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Plant Gene and Trait, 2016, Vol. 7, No. 7 doi: 10.5376/pgt.2016.07.0007
Received: 10 Jun., 2016 Accepted: 18 Jul., 2016 Published: 29 Jul., 2016
Tripathy S.K., Mishra D.R., Mishra D., Mohanty S.K., Dash S., Swain D., Mohapatra P.M., Pradhan K.C., Panda S., Reshmi Raj K.R., and Mohanty M.R., 2016, Inheritance pattern of oil content in sesame (Sesamum indicum L.), Plant Gene and Trait, 7(7): 1-6 (doi: 10.5376/pgt.2016.07.0007)
Genetics of oil content was studied in a set of 12×12 half diallel crosses of sesame which indicated importance of both dominant and additive gene action. TMV 5, Pratap and Phule Til-1 emerged as a good general combiner for high oil content. Among the crosses, B67×E8, B67×RT103, RT103×T13 exhibited positive and significant SCA effect indicating non-additive gene action for high oil content. Study of various genetic parameters revealed that just one group of genes or loci with ‘dominant’ and ‘increasing’ alleles might be involved in the synthesis of oil in seeds and involvement of modifiers in the background genotype could not be ruled out.
Introduction
Vegetable oil consumption is estimated to be 200 billion kilograms by 2030 (Troncoso-Ponce, 2011). Among oilseed crops, sesame (Sesamum indicum L, Family: Pedaliaceae) is considered as the queen of high quality vegetable oils for human consumption as it contains high levels unsaturated fatty acids and antioxidants e.g., sesamol, sesamin, sesamolin and sesaminol (Nupur et al., 2010). Besides, sesame oil is rich in carbohydrate, protein, calcium and phosphorus and used as a source of biodiesel with superior environmental performance (Ahmed et al., 2010). Its unique semi-drying property makes it suitable for use in paint formulation (Bedigian, 2003). In addition, sesame seed is traditionally used for direct consumption as well as for confectioneries, cookies, cake and margarine and in bread making. It is also useful in the manufacture of soaps, cosmetics, perfumes, insecticides and pharmaceutical products (Warra, 2011). The oil is highly resistant to oxidative deterioration due to the presence of antioxidant lignans (Mohamed and Awatif, 1998). Besides, it serves as natural health promoting foods that has the potential to prevent various disorders such as hypertention, oxidative stress-associated and neuro-degenerative diseases (Nakano et al., 2002).
Sesame ranks 9th position among top 13 oilseed crops which make up 90% of the world production of edible oil (Adeola et al., 2010; http://www.statista.com/statistics/267271/worldwide-oilseed-production-since-2008/). India shares largest area (29.8%) under sesame and ranked as the largest producer of sesame seeds (15%) in the world with an estimated production of 636,000 metric tonnes and productivity of 3419kg/ha in 2013 (FAOSTAT, 2013). It is projected that India's total edible oil consumption will increase 5.5% to 6.0% per annum. Therefore, there is an urgent need for enrichment of oil content of sesame. A gene family comprising 34 Lipid transfer protein type 1 (LTP1) genes are confirmed to have major role in lipid biosynthesis (Wang et al., 2014). LTP1 family is reported to benefit oil accumulation by strengthening the transport of fatty acids, acyl-CoAs, and other lipid molecules (Kader, 1996). Variation and selection are the two basic requirements of genetic improvement in any crop. Without variation, selection becomes ineffective. There exists a wide array of variation in oil content (43.3%~51.7%) among the available genotypes (Spandona et al., 2013) and it can be increased by conventional breeding methods. Compared to other edible oil crops such as soybean (Glycine max), rapeseed (Brassica campestris), mustard (Brassica juncia), peanut (Arachis hypogaea) and olive (Olea europaea), sesame seeds harbour comparatively higher oil content (~55% of dry seed), and is thus an attractive potential model for studying lipid biosynthesis (Ke et al., 2010). However, insight into the pattern of inheritance for biosynthesis of high oil content in sesame is largely unexplored. Sesame oil is more variable in terms of quantity of oil than quality (fatty acid composition) (Baydar et al.,1999). Erucic acid content remained unaltered while stearic, linolenic and arachidic acid contents were reported to be least affected over changing environments (Were et al., 2006). There is no conclusive information on the number of genes controlling oil content and the exact nature of the gene (s) meant for biosynthesis of lipids although many researchers (Abatchoua, 2015; Vekaria et al., 2015; El-Bramawy and Shaban, 2008; Madhusudan and Nadaf, 2009; and Murty and Hashim, 1973) addressed this problem using different base materials. The knowledge of gene action for expression of oil content helps in proper planning and selection of appropriate breeding method. Therefore, an effort was undertaken to study the gene action underlying the oil content using a 12×12 half diallel set of crosses in sesame.
