Cytogenetical Studies in Some Triploid Mulberry Varieties (Moraceae)

Abstract

SummaryThe mulberry is an economically important crop, cultivated for its foliage to rear the silkworm Bombyx mori L. Its chromosome number varies from 2n = 28 to 2n = 308 with ploidy level from x to 22x. In the present investigation, three triploid mulberry varieties, namely, S 41 , S 1635 and BC 2-59 , have been analyzed for detailed meiotic studies. Based on the chromosome configuration and other meiotic behaviour, x = 14 has been considered as the basic number of the genus. Meiosis was highly irregular. Various anomalies, such as the occurrence of two nucleolus, association of single trivalent with nucleolus, unequal separation and precocious movement of chromosomes, laggards, and occurrence of multivalents, have been observed. The low pollen fertility and seed set may be due to genic or physiological causes. Triploid mulberry varieties have higher leaf yield and better nutritive qualities from the point of silkworm rearing (Seki and Oshikane 1959, Sugiyama 1959, Abdullae 1962, Mustafaev 1970, Dzhafurov and Alekperova 1978. Triploid varieties are extensively cultivated in Japan, particularly in its northern parts, for their superior quality of leaves and cold and disease resistance (Hamada 1963, Sugiyama 1959. Tripoloids are occasionally found in the natural population (Hamada 1963). Generally, triploids are obtained by crossing tetraploids with diploids, and for this, tetraploids are first induced and then crossed with diploids. In the mulberry, both natural and induced triploids have been reported (Osawa 1920, Seki 1959, Das et al. 1970, Dwivedi et al. 1989. Many triploid varieties of mulberry are considered superior than diploids in yield and nutritive qualities of the leaf (Seki and Oshikane 1959, Dzhafurov andAlekperova 1978). The cytogenetical information available in triploids is fragmentary and only preliminary observations have been made by earlier workers (Tojyo 1966, Agaev andFedorova 1970). The information on breeding systems and the evolution of different mulberry polyploids are highly useful in evolving elite genotypes required for commercial cultivation. In the present study, an attempt has been made to analyze the meiotic behaviour in three triploid varieties of the mulberry. Key words Materials and methodsThe mulberry varieties used in the present study are S 41 , S 1635 , and BC 2-59 . For meiosis, flower buds of appropriate stages of development were harvested at 9:20 a.m. during sunny days and fixed in 1 : 3 acetic-alcohols for 24 h and preserved in 70% ethanol. Anthers were squashed in 2% acetocarmine stain. Photo-micrographs were taken using a Labomed microscope fitted with a Nikon

Cytomorphological studies of two mulberry varieties (Moraceae)

“…In this variety, the trivalents frequency was high and various types of chromosomal configurations (' >-' '---' and 'v') were observed. Different types of chromosomal configurations found in the present study corroborated the findings of Das et al (1984), Basavaiah et al (1990) and Venkatesh and Munirajappa (2012) in triploid mulberry varieties. Telophase I was also observed (Figure 2e).…”

Comparative Micro-morphological and Karyomorphological Studies in Three Mulberry Varieties (<i>Morus</i> spp.)

“…But in the present study as well as the observations made by others rule out the existence of secondary association of chromosomes in the majority of Morus spp. (Venkatesh 2007).…”

“…For a few Indian species, cytogenetical investigations were carried out by Das et al (1970), Kundu and Sharma (1976), Gill and Gupta (1979) and Venkatesh et al (2013a). Most of the natural species of Morus is diploid with 2n=28 chromosomes, but few are polyploids (Venkatesh 2007). Cytogenetical information available today is confined only to chromosome counts and meiotic behaviour of a few species.…”

Cytogenetic characterization of a triploid mulberry (Morus spp.) cultivar Suvarna-2

“…confirmation of ploidy and chromosome behavior during meiosis of genotypes is very much essential in polyploidy breeding. In mulberry, the ploidy status, size, nature, pairing behavior and segregation of chromosomes during meiosis have been studied by various workers (Osawa, 1920;Sinoto, 1929;Kundu and Sharma, 1976;Gill and Gupta, 1979;Katsumata, 1979;Ogurtsov, 1979;Dandin et al, 1989;Basavaiah et al, 1990;Chakraborti et al, 1999;Munirajappa, 2013 andVenkatesh et al, 2014). In the present study, an attempt has been made to understand the meiotic behavior in a triploid mulberry cultivar Suvarna-2 which is recommended for cultivation in south india (Anonymous, 2015).…”