DEVELOPMENT OF WILT-RESISTANT TOMATOES. 3 
recognize it and either plants or sells the seedlings. Wherever such 
seedlings are used they spread the disease. In the Middle West the 
practice of using tomato plants grown in Maryland, Delaware, and 
the Southern States when there is a shortage of locally grown plants 
is attended with this danger. 
Although wilt does not at present cause so much loss as tomato 
leaf-blight (Septoria lycopersici) , it is much worse than blight wher- 
ever the soil becomes thoroughly infested with the wilt fungus. It 
therefore threatens the future success of the tomato-canning indus- 
try and should by all means be brought under control. 
The only means of controlling wilt successfully has been developed 
in recent years. As the wilt fungus lives in the soil and invades the 
tomato plant through its roots, it lies beyond the reach of chemical 
sprays, such as Bordeaux and other mixtures commonly used for the 
control of fruit and foliage parasites. It multiplies rapidly in the 
tomato plant, as it has no competition for its food supply, and it 
becomes thoroughly distributed through the soil with the plowing 
under of dead vines. If a piece of wilt-infested land be used suc- 
cessively for growing tomatoes it soon becomes so full of the fungus 
that ordinary varieties of tomatoes can not be grown on it. Rotation 
of crops forces the wilt fungus to compete with other fungi for its 
food and therefore reduces it to a minimum, but so far as known does 
not eradicate it, as it is capable of living long periods, if not indefi- 
nitely, on the organic matter in the soil. Treating the soil with 
chemicals for the control of wilt has not given results of economical 
value. Large quantities of lime retard its development, 2 but do not 
otherwise inhibit its activities. The only successful means of con- 
trolling wilt is through the development of resistant varieties. 
DEVELOPMENT OF RESISTANT VARIETIES. 
SELECTION OF MATERIAL. 
It is necessary in breeding for wilt resistance to have at least one 
variety with some resistance to the disease as a basis for selection or 
crossing. If it possesses only moderate resistance but exhibits it in 
diverse degree in individual plants, it will serve as a starting point. 
If it possesses considerable resistance but lacks yield and quality, 
its resistance can be combined with other desirable qualities by cross- 
ing. If, in addition to partial resistance, it is characterized by 
superior yield and quality of fruit, it will facilitate the work by 
eliminating crossing and the breaking up of the type. 
In searching for suitable material for resistant foundation stock 
the writer has tested the best canning varieties, the extra large 
2 Edgerton, C. W., and Moreland, C. C. Tomato wilt. La. Agr. Exp. Sta. Bui. 174, 
54 p., 19 fig. 1920. Literature cited, p. 54. 
