July 14, 19*3 
Degeneration Diseases of Irish Potatoes 
115 
(27) About 10 days were required for the mild mosaic virus to diffuse 
from inoculated leaves to the tubers. 
(28) Mosaic plants from the same seed tubers sometimes show different 
symptom complexes in different environments. Mottling is suppressed 
by southern regions and by higher temperatures. Dwarfing of the 
tubers, and therefore reduction of yield rate, was more pronounced in 
a southern region. 
(29) Shading tended to increase mosaic mottling and decrease leaf rolling. 
(30) In duplicate plots leaf roll and mosaic were contracted by healthy 
lots growing between rows of diseased lots, more in some regions than 
others. 
(31) Selection of tubers without knowledge of the parent plants can 
not eliminate seed from diseased plants infected late the preceding 
season. 
(32) The digging of selected healthy hills progressively later in the 
growing season was correlated with greater numbers of aphids and with 
greater amounts of disease in the progeny. 
(33) Hill selection in fields containing diseased plants throughout the 
growingseason is disappointing as a means of eliminating disease, but some¬ 
times gives better results than using unselected stock from the same field. 
(34) Proximity and a heavy aphid infestation increased the spread 
of mild mosaic, ^vhile sufficient isolation from diseased stocks reduced 
it so that a state of freedom from the disease was maintained. Isolation 
by 30 meters was insufficient, and over 400 meters was sufficient. 
(35) Conditions that reduced aphid dispersal from diseased to healthy 
hills also reduced the amount of disease transmission. 
(36) Potato degeneration is largely, and possibly is entirely, a result 
of the increase of, and injury by, certain degeneration diseases. 
(37) The potato degeneration-disease problem is on the whole similar 
for all potato-growing regions, but is complex enough to vary somewhat 
from one region to another. 
LITERATURE CITED 
(1) Anonymous. 
1919. MOSAIC DISEASE AS A FACTOR INFLUENCING YIELD. In Potato Mag., 
v. 2, no. 5, p. 11, 27. 
<2) Allard, H. A. 
1914. the mosaic disease of tobacco. U. S. Dept. Agr. Bui. 40, 33 p , 7 P 1 * 
< 3 ) - 
1917. FURTHER STUDIES OF THE MOSAIC DISEASE OF TOBACCO. In JOUT. Agr. 
Research, v. 10, p. 615-632, pi. 63. 
<4) Atanasoff, D. 
1922. stipple-streak disease of potato. Meded. Landbouwhoogeschool 
Wageningen, deel 24, verhandel. 5, 32 p., 5 pi. 
{5) Barrus, M. F. 
1917. physiological diseases of potatoes. In 9th Ann. Rpt. Quebec Soc. 
Prot. Plants, 1916-17, p. 45 “ 53 > 3 fi g- 
< 6 ) - 
1918. POTATO-MOSAIC AND CERTIFIED SEED. In Potato Mag., v. 1, no. 4, p. 
I3-I4- 
<7) -and Chupp, Charles C. 
1922. yellow dwarf of potatoes. In Phytopathology, v. 12, p. 123-132, 
1 fig., pi. 7-8. 
<8) Blodgett, F. M. 
1922. THE RELATION OF TIME AND TEMPERATURE TO THE KILLING OF POTATOES 
and potato mosaic virus. (Abstract.) In Phytopathology, v. 12, 
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<9) Burns, G. P. 
1921. TIP-BURN AND the LEAFHOPPER. 
n, p. 56-57. 
(Abstract.) In Phytopathology, v. 
