Maya, 1921 
Collar-Rot of Tomato 
183 
CROSS INOCULATION 
As the potato, which is sometimes grown in rotation with the tomato, 
and the horse nettle Solatium carolinense I/., which is a common weed in 
the Middle Atlantic States, are closely related to the tomato, inocula¬ 
tions of these plants were made with collar-rot fungi. Young shoots 
were inoculated at the base of the stem with mycelium from a fresh 
culture, as described in previous experiments. The results are given in 
Table IV. 
Table IV .—Effect of inoculating potato and horse nettle with collar-rot fungi 
Fungus. 
Host. 
Number of 
shoots in¬ 
oculated. 
Number of 
shoots in¬ 
fected. 
Percentage 
of shoots 
infected. 
Macrosporium solani . 
Potato 
43 
A * *7 
38 
25 
88 
53 
Verticillium lycopersici . 
Rhizoctonia solani . 
41 
45 
50 
50 
50 
50 
Control. 
Macrosporium solani . 
Horse nettle. 
.do 
48 
34 
5 
0 
96 
68 
10 
Verticillium lycopersici . 
Rhizoctonia solani . 
Control. 
0 
The percentage of infections produced on potatoes was higher for 
Macrosporium solani than for Verticillium lycopersici. Moreover, the 
lesions caused by M. solani were very prominent (PI. 42, B), while those 
caused by V. lycopersici (PI. 44, A) were smaller and more superficial. 
Only one potato shoot inoculated'with Rhizoctonia solani was infected. 
As shown by Edson and Shapovalov, 1 strains of R. solani differ markedly 
in their power of infecting potato plants. Although we used on potato 
the strain that seemed to give the best results on tomato, it was evidently 
not a strong potato parasite. 
Since all the potato control plants (PI. 44, B) were healthy, the com¬ 
parative results obtained with these three fungi are probably reliable. 
The results on horse nettle are also of importance, since they show 
that all three parasites are able to infect this plant. Macrosporium 
solani and Verticillium lycopersici (PI. 45) produced numerous, well- 
marked lesions. Rhizoctonia solani produced only a few, but they 
suffice to show that it can infect this host. 
As the source of this disease is at present chiefly in the seed bed, it 
can be largely controlled by sterilizing the seed-bed soil. If allowed to 
go unchecked it may ultimately accumulate in fields in which conditions 
are favorable for its development. Since its spread will be facilitated 
by susceptible hosts, both the potato and horse nettle should be kept out 
of prospective tomato fields in collar-rot infested areas. 
1 Edson, H. A., and Shapovalov, M. 
*13-220, pi. 24-26. 1918. 
POTATO-STUM LESIONS. 
In Jour. Agr. Research, v. 14, no. 5, p. 
