Gamma irradiation effect on germination and quantitative traits in M1 generation of sesame (Sesamum indicum L.)

Introduction

Sesame (Sesamum indicum L.) is one of the oldest known oilseed crops, domesticated nearly 3,000 years ago, and believed to be the first oil used by humans. It is often referred to as the "Queen of Oilseeds" and is considered an orphan crop due to the limited research attention it receives. However, in the last two decades, the demand for sesame has increased owing to its high-quality oil, rich protein content, antioxidant compounds, and adaptability to extreme climatic and soil conditions (Myient et al., 2020) [21] . Sesame oil consists of approximately 85% unsaturated and 15% saturated fatty acids. Among the unsaturated fatty acids, linoleic acid (~46%) and oleic acid (~38%) are predominant, while palmitic acid (~12%) and stearic acid (~4%) make up the saturated portion. The high content of unsaturated fatty acids in sesame oil provides various health benefits and is believed to reduce the risks of cardiovascular diseases, cancer, and damage to the brain and liver. Globally, sesame is consumed in the form of processed oil (65%) and whole grain (35%) (Teklu et al., 2022) [36] . Most of the yield improvement efforts in sesame have been carried out using conventional breeding methods by utilizing the natural variability present in the germplasm. However, the available genetic variability is often insufficient to isolate highly desirable genotypes. As a result, the progress in yield improvement through conventional breeding has been limited. In such a situation, induced mutagenesis serves as a valuable alternative or supplement (Brock, 1971) [7] to enhance variability in quantitative traits. At present, plant breeders have access to a wide range of physical and chemical mutagens that can induce genetic variation when applied effectively. Among these, physical mutagens such as ionizing radiation have been frequently and successfully used to create variability in several crop species, including sesame (Saha and Paul, 2017) [32] . Mutation breeding has proven to be a useful technique for generating new and additional variation in both qualitative and quantitative traits. In this context, the present investigation was conducted to study the effect of gamma irradiation on quantitative traits to induce variability in three sesame genotypes, namely GT-10, TKG-22, and Gophya Local.

Materials and Methods

The experimental material used in the present investigation included three sesame genotypes, namely GT-10, TKG-22, and Gophya Local. Dry, uniform seeds of all three varieties were exposed to gamma radiation doses of 400Gy, 500Gy, 600Gy, and 700Gy at the Bhabha Atomic Research Centre (BARC), Trombay, Mumbai. Untreated seeds of each variety were maintained as control. The treated and control seeds were sown in a field experiment laid out in a Randomized Block Design (RBD) with five replications. Row-to-row and plant-to-plant spacing of 30 cm and 10 cm, respectively was maintained. All recommended agronomic practices and plant protection measures were followed uniformly across all treatments. The objective of this study was to assess the impact of gamma irradiation on seed germination (%) and a range of quantitative traits in the M 1 generation, including days to 50% flowering, days to maturity, plant height, number of branches per plant, number of capsules per plant, capsule length, number of seeds per capsule, 1000-seed weight (g), and seed yield per plant.

Results and Discussion

Physical mutagens can induce various types of alterations in biological materials during the M 1 generation, such as physiological injury, point mutations, and chromosomal aberrations. According to Gaul (1970) [11] , the extent of biological damage may serve as an indicator of the mutagenic effect. The impact of gamma rays on germination percentage at doses ranging from 400Gy to 700Gy in the three sesame genotypes (GT-10, TKG-22, and Gophya Local) is presented in Table 1. Similarly, the effects of gamma irradiation on quantitative traits such as days to 50% flowering, days to maturity, plant height, number of branches per plant, number of capsules per plant, capsule length, number of seeds per capsule, 1000-seed weight (g), and seed yield per plant were studied for all the radiation treatments. The results for these traits are shown in Tables 2,3, and 4 for genotypes GT-10, TKG-22, and Gophya Local, respectively.

