​Binasoybean-6: A High Yielding Mutant Soybean Variety Developed through Sustainable Mutation Breeding

Soybean [Glycine max (L.) Merr.] is a short day, photoperiod-sensitive and self-pollinated leguminous crop that provides superior protein and edible oil (Guo et al., 2020; Çirka et al., 2021). Presently, soybean is one of the world’s most important economic legume crops. Birt et al., (2004) reported that cancer, blood serum cholesterol, osteoporosis and heart disease etc. reduces by consumption of soybean-based foods. Due to high protein content, ready availability and relatively low cost, the by-product of soybean processing, soybean meal is widely used as forage (Krishnan and Jez, 2018).
       
Mutation breeding is important for understanding the phenology of seed crops and for maximizing yield in a given environment. Genetic, environmental factors and the interaction between the two factors control the yield and yield related traits of soybean (Mao et al., 2017). Genetic variation due to induced mutation plays an important role in adaptation to different environments. Generations of new and improved varieties can be enhanced by new sources of genetic variation. Therefore, evaluation of genetic divergence and relatedness among breeding materials has significant implications for the crop improvement (Bisen et al., 2015; Jain et al., 2018). Knowledge on mutation breeding in soybean could help breeders and geneticists to understand the structure of genotypes, predict which combinations would produce the best mutant and facilitate to widening the breeding material for selection. The effect of gamma rays in yield and yield attributes in soybeans has been poorly understood. In the present study, gamma rays from Co⁶⁰ sources has been used in soybean genotypes for maturity and yield related traits. The derived mutants were analyzed for identification of the superior breeding material. The objectives of this study are to determine the mutational effects of gamma irradiation under different environments and the interaction of environments on soybean yield.

Four popular soybean varieties viz. Shohag, BDS-4, BAU-S/64 and BARI Soybean-5 were irradiated using Co⁶⁰ gamma rays in Mutation Breeding Laboratory at Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh. Seeds were exposed to 150, 200, 250, 300 and 350Gy doses of gamma rays for growing M₁ generation in Rabi season 2006. Seeds of each M₁ plants were harvested and kept separately. In M₂ generation plants were grown in plant-progeny rows in Kharif-II (July to November) season of 2006. A large numbers of variants were observed and desirable variants were selected to grow M₃ generation. M₃ variants obtained from all the four parents were grown during Rabi season 2007 following plant-progeny rows for selecting desirable mutants. The selected desirable mutants were grown as M₄ and then M₅ generations to study in respect of earliness, seed yield and yield contributing characters during Rabi and Kharif-II seasons 2008. Finally, a total of 28 desirable mutant lines from all the four mother genotypes were selected for evaluation in M₆ generation.
       
Observation trial was conducted in Rabi 2009 at BINA HQ farm, Mymensingh with those 28 (SBM-1 to SBM-28) selected M₆ mutant lines namely SBM-1, SBM-2, SBM-3, SBM-6, SBM-10, SBM-21 and SBM-23 obtained from Shohag; SBM-4, SBM-5, SBM-11, SBM-13, SBM-14, SBM-27 and SBM-28 obtained from BAU-S/64; SBM-7, SBM-8, SBM-16, SBM-17, SBM-19, SBM-20 and SBM-26 obtained from Bangladesh Soybean-4; and SBM-9, SBM-12, SBM-15, SBM-18, SBM-22, SBM-24 and SBM-25 obtained from BARI Soybean-5. From this study, the mutant line, SBM-22 derived from the variety BARI Soybean-5 irradiated with 300Gy of gamma rays was found to be superior regarding earliness, higher seed yield and other desirable agronomic traits. Considering the superior performance of SBM-22, preliminary yield trial (PYT) along with 28 mutant lines including SBM-22 was conducted at BINA sub-station farm Magura during Rabi season 2010. Different trials were conducted in different agro-ecological zones of the country like as Mymensingh, Rangpur, Magura, Cumilla, Chandpur and Noakhali districts during Rabi season of 2010-2018.
       
All of these experiments were laid out in a randomized complete block design (RCBD) with three replications. Spacing maintained among rows was 30 cm and 5-7 cm between plants in rows (Malek et al., 2012). Data on various characters such as plant height, number of branches/plant, pods/plant and seeds/pod was taken from 10 randomly selected plants from each plot. Maturity period was counted from seed sowing to the day when the plants and pods of each plot turned into yellowish brown color and almost all the leaves shed. Seed yield of each plot was recorded after proper sun-drying of seeds and then converted into kg/ha. The recorded data were analyzed statistically following Gomez and Gomez (1984) and the mean values were compared by DMRT at 5% level of significance.

