May 1, 1920 Philippine Downy Mildew of Maize 103 



roughly grouped under the types described above. The discolorations, 

 growth changes, and other efifects of the disease all differ markedly in 

 accordance with time of infection, the varietal and individual character 

 of the plant attacked, and the conditions of the environment. Hence 

 there are encountered not only such diseased specimens as can be in- 

 cluded conveniently in the three types recognized by Palm but also some 

 plants which show symptoms intermediate between the types and others 

 which show various combinations of these symptoms. 



The occurrence of such sharply marked categories of symptoms as 

 those described by Palm might with some justice be suspected to be the 

 manifestation of different biologic strains of the causal fungus. In the 

 Philippine maize-mildew, however, cross inoculations with spores from 

 infected plants corresponding to Palm's symptom types, as well as 

 biometric studies of the spores and conidiophores from these plants, dis- 

 prove this assumption. Moreover, a series of experiments in which sev- 

 eral varieties of maize were inoculated in various ways at different ages 

 and subjected to different environmental conditions, although not en- 

 tirely completed, has shown that the changes of color and growth pro- 

 duced in the plant by the disease differ with variations in these factors. 

 All the evidence of field observations Also supports this conclusion. In 

 general, then, while the symptoms of the Philippine maize-mildew resem- 

 ble those of the Javan, they appear to be much more varied and less 

 easily grouped into sharply defined categories. 



In the related Formosan downy mildew, Miyake (74) has described in 

 detail only the symptoms shown by attacked sugar cane, which is the 

 host most severely affected. He states that in maize the stripes are not 

 particularly pronounced and the plant is not noticeably hindered in 

 growth, for it ripens and shows only a slight decrease in yield. While 

 this description would fit occasional plants attacked by the Philippine 

 maize-mildew, it by no means depicts adequately the injurious effects in 

 even the average case and would seem to indicate that the Formosan 

 mildew is far less destructive to maize than is the Philippine. 



Upon comparing the maize downy mildew of the Philippines with that 

 of British India described by Butler (4), it is to be noted that the symp- 

 toms of the latter resemble in general those seen in the Philippines, al- 

 though in the Indian disease more emphasis is laid on the checking of the 

 intemode growth and the consequent stunted appearance of the at- 

 tacked plants than seems to be warranted from observation in the 

 Philippines. Moreover, although the maize-mildew of British India has 

 been present in that country since 191 1, it has,in marked contrast to the 

 Philippine disease, caused only slight sporadic injury. 



HOSTS 



Under field conditions throughout the Philippine Islands maize is the 

 only crop, on which the downy mildew occurs with sufficient severity to 

 attract attention or to occasion appreciable loss. In the trial plots at 



