the attention of the writer in 

 August, 1920, when such a case was described by a seed contractor 

 in one of the mentioned localities. Stock " mother seed " of a given 

 variety which later was proved to be infected with Phoma was dis- 

 tributed among several seed growers in 1919. A trial row was 

 planted in 1920 by the contractor, and when examined in August by 

 the writer the plants showed a high percentage of black-leg. One of 

 the 1919 plantings for seed examined in 1920 showed black-leg infec- 

 tion on 25 per cent of the seed plants,* while the several other fields 

 from the same "mother seed" were undoubtedly infected. Thus, 

 approximately 2,000 pounds of commercial seed became infected as 

 a result of the introduction of the parasite on a small quantity of 

 stock seed. Much of such seed infection can be prevented by growing 

 stock seed from seed heads carefully selected for freedom from dis- 

 ease followed by careful inspection during the following season. By 

 applying this method in Wisconsin black-leg has been successfully 

 avoided and comparatively large quantities of disease-free "mother 

 seed " have been produced. 



Black-leg has not as yet been reported from the Puget Sound 

 region, and an inspection of more than 30 seed fields in that region 

 in June, 1919, yielded no sign of the disease. Inasmuch as most of 

 these seed fields are started from " mother seed " grown in the East 

 or abroad and none of the growers practice seed treatment, it is 

 inevitable that some infected seed is sown. It would seem from 

 comparison with our Wisconsin experience that this absence of the 

 disease, as noted in the seed fields, must therefore be attributed to 

 local climatic conditions restrictive to the development of the fungus. 

 This was rendered the more probable by the results previously re- 

 corded {11) with some Wisconsin-grown seed known to be infected 

 with Phoma. This was seed No. 2-18, which, as used in Wisconsin, 

 resulted in high percentages of infection before the end of the season 

 (see Tables VII and IX). Of this, 2 pounds were sent to the Puget 

 Sound section for propagation after treatment for 30 minutes with 

 mercuric chlorid. This was sown at Mount Vernon, Wash., about 

 May 25, and when it was inspected seven weeks later, July 14, only 

 four infected seedlings were found in the entire bed. These were 

 evidently cases of primary infection with no spread whatever to the 

 adjacent j)lants. In 1920, samples from two lots of badly infected 

 seed were sown in this locality and portions of the same lots sown 

 at Madison, Wis. In the latter region the fungus appeared in 

 numerous primary infections within two weeks, and the disease had 

 become widespread by transplanting time (see Table VI). Since 



* The writer is indebted to Mr. I. H. Vogel, of Cornell UniviTsity. fm- iuformation re- 

 garding this field. 



