Analysis of variance
The analysis of variance indicated that the variation due to genotypes was significant for days to 50% flowering and maturity and pods/plant. The variation due to treatment (EMS) was significant for all the characters-germination, survival, seedling height, days to 50% flowering, plant height at maturity, pods/plant, seeds/pod and 100-seed weights. The genotypes x doses interaction was significant for the characters-seedling height, pods/plant and the seeds/ pod (Table 1). These results were similar to the previous findings of
Dinkar (2020).
Mean performances in M1 generation
In the present investigation, the per cent germination decreased with increasing the concentrations of mutagen in both varieties. Nevertheless, it varied depending on the variety. A more significant reduction in germination compared to the control was observed at higher concentrations in both varieties. The germination percentage was the highest in controls of both the varieties (94.50%) in
Kashi Nandini and (94.0%) in
Kashi Uday. The lowest germination percentage was at higher concentrations in the varieties, 46.5% in
Kashi Nandini and
Kashi Uday at 0.40% EMS, indicating a more biological injury to seed germination with an increase in concentrations of EMS. The maximum reduction in germination over control occurred at 0.40% EMS, while the minimum reduction was at 0.01% EMS in both varieties (Table 2). A similar inhibitory effect on seed germination was evident in several earlier reports of
(Ciftci et al., 2006) in pea. A progressive decrease in the survival till maturity was evident with an increase in concentrations of mutagen (EMS) in both varieties. The decrease in survival was more (40.5 and 41.0% in
Kashi Nandini and
Kashi Uday, respectively) at 0.40% EMS concentration compared with both the controls 85.5% in
Kashi Nandini and 85.0% in
Kashi Uday (Table 2). These findings are in close agreement with the earlier reports of
Sharma et al., (2010) and
Govardhan and Lal (2013) in field pea (
Pisum sativum L). The rapid infusion of chemical mutagens and their ability to produce damage to genetic material could be one of the causes of reducing survival percentage.
Lethal dose (LD50)
The LD
50 value varies with biological materials, nature of treatment and subsequent environmental conditions
(Babaei et al., 2010). The LD
50 values were at 0.40% EMS in both the varieties based on germination percentage (0.378% in
Kashi Nandini (Fig 1) and 0.376% in
Kashi Uday (Fig 3). The LD
50 values based on survival percentage were 0.328% in
Kashi Nandini (Fig 2) and 0.336% in
Kashi Uday (Fig 4). The LD
50 values vary from genotype to genotype, depending on the differences in their genetic constitutions, same results were also reported by
Karthika and Laxmi (2006) in Soybean,
Jain and Khandelwal (2008) in mungbean.
Pollen sterility
An increase in pollen sterility in correspondence with the increase in EMS concentrations was evident in both varieties. The mutagenic treatments caused a high level of sterility in the M
1 generation of both varieties compared to control. The minimum per cent pollen sterility was 1.79 in
Kashi Nandini and 2.19 in
Kashi Uday (Plate 1). The maximum pollen sterility was 40.49 and 38.67% in
Kashi Nandini and
Kashi Uday, respectively, observed at higher concentrations (0.40% EMS). Higher doses of chemical mutagen (EMS) were more effective, showing an inhibitory effect on pollen fertility (Plate 2 and 3), which is in tune with the results of
Satpute and Fultambkar (2012) and
Sangle et al., (2011) in red gram.
Mean performance for quantitative characters in M1 generation
In the present experiment, the response of the two varieties of garden pea was variable for the seedling height at different concentrations of EMS (Table 2). Seedling height was the highest in controls. At concentrations, 0.05% and 0.20% EMS, the seedling heights were 10.4 cm and 10.3 cm, respectively, above the mean (9.9 cm) and the lowest value observed at 0.10% EMS (8.9 cm) in
Kashi Nandini. At the same time, in
Kashi Uday, the highest seedling height was at 0.01% EMS (9.91 cm) and the lowest at 0.40% (9.4 cm).
Govardhan and Lal (2013),
Umavathi and Mullainathan (2015) and
Deshpande and Malone (2019), obtained similar results on seedling height. Plant height at maturity had the highest value at 0.20% EMS (58.2 cm) above the control (57.7 cm) and the lowest value at 0.40% EMS (40.3 cm) in
Kashi Nandini (Table 3).
Kashi Uday showed the highest plant height at 0.2% EMS (59.2 cm), also above the control (57.9 cm) and the minimum at 0.40% (39.2 cm).
