Page images
PDF
EPUB

should be mixed with good soil (half and half) before being applied These bodies all contain valuable rourishment for the trees. They wil also guard against many depredations from insects. Care should be taken not to use the gas lime too liberally.

[ocr errors]

RESEARCHES, Resulting in the discovery of the cause of the so called Blister and Curl"

in the Leaves of Peach Trees, and the decay in the Peach Fruit; with some observations on the Development of the Peach Fungus (Sphaerotheca Persica).

BY J. H. SALISBURY, M, D., AND C. B. SALISBURY. For some years, in this country, the disease which produces the “ Blister and Curl" in the peach leaf, and decay in the peach fruit, has widely prevailed, and produced extensive ravages. It often has destroyed entire orchards of peach trees, by killing the leaves in the early part of the season. Young and vigorous trees are generally able to live through it, yet not without being materially injured. The disease attacks the young leaves as fast as they make their appearance. It produces its greatest ravages—in this climate generally-from the 10th of May to the 15th of June. By the 15th of June the new sprouts have nearly completed their growth, and but few new leaves subsequently make their appearance. The disease, hence, has but little chance to spread further than it already has gone—it being one confined in its destructive ravages to young and tender leaves and new shoots. The leaves, by the 15th of June, having become quite firm in texture, those which are not killed or too much enfeebled and involved in the disease, begin to revive, and the trees, if not too greatly injured, begin to assume, from this date, a more and more healthy appear. ance.

Various have been the theories respecting the cause of this disease. The one most generally received among fruit-growers is that which attributes it to spring frosts.

About the middle of May, 1862, my attention was particularly called to the careful study of the disease. On dissecting the leaves, and subjecting them to a careful microscopic examination, I found the parenchyma filled with several layers of fine myceliated threads, crossing and anastomosing with each other in various ways, forming a complete net-work among the leaf-cells (Lign. Y, Fig. 5.) On examining carefully the surface of the

leaves under the microscope, small pearl-white moniliform threads were found, making their appearance externally and proceeding from the interlacing and anastomosing filaments within the leaves.

The leaves of many different trees in different orchards were examined, and wherever a leaf was affected with the blister and curl, or either, much or little, there was found the mesh of interlacing and anastomosing filaments (fig. 5) in its parenchyma; and often, on its surface, could be discovered the moniliform fertile threads (Lign. Y, fig. 1.) In the healthy leaves there appeared no such growth. Under and near the peach trees were noticed the leaves of the Ohio Blue Grass (Poa pratense), generally white with a similar growth to that on the leaves of the peach trees (Lign. Z, fig. 3), imparting to them an appearance as if a coating of fine white powder had been sprinkled over the surface, and giving the grass an unhealthy aspect.

DESCRIPTION OF FUNGUS. Group Ascomycetes.-Asci formed from the fertile cells of an hymenium. Sporidia definite, or indefinite, produced from the protoplasm of elongated or dilated cells. The fertile plants are frequently accompanied by inarticulate or separate, simple or branched threads, which are abortive asci, known under the name of Paraphyses.

Order Perisporiacei.--Asci often evanescent. Perithecia free, astomous; at length dehiscent, often surrounded by variously shaped threads distinct from the mycelium. Asci springing from the base, tubular or saccate, often absorbed at an early stage ; occasionally solitary.

Genus SphaerothecaSphaerotheca Persica, Salisb.-- This plant—which is a true parasitic fungus—belongs to the group or division Ascomycetes; the order Perisporiacei and the Genus Sphaerotheca. I do not find specific descriptions that are applicable in all respects to this species. The nearest approach to it is the S. Castgnei. I therefore name it after the specific name of the peach plant, to which it is so destructive.

This epiphytal plant is one of the simplest of fungi. It belongs to a group which is distinguished by the great development of the mycelium. Many of these grow on living leaves, and are very destructive—either by directly diverting the nutritive juices from their proper office and appropriating them to their own use, or by blocking up the stomates and impeding respiration and the free action of the rays of light and of the surrounding atmosphere, thereby involving them in disease which often results in death. The fertile threads are moniliform (figs. 1, 2, 3, Lignographs Y and 2), made up of oblong oval sporidia, arranged end to end, from wbich the enveloping asoi are evanescent, or are early absorbed. The sporidia are shed from the summit of the threads, as they mature. They are very prolific on the tender leaves of the peach tree and poa pratense, from the 10th of May to the 15th of June, in this climate (in New York and the Eastern States the range is from about the 15th to 20th of May to the 20th and 30th of June), covering the leaves with piles of pearl white sporidia. During this period they are furnished with abundant nourishment from the young, tender and vigorously growing leaves, to which they are mainly confined; and the threads are mostly fertile, producing enormous numbers of sporidia.

From the 15th of June to the middle of August or first of September, the fertile threads are constantly decreasing, and the sterile threads (figs. 2, fand 4) begin to appear among the fertile ones. These sterile threads are longer and much more slender than the fertile threads, and are not moniliform. During this period, these sterile threads appear abundantly on the young, tender twigs (fig. 4). They occur also, to some extent, on the leaves, mingled with the fertile threads (fig. 2, 1). These sterile or inarticulate threads are abortive asci, usually simple; and are called paraphyses. They constitute one of the peculiarities of the Ascomycetous group.

From the 15th of June to the 1st of September may be denominated the period (in this fungus on peach leaves and sprouts) of sterile development. This sterile growth exhausts the peach plant very much less than the fertile or period of reproductive growth which precedes it. The result is, those peach trees which have not become too much exhausted, revive and constantly assume a more and more healthy appearance, as they advance into this stage of sterile growth, and the fungus plants grow more and more sickly, and there is less and less of the sterile threads. By the first of August they have entirely disappeared from the leaves of the pos pratense.

