Dry seeds of three chickpea genotypes having different seed coat colours viz; Noor 91 (white), Punjab 91 (brown) and C 141 (black) were treated at 40, 50 and 60 Kr separately and with gibberellic acid (GA3) for studying the effects on 100-seed weight, grain yield, biological yield, harvest index, days to flowering and maturity in M1 generation. Highly significant (p<0.01) variation within genotypes, treatments and also for their interaction was observed for all the characters. Statistically higher 100-seed weight was observed with the combine treatment in the three genotypes as compared with gamma irradiation. Combine treatment normalized the grain yield in Noor 91, while decreased in Punjab 91 however, stimulation was recorded at 40 and 50 Kr in C 141. Stimulation in biological yield was recorded at 40 Kr with the combine treatment in Noor 91 and C141. Harvest index decreased with gamma irradiation in the three genotypes while, stimulation was recorded in C 141. Days to flowering and maturity increased with gamma irradiation however, with combine treatment these values were reduced.
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Mutation breeding is now widely used for inducing genetic changes and creation of new genetic resources, particularly in crops that are not easily amenable to improvement through conventional techniques (Awan, 1991). It is well established that mutagenic agents are effective for inducing genetical changes in treated population (Kalia and Gupta, 1988a, b). Notwithstanding, little natural variability in chickpea for conspicuous morphological and physiological characters, several workers have attempted for induction of mutation using either physical or chemical mutagens for evolving new genotypes (Hassan and Khan, 1991; Shamsuzzaman and Shaik, 1991). Radiation, therefore, appears to be a useful tool in plant breeding and genetics. The primary objectives of mutation are to enhance mutation frequency, widen the mutation spectrum and realize directed mutagenesis.
Gamma radiation in combination with other chemical mutagens is applied for widening the frequency and mutation spectrum for extra genetic variability. Effect of gamma radiation is changed with the radio protective effect of gibberellic acid. It has been established that the impaired growth due to gamma irradiation can be restored by exogenous application of gibberellic acid. Gibberellic acid serves manifold growth related functions in plants by enhancing replication, transcription and different enzymatic systems (Zhebrak, 1989; Ali and Ansari, 1989; Arora et al., 1989). It brightens the scope for increasing both the frequency and spectrum of mutation. Therefore, it was planned to determine the effectiveness of gamma irradiation and efficiency of gibberellic acid to modulate the radio sensitivity for various morphological characters.
Materials and Methods
Dry seeds were exposed to gamma irradiation at doses of 10, 20, 30, 40, 50, 60, 70, 90 and 110 Kr to 1000 seeds for each treatment in three genotypes at Nuclear Institute for Food and Agriculture (NIFA), Peshawar. A part of the irradiated seeds after one hour of soaking under continuous aeration, were subjected to 0.5 mM aqueous solution of gibberellic acid for 16 hours with constant shaking. Non irradiated seeds soaked in water were kept as control in the case. After treatment seeds were washed in running tap water and then were dried on blotting paper. On the basis of seedling performance doses of 40, 50 and 60 Kr were selected for inducing genetic variability on large scale. Treated along with control seeds were sown in split plot design with three replications at Barani Agriculture Research Institute (BARI) Chakwal in 1995 to raise the M1 generation. Data on 20 consecutive plants from the middle row was appropriately recorded for various characters.
RESULTS AND DISCUSSION
The analysis of variance for the effect of different doses of gamma irradiation separately and with the post mutagenic application of gibberellic acid on various plant characteristics in M1 population of chickpea is presented in Table 1. It indicates highly significant variation within genotypes and treatments for all characters. The genotype-treatment interaction was also highly significant for all the characters. It reflects highly inconsistency in sensitivity of genotypes for all the characters across various treatments.
