NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
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blights of Ficus stiputata and Evolvulus nummularius. The principal distinctive
feature lies in the definite cord-like arrangement which the mycelium
assumes in passing from one nutritive area to another. The distinction,
however, is not an absolute one, for, although in the two latter blights the
mycelium never forms such definite cords, it does tend to become aggregated
in the form of strands in passing from one leaf to another or when spreading
out from the edges of an exhausted leaf over neighbouring non-nutritive
surfaces such as glass or water. The distinction thus is one of degree and
not of kind. In none of the specimens which have yet reached me have there
been any traces of true sclerotia either within or on the blighted tissues or in
the substance of the mycelial cords, but this may very probably have been
owing to the fact that the normal development of the mycelium was arrested
by the conditions to which it was subjected after the affected shoots were
detached. In certain cases renewed active growth occurred in some of the mycelial
cords when subjected to the influence of a moist atmosphere, but in the
absence of fresh foliar surfaces as a source of new stores of nutritive material it
was soon arrested. The phenomena certainly render it extremely probable that
the disease is a sclerotial one, but the question is one which can only be deter
-
mined in a site in which both parasite and host-plant are at home, but in any
such site a little careful observation would be all that would be necessary to
decide it.
In the absence of precise information in regard to the true nature of the
parasite and the exact form and site of development of the reproductive apparatus,
all that can be suggested with a view to the prevention of the disease is that
whenever it makes its appearance all infected shoots should, as far as possible,
be at once removed and burned. Such treatment will prevent the development
of any true sclerotia, should such bodies be normal constituents in the develop
-
mental cycle of the parasite, and will at the same time secure the destruction
o
f the dense mycelial cords on the bark the tissue of which does not merely serve
as a means of spreading the disease from one leaf to another, but is also capable
of retaining its vitality in a dormant condition for some time under conditions
fatal to the mycelium generally, and is therefore capable of ensuring the persis
-
tence of the disease during periods prohibitive of its active extension.
c. Root-blight dependent on the presence of a destructive fungal mycelium.
—Specimens of this disease were sent to me for examination by Dr. King
during the winter of the year 1877. As I have already published a note regard
-
ing the subject in Part III of this periodical, it is unnecessary here to do
more than to give a brief recapitulation of the characteristic phenomena. The
morbid changes were purely confined to the lower extremity of the
stems and the bases of the larger roots, and presented themselves externally in the
form of numerous, conspicuous, irregularly-nodulated swellings, which occurred
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so closely over the base of the stem and origins of the larger roots as to be more
or less completely confluent, whilst farther out along the course of the roots they
occurred in isolated patches (Plate III, Fig. 6). Where they were present, the
bark no longer retained its normal smooth texture and grey colour, but was
roughened, friable, and deep brown, owing to the mixture of earth, derived from
the surrounding soil, with the disintegrated tissues. In certain sites masses of
material of rusty-brown colour and spongy texture were visible in fissures of
the surface, and, on removing portions of the disintegrating bark, these were seen
to form portions of sheets and strands of similarly coloured material traversing
the tissues in every direction. Such material was present throughout the entire
thickness of the cortical tissues, and specially abundant at the level of the bast,
where it was in many places spread out so as to form a continuous stratum over
large areas. The wood appeared to be comparatively little affected, but was
here and there interrupted by distinct wedge-shaped portions of a greyish
tissue, with narrow, sinuous, blackish margins.
On microscopic examination, the rusty-brown substance was found to be
composed of dense, felted masses of mycelial filaments of brownish or greenish
colour, and in those areas in which the invasion of the disease was progressing,
but in which the tissues still retained their continuity, the cortex and bast were
found to be everywhere permeated by fine filaments forcing their way between
the constituent elements. In the earlier stages of dis ease, the wood appeared
to be entirely unaffected, but, where it was far advanced, the mycelium tended to
invade the medullary rays and to give rise to the discoloured radii previously
alluded to.
