16 
BULLETIN 1288, U. S. DEPARTMENT OF AGRICULTURE 
wild varieties obtained through the Office of Foreign Seed and 
Plant Introduction have shown about the same degree of suscepti- 
bility to this disease. In fact, the most resistant varieties seen 
are those developed by the United States Department of Agricul- 
ture for resistance to wilt (6) 1 and hybrids from them (fig. 9). 
Although these varieties possess a little resistance to leaf-spot and 
have transmitted an intensification of this quality to some of their 
hybrids, neither they nor their hybrids are resistant enough to 
fully meet commercial needs. Further crossing and selection may 
lead to greater improvement, but the most hopeful possibility lies 
in the introduction of a resistant wild form that possesses desirable 
fruit and vine qualities for crossing. At present no varieties are 
known more resistant than the Marvel, Norton, and Norduke and 
some of their unnamed hybrids. 
Fig. 9. — Comparative resistance to leaf-spot of tomato varieties growing in the same 
experimental plat: A, Commercial varieties defoliated by Septoria lycopersici; B, the 
Marvelosa variety, developed from a cross between Marvel and Ponderosa. This is a 
promising new pink-fruited variety showing partial resistance to leaf-spot 
SUMMARY 
Tomato leaf -spot, or blight, causes an average annual loss of 
approximately 250,000 tons of commercial tomatoes in the United 
States. 
The use of Bordeaux or other copper-spray mixtures has given the 
most effective control of leaf -spot in the past, but the profits from 
spraying are variable and not always sufficient to justify the ex- 
pense. A more effecth^e and economical method of control lies in 
the use of modified field practices. 
The effects of tomato leaf -spot epidemics can be largely avoided by 
setting out large, stocky, well-hardened plants early in the spring. 
As the leaf-spot fungus has a high minimum sporulation tempera- 
ture, viz, 59° F., and therefore seldom infects tomato plants in the 
field in the Middle Atlantic and Middle Western States, the region 
where it is severe, before June 15 to 30, these early plants escape 
more leaf-spot than the small plants commonly set late. 
Tritehard. F. 
resistant tomato. 
J., and Porte. W. S. 
i Manuscript.) 
History and description of the Norduke wilt- 
