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DISCUSSION
In all the varieties, the germination percentage was found to be decreased with
increasing doses/concentrations of mutagens in M1. Saha (1968), Rajput (1970), Padavai
and Dhanavel (2004), Singh and Kaul (2005) reported this type of effect of mutagen on
germination percentage in Pisum sativum, Oryza sativa, Triticum aestivum, Glycine max
and Cicer arietinum respectively. Reduction in germination percentage at higher doses of
mutagenic treatments has been explained due to delay or inhibition of physiological and
biological processes, necessary for seed germination which includes enzyme activity
(Kurobane et al., 1979).
The survival percentage also showed decreasing trend with increasing doses/
concentration of mutagens in all the varieties. Bajaj et al. (1970) reported that reduction
in survival might be due to retardation or complete stoppage of metabolic functions as a
result of mutagenic treatments. A considerable decrease in plant survival may be
attributed to the series of events occurring at the cellular level which may affect the
macromolecules and bring about a physiological imbalance in the cells as a consequence
of exposure to ionizing radiation mutagens. Progressive decrease in the rate of plant
survival with the increase in doses of physical mutagens has also been reported by
Sudhakaran (1967) in Vinca rosea.
The growth in terms of plant height, number of tillers etc. was inversely
correlated with the doses of mutagens. According to Mackey (1951), Mikaelson (1968)
production of growth retarding substances and inhibition of DNA synthesis had also
been attributed for the growth inhibition respectively. Such results were also reported by
Khan et al. (2000) in mung bean, Bajaj et al. (1970) in Phaseolus vulgaris. According to
Evans and Sparrow (1961) irradiation induced growth inhibition is basically due to
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genetic loss following the formation of chromosome aberrations. Singh et al. (2000)
reported increase in plant height in urdbean whereas Das and Prasad (1978) have
achieved dose dependent increase or decrease in plant height in M2 generation in
Lathyrus sativus. A linear dependency of seedling height on the dosage of physical and
chemical mutagens have been reported by Mikaelsen et al. (1968), Siddiqe and
Swaminathan (1968) and Wang et al. (1995). A gradual decrease in average number of
branches plant-1 with increasing dose of chemical mutagen over that of control was
reported by Jahangirdar (1975) in Foeniculum vulgare. Joshi (1983) reported that
reduction in number of branches plant-1 due to mutagenic treatment must have taken as a
result of formation of less axillary buds and distribution in auxin formation and
distribution coupled with chromosomal aberration.
In general the average number of panicle per plant decreased with increasing
doses of all the mutagen in all the varieties. It is in accordance with the report by Singh
et al. (2000). Peduncle length also showed decreasing treads with the increasing doses of
mutagens Chatterji et al. (2011) also reported similar trends in Papaver sominifera after
induced mutagenesis.
Dry inflorescence yield and husk yield were also found to be decreased with
increase in doses of mutagen. Which is in consonance with the findings of Lal et al.
(2000). Rajib et al. (2011) reported similar results in Dianthus caryophyllus.
There was a dose dependent decrease in 100 seed weight in all varieties for all the
treatments. Similar results were reported by Sharma (1991) for gamma rays, EMS and
combined treatment on green gram. In majority of experiments, reduction in mean seed
weight in M2 and M3 has been reported (Scossiroli et al., 1966; Singh et al., 2000). The
reduction in mean seed weight may be due to higher frequency of mutations with
persistent negative effects for yield contributing traits. Waghmare and Mehra (2000)
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achieved considerably increased mean seed yield in M3 after gamma ray and EMS
treatments in Lathyrus sativus. The yield, as such, is a complex manifestation of large
number of genes involved in physiochemical processes of the plant system. Induced
mutations can contribute to the physiological efficiency of the plant for grain yield by
generation of more favorable correlations between various yield components (Waghmare
and Mehra, 2000).
Based on study of various morphological parameters, variety GI-1was found to
be more sensitive for mutagenic treatment. Varietal differences were also reported earlier
with respect to mutagen sensitivity in Lathyrus sativus (Nerker, 1977), Lens culinaris
(Sharma and Sharma, 1981), Arachis. hypogea (Mensah and Odadoni, 2007) etc.