All attempts at cultivating the mycelium with the view of obtaining
fructification failed entirely, which is hardly to be wondered at considering that it
had evidently been primarily developed parasitically in connection with the living
elements of the tissues, and that, by the time the specimens were submitted to
examination, the latter were already dead and dried up. A certain amount of
growth did occur in some cases, but it was soon arrested and was never attended
by the production of any distinct reproductive bodies. The phenomena
apparently indicated that the persistent masses of mycelium contained a certain
amount of intrinsic nutritive material stored up within them which served to
provide for a limited amount of growth, but that, when this had been expended,
the latter ceased in the absence of any living host-tissues as a source of further
supply. In those cases in which such limited growth occurred, the outer surfaces
of the bark became covered by a coating of an orange colour, consisting of
short, erect, emergent filaments originating from newly-developed horizontal
extensions of mycelium within the substance of the tissues. The development
of such emergent filaments in this case is probably an indication of the method
in which the extension of the parasite from the roots of one plant to another is
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Scientific Memoirs by
effected. The growth which occurred in the present instance was, no doubt,
very limited and only sufficient to give rise to a. superficial coating of mycelium
on the diseased tissues, but under normal conditions, where the mycelium is in
full vigour and the host-tissues still capable of affording abundant nutritive
supply, it may well be much more extensive and provide for the development of
mycelial strands capable of traversing considerable areas of the soil and so of
coming into contact with neighbouring healthy roots.
As the specimens neither contained nor yielded anything save masses of
purely mycelial elements, it is impossible to come to any definite conclusion in
regard to the precise nature of the parasite, but taking the characters of the
disease into account along with the well-ascertained fact of the destructive form
of root-blight which prevails in European coniferous forests in connection with
the invasion of the tissues by the mycelium of Agaricus melleus, Vahl., it
appears not improbable that it may be of Hymenomycete origin. Fortunately,
however, there can be no doubt in regard to the nature of the measures which
ought to be adopted in order to limit the extension of the disease in any area
within which it has established itself. All diseased plants ought to be at once
removed and burned, and special care should be taken to remove the roots as
thoroughly as possible, so that portions of them may not remain in the soil as
sources of infection. If possible, moreover, it would be desirable not to replant
the infected area for some time, and also to isolate it by means of digging a
trench around it sufficiently deep to pass below the lowest level in the soil to
which the roots normally penetrate. By such means any extension of mycelium
connected with residual fragments of roots remaining in the soil to neighbouring
uninfected areas would be effectually prevented, and in the absence of suitable
nutritive supply the parasitic elements would, in the course of time, die out
within the primarily infected one.
IV.—The Blight of the Opium Poppy ( Papaver somniferum )
caused by Peronospora arborescens, de By.
This is a form of disease which is capable of being as destructive to crops
of the opium-poppy as that caused by Phytophthora infestans is to crops of
potatoes ; indeed, the mischief which it produces is so great and so rapidly
diffused under favourable circumstances that it is probably only because opium
cultivation in India is generally conducted within relatively dry localities that
it is not absolutely extinguished by it. In regions like the lower Gangetic delta,
where atmospheric humidity is normally relatively high and often excessive, it is
almost useless to attempt to grow any of the ornamental varieties of the host-
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fructifications of which frequently give rise to the formation of variously coloured
patches on the originally uniform, pale-brown surface.
The fructifying filaments of the Peronospera are repeatedly dichotomously
ramified and terminate in a series of slender, conspicuously curved twigs, so
that the entire structure comes to resemble a miniature deer's antler in some
degree (Plate IV, Fig. 2). The terminal twigs are short and slender, and each of
them gives origin to a sporangium. The sporangia are, when fresh, almost colour-
less, of rounded-oval figure, with average diameter of 23 X 20 μ and contain a
mass of finely granular protoplasm within which a nucleoid body may frequently
be recognised (Plate IV, Fig. 2). I have not been able to follow out the farther
stages of their evolution after they have become detached. Many attempts
were made to cultivate them both in water and in neutral salt solution, but in no
case did any of them either germinate or give origin to zoospores. This may
have been owing to their very rapidly losing vitality after separation, or to an
incapacity for farther evolution save when in contact with the host-tissues, but the
very rapid extension of the blight under favourable circumstances unequivocally
indicates that they are normally capable of undergoing their ultimate develop-.
ment without delay.
