630 
Journal of Agricultural Research 
Vol. XXX, No. 7 
the finding of a satisfactory substitute 
citrus variety, to be propagated by 
budding, by cuttings, or from seed as 
might prove most desirable. 
The ideal would be to find a natur¬ 
ally immune or very highly resistant 
individual or race in present plantings 
of the West Indian lime, which is 
practically always propagated from 
seed, and so might offer possibilities 
along this line. The writer has ob¬ 
served certain differences in incidence 
of the disease that might indicate 
individual difference in susceptibility, 
but he has not yet observed a tree 
that seemed satisfactorily resistant 
under very severe infection conditions. 
Such may possibly exist somewhere, 
and its discovery would mean the quick 
reestablishment of the lime industry 
on a better basis in territory invaded 
by the lime wither-tip disease, where 
general economic conditions are favor¬ 
able. 
NATURAL INFECTION IN GROVES 
That the disease is very closely 
confined to the West Indian variety of 
lime is shown by general field observa¬ 
tions during many seasons in various 
parts of Florida, where the West 
Indian lime seems to be universally 
affected but where varieties of orange, 
grapefruit, lemon, tangerine, mandarin, 
citron, and even such lime varieties as 
Kusaie, Woglum’s Seedless, Buena 
Vista, Tahiti, and Persian are not af¬ 
fected when growing in close proximity 
to diseased West Indian limes. The 
only other variety observed to be 
affected under natural conditions has 
been the Dominican Thornless (or 
Spineless) lime, which supposedly origi¬ 
nated as a sport from the West India 
lime. 6 
FIELD TESTS 
During three seasons, 1919, 1920, 
and 1922, field tests were made on 
the March growth of various citrus 
varieties, species, and related genera 
to determine possible susceptibility 
to the lime wither-tip disease. These 
tests were made on property where 
the disease existed naturally on West 
Indian and Thornless limes. All of 
the tested trees were within 200 feet 
of such naturally infected lime trees, 
and yet no natural infection has been 
observed on them during the tests or 
during two subsequent seasons. The 
inoculum was a spore suspension, 
usually from freshly sporulating lesions 
on lime shoots, but sometimes from 
artificial cultures. Inoculations were 
made by wrapping cotton swabs 
lightly around the very tender shoots 
(usually 1 to 4 inches long, with many 
leaves in very susceptible stages), 
and covering for two days with par¬ 
affin paper. Control inoculations were 
made for every series on susceptible 
limes to determine the potency of 
the inoculum, and favorableness of 
condition, and water-blank controls 
were also made on the limes to deter¬ 
mine what part of the observed in¬ 
fection might have resulted from 
spores naturally present on the plant 
surfaces. The indications were that 
these last played a minor part during 
ordinary dry weather, as might be ex¬ 
pected, since the shoots chosen had very 
recently begun to develop, and since 
the Gloeosporium spores depend on 
dew drip or rain for their distribution. 
The results are given in Table I. 
The only evidence of any suscep¬ 
tibility is shown by the West Indian 
lime and by Dominican Thornless 
lime, which is a derivative of it. 
The tests included a representative 
lot of commercial citrus varieties, 
as well as a considerable range of 
unusual citrus varieties, species, and 
a few related genera. Puncturing 
did not increase materially the per¬ 
centage of susceptibility for the West 
Indian and the Thornless limes, in¬ 
dicating that the shoots selected for 
the tests were young enough to have 
practically maximum susceptibility 
without artificial injury. 
The field evidence is thus very strong 
that the lime wither-tip disease is 
closely restricted to the West Indian 
types of lime. 
GREENHOUSE INOCULATIONS 
Potted plants, three of each variety, 
were cut back severely so as to induce 
the sprouting of a considerable number 
of young shoots. When these were 
barely starting the plants were placed 
in an inoculation case where the air 
was kept practically saturated with 
moisture. Spore suspensions of G. 
limetticolum were atomized over these 
plants 10 times during 21 days. Then 
the young shoots, which had attained 
several inches in length, but were 
somewhat etiolated and quite succu- 
6 “In 1892 on Shelford [probably intended for “Shawford”J Estate, Dominica, a lime tree was noticed 
without the usual formidable spines. Seeds from this apparent “sport’’ were collected and sown. Some 
75% came true and a plot of spineless limes forms an interesting feature of the Dominican Botanic Garden. 
The plants in this plot are now bearing heavily, and the Curator reports that 80 to 90% of the seedlings 
raised are coming true.” Agricultural News, Vol. 1, No. 3, May 24, 1902, p. 38. 