Differential response of the varieties to the mutagenic concentration was reported by
Wani et al. (2004) in Lens culinaris.
Analysis of variance has been the most dependable statistical measure to find
the mutagenic effect on the polygenes. Estimation of its parameters viz., genotypic
coefficient of variation (GCV), phenotypic coefficient of variation (PCV), environmental
coefficient of variation (ECV), heritability (h2) and genetic advance (GA) for quantitative
characters of the five varieties of Plantago ovata provided ample evidence that
mutagenic treatments could alter mean values and create additional genetic variability for
quantitative traits. According to many workers, it is useful in designing effective
breeding programmes.
In M1 and M2 generations for all the varieties and all the mutagenic treatments,
genotypic coefficients of variability (GCV) were high for seed yield and husk yield.
High GCV indicate that variability was primary due to genotypic difference. For
maximum traits, PCV were found to be greater to that of GCV, indicating there by the
importance of environmental factors, which is in consonance with finding of Singh and
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Ghose and Gulati (2001), Mahla et al. (2003) in Indian mustard.
Variability alone is not much helpful in determining the heritable portion of
variation. The amount of advancement to be expected from a selection (for mutated
population) can be obtained by study of genotypic coefficient of variation along with
heritability (in broad sense).
In the present study in general, plant height, panicle/plant, and husk yield/plant
showed higher values for heritability and genetic advance. High heritability and genetic
advance for a character would indicate the predominance of additive gene action on the
trait and as such trait is likely to respond effectively to phenotypic selection (Johnson et
al., 1955; Sheeba et al., 2003). Low genetic advance with moderate heritability was
observed for several traits. Which showed that traits are most probably, governed by non
additive gene action.
The studies on relationship among yield and various morphological and quality
characters of the plant population which influence yield and quality are of great value
indeed, furnishing the plant breeder with an easy and fairly reliable means of isolating
high yielding and better quality genotypes from the breeding material. In Plantago, husk
yield plant-1 is considered as important morphological trait which has direct economical
value. The estimates of the correlation coefficients among the various characters in all
the varieties in both generations (M1 and M2) indicate that husk yield is more
significantly correlated with the plant height, peduncle length, seed weight than that of
other traits.
Positive and significant correlation among these traits indicates that with an
increase in these characters, husk yield could be increased.
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Cytology: Cytological studies indicates that mitotic index increases with increasing
doses of the mutagens, which may be as a result of accumulation of C-metaphase
configuration at zero hour recovers (Badr, 1983). Dividing cells also showed different
kinds of cytological anomalies.
Disturbed chromosomes may be either due to, hindrance of
prometaphase chromosome, or due to the effect of the tested Mutagens on spindle
apparatus, by causing partial inhibition of mitotic apparatus. The inactivation by
mutagens preventing them from being inserted in the spindle fibers, affecting the normal
kinetics of the cellular division (Mukherjee et al., 1990). Induction of disturbed stages
indicates that mutagen may be an eugenic which inhibited the spindle formation and
caused c-mitosis in metaphase (disturbance). The induction of laggard chromosomes
could be attributed to irregular orientation of chromosomes (Patil and Bhat, 1992). The
occurrence of laggards indicated that mutagen completely or partially affect the spindle
apparatus. Presence of lagging chromosome indicates complete failure of spindle
apparatus. Delayed terminalization, stickiness of chromosome ends and failure of
chromosome movements have lead to laggard chromosome. Magoon et al. (1958) also
support the above view but they specified that this could be due the change in homology
of the paired chromosome.
Considerable frequencies of bridges were also observed in anaphase and
telophase stages after all the treatments. It may be attributed to general stickiness of
chromosomes (Haliem, 1990) or due to the formation of dicentric chromosomes as a
result of breakage and reunion (El-Khodary et al., 1990). Chromosomal fragments were
a type of abnormalities also found to be observed during mitotic cell division after the
treatments. The induction of these abnormalities indicates the mutagenic capacity and
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clastogenic action of the mutagens on the chromosome which is now regarded to affect
the chromosomal DNA (Grant, 1978 and Chauhan and Sundaraman, 1990).