On making vertical sections through the thickness of affected portions of
the laminæ, the fructifying filaments are found to be continuous with a richly
ramified system of septate mycelial filaments filled with granular protoplasm
penetrating the entire thickness of the leaf between the superior and inferior
epidermis (Plate IV, Fig. 1). The filaments, as a rule, appear to be situated
between the cells of the host-tissues, but in some cases give origin to short,
simple, rounded, intracellular haustoria.
In some leaves the mycelium produces only sporangial fructification, but
in others innumerable oospores are also developed. They make their appearance
at a relatively late period and when the nutritive properties of the host-tissues
have been more or less expended. I have not yet been able to follow out
the details of the earlier stages of their development, but have obtained numer-
ous immature specimens in which the oogonium was still connected with two
filaments, one representing the one proper to it, and the other an adherent
antheridium, so that there can be no doubt that the fructification is of a truly
sexual character (Plate IV, Figs. 4, 5, 7). The mature oogonia are very readily
recognisable in the dead tissues owing to the thickness and bright reddish-
brown colour of their walls (Plate IV, Fig. 3). They are situated in the inter-
spaces of the open parenchyma beneath the stratum of palisade-cells, and in
many places are present in very large numbers. They vary very considerably
in size in different instances, but those of average size have diameters of 33 μ .
The walls are about 4.5 μ in thickness and surround a central space
which is almost entirely occupied by the oospore. The latter has a thin wall
Medical Officers of the Army of India.
121
surrounding a peripheral stratum of granular protoplasm including a large central
globule of apparently oily matter (Plate IV, Fig. 6). The following figures give
the detailed measurements of two mature oogonia and their contents :—
No. 1.
No. 2.
Diameter of oogonium
.
.
. 4 3 μ .
33 μ .
Thickness of the wall.
• 4·8 μ .
4·5 μ .
Diameter of the oospore .
.
. 32 μ .
21 μ .
Diameter of the interior of the oogonium 33·4 μ .
24 μ .
As the oospores have no tendency to undergo any farther evolution
immediately after their formation, and as it is only within the past week or
two that I have obtained specimens of them, I am unable as yet to follow out
their farther evolution.
The fact that they are produced in very large quantities accounts for the
regular recurrence of the disease from year to year, in any locality in which the
cultivation of the host-plant is annually conducted, and may even possibly
account for its regular reappearance in sites, like the Botanic Garden at Shibpur,
where long periods of years intervene between the cultivation of successive
crops ; for it is quite possible that they may be capable of retaining their vitality
in a dormant condition for a very long time. One thing is quite certain, and that
is that neither any of the cultivated varieties of Papaver Rhoeas, nor the
thoroughly acclimatised plants of Argemone mexicana which every year abound
in the neighbourhood of Calcutta are ever appreciably attacked. It is, of
course, possible that they may suffer, but to such a slight extent that the event
escapes notice, whilst at the same time it yet serves to secure the annual
production of a limited number of oospores which serve to secure the persist
-ence of the disease in a smouldering fashion, ready to break out actively when-
ever the presence of the favourite host-plant is provided ; and no doubt, during
the long periods during which the cultivation of Papaver somniferumare inter-
mitted in the Botanic Garden, numerous crops of it may be grown in the vicinity.
At the same time, however, it remains a possibility that the recurrence of the
disease on each occasion when the host-plant is grown may have been
dependent on strictly local causes and connected with the presence of oospores
in the soil persistingly retaining their vitality from the time at which they were
developed in connection with the presence of an antecedent crop.
