**1. Introduction**

Sericulture is as an important agriculture-based, labor intensive, exportoriented cottage industry, introduced more than 200 years ago in India. This industry consists of several sectors or processes that are linked to one another like a chain. They are mulberry cultivation, silkworms egg production, silkworm rearing, harvesting of cocoons, silk reeling, twisting and weaving and manufacturing silk fabrics. Mulberry silk is produced from silkworms (*Bombyx mori* L.), which form the base of silk production. Mulberry is a fast growing plant and hence farmers can harvest 5–6 silkworm crops in a year at an interval of 26–28 days. The marginal and

small farmers opted for sericulture since it was a remunerative crop as compared to other competing crops like Raagi, Jowar, Paddy, Potato and other vegetable crops.

*Morus* L. is an important genus of the family Moraceae under the order Urticales [1, 2] established the genus *Morus* with seven species viz., *Morus. alba, M. nigra, M. rubra, M. indica. M. tartarica, M. papyrifera* and *M. tinctoria.* Later, a number of species have been discovered by various workers from different parts of the world. Mulberry is a dicot, mesophytic, heterozygous and cross pollinated plant.

Importance of cytogenetical studies is very well understood in all most all agricultural crops. Even in mulberry breeding emphasis has been laid to understand the cytology of genotypes used as parents in breeding, in all sericultural advanced countries. In various mulberry genotypes, basic gametic and somatic chromosome numbers suggesting the ploidy level [3, 4]. These Cytogenetical data are useful to mulberry breeders in identifying and evolving promising genotypes and selecting the suitable species/varieties for commercial exploitation. Keeping this in view the identifying proper representation of genotypes of three species of mulberry has been discussed in this chapter.

#### **2. Chromosome numbers**

It is well established fact that cytological features are employed in differentiating and tracing the phylogeny of organisms. Cytotaxonomy based on chromosomal characteristics was most popular in plant taxonomy between 1930 and 1960 [5]. In such taxonomic studies chromosome number, chromosome morphology, chromosomal association, chromosome behavior and cytochemistry, etc., have yielded valuable results and revolutionized the phylogenetic interpretations.

Cytological studies in mulberry have been carried out in all sericulturally advanced countries. In view of their importance in breeding programs, chromosome numbers, chromosomal association and meiotic behaviors of various diploid, triploid, tetraploid and uneuploid genotypes of mulberry have been studied.

#### **2.1 Polyploidy**

The organisms having more than two genomes or two sets of chromosome in their somatic cells are called as polyploids. Among plants and animals, the polyploidy occurs in a multiple series of 3, 4, 5, 6, 7, 8, etc., of the basic chromosome numbers or genomes number and thus it causing triploidy, tetraploidy, pentaploidy, hexaploidy, heptaploidy, octaploidy, respectively. Polyploidy is most common among angiosperms.

The phenomenon of polyploidy is one of the widespread and distinctive features, which has played a major role in the evolution of higher plants. It plays important role in the natural selection and better adaptability of species in the new ecological niches.

In mulberry, polyploidy breeding techniques are found to be more suitable than mutation breeding techniques. A number of varieties have been developed in sericulturally advanced countries like Japan [6], China [7] and also in India [8]. In India, triploid mulberry varieties like TR8 and TR10 have been recommended in hilly areas of eastern states.

Polyploidy may arise by several ways. (1) The egg may be fertilized by more than one sperm. If normal haploid egg is fertilized by two haploid sperms a triploid will result. (2) There may be failure of mitosis. (3) Triploids may arise as a result of fertilization of unreduced gametes. Diploid gametes arise because of failure in meiosis. If these gametes are fertilized by haploid sperms, triploids are formed.

**3**

**Figure 1.** *Variety Vishala.*

*Studies on Basic Chromosome Number, Ploidy Level, Chromosomal Association…*

(4) An autotetraploids may arise either by the doubling of chromosomes or by

Vishala is developed by Central Sericultural Research Institute in Mysuru. It is fast growing variety, under ideal agro-climatic conditions (**Figure 1**). This variety yields 34,000 to 60,000 kgs and 14, 000 to 20,000 kgs of leaves/hector/year under irrigated and rain fed conditions respectively. Leaves are larger, dark green in color, unlobed and retain high moisture content. Stomatal frequency was found to be 260.