Plant growth, development and yield are strongly inhibited by the environmental effect which is an important factor for crop improvement as well as develop a new variety. Mean values for different characters of individual locations and combined over locations of the preliminary and multi-location trials during 2010 to 2014 are not shown, only the latest advanced trials in 2015, 2016 and 2018 are presented in Table 1 to 3.
 

 

 

 
Preliminary yield trial (PYT) of M7 soybean mutants during Rabi season 2010
 
Twenty eight M₇ mutant lines along with four mother genotypes were put into PYT at BINA Headquarters farm and BINA sub-station farm at Magura. Seeds were sown within first week of January 2010 (data not shown). BDS-4 produced the highest number of pods/plant (79) and showed non-significant difference with mutants SBM-27, SBM-28, SBM-14, SBM-13, SBM-12 and SBM-11 while SBM-26 produced the lowest number of pods/plant (44). Among the mutants, days to maturity ranged from 118 (SBM-05 and SBM-06) to 140 days (SBM-27). Two mutants SBM-16 andSBM-07 produced highest yield 3164 kg/ha and 2830 kg/ha respectively. Among all, 11 mutants, namely SBM-07, SBM-08, SBM-14, SBM-16, SBM-17, SBM-18, SBM-21, SBM-22, SBM-23, SBM-24 and SBM-25 gave higher seed yield than their mother varieties.
 
Preliminary yield trial (PYT) of M8 soybean mutants during Rabi 2011
 
Twelve selected M₈ mutant lines along with three mother genotypes were tested in PYT at BINA Headquarter’s farms and BINA sub-station at Magura (data not shown). Among the mutants, average days to maturity ranged from 100 (SBM-19) to 107 (SBM-12). Bangladesh Soybean-4 produced the highest number of pods/plant (55) having non-significant difference with two mutants, SBM-26 and SBM-12 while SBM-23 produced the lowest number of pods/plant (36). Ten mutants namely SBM-9, SBM-12, SBM-16, SBM-17, SBM-18, SBM-20, SBM-21, SBM-22, SBM-23 and SBM-26 produced higher seed yield than their mothers. SBM-15 (2416 kg/ha) and SBM-19 (2361 kg/ha) produced lowest seed yield when compared with other mutants.
 
Multi-location yield trial with promising soybean mutants during Rabi 2013
 
Four promising mutants SMB-9, SMB-15, SMB-18 and SMB-22 along with mother BARI Soybean-5 and another check variety Binasoybean-2 were evaluated in this trial at BINA HQ farm and BINA sub-station farm at Rangpur and Magura during January to April 2013 (data not shown). Days to maturity ranged from 103 (Binasoybean-2) to 112 days (SBM-18 and SBM-22). The mutants SBM-18 and SBM-22 produced significantly higher number of pods/plant (41 and 39, respectively) and seed yield (2642 and 2606 kg/ha, respectively).
 
Multi-location yield trial of advanced soybean mutants during Rabi 2014
 
Four promising mutants SMB-9, SMB-15, SMB-18 and SMB-22 along with their mother BARI Soybean-5 and another check variety Binasoybean-1 were evaluated at BINA HQ farm and BINA sub-station farms at Magura and Cumilla; farmers’ field at Chandpur and Noakhali during January to April 2014 (data not shown). Days to maturity ranged from 112 in Binasoybean-1 to 116 days in SBM-9. Number of seeds/pod ranged from 1.80 in SBM-9 to 1.92 in SBM-22; and hundred seed weight ranged from 12.42 in Binasoybean-1 to 14.58 g in BARI Soybean-5. All the mutants produced significantly higher seed yield than checks and particularly, SBM-18 and SBM-22 produced the highest seed yield (2793 and 2730 kg/ha, respectively).
 
On-station yield trials with advance soybean mutants during Rabi 2015
 
Four promising mutants SMB-9, SMB-15, SMB-18 and SMB-22 along with their mother BARI Soybean-5 and another check Binasoybean-2 were evaluated at BINA HQ farm and BINA sub-station farms at Magura and Cumilla during January to April 2015. On an average, maturity period ranged from 101 (SBM-15 and Binasoybean-2) to 105 days (BARI Soybean-5). Number of pods/plant ranged from 33 in Binasoybean-2 to 66 in SBM-9. Particularly, mutants SBM-18 and SBM-22 produced higher seed yield among the mutants and checks (Table 1). 
 