Effect of different doses of gamma rays on germination in M1 generation

The effect of various doses of gamma rays on germination in the M 1 generation is shown in Table 1. The data indicated that germination under laboratory conditions was reduced at all gamma ray doses in the GT-10, TKG-22, and Gophya Local genotypes compared to their respective controls. The greatest reduction in laboratory germination for genotype GT-10 was recorded at the 700Gy dose (28.40%), followed by 600Gy (37.80%), 500Gy (55.40%), and 400Gy (73.00%) compared to its control (92.80%). In genotype TKG-22, the maximum reduction was seen at 700Gy (30.20%), then 600Gy (44.00%), 500Gy (53.60%), and 400Gy (76.80%) compared to its control (94.80%). For genotype Gophya Local, the highest reduction was at 700Gy (33.80%), followed by 600Gy (51.40%), 500Gy (61.60%), and 400Gy (76.40%) compared to its control (93.40%). Under field conditions, the lowest germination in genotype GT-10 was recorded at 700Gy (26.65%), followed by 600Gy (35.82%), 500Gy (53.57%), and 400Gy (71.18%) compared to its control (90.43%). For TKG-22, the maximum reduction in field germination was observed at 700Gy (28.12%), then 600Gy (42.02%), 500Gy (51.10%), and 400Gy (74.73%) compared to its control (92.73%). In Gophya Local, the highest reduction was at 700Gy (30.28%), followed by 600Gy (49.10%), 500Gy (59.33%), and 400Gy (73.88%) compared to its control (90.33%). The LD 50 was found at 500Gy dose for GT-10 and TKG-22 genotypes, and at 600Gy dose for Gophya Local genotype. In this study, the effects of gamma rays on germination in the M 1 generation of three sesame genotypes were recorded, showing that germination percentage decreased with increasing doses in all genotypes tested. Raja Ramadoss et al., (2014) [27] reported similar results of reduced germination with higher gamma ray doses in sesame. The genotype GT-10 showed 55.40% germination at 500Gy, TKG-22 showed 53.60% at 500Gy, and Gophya Local showed 51.40% at 600Gy, indicating that LD 50 was reached at 500Gy for GT-10 and TKG-22 and at 600Gy for Gophya Local. These findings align with previous studies such as Kumari et al. (2016) [19] who recorded LD 50 between 450-600Gy for LKT-4 sesame variety; Uttarde et al. (2020) [37] at 500Gy; Ganesan (2001) [10] at 500Gy; Parthsarthi et al., (2020) [22] at approximately 417Gy for TMV7 and 389Gy for SVPR1 sesame varieties; and Boureima et al., (2009 ) [6] who determined LD 50 at 550Gy for cultivar "32-15" and 740Gy for cultivar "38-1-7". The LD 50 for Gophya Local genotype (600Gy) was higher than that of GT-10 and TKG-22 (500Gy). Although TKG-22 and Gophya Local are both white-seeded sesame, their responses to gamma ray mutagenesis varied. Different genotypes of the same crop often show varying LD 50 values, as reported by Sandhiya et al., (2020) [33] in sesame and Ramchandar et al., (2015) [28] in rice. Seed germination percentage decreased progressively with increasing mutagen doses, with more notable reductions at higher doses across all three genotypes. This reduction may be due to cellular-level disturbances (physiological or physical), including chromosomal damage or a combination of these effects (Khan and Tyagi, 2010) [17] . Varietal differences in response to mutagen treatment were observed, with GT-10 showing higher sensitivity than TKG-22 and Gophya Local. Such differential responses could be attributed to the genotypic background and the degree of selection pressure experienced by the cultivars during evolution (Julia et al., 2022) [15] . According to Chrispeds and Varner (1967) [8] , seed germination reduction may result from delays or inhibition in physiological and biological processes essential for germination, hormonal imbalance (Ananthaswamy et al., 1971) [1] , or inhibition of mitosis (Sato and Gaul, 1967) [35] .

Effect of different doses of gamma rays on quantitative traits of sesame genotypes in M1 generation

Significant differences were observed in all quantitative traits studied in the M 1 generation of the three sesame genotypes (GT-10, TKG-22, and Gophya Local). Mean values for these traits are presented in Table 2 (GT-10), Table 3

(TKG-22), and Table 4 (Gophya Local).