This variety is evolved from cross pollinated hybrids. It is medium branching and fast growing in tropical conditions and it is good rooter (**Figure 2**). It possesses wide acclimatization in different agro-climatic conditions. This variety yields 26,000 to 40,000 kgs and 13, 000 to 18,000 kgs of leaves /hector/year under irrigated and rain fed conditions respectively. Leaves are larger, dark green in color, unlobed and retain high moisture content. Stomatal frequency was found to be 234.

Each species of plants and animals is characterized by a particular chromosome complement or a set of genome, represented once in gametic haploid cell and twice

Genus *morus* exhibits a high degree of polyploidy ranging from diploid (2n = 2x = 28) to Decosoploid (2n = 22x = 308). Accordingly, its various

diploids and polyploidy complexes were reported in many species.

species show chromosome numbers ranging 28 to 308. Majority of the species are

*DOI: http://dx.doi.org/10.5772/intechopen.97143*

fertilization between two diploid gametes.

& size 138.30μm2

& size 126.40μm<sup>2</sup>

in somatic diploid cells.

.

.

**2.2** *Morus indica*

51/mm2

60/mm2

*2.2.1 Variety Vishala*

*2.2.2 Variety Kosen*

*Studies on Basic Chromosome Number, Ploidy Level, Chromosomal Association… DOI: http://dx.doi.org/10.5772/intechopen.97143*

(4) An autotetraploids may arise either by the doubling of chromosomes or by fertilization between two diploid gametes.

## **2.2** *Morus indica*

*Cytogenetics - Classical and Molecular Strategies for Analysing Heredity Material*

Mulberry is a dicot, mesophytic, heterozygous and cross pollinated plant. Importance of cytogenetical studies is very well understood in all most all agricultural crops. Even in mulberry breeding emphasis has been laid to understand the cytology of genotypes used as parents in breeding, in all sericultural advanced countries. In various mulberry genotypes, basic gametic and somatic chromosome numbers suggesting the ploidy level [3, 4]. These Cytogenetical data are useful to mulberry breeders in identifying and evolving promising genotypes and selecting the suitable species/varieties for commercial exploitation. Keeping this in view the identifying proper representation of genotypes of three species of mulberry has

been discussed in this chapter.

**2. Chromosome numbers**

**2.1 Polyploidy**

among angiosperms.

ecological niches.

areas of eastern states.

small farmers opted for sericulture since it was a remunerative crop as compared to other competing crops like Raagi, Jowar, Paddy, Potato and other vegetable crops. *Morus* L. is an important genus of the family Moraceae under the order Urticales [1, 2] established the genus *Morus* with seven species viz., *Morus. alba, M. nigra, M. rubra, M. indica. M. tartarica, M. papyrifera* and *M. tinctoria.* Later, a number of species have been discovered by various workers from different parts of the world.

It is well established fact that cytological features are employed in differentiating

and tracing the phylogeny of organisms. Cytotaxonomy based on chromosomal characteristics was most popular in plant taxonomy between 1930 and 1960 [5]. In such taxonomic studies chromosome number, chromosome morphology, chromosomal association, chromosome behavior and cytochemistry, etc., have yielded

Cytological studies in mulberry have been carried out in all sericulturally advanced countries. In view of their importance in breeding programs, chromosome numbers, chromosomal association and meiotic behaviors of various diploid, triploid, tetraploid and uneuploid genotypes of mulberry have been studied.

