RELATION OF HORSE NETTLE (SOLANUM CAROLIN- 
ENSE) TO LEAFSPOT OF TOMATO (SEPTORIA LYCO- 
PERSICI) 
By Fred J. Pritchard, Physiologist, and W. S. Porte, Scientific Assistant , Office oj 
Cotton, Truck, and Forage Crop Disease Investigations, Bureau of Plant Industry, 
United States Department of Agriculture 
INTRODUCTION 
Horse nettle (Solatium carolinense L.)> a weed closely related to 
potato and tomato and generally distributed in fields and waste places 
from Ontario to Massachusetts, Florida, Illinois, Nebraska, and Texas, 
has been found to be a host of the tomato leafspot, or blight, fungus. 
In Maryland, New Jersey, and Delaware, where tomato leafspot 
causes heavy annual losses, horse nettle (PI. 95, 96) is very common in 
waste places, in grass and grain fields, and even in cultivated crops. Its 
numbers in fields of tomatoes in the Middle Atlantic States, especially 
in Delaware, not infrequently exceed those of the tomato plants 5 to 20 
times. Moreover, it bears numerous spots (PI. 97, A) which in size, 
shape, color, and other appearances closely resemble leafspot of tomato 
(PI. 98, A). Observations of these facts caused the writers to determine 
whether or not horse nettle is a host of the tomato leafspot fungus. 
EXPERIMENTAL WORK 
MATERIAL and methods 
Young tomato and horse nettle plants were grown from seed in the 
greenhouse and used for inoculation when 1 to 5 inches high. Consider¬ 
able difficulty was at first encountered in germinating the horse nettle 
seed,.but this was finally overcome by setting the seed pots directly on 
the steam pipes. Both the tomato and horse nettle seedlings were in a 
thrifty condition when inoculated. Control plants were used in approxi¬ 
mately as large numbers as inoculated plants in ^ach experiment. 
The inoculations were made by spraying the plants with spores from 
a pure culture by means of either a DeVilbiss atomizer or a small spray 
pump, or by transferring minute pieces of mycelium from a rapidly 
growing culture to leaves moistened with distilled water. Both the 
inoculated plants and the controls were kept in a moist chamber 48 to 60 
hours and then transferred to benches in the greenhouse. 
INOCULATION OF HORSE NETTLE PLANTS WITH SEPTORIA LYCOPERSICI 
FROM TOMATO 
In the fall of 1919 about 25 horse nettle plants transferred from the 
field to the greenhouse and inoculated with a pure culture of Septoria 
lycopersici Speg obtained from tomato became infected with numerous 
Journal of Agricultural Research, 
Washington, D. C. 
yj 
(5 01 ) 
Vol. XXI, No. 7 
July 1, 1921 
Key No. G-235 