1 Results and Discussions
Unlike other quantitative traits such as, seed weight and protein content, genetics of oil content is not intensively studied. Seeds of F1 plants carry F2 embryos. Obviously, performance of F1 plant is reported (Snoad and Arthur, 1974; Prakash et al., 1977) to be dependent on F1 genotype and genotype of individual embryos, even if the influence of environmental factors is ignored. Besides, possible involvement of cytoplasmic factors as in case of seed coat colour in sesame (Laurentin and Benitez, 2014) can not be denied.
Analysis of variance (Table 1) revealed significant difference among parents and crosses for mean oil content (%) indicating that parents were genetically highly diverse and those also produced highly diverse F1 hybrids. Further, a perusal of Table 2 showed importance of both additive and dominant gene action for inheritance of oil content as revealed from the significant value of GCA and SCA. However, the ratio of GCA variance to SCA variance (0.449) suggests the relative importance of non-additive gene action for expression of oil content indicating effectiveness of selection of segregants in advance generations. These observations are in conformity with the findings of Praveenkumar et al. (2012) and Kavita et al. (1999). In contrast, the report of Ramesh et al. (2000), Aladji Abatchoua et al. (2015), Alege and Moustapha (2013) and Azeez and Morakinyo (2014) highlighted the predominance of additive gene action for this trait.
Table 1 Analysis of variance for mean oil content (%) of parents and crosses |
Table 2 Analysis of variance for combining ability |
Variability for seed oil content in sesame has been reported by several workers (Asghar and Majeed, 2013; Adeola et al., 2010; Nzikou et al., 2009; Shekhawat et al., 2013; Alege and Moustapha, 2013; Azeez and Morakinyo, 2014; Bisen et al., 2013). Wang et al. (2014) reported oil content as high as 59% in a sesame variety ‘Zhongzhi No. 13’ which is widely cultivated in china. Among the parents used in the present study, RT 103, TC 25, TMV 5 and CST 785 exhibited high oil content in seed (≥54.0%) (Table 3). Among these, TMV 5 was also shown to be a favourably good general combiner for oil content. Besides, Pratap and Phule Til-1 were identified as good general combiner. In contrast, E8 harboring lowest oil content (44.2%) was found to be the most poor general combiner for oil content in seed (GCA -appreciably higher magnitude in negative direction). In the present investigation, CST785 × Pratap, CST 785 × Madhabi, CST 785 × Phule Til 1, Pratap × T13, Pratap × Madhabi, RT 103 × T13 resulted high per se oil content (≥ 58%). Pratap, or Phule Til-1 (general combiner) was one of the parents in some of these crosses indicating role of both additive and non-additive gene action. Azeez and Morakinyo (2014) identified a cross S 530 × PACH with oil content as high as 57.58%.
Table 3 per se oil content (%) of parents & 66 crosses (upper half), estimates of general combining effects (diagonals) and specific combining effects (lower half) |
Table 4 Component of variation with standard errors in F1 generation for oil content in sesame |
Out of 66 cross combinations, only 15 crosses revealed significant positive SCA effects among which B67×E8, B67×RT 103, RT 103×T13 found to be best specific combiner for the trait. None of the general combiner for oil content (Pratap, TMV 5 and Phule Til 1) was involved in these specific cross combinations indicating substantial role of dominance and/or epistatic gene interaction for oil content in these crosses. Hybridization of selective parental genotypes followed by recurrent selection in the succeeding advance selfing generations can led to recovery of transgressive segregants with suitable gene combination for high oil yield (Aladji Abatchoua et al., 2015)
The estimate of regression coefficient (b = 0.1709) was not significant indicating uniformity of Vr and Wr leading to validity of the assumptions made by Hayman (1954a, b). The non-significant deviation of b-value clearly demonstrated the presence of non-allelic as well as allelic interactions for inheritance of the trait. The dominant effect (H1) was found to be higher than additive effect (D) which implied that the allelic interaction was well within the range of overdominance. This was also evident from the mean degree of dominance which was more than unity (1.470). However, the over-dominance observed may not be considered as index for true over dominance since the degree of dominance could be biased due to linkage, epistasis or both (Comstock and Robinson, 1952). The estimates of h2/H2 was <1.0 suggesting involvement of just one group of genes showing dominance. However, this parameter can be underestimated when the dominance effects of all the genes concerned are not equal in size and distribution, when the distribution of genes is correlated (Jinks, 1954), or when complementary gene interactions occur (Mather and Jinks, 1971). Murty and Hashim (1973) detected complementary nature of non-allelic interactions for inheritance of oil content in seed.