The organisms having more than two genomes or two sets of chromosome in their somatic cells are called as polyploids. Among plants and animals, the polyploidy occurs in a multiple series of 3, 4, 5, 6, 7, 8, etc., of the basic chromosome numbers or genomes number and thus it causing triploidy, tetraploidy, pentaploidy, hexaploidy, heptaploidy, octaploidy, respectively. Polyploidy is most common

The phenomenon of polyploidy is one of the widespread and distinctive features, which has played a major role in the evolution of higher plants. It plays important role in the natural selection and better adaptability of species in the new

In mulberry, polyploidy breeding techniques are found to be more suitable than mutation breeding techniques. A number of varieties have been developed in sericulturally advanced countries like Japan [6], China [7] and also in India [8]. In India, triploid mulberry varieties like TR8 and TR10 have been recommended in hilly

Polyploidy may arise by several ways. (1) The egg may be fertilized by more than one sperm. If normal haploid egg is fertilized by two haploid sperms a triploid will result. (2) There may be failure of mitosis. (3) Triploids may arise as a result of fertilization of unreduced gametes. Diploid gametes arise because of failure in meiosis. If these gametes are fertilized by haploid sperms, triploids are formed.

valuable results and revolutionized the phylogenetic interpretations.

**2**

## *2.2.1 Variety Vishala*

Vishala is developed by Central Sericultural Research Institute in Mysuru. It is fast growing variety, under ideal agro-climatic conditions (**Figure 1**). This variety yields 34,000 to 60,000 kgs and 14, 000 to 20,000 kgs of leaves/hector/year under irrigated and rain fed conditions respectively. Leaves are larger, dark green in color, unlobed and retain high moisture content. Stomatal frequency was found to be 260. 51/mm2 & size 138.30μm2 .

#### *2.2.2 Variety Kosen*

This variety is evolved from cross pollinated hybrids. It is medium branching and fast growing in tropical conditions and it is good rooter (**Figure 2**). It possesses wide acclimatization in different agro-climatic conditions. This variety yields 26,000 to 40,000 kgs and 13, 000 to 18,000 kgs of leaves /hector/year under irrigated and rain fed conditions respectively. Leaves are larger, dark green in color, unlobed and retain high moisture content. Stomatal frequency was found to be 234. 60/mm2 & size 126.40μm<sup>2</sup> .

Each species of plants and animals is characterized by a particular chromosome complement or a set of genome, represented once in gametic haploid cell and twice in somatic diploid cells.

Genus *morus* exhibits a high degree of polyploidy ranging from diploid (2n = 2x = 28) to Decosoploid (2n = 22x = 308). Accordingly, its various species show chromosome numbers ranging 28 to 308. Majority of the species are diploids and polyploidy complexes were reported in many species.

**Figure 1.** *Variety Vishala.*

Varieties, Vishala and S13 are belonging to Indian species and many cultivars belong to this species. Both the varieties were found to be 28 chromosomes (2n = 2x = 28) in their shoot somatic cells, during mitotic division, thereby confirming their diploid status. The diploid nature is related with fertility, normal growth, great vigorosity, adoptability and survivality of the diploid species. The typical characters of diploid are good elongation of branches and roots, good root initiation ability, good regenerating ability of buds, high yielding potential and easiness of raising saplings. Feeding value of leaves is highest for diploid, followed by triploid and tetraploid.

## *2.2.3 Variety Ber-S1*

It is an evolved variety from Berhampore Institute and showed uneuploid nature with 2n = 30 chromosomes (**Figure 3**). Morphologically uneuploid varieties are almost similar to the diploids in all parameters except minor variations. The uneuploid nature is related with fertility, normal growth, great vigorosity, adoptability and survivality of the uneuploids varieties. It possesses wide acclimatization in different agro-climatic conditions. This variety yield 24, 000 to 38, 000 kgs and 11, 000 to 16, 000 kgs of leaf/hector/year under and rainfed conditions respectively. Leaves are larger, dark green, unlobed and retain high moisture content. Stomatal frequency was found to be 238.20/mm2 & size 116.00μm<sup>2</sup> .

