**4. Meiotic behavior**

## **4.1** *Morus indica* **variety Vishaala**

Meiotic behaviors in the present study revealed that microsporogenesis was normal in diploid varieties. These varieties showed regular pairing of chromosomes in majority of PMCs similar to many other diploid mulberry varieties [16] and 14 bivalents. The present investigation also showed there were no secondary association of chromosomes and multivalents in diakinesis and metaphase- I. The behavior of chromosome in metaphase is an index of fertility. Occurrence of normal bivalents results in the regular separation at anaphase and regular meiosis leading to high percentage of pollen fertility.

#### **4.2** *Morus indica* **variety S13**

Uneuploid varieties have incomplete genomes. Individual chromosome may either be less than the diploid number (*monosomics* and *nullisomic*) or more than the diploid number (polysomic). These varieties revealed marginal irregular meiosis and pollen fertility was also slightly less in these varieties.

#### **4.3** *Morus alba* **varieties NAO Khurkul and KPG1**

Triploid varieties are characterized by highly irregular meiosis and very low pollen fertility. Irregular meiosis is the almost common feature of triploids in all plants. These varieties showed high frequency of trivalents which suggests the fair homology between its constituent genome and autotriploid nature of these varieties [17, 18]. Such irregular meiosis has been reported in other natural triploid mulberry varieties also [19, 20]. The most common aberrations observed includes the occurrence of univalent's, laggards, stickiness, precocious movement and in anaphase unequal number of chromosome segregate to the poles which again attribute to irregularities in chromosome pairing and their alignment on equatorial plate. These irregular meiosis leads to formation of aberrant, unbalanced microspore and finally resulted in the reduction of pollen fertility. Formation of such aberrant sporads in some mulberry triploids has been recorded by [21].

#### **4.4** *Morus latifolia*

#### *4.4.1 Varieties Kokuso and Icheihei*

Meiotic behavior was irregular in these varieties. Theoretically tetraploid forms revealed more quadrivalents in meiosis due to the presence of four homologous

**11**

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

chromosomes. Occurrence of high frequency of tetravalent in both the varieties indicates their relatively more stable autotetraploids nature. The presence of low frequency of trivalents and univalent's along with bivalents also indicates segmental homology of chromosomes and the allotetraploid nature of these varieties have been observed by [22]. Both the varieties showed low pollen fertility. The reduced pollen fertility of tetraploids could be attributed to association of chromosomes into multivalent during synopsis and other meiotic abnormalities which invariably results in loss of chromatin material [23–25]. Chromosome segregates unequally during anaphase leading to imbalanced chromosome complement in microspores

During the study of meiosis, nature of pollen mother cells (PMCs) at premeiotic interphase, nature of chromosomes at early stages of prophase- I, pairing behavior of chromosomes at diakinesis and metaphase-I, segregation of chromosomes at anaphase-I, separation of chromatids at anaphase-II, type and variations in tetrad, pollen size and pollen stainability were studied. The frequency of different types of chromosomal associations scored in 50 meiotic cells at metaphase. The bivalents showed 1 or 2 chaisma could not be distinguished, as the chromosomes

Basic chromosome numbers, ploidy level, chromosomal association and configurations and meiotic behaviors of eight mulberry varieties were studied. The present research work revealed the diploid chromosome number of 2n = 2x = 28 (Vishaala & Kosen), uneuploid chromosome number of 2n = 30 (Ber-S1 & S13), triploid chromosome number of 2n = 3x = 42 (NAO Khurkul & KPG1) and tetraploid chromosome number of 2n = 4x = 56 (Kokuso & Icheihei). High percentage of pollen fertility in diploid plants with 2n = 28 chromosomes indicate the dibasic

Variation in the chromosome pairing, assortment and pollen stainability in different varieties of mulberry indicate that they vary in genetic status. The basic number x = 14 appears to deep sited in the genus *Morus* and other numbers might have derived through secondary polyploidy, hybridization followed doubling of

The present investigation was carried out with objectives of generating useful information on Studies on basic chromosome number, ploidy level, chromosomal association and configuration and meiotic behaviors of eight mulberry varieties

The mulberry varieties studied (Genotypes) have unraveled diversity with respect of branching pattern, leaf yield, leaf color, size, lobation, shape, stomatal frequency and size, chloroplasts in the guard cells and trichomes density. The taxa studied were taxonomically distinct. The interaction between genotype and the

Based on the present findings diploids have 2n = 28, uneuploids have 2n = 30, triploids have 3n = 42 and teteraploids have 4n = 56 chromosomes. Meiosis has been found to be regular with high frequency of bivalents, high pollen stainability and development normal pollen grain in diploids compare to irregular meiosis characterized by the presence of high frequency of trivalents and univalent's, low pollen stainability and aberrant pollen formation in triploids and teteraploids. The reduced pollen fertility has been attributed to various meiotic anomalies. The role of chromosome repatterning coupled with polyploidy (both euploids and uneuploids) structural alternation of chromosomes and mutations in the evolution of the genus *Morus* is suggested.

environment is largely responsible for the diversity observed.

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

and also leads to pollen sterility.

were shorter.

nature of these taxa.

**5. Conclusion**

(Genotypes).

chromosome and uneuploid alteration.

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

chromosomes. Occurrence of high frequency of tetravalent in both the varieties indicates their relatively more stable autotetraploids nature. The presence of low frequency of trivalents and univalent's along with bivalents also indicates segmental homology of chromosomes and the allotetraploid nature of these varieties have been observed by [22]. Both the varieties showed low pollen fertility. The reduced pollen fertility of tetraploids could be attributed to association of chromosomes into multivalent during synopsis and other meiotic abnormalities which invariably results in loss of chromatin material [23–25]. Chromosome segregates unequally during anaphase leading to imbalanced chromosome complement in microspores and also leads to pollen sterility.

