DEVELOPMENT OF WILT-KESISTAISTT TOMATOES. 5 



best commercial varieties in quality of fruit were discarded without 

 regard to other qualities. The most promising strains remaining were 

 tested in subsequent years by repeated plantings on wilt-infested 

 land beside the best commercial varieties, beside the most wilt-resist- 

 ant varieties, and beside the best strains previously obtained by this 

 method. 



As it is difficult to determine accurately the degree of infection 

 in wilted plants, the writer has graded the resistance of strains by 

 a combination of characters correlated with the degree of infection, 

 viz, the percentage of infected plants, the percentage of dead plants, 

 and the yield of fruit. 



The percentage of infected plants is correlated with the degree 

 of infection in highly resistant material and is therefore useful in 

 determining resistance when no plants die and when marked fluc- 

 tuations in yields occur from variations in the environment. 



The percentage of dead plants is useful in making selections from 

 very susceptible material in which all or nearly all plants become 

 infected and varying percentages die. 



The yield of fruit is inversely correlated with the degree of in- 

 fection in both resistant and susceptible varieties or strains. It is 

 therefore useful in making selections for wilt resistance, but its 

 exclusive use for this purpose is likely to lead to erroneous con- 

 clusions, as yields are often affected by other factors than wilt, and 

 early susceptible varieties, such as Earliana and Texas Bell, partially 

 freed from the effects of the disease because of the low soil tempera- 

 ture in the early part of the season, not infrequently produce a large 

 part of their crop before they are killed by wilt. 



Yields in these preliminary tests were not determined from actual 

 weights of fruit but from general appearences ; in fact, the differences 

 were great enough to be easily distinguishable without the use of 

 weights. 



When the three characters, percentages of infected plants, per- 

 centage of dead plants, and yield of fruit, are judiciously used they 

 furnish a fairly effective and rapid means of determining resistance. 



VARIETAL RESISTANCE. 



The only naturally wilt-resistant varieties of tomatoes having fruit 

 of fair size and quality found by the writer are the Duke of York 

 •and the Buckeye State. In type of fruit and vine and in resistance 

 to wilt they appear to be one variety under two names. Livingston's 

 Globe possesses some resistance, enough, in fact, to be of economic 

 importance, but it is not so resistant as the varieties just mentioned. 

 Although the Duke of York and the Buckeye State produce large 

 fruit it is rather hard, especially at the stem end, and has a large 