## *2.2.4 Variety S13*

It is selected from open pollinated hybrid (OPH) of Kanva2 during 1986. This variety is characterized by short internodes and having a capacity of produces large numbers of branches. Leaves are thick and dark green unlobed with smooth surface. This variety best suited for rainfed condition and yield 16,000 to 18,000 kgs of leaf /hector/year (**Figure 4**). Leaves of diploids and uneuploids varieties are found to be

**5**

**Figure 4.** *Variety S13.*

**Figure 3.** *Variety Ber-S1.*

found to be 210.00/mm2

*Studies on Basic Chromosome Number, Ploidy Level, Chromosomal Association…*

succulent, rich in moisture and nutrient contents when compared to triploids and tetraploid varieties and are suitable to silkworm larvae [9]. Stomatal frequency was

. Varieties, Ber-S1 and S13 are belonging to Indian species and many cultivars belong to this species. Both the varieties were found to be 30 chromosomes

& size 128.00μm<sup>2</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.97143*

*Studies on Basic Chromosome Number, Ploidy Level, Chromosomal Association… DOI: http://dx.doi.org/10.5772/intechopen.97143*

*Cytogenetics - Classical and Molecular Strategies for Analysing Heredity Material*

Varieties, Vishala and S13 are belonging to Indian species and many cultivars

(2n = 2x = 28) in their shoot somatic cells, during mitotic division, thereby confirming their diploid status. The diploid nature is related with fertility, normal growth, great vigorosity, adoptability and survivality of the diploid species. The typical characters of diploid are good elongation of branches and roots, good root initiation ability, good regenerating ability of buds, high yielding potential and easiness of raising saplings. Feeding value of leaves is highest for diploid, followed by triploid

It is an evolved variety from Berhampore Institute and showed uneuploid nature

& size 116.00μm<sup>2</sup>

It is selected from open pollinated hybrid (OPH) of Kanva2 during 1986. This variety is characterized by short internodes and having a capacity of produces large numbers of branches. Leaves are thick and dark green unlobed with smooth surface. This variety best suited for rainfed condition and yield 16,000 to 18,000 kgs of leaf /hector/year (**Figure 4**). Leaves of diploids and uneuploids varieties are found to be

.

with 2n = 30 chromosomes (**Figure 3**). Morphologically uneuploid varieties are almost similar to the diploids in all parameters except minor variations. The uneuploid nature is related with fertility, normal growth, great vigorosity, adoptability and survivality of the uneuploids varieties. It possesses wide acclimatization in different agro-climatic conditions. This variety yield 24, 000 to 38, 000 kgs and 11, 000 to 16, 000 kgs of leaf/hector/year under and rainfed conditions respectively. Leaves are larger, dark green, unlobed and retain high moisture content. Stomatal

belong to this species. Both the varieties were found to be 28 chromosomes

**4**

and tetraploid.

**Figure 2.** *Variety Kosen.*

*2.2.4 Variety S13*

*2.2.3 Variety Ber-S1*

frequency was found to be 238.20/mm2

succulent, rich in moisture and nutrient contents when compared to triploids and tetraploid varieties and are suitable to silkworm larvae [9]. Stomatal frequency was found to be 210.00/mm<sup>2</sup> & size 128.00μm<sup>2</sup> .

Varieties, Ber-S1 and S13 are belonging to Indian species and many cultivars belong to this species. Both the varieties were found to be 30 chromosomes

(2n = 30) in their shoot somatic cells, during mitotic division, thereby confirming their uneuploid nature. Uneuploids plants have incomplete genomes. Individual chromosomes may either be less than diploid number (monosomic and nullisomic), or more than the diploid number (polysomic). Uneuploid chromosome number recorded in present work as well as reported by others are mainly due to extensive vegetative propagation followed for the multiplication of *Morus* spp. Therefore, the genus *Morus* has monobasic number x = 14. The polyploid numbers found in this taxa must have derived from this base number (x = 14) an account of auto and allopolyploidizaton. No doubt, vegetative propagation has helped for the perpetuation of uneuploids rather than their origin. Out breeding has played an important role in the origin of uneuploids due to the formation of gametes with unbalanced chromosome numbers.
