JOURNAL OF AffllfflniRAL RESEARCH 
Vol. XXX Washington, D. C., March 15, 1925 No. 6 
INFECTION AND DISSEMINATION EXPERIMENTS WITH 
DEGENERATION DISEASES OF POTATOES. OBSERVA¬ 
TIONS IN 1923 1 
By E. S. Schultz, Pathologist, Cotton, Truck, and Forage Crop Disease Investiga¬ 
tions, Bureau of Plant Industry, United States Department of Agriculture, and 
Donald Folsom, Plant Pathologist, Maine Agricultural Experiment Station. 
INTRODUCTION 
In a former publication 2 evidence 
was presented indicating that degenera¬ 
tion of the potato ( Solanum tuberosum 
L.) is brought about by at least seven 
diseases, for which the etiology remains 
to be demonstrated. It was established 
that although these diseases are quite 
similar regarding transmission, they dif¬ 
fer sufficiently in transmission and 
symptoms to be considered distinct, 
even in the same variety and in the 
same environment. Furthermore, it 
was shown that combinations of these 
diseases occur, usually causing more 
severe injury than a single disease. 
Insect transmissibility was proved for 
six diseases and for several combina¬ 
tions. 
These results suggested that further 
investigations might disclose additional 
similar maladies; that some unsolved 
apparent combinations might be re¬ 
duced to still simpler forms; that 
further knowledge of the reactions of 
different varieties to those single 
diseases and their combinations was 
desirable; that additional information 
on insect carriers, including different 
genera or species of aphids and other 
insects, deserved further attention; 
and that additional data on alternate 
hosts should be obtained. In order 
to secure further evidence on these 
and similar problems relating more or 
less directly to control, the investiga¬ 
tions presented in this paper were 
conducted. 
DESCRIPTION OF SYMPTOMS 
The symptoms of the different 
diseases to be considered will now be 
indicated. Four types of mosaic, 
mild, leaf-rolling, rugose, and crinkle 
mosaic, are recognized. Mild mosaic 
(pi. 6, A, 3; B, 4 and pi. 7, A, 2) is char¬ 
acterized chiefly by distinct mottling, 
wrinkling, some ruffling, and slight 
dwarfing in the foliage, and by reduc¬ 
tion in the yield rate of tubers without 
modification of their shape or color. 
Infection with juice inoculations is 
more difficult with mild mosaic than 
with rugose mosaic or streak. Leaf¬ 
rolling mosaic (pi. 6, A, 2; B, 2, and pi. 
9, C) differs from mild mosaic in its 
diffuse mottling and in a slight rolling 
of the middle and upper leaves; it 
resembles mild mosaic in the difficulty 
of infection by juice inoculations. 
Tuber symptoms resemble those of 
mild mosaic. Leaf-rolling mosaic is 
distinguished from leaf-roll (pi. 10, A) 
by the absence of distinct rolling, 
dwarfing, or rigidity, and of chlorosis. 
Rugose mosaic (pi. 6, A, 1; B, 1; pi. 
7, A, 1; and pi. 8, C and D) is character¬ 
ized by somewhat diffuse mottling, 
distinct dwarfing, rugosity, and a 
shorter life period (pi. 7, A, 1) and in 
current-season or late previous season 
infections (pi. 8, C) by brittleness, 
spotting, and streaking, resulting in 
abnormally premature death. Tuber 
reduction is more marked than in mild 
mosaic. Infection by means of leaf 
mutilation is easier with rugose mosaic 
1 Received for publication May 20,1924; issued June, 1925. This paper is based upon investigations con¬ 
ducted as a cooperative project between the Office of Cotton, Truck, and Forage Crop Disease Investiga¬ 
tions of the Bureau of Plant Industry, U. S. Department of Agriculture, and the Department of Plant 
Pathology of the Maine Agricultural Experiment Station. Unless otherwise indicated, the work was 
performed in northeastern Maine. The order of arrangement of the authors’ names is not intended 
to indicate that one cooperating institution contributed more than the other to the results. 
1 Schultz, E. S., and Folsom, D. transmission, variation, and control of certain degeneration 
diseases of Irish potatoes. Jour. Agr. Research 25: 43-118, illus., 1923. 
Journal of Agricultural Research, Vol. XXX, No. 6 
Washington, D. C. Mar. 15, 1925 
Key No. G-473 
19975—25f-1 
(493) 
