Cytological Studies of Desynaptic Stock in Pearl Millet, <i>Pennisetum typhoides</i> (Burm.) S. and H

Abstract

Desynapsis is defined as a condition in which chromosomes pair initially but as the meiotic division progresses, the chromosomes start falling apart. At diakinesis one can see all or most of these lying as unpaired chromosomes. The occurrence of unpaired chromosomes (univalents) is due to the failure of chiasma formation and is considered to be under the control of recessive genes when present in homozygous condition (Riley and Law 1965). Spontaneous or directed mutation of a single gene leads to unpairing of chromosomes which ultimately result in more univalents and proportionally less bivalents. This gene is sensitive to temperature variation and X-rays (Ahloowalia 1969a, Riley and Miller 1966, Sjodin 1970) and thus desynapsis is also the result of interaction between genotype and environment. Thus the stability of this gene has not been established yet. This paper deals with some of the cytogenetic observations recorded on desynaptic plants in pearl millet. Material and methodsDuring the cytological investigations of chromosomal abnormalities in the genetic stocks of pearl millet, BG-32 (Bold grain) was showing a high frequency of univalent chromosomes. Many plants in this genetic stock showed the desynaptic condition of varying degrees. The young panicles of these plants were collected and fixed in alcohol: acetic acid (3:1) for 24 hours, and then smears were made in acetocarmine. The observations were made from the fresh slides and photographs were taken. Pollen fertility on the basis of stainability reaction with potassium iodide (KI) was determined. Seeds per square cm were calculated under selfed and crossed conditions. ResultsIn normal as well as in the desynaptic plants the chromosome number was 2n=14. Normal plants showed 7II (Fig. 1). In desynaptic plants the bivalent variation was from 0-5 bivalents per cell (Table 1 and Fig. 2). The average number of bivalents were 1.934 per pollen mother cell. The univalents present were scattered around without any set pattern. Metaphase I was very irregular. The spindle apparatus was formed but all the chromosomes did not lie along the equatorial plate.

Cytogenetics of Crotalaria VI. Chiasma frequency and position, and univalent behaviour in a (partially) asynaptic mutants of C. juncea

“…Univalents are often found to be randomly distributed at metaphase I (John & Lewis, 1965;Singh et al, 1977;Dhesi et al, 1973). During the present investigation it was observed that the orientation of univalents was either polar or they 69 remained in the equatorial region, depending on the number of bivalents present in the cell.…”

Synaptic variation derived plausible cytogenetical basis of rarity and endangeredness of endemic Mantisia spathulata Schult

“…S1 and Table 2). John and Lewis [13] demonstrated the random distribution of univalents at MI, which was confirmed by Dhesi et al [5] in pearl millet and by Singh et al [37] in mung bean and in Anogeissus sericea var. sericea by Rao and Kumar [34], and recently Sharma et al [35] in Panax sikkimensis.…”

“…These observation draw support from various investigations on Schistocera gregaria [12], Crotalaria juncea [45] and in Phlox drummondii [33], thus confirm the deviant synaptic behavior of M. spathulata. Barring a few reports [5,6,34,35] the natural occurrence of synaptic mutants, particularly in natural populations of higher plants, is a rare phenomenon with little morphological variation to differentiate between the mutant and the normal individual [35]. Synaptic mutations have been reported in natural populations of perennial rhizomatous herbs i.e.…”

Cytogenetics of Tephrosia I. On the differential chromosome pairing in colchiploid stock of Tephrosia wallichii.

“…Tradescantia (Celarier 1955), Datura (Bergner et al 1934), Nicotiana (Clausen 1931), Triticum (Li et al (1945), Hordeum vulgare (Enns andLarter 1960, Sharma andReinbergs 1974), Allium cepa (Koul 1962, Kaul 1975, A. amplectens (Levan 1940), Pennisetum typhoides (Dhesi et al 1973, Singh et al 1977, P. ramosum (Jauhar et al 1971), Godetia (HA kensson 1943, Coleus (Vasudevan et al 1967), Rye grass (Ahloowalia 1969a, b), Solanum vendlandii (Cheenaveeraiah and Krishnappa 1968), Colocasia antiquorum (Krishnan et al 1970), Amorphophallus companulatus (Magoon and Sadasivaiah 1967), Sorghum (Sadasivaiah and Magoon 1965), Avena (Thomas and Rajhathy 1966), Pisum sativum (Gottschalk 1978). Contrary to the long list of desynaptic plants, asynapsis has been reported in only few viz.…”