Feb. i, i 9 2i Another Conidial Sclerospora of Philippine Maize 68 1 



Saccharum in the Visayan Islands should be regarded as throwing light 

 on the problem of the origin of the Philippine downy mildews of maize. 

 In the opinion of the writer this and other facts indicate that the native 

 grasses of the Philippines were the original hosts from which the downy 

 mildews passed and are passing to such very susceptible introduced 

 crops as maize. On the other hand, one should not overlook the possi- 

 bility that the wild Saccharum clumps might have been infected with the 

 downy mildew from badly diseased maize growing near. In this con- 

 nection it should be noted that in two cases where Sclerospora spontanea 

 was found on wild bugang grass (Saccharum spontaneum) the infected 

 clumps were so far distant and so protected from any downy-mildewed 

 maize that there was little possibility of their having been infected thus. 

 In the other cases the infected bugang clumps were much older than the 

 mildewed maize adjacent; and, because inoculation experiments have 

 shown that bugang grass is susceptible only as comparatively young 

 seedlings, there is little doubt that the infection in the grass clump had 

 been carried over in the perennial rootstocks and had not been caught 

 from maize. 



Moreover, it is worthy of note, also, that the wild Saccharum is very 

 resistant to the effect of the Sclerospora, while maize is exceedingly 

 unresistant. In contrast to the susceptibility to severe injury already 

 noted in maize, wild Saccharum, even though heavily infected, shows 

 only slight striping of the leaves (PL 78, B, C), remains undeformed, and 

 is not materially retarded in development. In spite of the downy 

 mildew the plants continue to grow vegetatively, to produce flowers 

 (PL 77, B), and to form, by tillering, dense clumps which by extensive 

 rootstocks persist from season to season, still supporting the active and 

 equally persistent parasite. Because, as a rule, it is the introduced host 

 which is most injured by a disease and the original, native host which is 

 relatively unaffected, the indications are that wild Saccharum and not 

 maize is the original host of Sclerospora spontanea. 



The finding of Sclerospora spontanea on sugar cane is a second point of 

 interest. Because, in Formosa, the closely related species 5. sacchari 

 Miyake had proved indiscriminately destructive to both sugar cane and 

 maize, the writer, while in the Philippines, made especial effort to dis- 

 cover instances of the transmission of downy mildew from one to the other 

 of these hosts. The single case in Cebu, however, was the only one noted. 

 In this instance the single clump of sugar cane infected with 5. spontanea 

 was situated at the extreme edge of the field, separated only by a narrow 

 trail from a large planting of badly downy-mildewed maize. Although 

 the whole sugar-cane field was carefully inspected, no other cases of 

 Sclerospora were discovered. It is natural to infer that the sugar-cane 

 plant was infected from the neighboring maize, especially since the two 

 parasites proved to be the same. It is rather surprising, however, that 

 this lone cane plant, of all the thousands examined in scores of different 



