Selection of rapeseed mutants for higher yield and yield contributing traits

Seven mutants along with the mother variety were evaluated following randomized complete block design with four replicates at four rapeseed growing areas of Bangladesh during 2013-2014 to observe their performances regarding seed yield and yield attributes, and to select promising mutants having higher seed yield with short maturity period. Analysis of variance showed highly significant variations among the mutants and the check for most of the characters studied in individual location and combined over locations. The mutant RM-01-07 required the shortest maturity period except Rangpur and the mother variety Binasarisha-4 required the longest. At Mymensingh and Rangpur, mutant RM-02-07 produced the tallest plant. Both at Mymensingh and Magura, RM-01-07 produced the highest number of siliquae plant and the mother variety produced the lowest siliquae plant. At Ishurdi, RM-10-07 produced the highest number siliquae followed by RM-03-07. Combined means over locations showed that the six mutants matured earlier except the mutant RM-03-07 and most of the mutants produced higher number of branches plant compared to the mother variety. Results over different locations also showed that the three mutants RM-01-07, RM10-07 and RM-04-07 produced significantly higher seed yield (1912, 1846 and 1862 kg/ha, respectively) which was 15.1, 12.1 and 11.1% higher than the mother variety, Binasarisha-4 with seed yield of 1661 kg/ha. These three mutants had also the higher number of siliquae than the mother variety. This suggests that gamma rays irradiation can be fruitfully applied to develop mutants with higher seed yield and other improved agronomic traits in oleiferous Brassica.


Introduction
The oleriferous Brassica plays an important role in vegetable oil production of the world.Rapeseedmustard is the third most important oil source in the world after soybean and oil plam.In Bangladesh, rapeseed-mustard is an important leading oil crop and according to BBS (2013) national average seed yield of this crop is only 998 kg/ha.Therefore, only 15% demand of edible oil is fulfilled from domestic production.As a result substantial amount of foreign exchange is spent for its import.To fulfill the requirement of edible oil from native production, attempts should be taken to increase the rapeseed yield as there is little scope of horizontal expansion of the rapeseed cultivation in the country.
For any plant breeding programme, creation of genetic variation followed by selection plays an important role in developing improved crop varieties.Therefore, genetic variations in useful traits are prerequisites for any crop improvement programme.Mutation breeding has been successfully applied in several crops to generate new sources of genetic variations and this technique has greatly enhanced the development of new crop varieties (Shu and Lagoda, 2007;Szarejko and Forster, 2007;Velasco et al., 2008).Utilizing mutation breeding, genetic improvement of both qualitative and quantitative yield traits has been successfully achieved in rapeseed Brassicsa (Das et al., 2004;Seyis et al., 2006;Spasibionek, 2006;Zhao et al., 2009;Malek et al., 2012a).Nearly 3000 mutant induced and mutant-derived crop varieties for commercial utilization proves that among the different methods, induced mutation is an effective breeding method for generating new germplasm in crop improvement (Ishige, 2009).Kharkwal et al. (2004) reported that using physical mutagens, 89% of the mutant varieties have been developed worldwide and gamma rays alone contributed 60%.
In this research, we evaluated the performances of those mutants along with mother variety during October 2013 to February 2014 at four rapeseed growing areas of Bangladesh regarding morphological parameters, yield traits and seed yield to select the promising one.

Materials and Methods
Seeds of rapeseed variety Binasarisha-4 were irradiated with 600, 700 and 800 Gy doses of gamma rays using Co 60 gamma cell to create genetic variations.Irradiated seeds were sown to grow M 1 generation at BINA, Mymensingh in 2009 for selecting desirable mutants in subsequent generations.Selection was made in each of M 2 , M 3 and M 4 generation based on desired agronomic traits.From M 4 generation, three M 5 mutants namely RM-01-07, RM-02-07 and RM-03-07 from 700 Gy, and four mutants namely RM-04-07, RM-05-07, RM-10-07 and RM-11-07 from 800 Gy were selected for further evaluation.These seven true breeding (homozygous) mutants along with the mother variety Binasarisha-4 were evaluated at four rapeseed growing areas of Bangladesh during 2013-2014 following randomized complete block design with four replicates.Seeds were sown on 24 October at Magura, 28 October at Ishurdi, 25 October at Rangpur and 3 November at BINA Headquarters farm, Mymensingh in 2013 maintaining unit plot size of 20 m 2 (5.0 m × 4.0 m) with a line spacing of 25 cm and 6-8 cm for plant to plant within rows.Recommended production packages like weeding, thinning and application of fertilizers, irrigation, pesticide etc. were done uniformly to ensure normal growth and development of the plants in each plot as and when necessitated.
Data were taken on different morphological traits and yield attributes like plant height, number of branches/plant, number of siliquae plant -1 and number of seeds siliqua -1 from 10 randomly selected representative plants from each plot at maturity.List of all the traits under study and their description of measurement have been presented in Table 1.The collected data were analyzed statistically according to the design followed using the analysis of variance (ANOVA) technique following Gomez and Gomez (1984).The mean values were compared by DMRT at 5% level of significance.