On-station and on-farm yield trials with advance soybean mutants during Rabi 2016
 
Four promising mutants SMB-9, SMB-15, SMB-18 and SMB-22 along with their mother BARI Soybean-5 and another check Binasoybean-2 were evaluated at BINA HQ farm and farmers’ field at Noakhali and Chandpur during January to April 2016. Maturity period ranged from 97 days in Binasoybean-2 to 108 days in SBM-18 and SBM-22. Mutant line SBM-18 produced the highest seed yield of 2584 kg/ha closely followed by SBM-22 (2561 kg/ha) and Binasoybean-2 (2508 kg/ha), whereas, SBM-15 (2281 kg/ha) produced the lowest seed yield (Table 2).
 
On-station and on-farm yield trials with advance soybean mutants during Rabi 2018
 
Two promising mutants SMB-18 and SMB-22 along with their mother BARI Soybean-5 and another check variety Binasoybean-1 were evaluated at BINA HQ farm and BINA sub-station farm at Magura and farmers’ field at Chandpur and Noakhali during January to April 2018. Maturity period ranged from 116 days in Binasoybean-1 and BARI Soybean-5 to 118 days in SBM-22. The mutant SBM-18 produced the highest seed yield of 2197 kg/ha followed by SBM-22 (2109 kg/ha). Compared with the mother variety, these two mutants (SBM-18 and SBM-22) were late (117 and 118 days) but both the mutants recorded higher number of pod/plant (56 and 52), seeds/pod (2.2 and 2.09) and 100-seed weight (13.9 and 13.5) respectively. Due to the higher yield attributing characters these mutants recorded higher yields than the mother variety (Table 3).
 
Overall performance of the new variety Binasoybean-6
 
Pooled data of yield and yield related attributes of the newly registered variety Binasoybean-6 has been analyzed considering the mean seed yield of all trials conducted during 2010 to 2018 (Table 4). The new variety Binasoybean-6 produced the higher mean seed yield of 2612 kg/ha compared to mother variety BARI Soybean-5 (2327 kg/ha). The mutant line SBM-22 was found to be tolerant to yellow mosaic disease and also showed the lowest incidence of insect-pests (hairy caterpillar and pod borer) infestation.
 

       
Mutation breeding can improve yield and yield attributes by the genetic improvement in soybean compared to conventional breeding (Manjaya, 2009; FAO/IAEA, 2018). From the present study it was observed that, most of the mutants performed comparatively superior over their respective mother varieties for seed yield and other yield contributing characters. These results were in agreements with other researchers (Ahire et al., 2005; Malek et al., 2014) who reported improved yield attributes in soybean mutants following mutagenesis. Malek et al., (2014) developed 27 soybean mutants by irradiating four soybean genotypes using gamma rays from the Co60 gamma source and 18 superior mutants were selected for better seed yield. In Bangladesh, average yield of soybean presently is 1.64 tons/ha as compared with world average. To overcome this bottleneck, viable alternative would be cultivation of a high yielding varieties (Malek et al., 2014). The average yield of the mutant SBM-22 is 2.6 tons/ha which can play a major role for bridge the yield gap of this crop in Bangladesh. Development of mutant variety Binasoybean-6 is a milestone in soybean breeding through induced mutagenesis.

The registered new mutant variety “Binasoybean-6” has been developed from BARI Soybean-5. The mutant line SBM-22 was found to be higher yielding as well as tolerant to yellow mosaic (YM) disease and also showed lower incidence of insect-pests infestation. Higher seed yield and improved yield attributes in the mutants revealed that induced mutations can successfully be employed to create genetic variations in soybean. This can be considered as a milestone achievement in mutation breeding. This variety may partially fulfill the challenges of increasing demand of edible oils and also has an opportunity for increase cultivable land under soybean in Bangladesh.

The authors are sincerely acknowledge Bangladesh Institute of Nuclear Agriculture (BINA) for all the support and facilities to conduct this experiment and Faculty of Sustainable Agriculture, University Malaysia Sabah for the initiatives to publish the research findings.