It is not easy to see what measures would be capable of effectually preventing
the recurrence and destructive diffusion of the disease in any locality such
as the neighbourhood of Calcutta in which the local conditions are such as to
provide for the constant and excessive development both of the sporangial
fructification and the oospores of the parasite. The oospores are of such small
size, and are produced in such abundance that even very minute fragments of
the blighted tissues may readily contain very large numbers of them, so that even
R
if the greatest care is taken to remove and destroy all diseased plants, a certain
number of them must almost inevitably escape, and if only a very few do so they
will be amply sufficient, in such a favourable locality, to originate devastating
disease. In any localities, however, in which such favourable conditions are
not present, and in which, in connection with the presence of relative atmos-
pheric aridity, the production of , the sporangial fructification is kept within
bounds, and therefore the rapid diffusion of the disease is prevented, much
might be done to limit the prevalence of it by the careful and early removal
and burning of all affected plants, and it is even possible that by means of
steady perseverance in such measures it might be totally extinguished.
V.—Root-blight of the Brinjal . (Solanum Melongena).
Specimens of this disease were sent to me in January 1894 by Mr. Mollison
who had obtained them in Gujerat. It was limited to the upper portions of the
subterranean part of the axis, being confined to those parts of the roots which
contain a medullary area of some magnitude, and thus resemble the stem rather
than the deeper portions of the radicular system in which the medulla is practically
absent. The external indications of its presence consisted of irregular swelling
and roughening of the surface, or of areas within which the outer surface of the
primary zone of wood had become exposed owing to the detachment of the
cortex, bast and outer stratum of wood in consequence of the friability in the
tissues which it ultimately tends to induce. On making transverse sections of
the diseased parts it was at once evident that the principal site of disease lay in
the secondary zone of wood, but in some places the bast was very conspi-
cuously abortive, and comparative measurements showed it to be throughout
abnormally thin in relation to the thickness of the axis. Microscopic
examination afforded confirmatory details (Plate V, Fig. 1). It showed that the
secondary zone of wood was in some places more or less completely absent,
and that everywhere else it was excessively malformed, no longer forming a
continuous stratum, but broken up into an aggregate of radiant masses separated
from one another by what appeared to be exaggerated medullary rays of non-
lignified tissue. The cause of the deformation was demonstrated very clearly,
in sections which had been subjected to prolonged treatment with solutions of
picro-carmine (Plate V, Figs. 2.5). In transverse sections which had been
treated in this way, the abnormal character of the secondary wood was rendered
very conspicuous owing to the sharp contrasts in colour which the various
portions of it presented, the lignified parts having acquired a bright-yellow tint
whilst the non-lignified ones, like the normal medullary rays of the primary
wood-zone, the bast and the medullary tissue, were of various shades of red
(Plate V, Fig. 1). Neither the cortex nor the bast showed the presence of any
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fungal elements, but a jointed mycelium was present in the substance of the
cambium, the wood and the outer portions of the pith. Filaments were present
in considerable numbers in the cambium, but the outer zone of the wood was
the area within which they specially abounded. In it they were present in
great numbers in the wood cells, the large pitted vessels and the proper tissue
of the medullary rays, whilst the abnormal unlignified areas between the
masses of woody tissue were everywhere crowded with them. Throughout the
greater part of the primary zone of wood they were almost entirely absent, the
pitted vessels and the wood-cells being entirely free from them and the medullary
rays containing traces of their presence only here and there. Just at the inner
edge, however, they again made their appearance in some numbers within the
medullary rays and here and there within the spiral vessels and from this area
they extended into the immediately adjoining strata of the pith.