Serial
No. Traits Methods of measurement 1

Days to maturity
The number of days from sowing to 70% siliquae turned into brownish colour 2 Plant height (cm) The height from the base to the tip of the main rachis 3 Branches plant -1 (no.)Total number of primary branches per plant 4 Siliqua plant -1 (no.)Total number of siliqua with seeds in a plant 5 Seeds siliqua -1 (no.)Total number of seeds in a siliqua 6 1000-seed wt.(g) One thousand seeds counted randomly and weighed 7 Seed yield (kg/ha) Weighing the seeds produced in a plot and then converted into kg/ha

Results and Discussion
Analysis of variance indicated highly significant variations (p ≤ 0.01) among the mutants and check for most of the studied characters in different locations indicating the presence of sufficient amount of genetic variability among the mutants.In rapeseed genotypes, significant variations have also been reported by others for various characters (Ali et al., 2002;Hasan et al., 2006;Mahmud et al., 2008).
Results of mean values of four individual locations and combined over four locations for all the characters have been presented in Table 2. Maturity period is the most important and frequent character which can be modified in oilseed Brassica using induced mutation.Significant differences were observed for days to maturity in different locations.At Mymensingh, two mutants RM-01-07 and RM-02-07 required shortest maturity period (87 days) having non-significant difference with other five mutants while Binasarisha-4 had the longest maturity period of 94 days.RM-01-07 required the shortest period of 80 days to mature while the mother variety Binasarisha-4 took the highest maturity period of 87 days at Magura.Mutant RM-01-07 required the shortest maturity period of 91 days having non-significant difference with five other mutants while Binasarisha-4 required the longest duration 98 days at Ishurdi.At Rangpur, Binasarisha-4 also required the longest duration of 88 days to mature.In combined over locations, days to maturity varied from 86 days in RM-01-07 to 92 days in Binasarisha-4 having non-significant difference only with the mutant RM-03-07.So, most of the mutants matured earlier than the mother variety.This result revealed that through induced mutation maturity period can be shorten.Induction of early maturity in the mutants of oilseed Brassica has been reported by Spasibionek (2006), Shah and Rahman (2009), Malek et al. (2012a) which confirm the present result.A significant variation was observed in plant height.At Mymensingh, mutant RM-02-07 produced the highest plant height (100 cm) closely followed by RM-05-07 (99 cm) while RM-11-07 produced the shortest plant of 91 cm.At Rangpur, RM-02-07 also produced the tallest plant (116 cm) which was closely followed by RM-01-07, RM-10-07 and Binasarisha-4 which was 115 cm, whereas RM-11-07 produced the shortest plant with 104 cm height.In combined over locations, mutant RM-01-07 produced the highest plant height of 110 cm followed by RM-10-07 (109 cm) while the mutant line RM-11-07 produced the shortest plant height of 102 cm.In case of number of branches/plant, mutant RM-01-07 produced the highest number of 2.7 branches/plant followed by the mutants RM-04-07 and RM-05-07 (2.5 branches/plant) while Binasarisha-4 produced the lowest number at Mymensingh.Mutant RM-10-07 produced the highest number of 3.2 branches/plant closely followed by RM-01-07 and RM-05-07 (3.1 and 3.0, respectively) while the mother variety Binasarisha-4 produced the lowest number of 2.3 branches at Magura.Binasarisha-4 produced the lowest number of 2.4 branches.Plant heights may vary due to the genetic effects present among the genotypes as well as the proper agronomic management.Development of shorter mutants in oilseed Brassica has been reported by Shah et al. (1990) and Malek et al. (2012a).These results also conform that using induced mutation plant stature can be altered in rapeseed-mustard.In case of number of branches plant -1 , all the mutants produced higher number of branches than the mother variety.The present results having more number of branched in the rapeseed mutants than the mother confirm the findings of Khatri et al. (2005) and Shah and Rahman (2009).
