December 31, 1915] 



SCIENCE 



941 



The latter does not cause a rapid destruction 

 of host tissue such as is seen in many cases of 

 recently established parasitism, but rather pro- 

 duces a temporary conservation of the host 

 cells followed by their gradual destruction, in 

 short, the type of development to be expected 

 in parasitism of long standing. Hence we 

 may safely conclude that the association of 

 Spongospora and the potato is an ancient one, 

 and we should therefore naturally look for the 

 original home of powdery scab in some very 

 early habitat of the potato. In 1891 Lager- 

 heim^ collected Spongospora in Quito, Ec- 

 uador, and stated that the disease was well 

 known in that region, but he gave no evidence 

 bearing on the question as to whether it had 

 long existed there or had been recently intro- 

 duced, possibly from Europe, where it has been 

 known to exist since 1841. Evidence on this 

 question is now at hand. 



Mr. O. F. Cook, of the Bureau of Plant In- 

 dustry, recently returned from South America, 

 bringing specimens of a large number of na- 

 tive varieties of potato from Peru. When 

 these collections were examined by the under- 

 signed pathological inspectors of the Federal 

 Horticultural Board at Washington, about one 

 third of the tubers were found to be affected 

 with powdery scab. Their identification of the 

 organism has been verified by Mr. 0. W. Car- 

 penter of the Bureau of Plant Industry. The 

 diseased tubers came from the eastern slope of 

 the Andes, all having been grown at altitudes 

 of 10,000 feet or more in the regions about 

 Cuzco and Ollantaytambo, Peru. Some of the 

 infected tubers were obtained direct from the 

 fields of the Indians near the upper limit of 

 potato cultivation in the Panticalla Pass, be- 

 tween the Urubamba and Lucumayo valleys, 

 at an altitude of over 12,000 feet. Mr. Cook 

 states that potatoes are never imported in these 

 localities, only the original native varieties 

 being grown. Hence introduction of the dis- 

 ease from Europe or any other foreign locality 

 into this region of primitive potato-growing 

 seems most improbable. Both host and para- 

 site are apparently indigenous. 



2 Lagerheim, G. de, ' ' Remarks on the Fungus of 

 a Potato Scab {Spongospora solani Bruneli)," 

 Jour, of Mycology, VII., 103-104, 1892. 



Further evidence tending to show that the 

 disease is native to Peru and not introduced 

 is furnished by the character of the disease it- 

 self as it develops on the Peruvian potatoes. 

 The sori are in general smaller and shallower 

 than those usually produced on most varieties 

 of European or North American tubers, and 

 show less destruction of host tissue, indicating 

 that the disease is not of a serious nature in 

 Peru. This inference is strengthened by Mr. 

 Cook's statement that the natives are not con- 

 cerned over the disease, in fact do not con- 

 sider it an injury. That the fungus is com- 

 mon and generally distributed is proved by the 

 fact that about one third of the tubers collected 

 in this region showed Spongospora sori. The 

 slight importance of the disease in Peru as 

 compared with its greater virulence in Europe 

 and North America is easily understood if 

 South Ajnerica is the native habitat of the 

 parasite. Ancient association of the host and 

 its parasite would naturally have developed a 

 high degree of resistance on the part of the 

 potato and have produced the balanced rela- 

 tion of host and parasite so commonly seen in 

 cases of long-established parasitism. 



The evidence indicates, therefore, that South 

 America, which is the native habitat of the 

 potato, is also the home of Spongospora. If 

 so, we may add one more organism to the al- 

 ready long list of parasites which are rela- 

 tively unimportant in their native habitats, but 

 which have developed greater virulence and 

 destructive power when introduced into new 

 regions, especially if in the new localities the 

 host plants have been subjected to more inten- 

 sive cultivation. 



The discovery of powdery scab on these 

 Peruvian potatoes shows the need of very care- 

 ful inspection of all imported plants and em- 

 phasizes the great importance of obtaining 

 healthy material for breeding or other experi- 

 mental purposes. Such material should be 

 entirely free from disease, even from diseases 

 which are apparently of little importance in 

 the native habitat of the host. 



G. R. Lyman, 

 j. t. eogers 



Federal Horticultural Board, 

 U. S. Department op Agriculture 



