TWO COFFEE DISEASES.

Br M. C. COOKE, M.A.

[PLATE CXXXV.]

THE

HE cultivation of Coffee under no circumstances is such a profitable investment as to offer great inducements for speculation; but, unfortunately, during the past six or seven years, no less than three resolute and determined enemies to the coffee crop have successively made their appearance, and spread dismay amongst the coffee planters. One of these, the Coffee Borer, though by no means of the least importance, it is not our present intention to molest. The other two, being obscure members of the vegetable kingdom, alone come within the province of the botanist to describe.

Until within a few weeks it was not known in Europe, at least as far as we can learn, that more than one fungoid pest was making havoc amongst the coffee plantations in the East. Recently communications from planters in Mysore were sent to the Government of India, and these reports, together with specimens of infected leaves, have been transmitted to the India Office in London, undergone investigation, and resulted in a Report, which establishes, without doubt, the existence of a second fungal disease, which, in India at least, seems to be more destructive than the one previously known.

The "coffee-leaf disease," as it is usually termed, in distinction from the "coffee rot," is caused by a parasitic fungus. Of this there is not the slightest reason to doubt, although some have held to the opinion that it is the result, and not the cause, of the disease. There being still a few who hold similar views respecting the potato disease, it is by no means surprising that the same theory should be applied to the coffee plant. Its first appearance in the island of Ceylon was in the year 1869; and recent Reports from the planters in Mysore date its first appearance in Continental India in the same or following year. When suffering from this disease the leaves are marked by brownish somewhat rounded spots (Pl. CXXXV. fig. d), the under

surface of which is covered with minute orange dust, consisting of the spores of the fungus. These spores only appear on the under surface of the leaf, but the spots are observable also on the upper surface. The fungus is truly an endophyte living within the tissues of the plant, and expanding outwards. To its presence Dr. Thwaites attributes stains which are produced on the bark of the young branches, and the pale translucent spots which are to be seen on the leaves previous to the outbreak of the orange-coloured spores.

From the delicate mycelioid filaments which constitute the root-like portion of this parasitic fungus, threads arise in bundles which burst through the cuticle and produce at the tips of the threads the orange-coloured spores. Each of these spores has a somewhat irregular form, ovate, pear-shaped, or more or less of a kidney shape, covered externally when mature with minute globose warts, principally on the convex side, the shorter side being usually smooth (Pl. CXXXV. fig. g). When fresh they are of a bright yellow or orange colour, but this speedily disappears in drying. The longest diameter of the spore is from 035 to 04 of a millemètre, and that of the warts about ⚫003– ⚫004 of a millemètre. We have observed these warts to leave the surface of the spores, and float in the medium in which the spores were examined as minute free globose bodies (Pl. CXXXV. fig. h). This was not noticed by Messrs. Berkeley and Broome in their examination of spores from Ceylon. Probably it may be dependent on the degree of maturity at which they had arrived. In the early stage the spores are smooth, and may be seen attached to the apices of the simple or branched threads on which they are produced (Pl. CXXXV. fig. f). When mature, the attachment is so slight that the least touch is sufficient to disengage them, and they appear to lie in little clusters on the discoloured spots, ready to be dispersed by the slightest movement of the leaves.

The fungus thus described was first determined and named by Messrs. Berkeley and Broome in the "Gardener's Chronicle," * shortly after its first appearance in Ceylon, under the name of Hemileia vastatrix, and was regarded as a very interesting addition to science, from its forming a link between moulds and rusts.

The mode of germination has not been observed in this country. It is scarcely probable that vitality in the spores will extend beyond the loss of the yellow colouring of the endochrome. In Ceylon, however, Dr. Thwaites reports that it is not difficult to induce germination. Mature spores removed from a diseased leaf and laid upon charcoal kept continually moist, he says,

"Gardener's Chronicle" for November 6th, 1889.