The maximum days to 50% flowering were recorded at 700Gy dose for all three genotypes, indicating delayed flowering compared to controls. These results are consistent with previous reports by Prabhakar (1985) [25] , Rahman and Das (1989) [26] , Ganesan (1995) [9] , Govindarasu (1995) [13] , Boureima et al., (2009) [5] , Saha and Paul (2017) [32] , RajaRamadoss et al., (2014) [27] , and Ravichandran and Jayakumar (2018) [30] . Gamma rays caused delayed flowering regardless of dose in cowpea (Girija and Dhanavel, 2013) [12] and black gram (Yasmin et al., 2016) [41] . All three genotypes exhibited delayed maturity at all gamma ray doses compared to controls, similar to observations by Saha and Paul (2017) [32] . Plant height decreased with increasing gamma ray doses in GT-10, TKG-22, and Gophya Local, with maximum reduction at 700Gy. Similar findings were reported by Boureima et al., (2009) [5] , RajaRamadoss et al., (2014) [27] , Anbarasan et al., (2015) [2] , and Ravichandran and Jayakumar (2018) [30] in sesame, Girija and Dhanavel (2013) [12] in cowpea, and Pepol and Pepo (1989) [23] in soybean. Plant height reduction may result from chromosomal damage affecting cell division and elongation (Walther, 1969) [40] . Negative shifts in mean plant height after mutagen treatment have been attributed to deleterious mutations occurring more frequently than beneficial ones (Virupakshappa et al., 1980) [39] . The number of branches per plant declined with higher gamma ray doses in all genotypes, with the highest dose (700Gy) having the strongest effect. This reduction may be due to mutagen toxicity affecting physiological parameters. Possible causes include auxin destruction (Rizwana et al., 2005 [31] ; Ravichandran et al., 2014 [29] , impaired assimilatory functions, mitotic inhibition, and chromosomal damage with associated physiological changes (Saha and Paul, 2017) [32] . A decreasing trend was also observed for the number of capsules per plant in the M 1 generation. The 700Gy dose caused the greatest reduction across genotypes. RajaRamdoss et al., (2014) [27] reported similar reductions in capsules per plant in sesame genotype TTVS-51 after gamma ray treatment. This reduction may be related to enzyme inhibition, changes in enzyme activity, or toxic effects of mutagens. Differential responses to gamma rays for this trait have been noted by Anbarasan et al., (2015) [2] . Capsule length decreased gradually with increasing gamma radiation doses in all genotypes, possibly due to physiological disturbances or genetic damage such as disrupted chromosomal coiling or pairing. The number of seeds per capsule also declined progressively with higher gamma radiation doses in all genotypes. Capsule traits including number of capsules per plant, capsule length, and seeds per capsule were all dose-dependently reduced. The highest gamma ray dose had the most significant impact, while the lowest dose (400Gy) showed effects similar to the control. Similar results have been reported by RajaRamadoss et al., (2014) [27] , Ravichandra and Jayakumar (2018) [30] , and in other crops such as safflower (Mallik Arjunaradhay, 1978) [20] , bhendi (Sasi, 2004) [34] , and cluster bean (Velu et al., 2007) [38] . The 1000 seed weight was notably reduced at the highest gamma ray dose compared to lower doses, which showed comparable effects. This reduction with increased gamma ray doses in M 1 generation has been reported by RajaRamadoss et al., (2014) [27] , Ariharasutharsan et al., (2022) [4] in sesame, Gunasekaran and Padavai (2015) [14] in peanut, and Girija and Dhanavel (2013) [12] in cowpea. Seed yield per plant declined with increasing gamma ray doses across all genotypes. This is consistent with findings by Anbarasan et al., (2014) [3] , RajaRamadoss et al., (2014) [27] , Ravichandran and Jayakumar (2018) [30] , and Ariharasutharsana et al., (2022) [4] in sesame, and also reported in green gram (Koteswara Rao et al., 1983) [18] and soybean (Kalpande et al., 2020) [16] . The reduction in seed yield caused by mutagens may be attributed to increased seed sterility due to physiological and biochemical disruptions during seed development (Prabhakaran, 1992) [24] . The yield decline might also be an indirect effect of altered yield-contributing components (RajaRamdoss et al., 2014) [27] .

Conclusion

In this study, seed germination percentage decreased progressively with increasing gamma ray doses, with a more significant reduction at higher doses. Similarly, all quantitative traits showed considerable reduction compared to controls, decreasing proportionally with higher gamma ray doses across the three sesame genotypes. The lowest dose of gamma rays had effects comparable to controls, while the highest dose significantly reduced quantitative traits. The reduction in these traits is likely due to physiological disturbances or chromosomal damage induced by gamma rays in plant cells. These results suggest that varying doses of gamma rays can be effectively used to induce variability in several quantitative traits of sesame.

