THE RELATION OF SOIL MOISTURE TO THE FUSARIUM 
WILT OF THE TOMATO 1 
Edward E. Clayton 
(Received for publication May 20, 1922) 
In an earlier article (3) the author has discussed the relation of temper¬ 
ature to the Fusarium wilt of tomato. In correlation with the temperature 
studies, inquiry was made into the relation of various amounts of soil mois¬ 
ture to the development of the disease. The earlier article includes an 
account of the disease and of the characters and source of the pathogen 
(.Fusarium lycopersici Sacc.), as well as of certain details as to experimental 
methods. These statements will apply in general to the moisture studies 
also, since the work along the two lines was carried on simultaneously. 
Review of Literature 
There are few records in the literature of plant pathology of controlled 
experiments dealing with the effect of soil moisture. However, a body of 
recorded observations offers suggestions as to moisture effects. In these 
it will be noted that the reference is sometimes directly to soil-moisture and 
at other times to soil aeration or drainage. Field observations have led to 
the belief that hot, dry weather favors the Fusarium wilt. Humbert (8) 
has recently made this statement, and, as he has supported the statement 
with meteorological data, there seems to be no reasonable doubt that practi¬ 
cally every serious outbreak of the disease comes during hot, dry weather. 
From a consideration of parasitic plant diseases in general, the most 
definite fact which has been brought out concerning soil-moisture effects 
has been that with saturation of the soil the host-parasite balance may be 
completely overturned. Recent literature indicates that usually this has 
resulted in a great increase in the amount of disease. Thus Johnson (9), 
in carefully controlled work with the Thielavia root rot of tobacco, found 
that saturation of the soil greatly increased the amount of disease. Rolfs 
(14) has reported that Rhizoctonia on a number of crops is most severe on 
poorly drained lands, and improvement of drainage has been recommended 
as a control measure for a wide variety of soil troubles. Hole (7), of the 
Indian Department of Agriculture, says that the sal-root fungus, Polyporus 
shoraae, is widely distributed throughout the sal forests of India, but that, 
so far as is known at present, it does damage only in those wet forests of 
Bengal and Assam in which conditions of soil aeration are known to be 
1 Investigations carried on at the University of Wisconsin under advisory relations 
with Professors L. R. Jones and E. J. Kraus, to both of whom the author is indebted for 
counsel and criticism. 
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