During the study of meiosis, nature of pollen mother cells (PMCs) at premeiotic interphase, nature of chromosomes at early stages of prophase- I, pairing behavior of chromosomes at diakinesis and metaphase-I, segregation of chromosomes at anaphase-I, separation of chromatids at anaphase-II, type and variations in tetrad, pollen size and pollen stainability were studied. The frequency of different types of chromosomal associations scored in 50 meiotic cells at metaphase. The bivalents showed 1 or 2 chaisma could not be distinguished, as the chromosomes were shorter.

Basic chromosome numbers, ploidy level, chromosomal association and configurations and meiotic behaviors of eight mulberry varieties were studied. The present research work revealed the diploid chromosome number of 2n = 2x = 28 (Vishaala & Kosen), uneuploid chromosome number of 2n = 30 (Ber-S1 & S13), triploid chromosome number of 2n = 3x = 42 (NAO Khurkul & KPG1) and tetraploid chromosome number of 2n = 4x = 56 (Kokuso & Icheihei). High percentage of pollen fertility in diploid plants with 2n = 28 chromosomes indicate the dibasic nature of these taxa.

Variation in the chromosome pairing, assortment and pollen stainability in different varieties of mulberry indicate that they vary in genetic status. The basic number x = 14 appears to deep sited in the genus *Morus* and other numbers might have derived through secondary polyploidy, hybridization followed doubling of chromosome and uneuploid alteration.

#### **5. Conclusion**

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

Quadrivalents were observed " ͜͡ ͜͡ " or "- - - -" types.

that, pairing of chromosomes is mainly governed by genes.

and pollen fertility was also slightly less in these varieties.

**4.3** *Morus alba* **varieties NAO Khurkul and KPG1**

some mulberry triploids has been recorded by [21].

**4. Meiotic behavior**

**4.1** *Morus indica* **variety Vishaala**

high percentage of pollen fertility.

**4.2** *Morus indica* **variety S13**

In tetraploid varieties various types of chromosomal associations ranging from uni- to quadrivalents are observed during diakinesis and metaphase-I. Frequencies of quadrivalents are more than that of uni-, bi- and trivalents. However, the occurrence of multivalent such as tri- and quadrivalents indicates its polyploidy nature.

The concept of assessing the nature of polyploidy based on the sole criterion of multivalent frequency appears to have a limited value. Several workers have shown

Meiotic behaviors in the present study revealed that microsporogenesis was normal in diploid varieties. These varieties showed regular pairing of chromosomes in majority of PMCs similar to many other diploid mulberry varieties [16] and 14 bivalents. The present investigation also showed there were no secondary association of chromosomes and multivalents in diakinesis and metaphase- I. The behavior of chromosome in metaphase is an index of fertility. Occurrence of normal bivalents results in the regular separation at anaphase and regular meiosis leading to

Uneuploid varieties have incomplete genomes. Individual chromosome may either be less than the diploid number (*monosomics* and *nullisomic*) or more than the diploid number (polysomic). These varieties revealed marginal irregular meiosis

Triploid varieties are characterized by highly irregular meiosis and very low pollen fertility. Irregular meiosis is the almost common feature of triploids in all plants. These varieties showed high frequency of trivalents which suggests the fair homology between its constituent genome and autotriploid nature of these varieties [17, 18]. Such irregular meiosis has been reported in other natural triploid mulberry varieties also [19, 20]. The most common aberrations observed includes the occurrence of univalent's, laggards, stickiness, precocious movement and in anaphase unequal number of chromosome segregate to the poles which again attribute to irregularities in chromosome pairing and their alignment on equatorial plate. These irregular meiosis leads to formation of aberrant, unbalanced microspore and finally resulted in the reduction of pollen fertility. Formation of such aberrant sporads in

Meiotic behavior was irregular in these varieties. Theoretically tetraploid forms revealed more quadrivalents in meiosis due to the presence of four homologous

Among different chromosomal associations, the bivalents in diploid and uneuploids, trivalents in triploid and quadrivalents in tetraploid were frequent. Majorities of quadrivalents were of ring type and other were chain types.

**10**

**4.4** *Morus latifolia*

*4.4.1 Varieties Kokuso and Icheihei*

The present investigation was carried out with objectives of generating useful information on Studies on basic chromosome number, ploidy level, chromosomal association and configuration and meiotic behaviors of eight mulberry varieties (Genotypes).

The mulberry varieties studied (Genotypes) have unraveled diversity with respect of branching pattern, leaf yield, leaf color, size, lobation, shape, stomatal frequency and size, chloroplasts in the guard cells and trichomes density. The taxa studied were taxonomically distinct. The interaction between genotype and the environment is largely responsible for the diversity observed.

Based on the present findings diploids have 2n = 28, uneuploids have 2n = 30, triploids have 3n = 42 and teteraploids have 4n = 56 chromosomes. Meiosis has been found to be regular with high frequency of bivalents, high pollen stainability and development normal pollen grain in diploids compare to irregular meiosis characterized by the presence of high frequency of trivalents and univalent's, low pollen stainability and aberrant pollen formation in triploids and teteraploids. The reduced pollen fertility has been attributed to various meiotic anomalies. The role of chromosome repatterning coupled with polyploidy (both euploids and uneuploids) structural alternation of chromosomes and mutations in the evolution of the genus *Morus* is suggested.

It may be concluded that more intensive biosystematics studies involving a large numbers of varieties /genotypes of a species definitely throw more light on the phylogeny and systematics of mulberry species. Such information's are highly essential and useful in mulberry improvement programmes.