In the present study, BS 5-18-6 had very high concentration of dominant alleles owing to lower value of both Vr and Wr , whereas, Madhabi with concomitant higher magnitude of Vr and Wr values showed high concentration of recessive alleles. TC 25 and Phule Til-1 had alleles relatively balanced.
Non-significant correlation coefficient value (r = 0.440) between (Wr + Vr) and (Yr) evidenced that dominance was shared between the increasing alleles at some loci and the decreasing alleles at others. Further, h2 being positive and higher in magnitude which envisaged that the total magnitude of increasing alleles surpassed than that of the decreasing alleles controlling oil content. Relatively high magnitude and positive value of F (Table 4) could be an indication for preponderance of dominant alleles for oil content in seeds (Mather and Jinks, 1971). In the present investigation, the proportion of genes with + ve and - ve effects (H2/4H1) was about 1: 5 (0.210) while the ratio of dominant and recessive alleles was estimated to be approximately 7: 5 (1.330). So, high oil content sesame varieties can be bred by increasing the concentration of dominant alleles (which are increasing in nature as well) through rigorous selection in the segregating population. Such a selection may also be helpful to get a residual genetic background where there is more expression of the gene(s) governing oil content.
Oil content was found to be inherited with a narrow sense heritability of 31.703% and broad sense heritability of 84.0% reaffirmed the fact that oil content in the present set of materials is governed by lower proportion of additivecomponent of genetic variation compared to non-additive components. Murty and Hashim (1973) studied inheritance of oil and protein content in a diallel cross of sesame and reported low heritability for oil (23%) and protein content (30%). Besides, Vekaria et al. (2015) revealed moderate estimates (50%); and Alege and Moustapha (2013) and Bisen et al. (2013).reported higher estimates of heritability (narrow sense) values for oil content in sesame. This envisaged variable genetic nature of oil content under different genetic background and therefore, improved breeding methods e.g., single seed descent (SSD) method may be considered useful for recovery of high oil yielding plants.
Thus, it is evident that inheritance pattern of oil content is dependent on nature of gene content in each parental genotype. The results emanating from this investigation can be utilized for future breeding programme to augment oil yield in sesame. Besides, genetic improvement for high oil content could be better handled by exploring candidate genes underlying biosynthesis of sesame oil; and identification and monitoring of quantitative trait loci (QTL) for increased seed oil content in succeeding segregation populations.
2 Materials and Methods
Twelve diverse genotypes of sesame with wide variation in oil content were crossed in all possible combinations to raise a set of half diallel crosses during Rabi 2014-15 (Mishra, 2016). Emasculation and pollination were carried out in late afternoon using Fevicol method (Das, 1990). All parents along with 66 crosses were laid out in RBD with three replications to raise F1 generation in Rabi, 2015-16. Each parental genotype and cross was grown in five rows of 3.5 m length with a spacing of 30 × 10 cm. The soil type of the location was sandy loam. Standard package of practices for sesame including need based irrigation, two hand weeding (at 20 and 40 DAS) and prophyletic spray of Prophanopus@2mL/L, sulfex@5g/L and Carbendazim@2g/L against pests and diseases were followed to raise a good crop. Oil content of three random seed samples from each replication of each cross and parent was analyzed (30 days after harvest following sundry, i.e. end of April, 2016) separately in duplicate with one standard check to minimize experimental error following a procedure of Aladji Abatchoua et al., (2015). The data were analysed following standard procedure of Griffing (1956) as well as Hayman (1954 a, b) for genetic interpretation on the nature of inheritance of oil content.
Authors'contributions
Swapan K. and D.R. conceived, designed, drafted and carried out genetic studies; MD, SK, DS, SD and PM performed the data analysis; KC, PS, KR and MR involved in rechecking of the drafted manuscript. All authors read and approved the final manuscript.
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