Apr. i, 1925 Susceptibility of Citrus to Gloeosporium Limetticolum 635 
The Dominican Thornless lime seems 
almost as susceptible as the ordinary 
West Indian lime. The percentages 
of experimental infection were very 
much the same for these two varieties; 
the experimental lesions on the former 
usually developed more rapidly and 
extensively than on the latter; but the 
natural grove infection seemed some¬ 
what less severe. This thornless type, 
commonly supposed to be a sport from 
the West Indian lime, is quite distinct 
from it in fruit, leaf, and stem charac¬ 
teristics. Seedlings from it seem to be 
more variable than those from the 
West Indian lime. Keys 8 has re¬ 
ported a peculiar dying and shedding 
of the flowers and very young pistils, 
due to an aborted condition of the 
stigmas, which might be confused with 
wither-tip attack. 
Is susceptibility to attack by G. 
limetticolum a dominant character in 
inheritance? The practically univer¬ 
sal susceptibility of West Indian lime 
seedlings would support a positive 
answer if the embryos result from true 
fertilization. On the other hand, the 
two hybrids tested that have West 
Indian lime parentage are nonsus- 
ceptible. Certainly the Dominican 
Thornless lime is very susceptible, 
and is the only citrus variety besides 
the West Indian lime out of several 
scores in the present tests for which 
there is unquestioned evidence of high 
susceptibility. It will be interesting 
and important from the standpoint of 
genetics to test the susceptibility of a 
considerable number of seedlings of 
the Dominican Thornless lime, as well 
as more hybrids of the West Indian 
lime. 
SUMMARY AND CONCLUSIONS 
The evidence here presented in¬ 
cludes field observations on a large 
number of citrus varieties, species, 
and related genera growing near lime 
trees that were always severely in¬ 
fected with lime wither tip, as well as 
the results of artificial inoculations 
made during three seasons on wounded 
and on unwounded tender shoots 
both in groves in Florida and in a 
greenhouse near Washington, D. C. 
The West Indian lime and the Domini¬ 
can Thornless lime have constantly 
shown a high degree of susceptibility 
to infection by Gloeosporium limetti¬ 
colum of very young leaf, stem, and 
fruit tissue. These two varieties are 
probably closely related to each other. 
None of the other varieties of limes 
tested has given undoubted indication 
of susceptibility. Certain strains of 
citron ( Citrus medica L.) have shown 
atypical invasion of wounded tissue 
by G. limetticolum in a comparatively 
small percentage of cases under green¬ 
house inoculation. Other varieties of 
limes (C. aurantifolia Sw.) as well as 
the majority of varieties of C. medica , 
have been absolutely immune to in¬ 
fection under the very severe condi¬ 
tions of the tests. This also holds 
true for certain first-generation hy¬ 
brids having West Indian lime parent¬ 
age that were subjected to test, and for 
representative varieties of round orange 
(C. sinensis Osb.), for grapefruit (C. 
grandis Osb.), for lemon (C. limonia 
Osb.), for kid-glove oranges (C. nobilis 
var.), and for a considerable number of 
miscellaneous species of Citrus and 
genera related to Citrus. 
The close restriction of suscepti¬ 
bility in so far as is known practically 
to two very closely related seedling 
horticultural varieties of lime gives 
promise for successful substitution of 
other types of lime for the susceptible 
ones as a means of ultimately escaping 
losses from the disease, and points to 
the availability of a wide range of 
immune breeding stock as a basis for 
hybridization. Susceptibility seems 
not to be a dominant character in 
first-generation hybrids with other 
citrus species, but the natural seed¬ 
lings of the West Indian lime, prac¬ 
tically without exception, are highly 
susceptible. However, there is the 
possibility that a natural seedling may 
be found possessing immunity and 
having the desired characters of the 
West Indian lime. Such a find would 
possibly result in most effective and 
satisfactory control of the very de¬ 
structive lime wither-tip disease. 
8 [Keys, A.] abnormal flowers of the spineless lime. Rept. Agr. Dept. Dominica [Brit. West 
Indies! 1922-23 : 23 - 24 . 1923 . 