Judging from these phenomena, it appears probable that infection did not
take place until after the development of the primary zone of wood and that the
original site in which the parasitic elements established themselves was the
cambium. Their presence there appears to have given rise, as it might have
been expected to do, to imperfect development of the secondary strata of both
wood and bast, whilst, at the same time, they invaded the tissue of the pre-
existent medullary rays to a certain extent and by means of them reached the
spirals and the adjoining portion of the pith. The nature of the changes
induced in the secondary wood and bast was of unlike character owing to the
fact that whilst they underwent excessive development in the tissues of the
developing wood they had no tendency to invade the new bast tissue. In con-
sequence of this there had been more defective formation of secondary bast,
but extremely abnormal as well as defective formation of the secondary wood,
many of the elements which ought to have contributed to its formation retaining
an embryonic character and thus giving rise to appearances which to casual
observation simulated those of hypertrophy of the medullary rays.
The distribution of the mycelium throughout the tissues of the axis explains
why in this case the disease, although in many points closely resembling the
so-called " Bangle-blight " of potatoes, should be of a chronic in place of an
acute type as the latter is. In the case of the stem of the potato-plant the
water-conducting system is a very limited one, consisting of a few isolated
bundles of fibro-vascular tissue (Plate I, Fig. 4), and as these are attacked by
the mycelium of the parasite the water-supply of all the tissues beyond the
invaded area is so seriously interfered with that rapid wilting necessarily occurs.
But in the case of the Brinjal, the water-conducting system of the base of the
stem is much more highly developed in the form of a continuous zone of wood,
so that when, as in the present instance, this is only very partially affected, the
water-supply, although interfered with, yet remains sufficient to prevent the
R 2
occurrence of total withering of the distal parts. The defect in supply is of
sufficient magnitude seriously to interfere with nutrition, but is not so great as
to determine immediate wilting and death from disproportion between root
-supply and foliar transpiratory loss.
As none of the specimens showed any indications of the development of
reproductive bodies of any kind in connection with the mycelium, it was, of
course, quite impossible definitely to determine what the precise nature of the
parasite was. When, however, the great prevalence of sclerotial blights in
India, and the localisation of the disease within the tissues of the host-plant
are taken into account, it appears not to be unlikely that the disease is of a
sclerotial type. In any case it is clear that the practical measures to be
recommended in contending with it are the avoidance of all excessive irrigation
and the careful removal and burning of all blighted plants and portions of the
dead tissues of such as have already died of the disease.
V I — S c l e r o t i a l R o o t - b l i g h t o f L u c e r n (M
e d i c a g o s p .
) .
The specimens of this blight, like those of the previous one, were obtained
from Mr. Mollison, who sent them from Poona, where (in April and May 1892)
the disease was very destructive to Lucern cultivated in the Government farm.
It was described as gradually extending from one side of a field to the
other, causing destruction of fully half of the roots as it did so, and giving rise
to a proportionate diminution in the amount of fodder obtainable from the area.
The crop was grown on soil "full of manure " and supplied with irrigation water
run along the course of furrows between the ridges on which the plants were
situated. As in the case of the previous blight, the disease was confined to the
bases of the stems and the origins of the larger roots. Where it was present,
the surface of the cortex was studded by great numbers of small prominences
which in sections were found to be owing to the presence of minute sclerotia of
irregularly rounded outline and with diameters of 0·2 m.m. and under (Plate V,
Fig. 6). Detailed microscopical examination showed that the tissues were
permeated by fungal mycelium, but that this, in place of being specially located
within the wood as in the case of " Bangle-blight" and the Brinjal root-blight,
was practically confined to the cortex, only here and there invading the bast
and then being confined to the most superficial strata in it. The cells in the
deeper part of the cortex were in many places crowded with masses of fungal
elements and at certain points dense strands of mycelial filaments forced their
way out through the corky strata to give origin to the sclerotial bodies
previously alluded to (Plate V, Fig. 7), those in an early stage of development
being still invested superficially by the remains of the outer layers of cork and
the more mature ones showing free upon the surface.