Mar., 1923] CLAYTON — SOIL MOISTURE AND FUSARIUM WILT 
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is very wide, 22 to 33 percent with the soil used in the moisture work, there 
was little object in controlling moisture exactly in the temperature experi¬ 
ments. 
Early in the work, owing to the fact that the disease appeared to develop 
equally well over a wide range of soil moistures, it was thought that soil 
moisture was of very minor importance as compared with temperature. 
However, it now seems that extreme drought would certainly check the 
development of the disease, regardless of temperature conditions. 
A brief consideration of the application of these findings to field con¬ 
ditions follows. The moisture results indicate that for a virulent develop¬ 
ment of the disease the plants must be rapidly growing. The temperature 
results showed that warm air and soil temperatures (27°-3i° C.) were 
essential for a virulent development of the disease. Therefore it would 
be expected that, under field conditions, a rainy period, inducing rapid 
growth, followed by hot weather, would furnish optimum conditions for the 
quick appearance and the rapid progress of the disease. Weather which 
was hot and moist would be favorable, but it was pointed out in the tem¬ 
perature work that an even warm or hot temperature is not nearly so effec¬ 
tive as the same temperature with intermittent periods of extreme heat. 
Bright, sunny days furnish this intermittent temperature, while during 
hot, moist weather the temperature is rather even. A warm, rainy period 
followed by hot weather would produce the disease more quickly than cool, 
rainy weather followed by a hot period, since under the former conditions 
infection would have occurred and growth of the fungus up the stem would 
have begun. Continuously dry weather which checks the growth of the 
plants should also check the development of the disease. 
Summary 
Tomato plants were grown in crocks of sterilized soil inoculated with 
a spore suspension of Fusarium lycopersici. The soil in these crocks was 
held at moisture contents ranging from 13 to 35 percent, the higher value 
representing complete saturation. 
The plants growing in soil with a low moisture content, 13 to 19 percent, 
were very resistant to the disease. 
The plants growing in soil which was kept saturated were immune from 
attack. 
In general, it was found that any moisture shortage sufficiently severe to 
check the vegetative vigor of the host checked the disease proportionally. 
When rapidly growing plants held at a temperature below 20° C. were 
brought into a temperature favoring the disease (25°-30° C.), they were 
soon attacked by the wilt. However, if the soil was allowed to dry out as 
soon as the plants were placed at the warm temperature, the appearance 
of the wilt was very much delayed. Thus, rapidly growing succulent plants, 
which had been susceptible to the disease, were made disease-resistant by 
allowing the soil to become very dry. 
