Aug. ii, 1923 
Irish Potato Foliage Degeneration Diseases 
259 
VARIATION IN THE PROGRESSIVE DEVELOPMENT OF MOSAIC SYMPTOMS 
Schultz and Folsom (jj, p. 316) recognize and describe five stages or 
degrees of severity of mosaic symptoms—“slight,” “slight plus,” 
“medium,” “medium plus,” and “bad.” The writer, while agreeing 
fully as to the significance and appropriateness of these terms, has, how¬ 
ever, used the slightly different terms, “mild,” “medium,” and “ex¬ 
treme,” respectively, for the conditions described by Schultz and Folsom 
as “ slight,” “ medium,” and “bad.” “ Mild ” mosaic in the present paper 
indicates faint mottling with approximately normal development of 
foliage; “medium” refers to a condition in which there is distinct mot¬ 
tling and some wrinkling and reduction in leaf area, and “extreme” is 
used in connection with the stage in which there is marked wrinkling 
and curling of leaves and a dwarfed or conspicuously spindling habit of 
the plant. The results of Schultz and Folsom (jj, p. 317) indicate that 
mosaic in northern Maine “ does not necessarily change much from year 
to year in any diseased stock after the first appearance of the effects of 
infection.” The results of the present investigation in part seem to 
agree and in part to differ with the foregoing statement. That is to say, 
it has been found that in Vermont mild mosaic may in some cases persist 
as mild mosaic for several seasons in a certain stock without marked 
change, but that from one season to the next sudden changes also occur, 
as from mild to extreme, or even from a condition noted as “healthy but 
adjacent to mosaic hills” to a condition of extreme mosaic as described 
in the succeeding paragraphs. 
As a result of observations on many plantings of tubers of known 
history both in the greenhouse and field, it was noted that much varia¬ 
tion exists in the progressive development of mosaic infection from year 
to year. In certain cases a condition of mild mosaic persists in the 
progeny plants through one or more subsequent seasons with compara¬ 
tively little change, while in other cases the increased seriousness of the 
disease as evidenced by the foliage symptoms is very marked between 
one season and the next. In the first instance tubers from plants exhib¬ 
iting a mild degree of infection produced the next season plants showing 
little, if any, increase or change in the seriousness of the symptoms (PI. 
2, A 2; D), while in the latter case tubers from other plants with 
very similar external symptoms produced the next season plants showing, 
even in the earliest stages of development, extreme mosaic symptoms 
(PI. 2, A 1; C). 
In illustration of the first condition described is cited the history of 
some tubers of the Green Mountain variety secured in 1919 from L. P. 
Boyd of Whitingham, Vt. The plants from which these tubers were 
taken were of large growth with leaves showing faint mottling but no 
wrinkling. There was apparently no reduction in area of leaf surface 
on account of the disease. Tubers from these hills planted in the experi¬ 
mental plots in 1920 gave plants showing only a faint mottling and no 
wrinkling or dwarfing throughout the season. Tubers from the 1920 
plants in the field plots were in turn planted in the greenhouse in the 
winter of 1920-21, and the foliage produced showed faint mottling, 
slight wrinkling, and symptoms of leafroll. Since the plants in the field 
during the season of 1920 were adjacent to leafroll hills, there was sufficient 
opportunity for the acquisition of this infection. There is seen, then, 
in the foliage of three successive generations of this particular lot (III-18- 
2-1919) only a slight increase in the seriousness of mosaic symptoms, 
