COLLAR-ROT OF TOMATO 
By F. J. Pritchard, Physiologist , and W. S. Porte, Scientific Assistant , Cotton , 
Truck, and Forage Crop Disease Investigations , Bureau of Plant Industry , United 
States Department of Agriculture 
INTRODUCTION 
A new disease of tomato seedlings, which takes the form of a rotting 
and girdling of the stems at the surface of the soil, has for the past three 
years caused heavy loss in Maryland, New Jersey, and Delaware. 
This is chiefly a seed-bed disease. Young, tender plants infected in 
the seed bed carry the disease to the field. Although field infections may 
occur also they do not appear to be common. Moreover, the hardened 
condition of the plants and the relative freedom of the field from the 
causal parasites make the opportunities for infection less favorable than 
in the seed bed. 
The most prominent symptom of the disease is the dark brown lesions 
on the stem at the surface of the ground (PI. 41, A, a, c) which often 
encircle the stems, forming a collar. These lesions also occur on other 
parts of the stem (PI. 41, A, b) but not so frequently as at the soil line. 
They enlarge and make the affected parts weak and brittle. There is 
very little infection of the roots. 
Diseased plants set in the field are commonly snapped off by the wind 
at the point of infection. Some recover by forming a callus over the 
wound, and others outgrow it by forming new roots above the diseased 
area. Plants which recover are seldom as productive, however, as those 
which have always been healthy. The estimated loss of the crop from 
this disease in Delaware in 1919 was 30 per cent. 
Rosenbaum 1 attributes the disease to Macrosporium solani, and Cook 2 
to Rhizoctonia. The writers have isolated from collar-rot material a 
Verticillium that also readily infects tomato seedlings and causes the 
typical symptoms of the disease. 
The present paper contains the results of inoculation experiments 
made with this species of verticillium and also with Macrosporium solani 
and Rhizoctonia solani. 
EXPERIMENTAL WORK 
MATERIAL AND METHODS 
The Verticillium used in these experiments was isolated from young 
tomato plants infected by collar-rot in seedbeds in Maryland. The 
1 Rosenbaum, Joseph, a stem disease of tomato caused by macrosporium solani e. & m. 
(Abstract.) In Phytopathology, v. io, no. i, p. 59. 1920. 
a Cook, Mel. T. the alternaria fruit rot and rhizoctonia stem rot of tomatoes. (Abstract,) 
In Phytopathology, v. 10, no 1, p 59. 1920. 
Journal of Agricultural Research, 
Washington, D. C. 
xr 
Vol. XXI, No. 3 
May 2, 1921 
Key No. G-227 
