HISTORY OF SILK

The origin of silk production and weaving is ancient and clouded in legend. The industry undoubtedly began in China, where, according to native record, it existed from sometime before the middle of the 3rd millennium BC. For many centuries the Chinese zealously guarded the source and methods of production of silk, but by the 1st millennium BC they had begun trading silk cloth abroad. Within a few centuries, caravans were regularly carrying silk to India, Turkistan, and Persia. According to legend, in about 140 BC, sericulture as well as silk spread overland from China to India. By the 2nd century AD India was shipping its own raw silk and silk cloth to Persia. (Japan, too, acquired and developed a thriving sericulture a few centuries later.)

Persia became a centre of silk trade between East and West under the Parthian (247 BC–AD 224). Silk dyeing and weaving developed as crafts in Syria, Egypt, Greece, and Rome. The workers used some raw silk from the Orient, but they derived most of their yarn by unraveling silk fabrics from the East. Silk culture remained a secret of Asia.

Eventually a strong demand for the local production of raw silk arose in the Mediterranean area. Justinian I, Byzantine emperor from 527 to 565, persuaded two Persian monks who had lived in China to return there and smuggle silkworms to Constantinople in the hollows of their bamboo canes (c. AD 550). These few hardy silkworms were the beginning of all the varieties that stocked and supplied European sericulture until the 19th century.

Silk culture flourished in Europe for many centuries, especially in the Italian city-states and (from 1480) in France. In 1854, however, a devastating silkworm plague appeared. Louis Pasteur, who was asked to study the disease in 1865, discovered the cause and developed a means of control. The Italian industry recovered, but that of France never did. Meanwhile Japan was modernizing its methods of sericulture, and soon it was supplying a large portion of the world's raw silk. During and after World War II the substitution of such man-made fibers as nylon in making hosiery and other garments greatly reduced the silk industry. Still, silk has remained an important luxury material and remains an important product of Japan, South Korea, and Thailand.

COUNTRIES WHERE SILK IS PRODUCED

Production of silk involves (1) the care of the domesticated silkworm (Bombyx mori) from the egg stage through completion of the cocoon and (2) the production of mulberry trees that provide leaves upon which the worms feed. The silkworm caterpillar builds its cocoon by producing and surrounding itself with a long, continuous fiber, or filament. Liquid secretions from two large glands within the insect emerge from the spinneret, a single exit tube in the head, hardening upon exposure to air and forming twin filaments composed of fibroin, a protein material. A second pair of glands secretes sericin, a gummy substance cementing the two filaments together.

Silk is a continuous filament within each cocoon, having a usable length of about 600 to 900 m (2,000 to 3,000 feet). It is freed by softening the binding sericin and then locating the filament end and unwinding, or reeling, the filaments from several cocoons at the same time, sometimes with a slight twist, forming a single strand. Several silk strands, each too thin for most uses, are twisted together to make thicker, stronger yarn in the process called throwing, producing various yarns differing according to the amount and direction of the twist imparted.

Silk containing sericin is called raw silk. The gummy substance, affording protection during processing, is usually retained until the yarn or fabric stage and is removed by boiling the silk in soap and water, leaving it soft and lustrous, with weight reduced by as much as 30 percent. Spun silk is made from short lengths obtained from damaged cocoons or broken off during processing, twisted together to make yarn. The thickness of silk filament yarn is expressed in terms of denier, the number of grams of weight per 9,000 m (9,846 yards) of length.

Silk has good strength, resisting breakage when subjected to weights of about 4 g (0.5 ounce) per denier. Wetting reduces strength by about 15–25 percent. A silk filament can be stretched about 20 percent beyond its original length before breaking but does not immediately resume its original length when stretched more than about 2 percent. Silk, lower in density than such fibers as cotton, wool, and rayon, is moisture-absorbent, retaining as much as a third of its weight in moisture without feeling damp, and has excellent dyeing properties. It is more heat-resistant than wool, decomposing at about 170° C (340° F). Silk loses strength over a long period of time without appropriate storage conditions and tends to decompose with extensive exposure to sunlight but is rarely attacked by mildew. It is not harmed by mild alkaline solutions and common dry-cleaning solvents. Friction imparts a static charge, especially in low humidity. The rustling sound associated with crisp silk fabrics is not a natural property of the fiber but is developed by processing treatments, and it does not indicate quality, as is sometimes believed.