commence to germinate in a few days. "This process consists in the spore becoming somewhat enlarged, and its contents converted into one or more globose translucent masses. From each of these a filament is developed, which grows very rapidly, and becomes more or less branched. At the termination of some of these branches secondary spores are produced in the form of radiating necklace-shaped strings of little spherical bodies of uniform size, and this form closely resembles the fructification of an Aspergillus." Another observer in Ceylon (Mr. Abbay) has seen another form of secondary spores arranged in single rows of spherical bodies, a good deal larger than those radiately arranged, but still exceedingly minute. These inconceivably numerous secondary spores may be easily carried by the wind into surrounding districts, and thus convey infection to distant plantations. In what precise manner infection is accomplished is still unknown. The minute secondary spores may be absorbed by the rootlets, or they may enter by the stomata, or they may even germinate on the surface and insinuate their growing points through the natural orifices of the leaves. Neither is it yet known whether the successive attacks to which a plant is subject are all the result of one inoculation, or whether a fresh infection precedes each outburst of the disease.

In some features there is a similarity between this fungus and the red rust of cereals. Both of them burst through the cuticle and appear on the surface as an orange-coloured dust; in both the spores are at first produced on pedicels: but beyond this there is great divergence, especially in the mode of production of the secondary spores, of which there is no similar instance amongst the Uredines. The germination of a large number of species amongst the Uredines has been observed, but hitherto in no instance have minute secondary spores, growing in chains, been recognised. There is doubtless another feature in which the coffee rust resembles the wheat rust: it is not likely to yield to the application of sulphur, as the white moulds usually do. Sometime since the application of a diluted Condy's fluid was recommended as an efficient check for the Hollyhock disease, and it is not improbable that what would succeed with the Puccinia would be beneficial in the case of the Hemileia; but hitherto it has been affirmed that nothing has proved effectual in checking the ravages of the coffee disease in Ceylon. Many of the coffee planters in Mysore declare that this disease in their plantations has not sensibly affected the quality or quantity of the crops; in others the contrary is affirmed.

The second, and more recently known, coffee disease has not at present been recognised in Ceylon, although Indian planters declare that it certainly has been present on coffee estates in

Mysore almost as long as the "coffee-leaf disease." Mr. G. Porter says that "it is very prevalent in the Mulnad portions (and more especially in the Kadur district) of the Mysore country. It is known as the 'kole roga,' or black rot,' and not only does it attack coffee, but it does great havoc in the betelnut gardens. He was told by the natives that they had hardly ever known a wet season without it, some years worse than others. It is this disease that coffee suffers far more from than

from that of the Hemileia vastatrix. It makes its appearance about July, when the leaves of the trees affected by it get covered with a slimy gelatinous matter, and turning black drop off; the berries likewise rot and fall in clusters. He estimates that the planters lose nearly one quarter of their crop each year by this plague. Gangs were sent round last monsoon to collect the diseased leaves, which were carried off the estate and burnt; and although this did some good, it was not the means of abating it to any extent."

The leaves affected with this "rot" are spotted on the under surface with large greyish-white irregular patches, sometimes occupying nearly the whole surface, sometimes in spots limited by the larger veins (Pl. CXXXV. fig. a). These patches are quite smooth to the naked eye, with all the appearance of a superficial incrustation. When moistened, the entire spot can be removed with the point of a lancet, by stripping it in a delicate hyaline film, somewhat like a film of gold-beater's skin, showing no attachment to the leaf, unless of a very slender and superficial nature; indeed, the film may be rolled up under the thumb and finger. Under the microscope this film is found to consist of a closely interwoven web of hyaline septate filaments, often branched, and crossing in all directions (Pl. CXXXV. fig. b). They are usually from 005 to 0075 of a millemètre in diameter. On the upper surface these threads are studded at irregular intervals with small globose echinulate spores, which are seated upon the threads, without any visible pedicel, although when first formed there appears to be a short stem, which is ultimately absorbed (Pl. CXXXV. fig. c). These spores are about equal in diameter to the diameter of the threads. The threads and spores seem to be agglutinated together into a film by some gelatinous medium, so that not a spore or thread can be removed from the mass without difficulty. In this feature the "rot differs from nearly all the Mucedines, in which the spores are so slightly attached that they float away on the application of moisture, whilst in the present instance no application of fluid avails to disturb a single spore.

In order to examine the fungus in as complete a manner as possible, a portion of the leaf is immersed for twelve hours in water, but this does not dissolve the mucus so as to free the