Morus alba L.
Author: J.M. Suttie
|The agronomy and use is similar for a range of closely related
"silkworm" mulberry species; this paper deals with them as a
Closely related species
Morus nigra L. the Black Mulberry, is a very distinct species, mainly grown for its larger fruit.
There are several North American species of Morus including the Red Mulberry Morus rubra Linn.
Mulberry is a very widespread and important crop for silkworm feed, fruit and timber as well as being an excellent amenity tree. Its leaves and young bark are recognized as excellent animal feed and are used as a by-product. The interest in mulberry as a purpose-grown fodder for larger livestock has developed in recent years; this gave rise to an Electronic Conference organized by the Animal Production Service of FAO (AGAP). A book arising from the conference (Sánchez, 2002) has provided much of the information in this document.
Fruit. It is a widely grown fruit which can be eaten fresh, preserved, vinified or, in some semi-arid areas, dried for winter use.
Timber. Mulberry provides excellent timber which is used for sports good (especially M. serrata) as well as local needs in furniture; it is also pollarded to furnish round wood.
Shade. Mulberry is an excellent and handsome shade tree and is often planted on field edges in irrigated, semi-arid lands where it is also valued for fruit, poles and timber. Its deep-rooting habit makes it a suitable tree for linear plantings.
In most countries mulberry is a highly valued tree; in some southern parts of the USA, however, Morus alba is said to be potentially invasive and to compete with native forest vegetation; male clones are sometimes used as avenue trees to avoid seeding as well as soiling of the ground by fallen fruit.
Morus alba is a tree which can reach over 20 m. in height but, in its cultivated form, is often coppiced, pollarded or pruned to a low-growing bush to facilitate the harvesting of fruit or leaves. The form of the tree can vary from pyramidal to drooping. The simple, alternate, stipulate, petiolate, light green leaves are cordate at their base but very variable in form, even on the same tree; some are unlobed while others may be almost palmate. In temperate and sub-tropical climates mulberries are deciduous; under tropical upland conditions they are in leaf throughout the year. The tree generally has a deep tap root with little surface rooting which makes it suitable for use near crop land. Mulberry trees are commonly dioecious but may be monoecious, and sometimes will change from one sex to another. The flowers are held on short, green, pendulous, nondescript catkins that appear in the axils of the current season's growth and on spurs on older wood. They are wind pollinated and some cultivars will set fruit without any pollination. Cross-pollination is not necessary. Male catkins are generally longer than female ones and are loosely arranged; after shedding pollen they dry and drop off. The juicy drupelets formed by the individual flowers on the catkin combine to form a sorosis, the characteristic mulberry fruit. Fruit colour is commonly black but can vary through light purple to white the "white" in the plants name refers to its leaf-buds. The juice of the fruit causes stains which are very difficult to remove from cloth.
Mulberries thrive in full sun and dislike crowded conditions; they prefer deep soils and need good drainage; they are frost resistant. Once these requirements are met mulberries thrive over a very wide range of warm temperate, sub-tropical and tropical conditions. Several species have been domesticated and innumerable cultivars selected over many centuries for both fruit and silkworm fodder so the plants great range is not surprising. Care must, of course, be taken in finding the best cultivar for the site and purpose. Mulberries are found throughout the Old World sub-tropics and temperate areas with hot summers and have been widely distributed with the spread of silkworm-rearing.
Silkworm strains have been bred to fit the various availability of mulberry fodder; in areas with a short season the moths breed only once or twice yearly, where the season is long multi-voltine strains are used. For growing mulberries as livestock feed (as opposed to multi-purpose trees which yield some forage), however, areas with a long or continuous growing season would seem the most promising; this is reflected in the countries which report on such work in Sánchez 2002: Brazil, Italy, Cuba, Colombia, Costa Rica and Tanzania.
For India, Datta (2000) states that mulberries are found north of 280 and that they thrive with an annual rainfall of between 600 and 2500 mm. The altitude in the tropics is given as sea level to 1,000 m. Mulberries are, however grown at considerably higher altitudes in the Himalaya-Hindu Kush region. They are widely grown in Northern Pakistan and Afghanistan within irrigated areas and in villages.