There are 58 countries where more or less silk is produced (total silk producing countries are more than 200). The following are the countries silk is produced:

Afghanistan, Algeria, Argentina, Bangladesh, Bhutan, Brazil, Bulgaria, Burma (Myanmar), Chile, China, Colombia, Conga, Egypt, Ethiopia, France, Ghana, Greece, Hungary, India, Indonesia, Iran. Italy, Ivory Coast, Japan, Kenya, North Korea, South Korea, Laos, Lebanon, Madagascar, Malaysia, Mauritius, Mexico, Morocco, Nepal, Nigeria, Pakistan, Papua New Guinea, Paraguay, Kampuchea, Peru, Philippines, Poland, Romania, Spain, Sri Lanka, Syria, Tanzania, Thailand, Tunisia, Turkey, Uganda, Russia, Venezuela, Vietnam, Yugoslavia, Zambia, Zimbabwe.

MULBERRY CULTIVATION - GENERAL ASPECTS OF MULBERRY

Mulberry forms the basic food material for silkworms and the bulk of the silk goods produced in the world are from mulberry silkworms.

Production of mulberry leaves on scientific lines is essential for organizing Seri­culture on sound economic lines. It is estimated that one metric ton of mulberry leaves is necessary for the rearing of silkworms emerging from out of one ounce of eggs, which will yield about 25 to 30 kg of cocoons of international standard. The cost of leaves works out to about 60 percent of the total cost of production of silk. The bulk of the leaves are required at the final stage of growth of the silkworm. One hectare of fertile land can produce about 15 to 40 tons of mulberry leaves over a twelve month period.

Morus is the Latin word for mulberry (French: muries, Italian: gelso, Japanese: lewwa). Mulberry plant is exploited in different ways for commercial production of silk, as mulberry is the chief food for Bombyx mori. Mulberry leaf protein is the source for the silkworm to bio‑synthesize the silk which is made up of two proteins, fibroin and sericin. Nearly 70 percent of the silk proteins produced by a silkworm are directly derived from the proteins of the mulberry leaves use of machines for cultural practices and for harvesting of leaves have helped to reduce of mulberry leaf.

Irrigation is an influencing factor on the growth of mulberry leaves. It is observed that irrigation, coupled with fertilizer application, can increase the production of mulberry leaf seven to eight times, over dry farming conditions in the tropical regions.

The soils grown to mulberry are mostly alluvial and volcanic types. Mulberry being highly responsive to fertilizer applications.

As in the other crops, mulberry is also not free from pests and diseases. In order to check the pests and diseases, use of insecticides harmless to the silkworm has been suggested.

Origin: Mulberry is believed to be a native either of India or China and it is believed to have originated on the lower slopes of the Himalayas. Towards the year 2800 B.C. Chin‑Nong, one of the successors of Empheras Fo‑Hi taught cultivation of mulberry in China. Silk industry took its origin in the province of Chang‑tong.

Rainfall: Mulberry can be grown in a rainfall range of 635 mm to 2 500 mm. Under low rainfall conditions, supplemental irrigation is necessary.

MULBERRY CULTIVATION (CONT…1) - BOTANICAL DESCRIPTION

Mulberry belongs to the genus MORUS. The number of species varies according to the author, as the species classified by some taxonomists are considered as varieties of the same species by the others. In any case, the number of species belonging to the genus Morus is more than twenty. There is considerable variation in each and every character of the species and the varieties described so far. Hooker (1885) has given the botanical description of the genus Morus as follows:

Trees or shrubs. Leaves alternate, entire toothed or three lobed, base three to five nerved, stipules small, lateral, caduceus. Flowers mono or dioeciously, spikate. Male flower sepals four imbricate. Stamens four, inflexed in bud. Pistil lode turbinate. Female flower sepals four, decussate, imbricate, and succulent in fruit. Ovary included straight one celled, style central, two partite or two fid; ovule pendulous, fruiting spikes or heads many, achene’s enclosed in the succulent perianth. Seed subglo­bose, albumen copious fleshy; embryo incurved, cotyledons oblong equal, radical ascending incumbent ‑ species few, tropical and temperate.

