DEVELOPMENT OF WTLT-KESISTANT 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 Bdgerton, C. W., and Moreland, C. C. Tomato wilt. La. Agr. Exp. Sta. Bui. 174, 

 54 p., 19 fig. 1920. Literature cited, p. 54. 



