RELATIVE SUSCEPTIBILITY OF CITRUS VARIETIES 
TO ATTACK BY GLOEOSPORIUM LIMETTICOLUM 
(CLAUSEN) 1 
By Harry R. Fulton 
Pathologist , Office of Fruit Disease Investigations , Bureau of Plant Industry , United 
States Department of Agriculture 
INTRODUCTION 
The lime wither-tip disease is caused 
by an actively parasitic fungus ( Gloeo - 
sporium limetticolum Clausen) which 
* attacks in their young or tender stages 
the leaves, stems, flowers, and fruits of 
the variety of lime known variously 
as West Indian, Mexican, Common 
Florida, or Key lime. This disease 
and the fungus causing it must be 
definitely distinguished from the longer 
known “citrus wither tip” and the 
fungus to which it has been generally 
attributed, Colletotrichum gloeospori- 
oides (Penz.). The latter seems to be 
in most cases a secondary invader 
rather than an active pathogen. 
Clausen 2 has called attention to mor¬ 
phological, cultural, and pathogenic 
differences in these two fungi. The 
writer has verified Clausen's main 
findings in this regard, and concurs in 
Clausen’s view that earlier writers 
included in somewhat confusing fashion 
two very different fungi and their 
effects in their discussions of wither tip 
of Citrus. 3 This confusion is not alto¬ 
gether surprising in view of the varia¬ 
tions which may occur in what is com¬ 
monly regarded as Colletotrichum gloeo¬ 
sporioides A but at the same time the 
two diseases have many points of 
difference in their grove manifestation, 
and the evidence is convincing that 
the lime wither-tip disease is caused by 
a distinct species, and not by a strain 
of C. gloeosporioides having unusual 
pathogenic abilities. Winston, 5 in con¬ 
nection with his studies of citrus 
tear stain, was unable to find, among 
numerous strains of C. gloeosporioides 
tested, any indication of active patho¬ 
genicity on very young fruits of various 
citrus species. 
Severe losses sustained by growers 
of limes in southern Florida, especially 
on the Keys, led to an investigation 
of the lime wither-tip disease and 
means of control. Spraying with cop¬ 
per-containing materials, such as Bor¬ 
deaux mixture or Burgundy mixture, 
has not proved to be entirely success¬ 
ful, due mainly to the fact that infec¬ 
tion spreads very rapidly during rainy 
weather, especially on very tender new 
shoots that are just expanding or on 
the blossom parts or on the fruit when 
quite small (less than inch in trans¬ 
verse diameter), thus making it difficult 
or impossible to apply with safety a 
protective spray-coating at the time 
when most needed. Secondary draw¬ 
backs to spraying may arise from the 
close and irregular spacing of the lime 
trees, from the rough topography of 
much of the land, from the relatively 
low value of the crop per tree, and from 
the necessity for special control of 
scale insects after using copper-con¬ 
taining sprays. Bordeaux mixture plus 
% to 1 per cent oil in the form of 
emulsion has given more satisfactory 
results in lime wither-tip control than 
straight Bordeaux mixture. 
It would be very desirable to find 
some variety of Citrus immune to 
attack by Gloeosporium limetticolum 
that might be grown as a substitute 
crop for the West Indian lime, with 
due consideration of the requirements 
for citric acid and essential oil produc¬ 
tion and for beverage use. Accord¬ 
ingly, a rather comprehensive investi¬ 
gation was undertaken along this line, 
with the hope that it might serve as a 
basis for further work by horticultur¬ 
ists, plant breeders, or plant patholo¬ 
gists looking toward the final solution 
of the lime wither-tip problem through 
1 Received for publication June 23, 1924; issued June, 1925. 
2 Clausen, R. E. a new fungus concerned in wither tip of varieties of citrus medica. Phyto¬ 
pathology 2: 217-234, illus. 1912. 
3 Rolfs, P. H. wither-tip and other diseases of citrus trees and fruits caused by colleto¬ 
trichum gloeosporioides. U. S. Dept. Agr., Bur. Plant Indus. Bui. 52, 20 p., illus. 1904. 
4 Burger, 0. F. variations in colletotrichum gloeosporioidejs. Jour. Agr. Research 20: 723-736, 
illus. 1921. 
3 Winston, J. R. tear-stain of citrus fruit. U. S. Dept. Agr. Bui. 924, 12 p., illus. 1921. 
Journal of Agricultural Research, 
Washington, D. C. 
( 629 ) 
Vol. XXX, No. 7 
Apr. 1, 1925 
Key No. G-480 
