The combined effect of gamma ray-induced mutations and advancements in agronomic practices has led to significant increases in grain yield per hectare over the past 50 years
(Borlaug, 1983). The wide range of variation observed for all the quantitative traits suggests that there is sufficient variability in these characters to exploit. Our study demonstrated that the application of physical mutagens gamma rays, led to significant improvements in various growth traits of black gram plants in the M4 generation. Among the different dose of gamma rays, a gradual increase of mean values was observed up to 300Gy when compared to control in M
4 generation. Beyond the optimal dose of 300Gy mutagen showed decreasing of mean values of quantitative traits (Table 3). Variability analysis showed an increase all the traits. The analysis of variance (ANOVA) revealed the significance degree among the treatment and control. The wide range of variation was recorded at 300Gy and Control variety compared to other two treatments. Those ranges are
Viz., plant height (38.6 and 36.4cm), day to 50 percent flowering (37.2 and 40.1 days), Number of pods (44.1 and 37.2), days to maturity (72.5 and 75.35 days) and yield per ha (1325 and 1056 Kg). The similar kind of wide range was observed more in the treatment 300Gy in earlier generation of M
2 and M
3 in the similar population. These findings suggest that the mutagenic treatments induced genetic variability in the black gram genome, which in turn contributed to the observed improvements in growth and yield characteristics as similar reported in chickpea in M
2 generation of Chick pea (
Wani and Anis, 2001). In the study by
Odeigah et al., (1998), the researchers investigated the effects of ethyl methane sulfonate (EMS) and gamma rays on various quantitative traits in cowpea during the M
2 generation. Their findings indicated that the treatments led to significant improvements in several traits compared to the control. Specifically, plant height, the number of peduncles per plant, the number of pods per plant, the weight of 1000 seeds, and the number of seeds per pod all showed increased values due to the influence of EMS and gamma rays. This suggests that these mutagenic treatments had a positive impact on the growth and yield characteristics of cowpea, highlighting their potential for enhancing crop performance.
Phenotypic and genotypic coefficient of variation of quantitative traits (PCV and GCV) are parameters for selecting genotypes possessing higher yield and growth traits depends largely on the existence and exploitation of genetic variability of the fullest extent. The estimates of range, phenotypic and genotypic coefficient of variability was presented in Table 3. The phenotypic and genotypic coefficient of variation expressed in terms of per cent was comparatively high at 200 Gy of gamma rays than control
viz., plant height (35.98; 37.85), day to 50 per cent flowering (24.50;24.59), Number of pods (85.89;85.98), days to maturity (140.21;141.05) and yield per ha (9.81;9.87). The PCV and GCV values were significant at P-0.05 and P-0.01 level, which positively correlated with their mean values of quantitative traits. The highest genetic coefficient of variation (GCV) was observed for the number of pods per plant, indicating that simple selection for yield may be more advantageous compared to focusing on individual yield components. Previous research by
Kumar (2008) also reported high GCV for traits such as the number of pods per plant, number of seeds per pod, and 100-grain weight in peas. These findings are consistent with the current study and suggest that phenotypic selection for these traits could be highly effective in improving yield.
Heritability (h
2), genetic advance (GA %) as percent of mean of quantitative traits. The wide range of variability was exhibited by heritability and genetic advance as per cent of mean. The heritability and GA as percentages of mean were high almost all dose of gamma ray treatment (Table 3). However, 300Gy of gamma rays revealed highest values of heritability with genetic advance as per cent of mean for plant height (79.2; 39.46), day to 50 per cent flowering (60.1; 54.86), Number of pods (78.2; 95.20), days to maturity (44.2;68.23) and yield per ha (79.1;91.66).
The study revealed high heritability with high genetic advance as percent of mean in all the quantitative traits at 300Gy of gamma rays in M
4 generation. When a trait shows high heritability coupled with high genetic advance, it suggests that the trait is largely influenced by additive genetic effects. In other words, the effects of individual genes on the trait are cumulative and not masked by interactions with other genes (non-additive gene action). This additive nature makes the trait more amenable to selection because the genetic progress achieved through selective breeding is likely to be more predictable and effective
(Unche et al., 2008). Kalpande et al., (2008) recorded high heritability for plant height, seed cotton yield /plant, number of bills/plant, number of sympodia/plant and average boll weight in F
3 generation of cotton. It indicated that predominance of additive gene action.
Among the 20 mutants evaluated in M
5 generation, the mutants BG-200Gy-P07 and BG-200Gy-P24 recorded for early 50% flowering (38 and 42 days). The mutant BG-200Gy-P07 was found to be observed as dwarf with plant height of 38.5 cm, however there was no significant difference observed in the remaining lines. Mutant lines BG-300Gy-P93 recorded more number of branches per plant (68.5nos.) followed by BG-300Gy-P42 (62.4nos).The mutant BG-300Gy-P33 and BG-300Gy-P42 were found to be observed as early maturing mutants (66 and 67 days). The mutants BG-300Gy-P41and BG-300Gy-P42 recorded with maximum yield of 1500 kg/ha and 1445kg/ha (Table 4). In this study 20 mutants were screened for MYMV resistance by infector row method using Co5 as susceptible check and categorization was done (
Gantait and Kantidas, 2009).
Bandi (2018) likely provided valuable insights into the genetic resistance of blackgram to MYMV, so aligning with the results suggests that methods and interpretations are sound. The results showed that the mutants PKT-BG-300Gy-P41, PKT-BG-300Gy-P42, PKT-BG-400Gy-P21 and PKT-BG-300Gy-P16 were resistant to MYMV with disease severity percentage between 0.01 to .0.052. Whereas the mutants PKT-BG-300Gy-P28 (5.3), PKT-BG-300Gy-P88 (5.3) and PKT-BG-300Gy-P43 (4.3) were found to be moderately resistant with disease severity percentage between 4 to 6. The overall performance of the mutants showed resistant nature even MYMV was in peak epidemic area in the particular season in the region.
Murugan and Nadarajan (2012) reported that the resistance to MYMV is dominant and suggested that the presence of a single dominant allele is sufficient to confer resistance to the disease.
Verma and Singh (1986) reported that the resistance to MYMV is recessive and implies that two recessive alleles are needed for the expression of resistance. The observed phenotypic expressions of MYMV disease incidence among the F
1 progeny revealed inconsistencies with the expected inheritance patterns, as reported by
Vadivel et al., (2023).