Plant Habitat: The plant is a perennial one, living for a number of years either cultivated or in wild state. Depending upon the type of cultivation, the plant is grown as a bush, tree or a middling.

Plant Height: The plants when allowed to grow as trees attain a height of 20‑25 m. with a girth of‑the trunk about eight m. in the case of Morus serrata.  Where the trees are grown as a fence, they are allowed to grow to the required height and then pruned at the desired height every year. The bush and the middling usually attain a maximum height of 1.5 to 1.8 M.

Stem: Mulberry plants show a number of stem colors depending upon their species, climate or origin. The Mysore Local, Kanva‑2 and Berhampore varieties of the species Morus indica are white to grayish white in colors.

MULBERRY CULTIVATION (CONT…2) – BUD AND METHODS OF BREAKING DORMANCY IN BUDS

Bud: In mulberry, generally one bud is found in the axial of a leaf. Sometimes two more independent buds on either side of the main bud are also found.

Causes for dormancy in bud: Earlier physiologists were of the opinion that low, temperature, nitrogen deficiency, inactivation of enzymes due to excessive accumulation of carbohydrate; photoperiodism etc. might be responsible for dormancy.

METHODS OF BREAKING DORMANCY IN BUDS:

Mechanical: Sometimes even under tropical climate, during winter period, the buds do not sprout quicily.

Chilling treatment: Gururajan (1962) reported the success of breaking dormancy in buds of Morus nigra by subjecting them to a low temperature of 0 to 6⁰C.

Chemical treatment: Iwata (1970) reported the effect of chemicals such as methyl cap rate on the sprouting of mulberry buds and retardation of growth of mulberry plants. Mulberry plants grown were sprayed by aqueous emulsion of methyl cap rate in summer with varying concentrations ranging from 0.01 M to 0.2 M.

Leaves: The size of mulberry leaf varies in different species and varieties. Varieties like Kanva‑2 are characterized by large leaves and varieties like "Mysore 'Local" bear only small leaves. The leaf size is an important character taken into consideration in selecting high yielding varieties.

Inflorescence: The inflorescence of mulberry is a CATKIN with its characteristic pendent or drooping peduncle, bearing unisexual flowers.

Male catkin: The male catkin is usually longer than the female catkin measuring 2.5 to 5 cm long.

Female Catkin: The female catkin is axillary, sometimes occurs in clusters.

Flower: The flowers of mulberry are small, usually sessile or infrequently shortly pedicillate, regular and unisexual.

Male flower: The male flower consists of four perianth leaves arranged in two whorls with imbricate aestivation.

Female flower: The female flower consists of four perianth leaves arranged in the same manner as in the male flower.

Pollination: Since the flowers of mulberry are unisexual, only cross pollination takes place.

Seed: Typical tree whose seeds are to be used for propagation by sexual means is select d from which dark purple colored ripe fruits are collected. These fruits are kept for one day for softening the pulp taking necessary precautions to prevent the pulp from rotting. The next day, these fruits are transferred to a trough containing water. Then by constant kneading of the fruits the seeds become squeezed out of the pulp. The water is decanted and the seeds are taken out, dried and stored under dry conditions.

Structure of seed: Mulberry seed is oval in shape with a nearly flat surface at the micropylar region.

Polyembryonic seed: Rare occurrence of seeds giving rise to two identical seedlings has been reported. Such seedlings were thought to be polyploids. Generally embryo is developed only from the egg cell in the ovule. Sometimes embryos may be formed from nucellar tissues also.

Storage of seed: Mulberry seeds may be viable for a few weeks or may be at the most for three months beyond that they may not be viable.

MULBERRY CULTIVATION (CONT...3) - CLASSIFICATION AND VARIETIES

Mulberry is a fast growing deciduous tree occurring in sub‑tropical, tropical and temperate climates. Koidzumi (1917‑1923) grouped mulberry into two sections on the length of the style of the female flower as Dolichostylae and Macromorus and each subdivided on the fea­tures of stigma, as shown below:

A. Dolichostylae:

(a) Pubescentes        Morus arabica Koidz.               (Arabiyaguwa Mizuhoguwa)

                                 M. mizuho Hotta

(b) Papillosae           M. mongolica Schn.                 (Chosenguwa Oniguwa)

                                 M. mongolica var.

                                 diabolica Koidz.

