May 1, 1920 Philippine Downy Mildew of Maize 105 



difficulties in securing artificial infection, these negative results are by no 

 means conclusive, although the successful infection of maize, sorghum, 

 and teosinte under the same conditions would seem to indicate that these 

 other relatives are far less susceptible. 



These inoculations will be detailed more fully in a later paper, but it 

 should be said here that they were made from, about 2 a. m. until dawn 

 because the spore production was found to take place at this time. It 

 seems highly probable that spore production is nocturnal in the other 

 related downy mildews of the Orient as well and that the uncertain 

 results of inoculations with them has been due to the failure to use fresh 

 spores. 



It is of interest to compare these results with those obtained for the 

 other related downy mildews of the Orient. In Formosa, Miyake (14) 

 successfully transferred Sderospora sacchari T. Miy. from sugar cane to 

 maize and teosinte and vice versa, but was unable to infect rice, sorghum, 

 wheat, or millet. In India, although their infection experiments were 

 unsuccessful, Butler (j) and Kulkami (lo) note the occurrence on teo- 

 sinte of the conidial stage of a Sderospora which they suspect may be 

 identical with that of maize {Sderospora maydis (Rac.) Butler.) 



In Java, no extensive attempts were made by either Rutgers {ig) or 

 Palm {15) to obtain artificial inoculation of other hosts with the Javan 

 downy mildew of maize {Sderospora javanica Palm). They state, how- 

 ever, that under conditions favoring infection in the field, neither sugar 

 cane nor the common wild alang-alang grass {Imperata sp.) was found 

 infected and that, although teosinte itself is immune, the hybrid between 

 teosinte and maize is, if anything, more susceptible than the variety of 

 maize from which it is derived. 



CAUSAL ORGANISM 



The fungus which causes this extremely destructive disease of maize 

 in the Philippines belongs to the Peronosporaceous genus Sderospora, as 

 Baker (i) and Reinking (77) already have reported. It should be noted, 

 however, that it shows especially close relationship, not to the type spe- 

 cies Sderospora graminicola (Sacc.) Schroet., which is distinguished by 

 the germination of the conidia by zoospores and the abundant production 

 of oospores, but to those other oriental members of the genus which are 

 characterized by the germination of the conidia by tubes and the partial 

 or complete lack of oospores. However, setting aside the question of the 

 affinities of the fungus for a later discussion, its characteristics will now 

 be considered. 



MYCELIUM 



As a rule, as soon as the maize plant shows any external indication of 

 the disease, the mycelium is found to be quite generally distributed 

 throughout the host tissue, the root being the only main organ which is 

 not extensively invaded. Thisin vasion is most marked in the vegetative 