In East Africa mulberry is grown as an occasional fruit tree up to at least 2 000 m. It also occurs on the Plateaux of Madagascar where there is a tradition of silk production, but Bombyx silk is probably a modern introduction; traditional Malagasy silk is made by several indigenous insects and a spider; the main moth is Borocera madagascariensis Boisduval which is fed on the leaves of the Euphorbiaceous "tapia" Uapaca bojeri Baill.
Its adoption has been expanded in Latin America, Central America and in the Caribbean, starting in the late 80s (Sánchez, 2000). Here, the commercial use of mulberry is first of all associated with regions where sericulture is common, and in other regions mulberries used to a lesser extent in orchards, recreational rural households and gardens (de Almeida and Fonseca, 2000).
CULTIVATION AND MANAGEMENT
Mulberry is often associated with mycorrhizae including Glomus mosseae and Glomus fasciculatum. Katiyar et al. (1995) found, in southern India, that the amount of phosphatic fertilizer needed for mulberry cultivation could be reduced by 75 percent when plants were inoculated.
In China seedlings, cuttings, grafted plants and layers are all used. The propagation of improved F1 seedlings is recommended (Huo, 2002). Seed can be broadcast on a well-prepared nursery at 15 kilos per hectare; a straw mulch is used until the seedlings sprout two true leaves. The seed beds are weeded and thinned. About 180,000 200,000 seedlings per hectare are produced.
In South India (Datta, 2002) three cuttings of 50 mm diameter and 25 cm long are planted directly at stake in 35 cm pits on a well prepared seed-bed leaving one bud exposed. Planting is done after the onset of the monsoon.
In the Indian Hills, however, direct planting of cuttings is not used (Datta, 2002), instead saplings of five to six months of age are planted during the monsoon.
In Japan mulberry propagation is generally carried out by grafting and by cuttings. Root grafting prevails because it is easy to handle and the grafted saplings have a high survival rate (Hiroaki et al., 2002).
In Colombia (Trujillo, 2002) recommends rooting cuttings(15 20 cm x 2 cm) in the nursery under plastic.
In China mulberry is often planted scattered on odd pieces of land but in pure gardens the density varies by region. In Zheejiang (East China) 10,000 15,000 plants per hectare are planted and pruned to a trunk height of 0.5 0.8 m. In Guandong 90,000 120,000 plants are used and trained to a low, trunkless type. In some areas they are intercropped with cereals (Huo, 2002).
In India spacing varies with zone and conditions. In southern India both rainfed and irrigated mulberries are planted at 90 cm x 90 cm, in 35 x 35 cm pits. In temperate areas the spacing varies according to conditions (90 cm x 90 cm; 150 cm x 150 cm up to 300 cm x 300 cm) and pit size is increased to 45 cm x 45 cm.
In Japan mulberry gardens are usually planted with 6,000 10,000 plants per hectare. In densely planted fields, designed for mechanical harvesting, more than 25,000 plants per hectare may be used. Standard application of chemical fertilizer to mulberry gardens is 300 kg of N, 140 kg of phosphate and 120 kg of potassium per hectare for alluvial soil, and 300 kg of N, 160 kg of phosphate and 200 kg of potassium for volcanic ash soil. In either case, application of at least 15,000 kg of compost per hectare is recommended (Hiroaki et al., 2002).
In Colombia Trujillo (2002) producing fodder for dairy stock, recommends between 25,000 and 32,000 plants per hectare with strict weeding. Three prunings are recommended to shape the plant; forage production increases up to the third year under a cutting regime. In Cuba Mártin et al. (2002) report 100 x 40 cm for fodder. In Colombia Boschini (2002) found that yield increased with planting density (in the range tested 60 cm x 60 cm 120 cm x 120 cm). In Brazil de Almeida and Fonseca (2002) used 300 cm x 60 cm.
In Japan the growth of mulberry is generally divided into three stages; new shoot development, growth and storage (Ohyama, 1970). New shoot development is a stage in which new shoots develop using reserves stored in stump or root the previous year. Growth stage is when carbohydrates and other substances are produced for vegetative growth by means of photosynthesis in leaves. Storage stage is when most photosynthetic substances are stored for next year's growth. In cultivated mulberry plants, however, photosynthetic organs are removed/harvested by pruning and leaf picking, thus disrupting the growth stage. The exploited mulberry plants resume growth using the remaining storage substances. (Hiroaki et al., 2002).