Bolbhat and Dhumal (2009) in horse gram reported similar results on plant height. Days to 50% flowering and maturity showed invariably delay in all the mutagen treated populations of both varieties (Table 3). The maximum delay in days to 50% flowering was at higher concentrations 0.30 and 0.40% EMS in both the varieties and the minimum days to 50% flowering was in controls. Late flowering might be due to insufficient production of hormones required for flowering (
Tambe 2009). Treatments with higher concentrations took the maximum days to maturity. Days to maturity was maximum at 0.40% EMS (97 days in
Kashi Nandini and 97.5 days in
Kashi Uday), while the minimum was in controls, 79 84 days in
Kashi Nandini and
Kashi Uday, respectively (Table 3). These results were similar to
Dhanavel et al., (2008). EMS at higher concentrations showed a decrease in pods/plant and seeds/pod in both varieties, the lowest at 0.30 and 0.40% EMS. Treatment with 0.2% EMS showed more pods per plant in
Kashi Nandini and was above the control. In
Kashi Uday, 0.2% of EMS exhibited a greater number of pods per plant, which is a close agreement with the findings of
Mullainathan and Umavathi (2018),
Dhanavel et al., (2008).
The seeds/pod were the highest in controls (6.5 and 6.75 in
Kashi Nandini and
Kashi Uday, respectively). Among the treatments, the seeds/pod were the highest at 0.10% EMS followed by 0.05% EMS. The minimum number of seeds/pods was at higher concentrations, 0.30 and 0.40% EMS in
Kashi Nandini. In the case of
Kashi Uday, the seeds/pod among treatments was the highest at 0.05% EMS, followed by 0.10% and 0.15% EMS, while the minimum was at higher concentrations, 0.30 and 0.40% EMS. The controls registered the highest 100-seed weights. The 100-seed weights were the highest among the treatments with 0.20% EMS, followed by 0.05 and 0.15% EMS. The lowest 100-seed weights were for the highest concentrations 0.30 EMS and 0.40% EMS in
Kashi Nandini. At the same time, in
Kashi Uday, the 100-seed weights had the highest value at 0.20% EMS (31.7), followed by 0.10% EMS (30.8),0.15% EMS (30.5) and 0.01% EMS (29.6); the lowest values recorded at 0.30% EMS (27.0) and 0.4% EMS (26.0) (Table 4). Similar results of decreasing 100-seed weights at higher concentrations support the findings of
Biradar (2004).
Frequency of chlorophyll mutants
The frequency of occurrence of chlorophyll mutants increased with increasing concentrations of EMS (Table 5). Albino mutants were more frequent than the other three chlorophyll mutants, Viridis, Xantha and Chlorina (Plate 4). In both
Kashi Nandini and
Kashi Uday, the high concentration (0.2% EMS) induced a high frequency of chlorophyll mutants (2.143%) and (2.105%), respectively, whereas the lowest frequency of chlorophyll mutants was at 0.1%EMS, 1.563% in
Kashi Nandini and 1.714% in
Kashi Uday. In the two varieties,
Kashi Uday showed the highest mutation frequency. The two varieties of garden pea differed in their response to EMS concerning the frequency of chlorophyll mutations, which was in agreement with Basvaraj (2002) in soybean and
Dhulgande et al., (2010) pea conclusively stated that various concentrations of mutagenic treatments had independent responses towards the frequency and spectrum of chlorophyll mutations.
Mutagenic effectiveness of EMS for chlorophyll mutations
The effectiveness of chlorophyll mutations was the maximum at 0.10% EMS (2.604) and the minimum at 0.20% EMS (1.785) in
Kashi Nandini. On the other hand, in
Kashi Uday, 0.10% EMS (2.857) showed the maximum mutagenic effectiveness, while the minimum was at 0.20% EMS (1.754), indicating that 0.10% EMS is the most effective in inducing chlorophyll mutants in both varieties, followed by 0.15 and 0.20% EMS. The mutagenic effectiveness of EMS decreased with an increase in the concentrations of mutagen in both the varieties (Table 5), which agreed with the findings of
Sharma et al., (2010).
Mutagenic efficiency based on pollen sterility and per cent lethality
The mutagenic efficiency based on pollen sterility was the maximum at 0.05% EMS (1.60), while the minimum was at 0.4% EMS (0.24) in
Kashi Nandini. In
Kashi Uday, the efficiency of mutagen was the maximum at 0.05% EMS (0.72) and the minimum at 0.4% (0.26), indicating that in both varieties, the mutagenic efficiency differed at different concentrations of EMS. Also, mutagenic efficiency decreased at higher concentrations of EMS (Table 6), which aligned with
Kousar and Babu (2010) reporting the highest mutagenic efficiency at lower doses. The mutagenic efficiency based on per cent lethality was the maximum at 0.30 and 0.40% EMS (0.714), while the minimum was at 0.05% EMS (0.543) in
Kashi Nandini. In
Kashi Uday, the highest efficiency of mutagen was at 0.4% EMS (0.833) and the minimum was at 0.05% EMS (0.549). The results from the present experiment indicated that in both the varieties, the efficiency of chemical mutagen (EMS) based on the lethality in M
1 generation showed an increase with increasing concentrations of mutagen (Table 7), which was in agreement with
Sharma et al., (2010) and
Ariraman et al., (2015).