i«0 



JOURNAL OP AGMCIILTHAL RESEARCH 



Vol. XX Washington, D. C, February i, 1921 No. 9 



ANOTHER CONIDIAL SCLEROSPORA OF PHILIPPINE 



MAIZE 



By William H. Weston, Jr. 



Pathologist in Charge of Downy Mildew Investigations, Office of Cereal Investigations, 

 Bureau of Plant Industry, United States Department of Agriculture 



Each year in the Philippine Islands the valuable maize crop suffers 

 very severe losses from the destructive activities of downy mildew (Scleros- 

 pora spp.). While the writer was studying this disease during the past 

 two years his attention was naturally directed to the question whether 

 the widespread destruction of maize throughout the thousand-mile extent 

 of these scattered islands was due in all cases to the same species of 

 fungus. A comparative study of material collected from many parts of 

 the provinces of Batangas, Laguna, and Rizal in the island of Luzon, 

 where the disease is most serious and where it was studied most inti- 

 mately, showed that in all cases the same causal fungus was involved. 

 This species of downy mildew was described in an earlier paper (12) 1 as 

 Sclerospora philippinensis. It was only natural to suspect that some of 

 the abundant Philippine wild grasses related more or less closely to maize 

 would be found to harbor this or other Sclerosporas. As on the widely 

 distributed wild grass Saccharum spontaneum L. (PI. 77, A) the oogonial 

 stage of a Sclerospora had been very commonly encountered in great 

 abundance, this grass was obviously an object of suspicion. In Luzon, 

 however, despite extensive search, no conidial stage was seen on this host. 



During a trip to the more southern Visayan Islands of Cebu, Bohol, 

 and Leyte, in which maize is a crop of very great importance, the writer 

 found that there, also, the maize plantings were suffering heavy losses 

 from downy mildew. As no microscope was carried, no study of the 

 causal organism was made at night during the period of conidium pro- 

 duction. However, inasmuch as the symptoms and the general effect of 

 the downy mildew were the same in these southern islands, the writer 

 inferred that the causal organism was that which he had found so widely 

 distributed on maize throughout the northern island of Luzon. Also the 

 wild grasses of these southern islands were carefully examined as possible 



1 Reference is made by number (italic) to " Literature cited," p. 684. 



Journal of Agricultural Research, Vol. XX, No. 9 



Washington, D. C Feb. 1, 1921 



wq Key No. G-217 



(669) 