References

1. Ananthaswamy HN, Vakil UK, Sreenivasan. Biochemical and physiological changes in gamma irradiated wheat during germination. Radiat Bot. 1971;11:1-12.
2. Anbarasan K, Rajendran R, Sivalingam D. Studies on the mutagenic effectiveness and efficiency of gamma rays, EMS and combined treatment in sesame (Sesamum indicum L.) var. TMV3. Res J Pharm Biol Chem Sci. 2015;6(4):589595.
3. Anbarasan K, Rajendran R, Sivalingam D, Chidambaram ALC. Studies on the effect of EMS and colchicine in M1 generation of sesame (Sesamum indicum L.) var. TMV3. Int Lett Nat Sci. 2014;4:207-214.
4. Ariharasutharsan G, Parameswari C, Sandhiya V, Murugan E, Vanniarajan C. Effect of gamma ray and gamma ray + EMS combination treatment on M1 and M2 generations of white seeded sesame (Sesamum indicum L.). Res Crop. 2022;23(1):92-99.
5. Boureima S, Diouf M, Silme RS, Diop T, Van Damme P, Cagirgan MI. Radiosensitivity of African sesame cultivars to gamma rays. Turk J Field Crops. 2009;14(2):181-190.
6. Boureima S, Diouf M, Silme RS, Diop T, Van Damme P, Cagirgan MI. Radiosensitivity of African sesame cultivars to gamma rays. Turk J Field Crops. 2009;14(2):181-190.
7. Brock RD. The role of induced mutations in plant improvement. Radiat Bot. 1971;11:181-196.
8. Chrispeels MJ, Varner JE. Gibberellic acid enhanced synthesis and release of α-amylase and ribonuclease by isolated barley and aleurone layers. Plant Physiol. 1967;42:398-406.
9. Ganesan J. Induced mutations for sesame improvement. IAEA Res Rep. 1995;1:38.
10. Ganesan J. Development of an ideal plant type and male sterility system in sesame suitable for summer rice fallow in the coastal regions of Tamil Nadu. In: Sesame Improvement by Induced Mutations. IAEA, Vienna; 2001. p. 117-122.
11. Gaul H. Mutagen effects observable in the first generation. Manual on Mutation Breeding. IAEA Tech Ser No. 119. Vienna: IAEA; 1970. p. 85-99.
12. Girija M, Dhanavel D. Effect of gamma rays on quantitative traits of cowpea in M1 generation. Int. J Res Biol Sci. 2013;3(2):84-87.
13. Govindarasu R. Mutagenic studies with narrow and broad genetic bases in sesame (Sesamum indicum L.) [PhD thesis]. Annamalai University; 1995.
14. Gunasekaran A, Pavadai P. Effect of gamma rays on germination, morphology, yield and biochemical studies in groundnut (Arachis hypogaea L.). World Sci News. 2015;23:13-23.
15. Julia T, Sastry EVD, Singh NB, Renuka T, Reetisana N. Study of biological damage in M1 generation of Indian mustard (Brassica juncea L. Czern and Coss). Biol Forum. 2022;14(2):634-637.
16. Kalpande HV, Borgaonkar SB, Chavan SK. Mutagenic induction of yield contributing traits in soybean (Glycine max (L.) Merrill) with gamma irradiation and EMS. Int. J Curr Microbiol App Sci. 2020;9(6):3057-3063.
17. Khan MH, Tyagi SD. Studies on effectiveness and efficiency of gamma rays, EMS and their combination in soybean [Glycine max (L.) Merrill.]. J Plant Breed Crop Sci. 2010;2(3):55-58.
18. Koteswara Rao Y, Seetharama Reddi N, Subramanyyam D. Effect of induced mutagenesis on polygenic variability in green gram. Andhra Agric J. 1983;30(3):200-202.
19. Kumari V, Chaudhary HK, Prasad R, Kumar A, Singh A, Jambhulkar S, et al. Effect of mutagenesis on germination, growth and fertility in sesame (Sesamum indicum L.). Annu Res Rev Biol. 2016;10(6):1-9.
20. Mallik Arjunaradhaya K. Induced mutagenesis in safflower (Carthamus tinctorius L.) by using gamma rays, ethyl methane sulphonate alone and in combinations. Mysore J Agric Sci. 1978;12(1):172-179.
