66 
Journal of Agricultural Research 
Vol. XXV, No. 2 
INOCULATIONS PERFORMED IN 1920 
In 1920, leaf-mutilation inoculations were performed without any 
effects .appearing before digging time, but some effects from the inocula¬ 
tions were apparent in 1921 in the second generation. The tubers were 
split in two and planted as two-hill tuber units. In 69 of the 90 series 
the juice was obtained from mosaic Green Mountains while the inocu¬ 
lated plants were mostly of different varieties in the Rural, Cobbler, and 
other groups, a few being Green Mountain controls. Progeny of these 
inoculated plants were diseased, with mosaic or curly dwarf, in 24 of 428 
tuber units, or in about 6 per cent, and progeny of the controls in 7 of 
509, or in about 1 per cent. This difference is not very significant, 
especially since the diseased units were not grouped in correlation with 
any condition of inoculation. In 21 of the 90 inoculation series the 
inoculated plants were Green Mountains of a certain strain while the juice 
or inoculum was obtained from other varieties except for a few Green 
Mountain controls. Five of these undoubtedly were successful in 
producing infection, and all are considered in detail in Table XII. Here 
it must be remembered that the terminology was more general regarding 
diseases than at present. The controls were hills in the same tuber units 
as the inoculated hills. 
It is noteworthy that the stocks which served as the sources of 
inoculum in Series 5, 14, and 17 apparently recovered from mosaic in 
1921. This apparent recovery was noted for other stocks, both by the 
writers in strains all mild mosaic for several years previously and by 
seed-certification officials over several States, and is to be attributed to 
seasonal modification or masking of symptoms. It will be discussed 
more fully later. It is probable that mild mosaic was not apparent 
even when the virus was present. 
Inoculations in Series 5 and 8 were successful in inducing “mosaic,” 
(probably not of the mild type) with symptoms in the progeny of slight 
dwarfing, slight winkling, slight burning, and mottling or chlorosis. 
Inoculation Series 2 and 16 would be considered successful also if the 
controls were healthy. Possibly the. controls were infected by insects 
from the adjacent inoculated plants. Inoculation Series 3 and 4 were 
partly successful, being performed under control (insect-cage) conditions 
as a duplicate of Series 2. Inoculations in Series 7, 19, and 66 were 
successful in inducing “curly dwarf,” with symptoms consisting of 
marked dwarfing, ruffling, curling, brittleness, stem streaking, and 
burning (PI. 11, A, B, 2, 3, 5; 12, A, B). Disease appearing in 1921 as 
a mosaic was thus induced in Green Mountains by inoculation with 
juice from mosaic and curly-dwarf plants of the Rural type, and curly 
dwarf was induced with juice from dwarfed and wrinkled Netted Gems, 
curly-dwarf Green Mountains, and curly-dwarf Irish Cobblers. The 
third generation of representative parts of Series 8 and 19 were grown 
in 1922, a season unusually favorable for the detection of mosaic mot¬ 
tling. Series 8 contained leaf-rolling mosaic, rugose mosaic, spindling- 
tuber disease, and various combinations including mottled curly dwarf 
in the majority of the tuber units, with the controls mostly healthy. 
Series 19 consisted almost entirely of unmottled curly-dwarf plants 
(p. 60), with the controls mostly healthy. It is to be concluded that the 
open-field leaf-mutilation inoculations in 1920 at least transmitted 
rugose mosaic, a combination of leaf-rolling mosaic and spindling-tuber 
disease, and unmottled curly-dwarf. 
