Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1915-05-27
The ORGANISM OF
:. THE POTATO scAB
Certain Studies on the Effect of
Temperature, Sunlight and
Moisture upon the Growth
and Development Of the Or
ganism Which Causes Com
mon Potato Scab.

mon Potato Scab.
Orono, Me-, May 25-(SpeciaD.-The
plant Psychologists Of the Maine Agri-
cultural Experiment Station have been
growing in pure cultures for nearly
eight years the organism which causes
common potato scab. During this
time the same germ has been isolated
from potatoes from various parts OF
this country, and also from tubers OBJ
tanned from quite widely separated
portions Of Europe. In the same period
several different strains have been
tested at various times, and found to
be capable of causing the disease. The
organism itself. while long classed as
a fungus is apparently more closely
related to the bacteria.
BY studying the germs of such dis
eases in pure cultures in the laboratory
it is frequently possible to discover
some facts about the life history Of the
organism which suggests a mode OF
attack to effect its control 1t is by
means Of such studies as these supple
mented by field observations that this
Station was able to work out a COM
paratively simple, inexpensive. but eff
fective method of control in the case
of the blackleg of potatoes which is
also a bacterial disease.
In long series Of tests to determine
the effect of temperature upon the de-
velopment and growth Of the common
potato scab organism. it was found that
it could make q very slight growth
even as high as l05 degrees F., but at
this temperature the organism soon
died. The most rapid growth was OBJ
tanned between Il and IS degrees F.,
although a very rapid development &C.
CURED at first when cultures were
placed at a. temperature slightly below
95 degrees F. Growth dropped off very
rapidly below IS and practically ceased
at little below As degrees F.
| This indicates that probably the
| Il
occurred during the hottest part Of the
summer, and that as fall approaches
the growth and spread Of the organ
ism decreases and finally ceases.
| Exposure TO temperatures below
freezing did not always kill the para
site.
| Some very interesting results were
obtained by studying the effects of
direct sunlight upon the potato scab
organisms. This was done in the fol-
lowing manner: A small quantity of
the growth in a pure culture, which is
made up of numerous minute living
/ bodies, was introduced into a suitable
nutrient substance containing a jelly
| like material which hardens upon
cooling. This jnoculated material was
then poured into a stefilized glass dish
and allowed to set After which the
dishes were exposed to direct sunlight
after first covering one-half of each
with an opaque material. The effect OF
this exposure could easily be ascer-
| tanned after the plates had been al
lowed to stand a day or two under
temperature conditions favorable for
growth. since each one Of the living
| germs introduced into original culture
medium would then grow into colony
visible to the naked eye. 1t was found
that an exposure Of ten minutes to the
direct rays of the sun killed nearly all
Of the germs on the uncovered sides of
the plate, while on the covered side a
profusion of living colonies appeared.
This effect If sunlight upon the veg
etativc portions of the organism caus-
ing the disease has considerable signi-
fcance in a practical way. and in a
measure explains the beneficial results
obtained in the control of potato scab
when the seed tubers are first exposed
to sunlight for some time before plant
ing.
The exposure Of seed potatoes to sun
light for several days before planting
is undoubtedly a very wise practice
and should be followed wherever feas-
ible. Not only do the suns rays here
produce a germicidal effect as else
where, but they bring about certain
other desirable changes. The average
Maine potato storehouse Is designed
to keep the potato throughout the win
ter and into the spring. in as near the
condition in which it came out of the
ground in the fall as possible. Thu
better houses serve this condition ad
mirably. but in doing so they are no
getting the seed potato ready to ger
inmate. If the potatoes from these
houses could be taken to a somewha
warmer room where they would b.
exposed to sunlight, or at least t.
plenty Of diffused daylight for SOM
days, or possibly week or two be
fore planting. much Of the trouble
from failure to terminate, especial!
in cold late springs, would undoubted
ly be eliminated. Potato tubers will
not produce long sprouts when exposed
to the light. Those which show ar
so short and firm that there Is yer!
little danger Of breaking them off II
planting.
In the same series Of studies unde
consideration it was found that tn
potato scab organism IS quite suscept
ible to drying. Since it exists In tn
moist tissues just beneath the seal
spots, the organism can secure sufti
cient moisture to maintain its life owe
winter, and hence this observation re
gardng the effect of driving are o