The period then of the greatest ravages of the S. Persica, in any locality, is from the moment the young leaves make their appearance till the tissues of the leaves become firm; at which time the trees that survive begin to assume a more healthy aspect. In instances where the leaves are killed early in the season, and the trees not killed, another crop of leaves often make their appearance; which second crop—although presenting generally a feeble appearance-are not usually much affected with this fungus. The mycelium is greatly disproportionate to the fertile threads. Often leaves become curled and killed, before any signs of either fertile or sterile threads appear above the surface. When, however, the fertile threads do appear, they are prolific. They consist of very large, oblong, prolate, spheroidal sporidia; occasionally single; but generally consisting of more or less erect simple or compound moniliform chains (threads) of sporidia (fig. 1). Sporidia simple, whether single or arranged in neck. laces; sporidia armed with processes at each end, by which they are united to each other. In the advanced stages of the fertile plants, pyeinidia are not infrequent; sporidia deciduous falling from the summit of the moniliform threads as they mature.

Fig. 1, Lignograph Y, represents the appearance, in Central Ohio, of the fertile plants on the peach leaf, on the 20th of May. At this date they were very prolific-killing the leaves on most of the older and weaker trees. The leaves on the young vigorous trees were twisted, ourled, blistered, overgrown and yellowish.

Fig. 2, d, e, f, represents the appearance of the plants on the leaves, on the 5th of July. The sterile plants () and maturer threads, with pyenidia (EE), had begun to show themselves among the fertile threads (d). On the older leaves, at this date, the plants had the appearance seen in fig. 6, a, b, c.

Fig. 3 represents the plants as they appeared on the leaves of the poa pratense on the 20th of June. They were very prolifje, covering the whole surface of the leaves with their white sporidia.

Fig. 4, Lignograph Aa, represents the appearance of the sterile plants on the young shoots of the peach tree, July 21st. The numerous sporidia attached to them and lying at their base, probably have fallen from the fertile plants, off the young leaves. The paraphases are, however, said, in some instances, to provide sporidia from their summits.

Fig. 2, E, E, are mature plants with enlarged joints, called pyenidia. These pyenidia are of a light-yellow color, and are filled with stylospores.

Figs. 1, 2 and 3, Lignographs Y and Z, represent fertile plants, during their reproductive stage—from May 10th to June 15th. After June 15th these fertile plants rapidly disappear, except on such new leaves as make their appearance thereafter-on which they are often found, but present generally a sickly, feeble appearance, when compared with the vigorous growth on the leaves from the 10th of May to the 15th of June. After the 20th of July, there can scarcely be found a plant on the leaves in this stage of development; they nearly all have the appearance as seen at fig. 6, a, b and c, Lignograph Y. Occasionally may be found a new leaf where the appearance is presented as seen at fig. 2, d, e and f.

Fig. 5, Lignograph Y, represents the appearance of the mycelium in the parenchyma of leaves. The mycelium is often largely developed before there is any appearance of fertile threads on the surface. The indi. cation of its presence-where there are no external threads-is the blistering and curling of the leaves.

The young twigs and sprouts are also attacked with this fungus. It generally appears on them during the last half of June. They produce, mostly, only sterile tbreads.

The peach fruit is often attacked, about the time it is from one-third to two-thirds grown; but the fungus is usually neither thrifty por prolific, till the peaches approach maturity. It however often destroys jube entire crop before the fruit matures. If the fungus is in the trees, and the peaches escape till they begin to ripen, it then usually makes great ravages. At this stage of the fruit, the mycelium grows with great luxuriance in its tender, rich flesh, and decay keeps progress with the advance of the mycelium. An entire peach will often decay in from 24 to 72 . hours—the length of time required varying with the temperature and hygrometic condition of the atmosphere. Often on the decayed surfaces may

be discovered the fertile, moniliform threads, both simple and com. pound (fig. 7 a, Lignograph Bb). The sporidia are smaller in size on the fruit, than in plants on the leaves. Fig. 7 shows the mycelium, and the fertile threads on the fruit.; figs. 1, 2, 4, 5, and 6 sbow the fertile and sterile threads and mycelium of the leaves and twigs. The mycelium of the leaves is more filamentous and less fleshy than that of the fruit, and the sporidia of the concatenated, fertile threads larger.

OBSERVATIONS CONNECTED WITH THE DECAY OF THE FRUIT AND WITH

FUNGOID DEVELOPMENT.

A young, vigorous tree, the leaves of which had been severely attacked with the peach fungus in the early part of the season, but which had by the middle of August quite recovered, was loaded with fruit. The fruit had escaped the fungus during the early part of the season. About the 16th of August the peaches began to get mellow. About the same time they began to decay rapidly. Soon after the decay commenced, a white, almost invisible mould (suon turning to a brownish yellow) appeared in spots on the surface of the affected parts. On examining this under the microscope, the appearance was presented as seen at fiy. 7, a and b* The line cd in the figure, represents the line described by the surface of the peach; all above this line belongs to the aerial portion of the plant; these are the fertile threads that bear the sporidia. All below the line cd, represents the mycelium or roots, inside the surface of the peach.

The mycelium is large, rugged, and of luxuriant growih. It advanced with great rapidity through the soft tissues. As fast as the mycelium

[ocr errors]

• The peaches on this tree were srly all destroyed in a few days by die 8. Pr sichThe fruit of many other trees in the fame orcbard decayed in the same way. I mention this came as 1 sample of what often ocears when the trees are filled with this fungus.

« PreviousContinue »