                                 M. nigriformis Koidz.              (Karaoniquwa)

                                 M. notabilis Schn.                    (Marubaguwa)

                                 M. bombycis Koidz.                 (Yamaguwa)

                                 M. rotundifolia Koidz.              (Shamuguwa)

                                 M. acidosa Criff.                       (Shimaguwa)

                                 M. kagayamae Koidz.               (Hachijoguwa)

B. Macromorus:

(a) Pubescentes        M. serrata Royb.                            (Tenjikuguwa)

                                 M. nigra L.                                    (Ruromiguwa)

                                 M. tiliaefolia Makino.                   (Keguwa)

                                 M. cathayama. Memsl.                  (Karakeguwa)

(b) Papillosae           M. mosozygia stapf.                      (Afurikaguwa)

                                 M. laevigata Wall.                         (Nagamiguwa)

                                 M. insignia Buv.                            (Amerikaguwa)

                                 M. macroura Miq.                         (Mareiguwa)

                                 M. rubra L.                                    (Akamiguwa)

                                 M. mollis Rusby.                           (Yaharaguwa)

                                 M. celtidifolia Kunth.                   (Enokiguwa)

                                 M. microphylla Buckl.                  (Himeguwa)

                                 M. boninensis Koidz.                    (Ogasawaraguwa)

                                 M. lhou Koidz.                              (Roguwa)

                                 M. alba L.                                      (Karayamaguwa)

                                 M. atropurpurea Roxb.                  (Kantonguwa)

Hotta (1930) divided mulberry species into two groups according to the shape and situation of cystolith cell in leaves, Dolychocystolithiae and Brachycystolithiae.

Group 1. Dolychocystolithiae:

Morus bombycis, M. kagayamae and M. australis.

Group 2. Brachycystolithiae:

Morus latifolia, M. alba and M. tilaefolia.

MULBERRY CULTIVATION (CONT...4) - ANATOMY AND EMBRYOLOGY

Anatomy of the Root: Mulberry is a deep rooted perennial plant. Its root system is very well developed though the growth and spread of the root depend upon the texture of the soil.

Internal structure of a root: There is a single layered epidermis which consists of tubular shaped cells, closely arranged without inter‑cellular space, Its outer walls are not cutinized and a few of the epidermal cells enlarge into root hairs.

Structure of a secondary root: The knowledge of anatomy of a root is of primary importance in the vegetative propagation such as selecting a proper plant for preparation of cutting and stock for grafting.

Anatomy of stem: The anatomy of the stem is similar to that of any dicotyledonous stem. The primary stem consists of a single‑layered epidermis with tubular shaped cells closely arranged without inter‑cellular space.

Secondary stem: The secondary stem of mulberry shows the union of the cambial strips of the vascular bundles, a continuous ring of cambium is devel­oped which cuts off secondary xylem towards inside and secondary phloem towards outside.

Anatomy of leaf:

Anatomy of the Petiole: The internal structure of the petiole of mulberry is like the primary tissues of the stem. The epidermis is single layered. Some of the cells are drawn into epidermal hairs in certain species.

Anatomy of leaf blade: The leaves are dorsiventral with reticulate venation. The upper epidermis consists of a single layer of tabular shaped cells closely arranged without intercellular space.

Embryology:

Microsporogenesis: Anther to begin with, is a mass of meristematic cells. A row of three hypodermal cells forms the Archesporial cells. These cells on pericinal division give rise to primary parietal cells and primary sporogenous cells.

Mega sporangium:The mega sporangium or the ovule arises as an out­ growth of thematic cells on placenta. This soon differentiates into funicle and nucellus.

Male Gametophyte: Each pollen grain divides asymmetrically into a large or tube cell and‑a small generative cell. Pollen grains are bicelled at the time of shedding.

Female Gametophyte: The functional megaspore undergoes three successive mitotic divisions forming eight nucleate embryo sac. The embryo sac is pear‑shaped.

Fertilization: After pollination is effected, the pollen grains germinate on the stigma. The rate of growth of pollen tube is generally influenced by environmental con­ditions, especially temperature.

Fruit: The fruit of mulberry is a multiple one, as all the flowers of the inflor­escence give rise to a single fruit.