Management of established stands
Mulberry fodder is generally cut and carried; the plant is not suited to continuous grazing. Optimal cutting intervals seem to vary with cultivars and probably ecological conditions. Weeding and maintenance fertilizer are generally necessary. There is no information on the longevity of stands grown for livestock but well maintained silkworm gardens are long-lived.
In addition to the pruning used to form the initial bushes and the regular defoliation for forage, periodic pruning to maintain the desired bush type may be necessary; some are pruned on a short trunk, others are trunkless.
Mulberry produces masses of seeds and these are generally easy to harvest and germinate well. The seeds should be removed from the ripe fruit as soon as ready (for small quantities careful use of a liquidizer with plenty of water will separate seed from pulp). After harvest treatment of seed varies according to region, and probably with the different seasons of harvest and sowing. The seed can be dried and stored but immediate sowing is often recommended; stratification of M. alba seed in sand for several months is sometimes recommended.
CROP USE AND GRAZING MANAGEMENT
Mulberry is palatable to all classes of herbivorous livestock and is well suited to such small animals as rabbits and cavies. It is not adapted to grazing. Most of the experimental large scale systems described in Sánchez (2002) are based on cut and carry.
High Pollarded trees are widely used in the western Himalaya and Afghanistan for multipurpose use the tall (2.5 3 m.) trunk keeps the foliage above the grazing livestock. When poles are harvested they are usually left on the ground for a few hours and the small stock strip them of leaves and bark.
In Pakistan, where silkworms are important in the mountainous tracts, up to 600 kilos of mulberry leaves are required to rear silkworms obtained from one packet of silk-seed. Thus, 22,000 to 24,000 tonnes of mulberry leaves are consumed each year. Iqbal (1991) has reported that the value of the leaves required to rear one packet of silk seed is Rs. 200 to 300. The total value, therefore, is about Rs.10 million, based on an average price of Rs.250. Net return to the rearers is estimated at Rs.2 140 per packet (Iqbal, 1991), generating a total net income of Rs.45.6 million to the silkworm rearers in the country.
Mulberry is generally used fresh although in the Western Himalaya old dry fallen leaves are gathered as winter feed and litter.
Young mulberry leaves and twigs are a high quality fodder, readily accepted by all classes of stock.
Sánchez (2002) gives the following table.
Chemical composition from several different studies referred to in the electronic conference by different authors (% of DM).
1) Benavides, 2000; 2) Benavides et al., 2000; 3) Sánchez, 2000a; 4) Kitahara et al., 2000; 5) Liu et al, 2000; 6) Schmidek et al., 2000a; 7) Schmidek et al., 2000b; 8) Trujillo, 2000; 9) Angeloni, 2000;
There is a very rich store of genetic resources for mulberry and, although it has been exploited over centuries for both fruit and silkworm feed, the study of mulberry specifically for the feeding of large livestock is just beginning. The many allied species are mentioned above.
"Generally, mulberry is a diploid plant with 28 chromosomes (2n=28). However, it is rich in ploidy and a lot of triploid varieties have been found especially among Morus bombysis Koidz. It is said that M. cathayana Hemsl. has tetraploid, pentaploid and hexaploid varieties. Both M. serrata Roxb., indigenous to India, and M. tiliaefolia Makino, originally from Japan and Korea, are known to be hexaploid. M. boninensis Koidz. is a tetraploid being endangered due to cross contamination with M. acidosa Griff. M. nigra L. is dexoploid (2n=308), the largest number of chromosomes among phanerogams." (Hiroaki et al., 2002).
PESTS & DISEASES
The crop is not greatly bothered by pests and diseases; the main ones are summarised by Sánchez (2000) as follows.
Key pest of mulberry (Datta, 2000; de Almeida and Foneseca, 2000):
Name of pest:
Maconellicoccus hirsutus (mealy bug); causes Tukra in mulberry
Diaphania pulverulentalis (leaf roller)
Spilarctia obliqua (Bihar hairy caterpillar)
Migdolus fryanus Westwood (Longhorn beetle)
"Cutting-Prone" ants (Sauba ant)
Meloidogyne spp. (Nematodes)
Key disease of mulberry (Datta, 2000; de Almeida and Foneseca (2000):
Leaf: leaf spot, leaf rust, powdery mildew, leaf blight, bacterial blight, Phylactinia corylea
Soil borne: root rot (white, violet), root knot, mulberry withering
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