A significant variation was found among the mutants and mother variety on the number of siliquae plant -1 in Mymensingh, Magura and Ishurdi.Both at Mymensingh and Magura, RM-01-07 produced the highest number of siliquae plant -1 (90 and 96, respectively) and the mother variety produced the lowest number (61 and 68, respectively).At Ishurdi, RM-10-07 produced the highest number siliquae (80) followed by RM-03-07 with 77 number.Combined means showed that the highest number of siliquae plant -1 (78) was produced by RM-01-07 and other three mutants, RM-10-07, RM-02-07 and RM-04-07 produced 72, 71 and 70 number of siliquae plant -1 , respectively while the lowest number (62) was found in Binasarisha-4.Significant differences were observed for 1000-seed weight in different locations.On an average, the five mutants RM-01-07, RM-02-07, RM-03-07, RM-04-07 and RM-10-07 produced significantly higher 1000seed weight than Binasarisha-4.Other two mutants RM-05-07 and RM-11-07 produced statistically equal seed weight with mother variety.In oilseed Brassica, as a consequence of mutagenesis, Javed et al. (2003), Khatri et al. (2005) and Malek et al. (2012a) reported higher siliquae number in developed mutants over their mothers.Number of seeds siliqua -1 did not differ significantly both in individual locations (except Mymensingh) and combined over locations.In rapeseed-mustard, Javed et al. (2003) reported that seed size has direct influence on seed yield.Present result showed that most of the mutants gave higher seed weight than Binasarisha-4.Generation of bold-seeded mutants in rapeseed-mustard has also been reported earlier by Chauhan and Kumar (1986) and Shah et al. (990).
The mutants RM-10-07 produced the highest seed yield of 1817 kg/ha followed by RM-01-07 (1812 kg/ha) and RM-03-07 (1783 kg/ha) which was 11.3, 11.0 and 9.2 % higher than the mother variety Binasarisha-4 at Mymensingh.At Magura, the five mutants RM-04-07, RM-01-07, RM-10-07, RM-11-07 and RM-05-07 produced significantly higher seed yield of 2305, 2070, 2055, 2041 and 1944 kg/ha, respectively than Binasarisha-4 (1766 kg/ha).Mutants RM-01-07 produced the highest yield (2121 kg/ha) at Ishurdi.At Rangpur, seed yield and its components showed non-significant differences among the genotypes.Combined means over four locations showed that three mutants namely RM-01-07, RM-04-07 and RM-10-07 produced significantly higher seed yield (1912, 1846 and 1862 kg/ha, respectively) than mother variety Binasarisha-4 (1661 kg/ha) and in percentage, their seed yield were 15.1, 11.1 and 12.1% higher than Binasarisha-4 while other four mutants produced statistically similar seed yield with Binasarisha-4.Results also showed that three high yielding mutants also produced significantly higher number of siliquae/plant than mother variety.In plant breeding, generation of genotypes having improved yield contributing characters is the main objective for achieving higher yield.In oilseed Brassica, the most important yield attributes responsible for the increased seed yield are the siliquae number, seed number in siliqua and individual seed weight.Seed yield is a complex quantitative character governed by a large number of genes and is greatly affected by environmental fluctuations.For considering as a promising variety of a particular crop, seed yield is the most important.In rapeseed-mustard, mutants having higher seed yield over mother varieties were also reported earlier by Javed et al. (2003), Seyis et al. (2006), Zhao et al. (2009), Brave et al. (2009) and Malek et al. (2012aMalek et al. ( , 2012b)).
In seed yield and its attributes and other morphological traits variations were observed among the locations which are due to the variations in environments among the locations.

Conclusion
It was observed that among the mutants and mother variety, three mutants RM-01-05, RM-04-05 and RM-10-05 performed better for seed yield and yield contributing characters which can be selected for further trials to be registered as varieties.Moreover, this suggests that gamma rays irradiation with 700 to 800 Gy can be fruitfully applied to induce mutants in B. napus with higher seed yield and other improved agronomic traits.