100-seed weight decreased significantly with an increase in gamma irradiation (Table 2). In the previous research, similar observations for this character was recorded in chickpea (Rao, 1988), in mungbean (Khan, 1984) and in Pennisetum (Aslam et al., 1985). However, heavier seeds were produced with the application of GA3. This increase in 100-seed weight may be due to the radio protective effects of GA3 and enhancement of template activity. The grain yield reduced significantly at various levels of irradiation. Similar results for this character was obtained in various crops; in chickpea (Mahto et al., 1989), in lentil (Eser et al., 1991; Tripathi and Dubey, 1992), in Pennisetum (Aslam et al., 1985), in Cajanus cajan (Kumar and Sinha, 1989) and in Phaseolus vulgaris (Svetleva and Dimeva, 1991). However, with the application of GA3 grain yield increased significantly at 40 and 50 Kr and decreased at 60 Kr. Grain yield decreased significantly or non-significantly with gamma irradiation in the three genotypes as compared to their respective controls. However, the response of genotypes varied greatly at different doses. Genotypic differences due to various gamma irradiation were also observed by Mahto et al. (1989) in chickpea and Aslam et al. (1985) in Pennisetum. Application of GA3 had changed the effects of gamma irradiation significantly in the three genotypes except at 60 Kr in Punjab 91 indicating the possibility of increasing the variability for grain yield in chickpea.
Both the mutagenic treatments decreased the biological yield significantly as compared to their respective controls.
|Table 1:||Mean of Squares for different characters of M1 generation in chickpea genotypes.|
|** 0.01 probability highly significant|
|Table 2:||Effect of gamma irradiation separately and with gibberellic acid on various characters in M1 generation of three chickpea genotypes.|
The irregular response of biological yield with gamma irradiation may be due to the kind and extent of biological damage, while the consistent decrease in biological yield may be accounted for the protective and repairing activity of GA3. Table 2 showed that in the three genotypes biological yield decreased inconsistently at various gamma irradiation dosages. Post mutagenic application of GA3 significantly changed the biological effects of gamma irradiation either in positive or negative direction. This suggests that the treatment of GA3 could be useful for inducing extra variability.
Gamma irradiation decreased the harvest index significantly with both treatments as compared to their respective controls. Contrary to this, Yousaf et al. (1991) have recorded little variation in harvest index percentage under different gamma irradiation in lentil. The change in the results might be due to different genotypes and places of experimentation. However, application of GA3 significantly increased the harvest index percent at 40 and 50 Kr by modulating the effects of gamma irradiation.
Highly significant interaction between genotype and treatment indicate varied response of harvest index towards the various doses of gamma irradiation. Gamma irradiation decreased the harvest index differently at all the treatments in the three genotypes as compared to control. However, with the application of GA3 stimulation in harvest index over control was recorded in C141 genotype. The results of the present study further reveal that the application of GA3 has changed the effects of gamma irradiation, which might increase the variability for this character in chickpea.
Gamma irradiation significantly and progressively increased the number of days to 50 percent flowering at various levels of irradiation as compared to control. Late flowering in M1 generation as compared to control have also been reported in pea (Khan et al., 1990; Amjad et al., 1993), french bean (Svetleva and Petkova, 1992). However, a non-significant delay in flowering with gamma irradiation was reported by Yousaf et al. (1991) in lentil. However, post mutagenic treatment with GA3 decreased the time to 50 percent flowering.
Highly significant interaction of varieties and doses indicate that the response of varieties to various levels of irradiation is quite variable. The results show a relative delay in 50 percent flowering over control in the three varieties. Application of GA3 reduced the number of days to 50 percent flowering at different intensities of gamma irradiation. This decrease in time could be due to the repairing process of GA3, which might bring the population to a physiological state for early flowering.
Gamma rays consistently delayed in crop maturity with an increase of radiation intensity as compared to control. The results obtained in this study are in line with those of Hassan et al. (1988) in wheat, Tripathi and Dubey (1992) in lentil and Kumar et al. (1993) in pea. Post mutagenic application of GA3 decreased the time to crop maturity.
A linear increase in time to crop maturity was recorded with gamma irradiation in the three genotypes as compared to control. However, with GA3 treatment less number of days were taken to maturity at various levels of irradiation in the three genotypes. The application of GA3 modulated the effects of gamma irradiation either in positive or negative direction. This may leads to the induction of new genetic variation for different characters and widens the germplasm pool. In a breeding programme extent of genetic variability is more important than the total variability. Post mutagenic application of GA3 may prove to be useful in widening the genetic spectrum and consequently the selection of new genotypes with better genetic architecture in regards with the yield improvement in chickpea.
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