PRODUCTION AND DISPERSAL OF CONIDIA IN THE 
PHILIPPINE SCLEROSPORAS OF MAIZE 1 
Pathologist in Charge of Downy Mildew Investigations, Office of Cereal Investigations 9 
Bureau of Plant Industry , United States Department of Agriculture 
By William H. Weston, Jr. 2 
INTRODUCTION 
The members of the genus Sclerospora have come to be recognized as 
among the most destructive of the downy mildews (Peronosporaceae). 
They long have been responsible for considerable injury to such cereals 
as millet and wheat in Europe and have recently occasioned alarming 
losses of maize and related crops in the Orient. 
The genus is known to produce two types of spores; conidia which are 
not at all hardy but serve to spread the disease rapidly under favorable 
conditions, and resistant oospores which enable the fungus to persist 
through such unfavorable circumstances as drought, extremes of tem¬ 
perature, or freezing. Unfortunately, however, comparatively little has 
been known of the methods of spore production and dispersal in the case 
of these fungi, and it can even be said, as Butler (j), 3 who has contributed 
largely to our knowledge of the oriental forms, remarks: 
The life history of the cereal downy mildews, which all belong to the present genus, 
is the most obscure among the Peronosporaceae. 
By the early European workers who described the type species {Sclero¬ 
spora graminicola (Sacc.) Schroet.) on which the genus Sclerospora was 
founded, most of the emphasis was laid on the oospores, and very little 
attention was paid to the conidial stage, the meager descriptions and 
illustrations of this phase obviously depicting herbarium material unfa¬ 
vorable for study (ir, p. 437-439, fig. 7). Recent investigation of the 
several downy mildews of the Orient, however, has of necessity dealt 
chiefly with the conidial stage, as in almost all of these cases the oospores 
apparently play little, if any, part in the life history. As a result, our 
appreciation of the importance of the conidial phase of Sclerospora has 
been increased, and our knowledge of the characteristics of the conidi- 
oohores and conidia has been augmented by further information. 
Unfortunately, however, the available information concerning the 
conidial stage of the Sclerosporas is still all too scanty. For instance, no 
data have been furnished on the process of conidiophore and conidium 
production, its duration, its amount, and its relation to environmental 
conditions. Yet such information is obviously of primary importance, 
as spore production and dispersal are intimately related to the distribu¬ 
tion and severity of the disease; and in a complete knowledge of all phases 
of these processes lies the means of intelligently effecting control. 
During the past two years the writer studied the destructive downy 
mildews of maize which are common in the Philippines and found that 
1 Accepted for publication Aug. 31, 1921. 
s The writer wishes again to express his gratitude to Dean Baker, Prof. Reinking, and Prof. Elayda, of 
the Philippine College of Agriculture, for kindly supplying laboratory accommodations and other aid, and 
to Dr. Merrill, of the Philippine Bureau of Science, for generously extending the facilities of that institution. 
8 Reference is made by number (italic) to "Literature cited," p. 277-278. 
Journal of Agricultural Research, 
Washington, D. C. 
aca 
Vol. XXIII, No. 4 
Jan. 27, 1923 
Key No. G-a7i 
22330-23--2 
(239) 
