TOLERANCE AND RESISTANCE TO THE SUGAR CANE 
MOSAIC 1 
By C. W. Eduertox, Plant Pathologist , and W. G. Taggart, Assistant Director , 
Louisiana Agricultural Experiment Station 
A survey of the literature of mosaic 
diseases discloses a rather general belief 
among pathologists that (1) a plant 
once affected with mosaic is always so 
affected and (2) that with favorable 
environmental conditions an affected 
plant shows a gradual deterioration. 
There are a few recorded exceptions, but 
the small number of these makes only 
more prominent the general belief. 
Where plants are propagated by 
seed, a condition of this nature is not 
particularly important, since appar¬ 
ently but few mosaic diseases are 
transmitted from one year to the next 
through seed. But where plants are 
propagated vegetatively, if this belief 
is true, the resulting conclusion is 
serious, for with plants like sugar cane 
or potatoes which are propagated by 
cuttings or tubers, a plant once affected 
must always remain affected, and after 
a sufficient length of time should show 
a deterioration that would make it unfit 
for planting. The only hope in such 
a situation would seem to be to grow 
healthy plants in some section where 
the mosaic did not spread rapidly and 
thus to keep a supply of healthy plants 
for propagation purposes. Such a 
course might be possible with potatoes 
but it would be impossible with sugar 
cane in a State like Louisiana, where 
the requirement for planting is from 
3 to 5 tons per acre. If with such a 
crop the spread of the mosaic is ex¬ 
tremely rapid—as it is on sugar cane in 
Louisiana—a 100 per cent infection 
must soon be reached, and with no 
healthy cane for planting we should 
expect from the general belief that 
there would be a gradual deterioration 
and possibly the failure of the crop 
unless fortunately a resistant variety 
could be found which might be sub¬ 
stituted for the susceptible ones now 
being grown. 
If, on the other hand, we consider 
conditions as they actually are, we 
find that in countries like Java, where 
sugar cane has been infected with 
mosaic for many years, a decidedly 
different situation. Instead of the 
canes being in bad condition we find 
what are called “tolerant” canes, 
canes that are affected with the mosaic 
but are not injured to a great extent. 
In many of the tropical sugar countries 
where the mosaic disease has been 
severe in recent years the Java seed¬ 
lings are replacing the old standard 
varieties because of their tolerance to 
the mosaic. We also occasionally find 
in other countries the occurrence within 
a variety of a strain which is markedly 
resistant or immune. Possibly the 
Toledo cane which was reported from 
the Philippines in 1923 is an example 
of this. 2 
From the experiments and observa¬ 
tions on the mosaic disease in Louisiana 
made during the past several years 
there have developed a number of 
things which have a bearing on the 
general mosaic problem and which also 
may be important in the control of 
mosaic diseases on vegetatively propa¬ 
gated plants. These results have a 
direct bearing on the general statement 
made in the introductory paragraph 
of this paper. 
Soon after the recognition of the 
mosaic disease on sugar cane in 
Louisiana it became evident that con¬ 
ditions were excellent for its rapid 
spread and that it was useless to try to 
stamp it out or even to keep it under 
control. The Louisiana workers real¬ 
ized that the disease would spread 
rapidly across the State and would 
soon reach a point of maximum infec¬ 
tion. As a matter of fact, the spread 
has been faster than-was even antici¬ 
pated at that time. Furthermore, 
experiments to test the possibility of 
keeping the disease in check by roguing 
the fields proved futile. Confronted 
with the idea that a plant once affected 
is always affected and that plants 
affected with a mosaic disease show a 
gradual deterioration, a solution of the 
problem did not seem remarkably 
hopeful. However, several lines of 
investigation were started. 
1 Received for publication May 24, 1924 —issued February, 1925. 
2 Hind, R. R. Toledo cane, a mosaic-immune variety. Sugar Cent, and Plant. News. 4 : 105-107, 
110, illus. 1923. 
Journal of Agricultural Research, 
Washington, D. C. 
(501) 
Vol. XXIX, No. 10 
Nov. 15, 1924 
Key No. La.-4 
