62 



SCIENCE 



[N. S. Vol. XXXVIII. No. 967 



to numerous friends and acquaintances in 

 other parts of the United States. In asking 

 for these specimens the fact was emphasized 

 that potatoes affected by scab which differed 

 in appearance from the ordinary type of the 

 disease were especially desired. 



As soon as received all lots of tubers were 

 subjected to careful microscopic examination 

 for the presence of Rhizoctonia and for the 

 spore " balls " of Spongospora suhterranea 

 (Wallr.) Johns., or the fruiting bodies of the 

 organism which is the cause of the powdery 

 scab. None of the specimens showed the 

 characteristic, superficial appearance of the 

 last-named disease and the microscopic exam- 

 ination failed to establish its presence in any 

 case beyond doubt, but practically all, regard- 

 less of the source, showed Rhizoctonia threads 

 in the diseased areas. In addition poured 

 plates were made from a large number of 

 tubers from different sources and in every 

 case tried the organism known as Oospore 

 scabies Thaxter was isolated from some of the 

 scabby spots. 



A few of the tubers received showed small 

 but rather pronounced pits upon their sur- 

 faces. Since these were usually more or less 

 lined with Rhizoctonia threads it seemed pos- 

 sible that this fungus might be the primary 

 or secondary cause of the pitting. Specimens 

 of all lots of tubers of this kind and a consid- 

 erable number of others, including samples 

 from several different states, were planted in 

 ten-ineh pots in the greenhouse. Before 

 planting the pots and soil were sterilized by 

 heating for two hours under steam pressure 

 at 20 pounds. The pots were then placed in 

 sterilized saucers upon a raised, slat-work 

 platform. The platform was constructed of 

 new lumber and it and the bench upon which 

 it rested had been previously washed with a 

 strong solution of formaldehyde. The pots 

 were watered with boiled water and all other 

 precautions were taken to avoid cross infec- 

 tion or outside contamination. 



The tubers from a part of these pots have 

 just been harvested and in two instances 

 rather surprising results were obtained in that 

 in both well-developed and typical cases of 



powdery scab were found.' A careful reex- 

 amination of other tubers from the original 

 lots of specimens, which are now badly dried 

 out, was then made and these showed the 

 presence of a small number of yellowish brown 

 bodies, now considerably shrunken, but which 

 are evidently the dried spore balls of the 

 causal organism. One of the original lots was 

 sent by Dr. George E. Stone from Massachu- 

 setts, while the other was received from Ne- 

 braska through the courtesy of Mr. W. A. 

 Orton, of the Bureau of Plant Industry at 

 Washington. 



No conclusive evidence of the presence of 

 powdery scab in other parts of the United 

 States has been obtained, but tubers which 

 show a few bodies in the diseased areas which 

 somewhat resemble those upon the tubers de- 

 scribed above have been received from one 

 locality each in Maine, Vermont and Wiscon- 

 sin. These have recently been planted in 

 pot-s in the greenhouse, but it will be some 

 time before a final decision can be made. 



The fact that the disease has been obtained 

 from such widely separated localities as Mas- 

 sachusetts and Nebraska would indicate that 

 it may be quite generally distributed in the 

 United States and suggests the possibility that 

 it may be a factor in the cause of potato scab 

 in this country. In order to obtain farther 

 light on this and on the subject of potato scab 

 in general the writer of this note wishes to 

 obtain specimens of scabby tubers from as 

 many different localities as possible, and will 

 gladly pay transportation charges on any 

 which are sent in response to this request. 

 W. J. Morse 



Maine Agricultural Experiment Station, 

 May 27 



• Mr. M. Shapovalov, to whom credit should be 

 given for carrying out a large part of the details 

 of the work upon which this statement is based, 

 isolated cultures of Oospora scabies from the two 

 tubers which produced the crop affected with 

 powdery scab. He has also demonstrated that the 

 cultures thus obtained are capable of causing, 

 upon inoculation, the typical form of scab which 

 is associated with the last-named organism. Hence 

 it is evident that both forms were present on both 

 lots of tubers. 