21. Myint D, Gilani SA, Kawase M, Watanabe KN. Sustainable sesame (Sesamum indicum L.) production through improved technology: an overview of production, challenges and opportunities in Myanmar. Sustainability. 2020;12:3515.
22. Parthasarathi G, Arumugam Pillai M, Kannan R, Merina Prem Kumari S, Binodh AK. Optimal lethal dose determination for gamma rays and EMS induced mutagenesis in TMV7 and SVPR1 sesame (Sesamum indicum L.) varieties. Curr J Appl Sci Technol. 2020;39(28):136-144.
23. Pepol P, Pepo P. Preliminary experiment on inducing soybean mutants by fast neutron seed irradiation. Soybean Abstr. 1989;12(5):4-7.
24. Prabakaran AJ. Identification of male sterile sources through wide hybridization and induced mutagenesis in sesame (Sesamum indicum L.) [PhD thesis]. TNAU, Coimbatore; 1992.
25. Prabhakar LV. Studies on induced mutagenesis in Sesame indicum L. [MSc thesis]. TNAU, Coimbatore; 1985.
26. Rahman A, Das ML. Evaluation, selection and mutation induction in sesame strains. In: Proc. 14 th Annual Bangladesh Science Conference, Dhaka; 1989. p. 37.
27. RajaRamadoss B, Ganesamurthy K, Angappan K, Gunasekaran M. Evaluation of the effect of gamma rays on sesame genotype TTVS 51 and TTVS 19 in M1 generation. Int J Dev Res. 2014;4(2):273-277.
28. Ramchander S, Ushakumari R, Arumugam Pillai M. Lethal dose fixation and sensitivity of rice varieties to gamma radiation. Indian J Agric Res. 2015;49(1):24-31.
29. Ravichandran V, Jayakumar S. Effect of gamma rays on quantitative traits of sesame (Sesamum indicum L.) in M1 generation. Int J Adv Res. 2014;2(8):593-597.
30. Ravichandran V, Jayakumar S. Effect of gamma rays on quantitative traits of sesame (Sesamum indicum L.) in M1 generation. Pharma Innov J. 2018;7(10):547-550.
31. Rizwana BM, Kalamani A, Ashok S, Makesh N. Effect of mutagenic treatments on quantitative characters in M1 generation of cowpea (Vigna unguiculata L. Walp). Adv Plant Sci. 2005;18(11):505-510.
32. Saha S, Paul A. Gamma irradiation effect on yield and yield attributing traits of sesame (Sesamum indicum L.) in M1 generation. J Pharmacogn Phytochem. 2017;6:1311-1315.
33. Sandhiya V, Kumar M, Parameswari C, Vanniarajan C, Kumaravadivel N, Sakthivel N, et al. Determination of optimum dose of chemical mutagen for large scale seed treatment of white seeded sesame (Sesamum indicum L.) varieties. Electron J Plant Breed. 2020;11(1):238-242.
34. Sato M, Gaul H. Effect of EMS on fertility in barley. Radiat Bot. 1967;7:7-15.
35. Teklu DH, Shimelis H, Abady S. Genetic improvement in sesame (Sesamum indicum L.): progress and outlook -a review. Agronomy. 2022;12:2144.
36. Uttarde RB, Bolbhat SN, Admuthe NB, Kumavat VS, Bhor AK. Induced mutations in sesame (Sesamum indicum L.). Int. J Creat Res Thoughts. 2020;8(3):3171-3176.
37. Velu S, Mullainathan L, Arulbalachandran D, Dhanavel D. Effect of physical and chemical mutagens in cluster bean (Cyamopsis tetragonoloba L.) in M1 generation. Crop Res. 2007;34(1-3):252-254.
38. Virupakashappa K, Mahishi DM, Sivashankar G. Variation in cowpea following hybridization and mutagenesis. Indian J Genet. 1980;40(2):396-8.
39. Walther F. Effectiveness of mutagenic treatment with ionizing radiation in barley. In: Induced Mutation in Plants. IAEA, Vienna; 1969. p. 261-270.
40. Yasmin K, Arulbalachandran D. Effect of gamma rays on morphological and quantitative traits of black gram (Vigna mungo (L.) Hepper) in M1 generation. Int. J Curr Trend Res. 2016;4(2):5-12.