Unseparated anaphase (delay of separation) was observed which could be due to
stickiness (Abdel-Hamied, 1995). Stickiness was more frequent chromosomal
abnormality, found at all the doses of mutagenic treatments, in all the varieties.
Stickiness has been attributed to the entanglement of inter-chromosomal chromatin fibers
that leads to sub-chromatid connection between chromosomes (Klasterska, 1976). The
presence of stickiness in the chromosomes reflected highly toxic effects, it was
irreversible and might lead to cell death ( Liu et al., 1995). The mutagens might have
affect the physiological properties of DNA and proteins, and form complexes with
phosphate groups of nucleotides of the nucleic acids causing inhibition in protein
synthesis (Karlik et al., 1980). In contrast, Patil and Bhat (1992) suggested that,
stickiness is a type of physical adhesion involving mainly the proteinacious matrix of
chromatin material.
The results also indicate that mutagenic treatments induced large range of
chromosomal abnormalities in PMCs of all the varieties. Out of these anomalies,
chromosomal stickiness was most common; this may be due to depolymerization of
nucleic acid caused by mutagenic treatment or due to partial dissociation of nucleioprotein and alteration in their pattern of organization (Bhat et al., 2005). Fragmentation
was more frequently reported in γ-rays treatments. Breakage of chromosomes due to
gamma radiation treatment was reported earlier by New Combe (1942).
Sax (1941) thought that the breaks induced in chromosomes after irradiation
might be due to a change in molecular constituents of chromosomes. Higher exposure
which caused a permanent breakage effects, had been, invariably lethal to the cell.
Dubnin (1964) opined that the frequency of breakage must be much higher than visible
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after irradiation, this being attributed to a single break followed by the rejoining of the
broken ends, leaving no indication of the original breakage. Sparrow (1966) concluded
that if irradiation was carried out at the early interphase stage, the degree of reunion
would be increased and this would result in bridge and ring formation.
Multipolar movement of chromosomes, unorientation of univalents and bivalents
and appearance of lagging chromosomes, suggested the spindle disturbances due to
mutagenic treatments. Presence of acentric lagging fragments and micronuclei indicated
that the former has given rise to the latter, leading to the degeneration as has already
been reported by earlier workers (Biswas and Bhattacharya 1975). Multivalents,
observed at metaphase I may be the outcome of complex translocation. Syndiploid PMCs
or PMCs with extra chromosomes were also observed which are in agreement to report
of Raghuvanshi and Singh (1979) in Impatiens balsamina. Presence of acentric lagging
fragments and micronuclei indicated that the former has given rise to the latter, leading
to the degeneration as has already been reported by earlier workers(Biswas and
Bhattacharya 1975).
The chiasma frequency per Chromosome however was decreased continuously,
as the dose rate was increased. In Phalaris, Prasad and Godward (1969) also noted that
there was slight reduction in the number of chiasmata per cell due to irradiation. Patil
(1968) noted that gamma rays induced aneuploidy in Arachis hypogea.
Conclusively, the results show that though the percentage of chiasma frequency
per chromosome, continuously decreased, as the dose rate was increased but pollen
fertility remained unaffected in treated plants, showing the normal meiotic behaviour of
chromosomes.
The karyotype analysis, varieties of Plantago ovata showed the presence of
diploid chromosome number 2n =8. Karyotypes are one of the parameters by which
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authentic identification of a specimen is possible, since varieties usually possess the same
chromosome numbers and major chromosomal differences do not exist among different
varieties of a species. The karyotype of all the considered varieties showed almost
similar trends but mild variation is also exist. In addition to similarity in the karyotype,
TF% and arm ratio values of each chromosome pair were not significantly different
conferring that they belong to the same species and have a close relationship. Although,
on the basis of morphological criteria, varieties can be distinguished from each other but
at the chromosomal level, both remain undistinguished. These facts indicate that external
morphological variations in this species occurred independently of the chromosome
variations and that the morphological differences between varieties are caused by several
genes. These findings further indicate that all varieties differ morphologically but
cytotaxonomically have no marked variation (Kolar, 2012).
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