Research Report

Heritability and predicted gain from selection in components of crop duration and seed yield in sesame (Sesamum indicum L.)  

Bachubhai Arjanbhai Monpara , Shrikant Sanjayrao Khairnar
Agricultural Research Station, Junagadh Agricultural University, Amreli 365601 (Gujarat), India.
Author    Correspondence author
Plant Gene and Trait, 2016, Vol. 7, No. 2   doi: 10.5376/pgt.2016.07.0002
Received: 01 Jan., 2016    Accepted: 01 Mar., 2016    Published: 01 Apr., 2016
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 Preferred citation for this article:
Monpara B. A., and Khairnar S. S., 2016, Heritability and expected genetic gain from selection in components of crop duration and seed yield in sesame (Sesamum indicum L.), India, Plant Gene and Trait, 7(2): 1-5 (doi: 10.5376/pgt.2016.07.0002)

Abstract

The duration of maturity in sesame is dependent on several physiological and phenological variables, which are interrelated and could be manipulated separately in breeding programme. For effective manipulation of these traits, knowledge of genetic architecture is prerequisite. Therefore, seventy diverse sesame genotypes were studied to know the heritability and predicted gain for components of crop duration, correlation among themselves and to identify superior genotypes to be utilized in future breeding programmes. Sizeable variability was revealed among genotypes for studied traits. Genotypic coefficient of variation (GCV) was high (>20%) for seed yield and capsules per plant with high heritability (>80%) and high genetic advance as pecentage of mean (>20%). Also, reproductive period and seeds per capsule expressed high heritability coupled with high genetic gain and moderate GCV. All these key components seem to be under the control of additive gene action, which is fixable. Large environmental effect for primary branches per plant was detected. Correlation of capsules per plant was significant positive and physiological maturity was significant negative with seed yield per plant, but both were correlated negatively with each other. Besides this, association of reproductive period was significant positive with physiological maturity and significant negative with vegetative duration. Simultaneous selection for capsules per plant and crop maturity duration would serve the purpose of improvement in these traits and yield in sesame. Top yielding isolated lines can be utilized for enhancing yield potential through increasing capsules per plant and earliness.

Keywords
Reproductive period; Seed yield; Genetic variability; Correlation

Sesame is the oldest and one of the major oilseed crops, often called the queen of oil. Sesame seeds offer 50%~60% oil and 18%~25% protein in it (Sabah El Khier et al., 2008). The seeds are highly nutritious and important row material for confectionary industries. Seeds with hulls are rich in calcium (1.3%) and provide a valuable source of minerals (Onsaard, 2012). Sesame oil has excellent stability due to the presence of natural antioxidants such as sesamolin, sesamin and sesamol (Crews et al., 2006). Due to its distinct flavour, sesame oil is important in the food industries (Elleuch et al., 2010). Despite its nutritional value and medicinal importance, average productivity of this important oil seed crop of India is 342 kg of seed/ha, which is far below the average productivity of China (1 487 kg/ha) and Egypt (1 333 kg/ha) (FAO, 2013). Sesame is highly drought tolerant, grows well in various types of soils and regions, and is excellent for rotation with other crops; however, farmers grow this crop under rained conditions with low management input (Cagirgan, 2006).

Sesame is known as a plant breeder’s dream crop because of great genetic variability exists in it (Janick and Whipkey, 2002). Crop duration is one of the major factors limiting crop growth and productivity in sesame (Saravanan et al., 2000). Vegetative and reproductive periods are the two important components those determines crop duration. In fact, seed mass accumulation is determined during the seed filling process and seed filling is an important component of reproductive phase. The length of the vegetative period is also an important component of crop growth duration during which size of the floral structures and thereby the sink capacity is determined (Monpara, 2011). Thus, the strategy for increasing seed yield should be an optimum balance between lengths of vegetative and reproductive periods for maximum assimilate partitioning. Understanding of genetic control of these physiological traits is essential for their effective manipulation. Such information particularly in sesame is very limited (Banerjee and Kole, 2009). Therefore, present study was conducted to determine the genetic architecture of components of crop duration and seed yield in sesame and to assess correlations among various traits.

1 Results
Genotypic variation found significant for all nine traits studied (Table 1). The minimum and maximum values for each trait indicated substantial range of differences among the genotypes particularly for reproductive period and capsules per plant. However, good yardstick for determination of variability is the estimation of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV). The GCV and PCV were high (>20%) in magnitude for seed yield and capsules per plant (Table 1). These estimates were low (<10%) for vegetative period, physiological maturity, plant height and capsules per plant. Barring primary branches per plant, all the characters manifested high magnitude of heritability (>70%). Genetic advance as percentage of mean was high (>20%) for seed yield per plant followed by capsules per plant, reproductive period and seeds per capsule and low (>10%) for vegetative period.
 
 
Table 1 Mean values, genotypic variance and genetic parameters for components of crop duration and seed yield
**significant at 0.01 probability level, GCV= genotypic coefficient of variation, PCV= phenotypic coefficient of variation, h2 = Broad sense heritability and GA= genetic advance
 
Phenotypic correlation coefficients among eight characters are shown in Table 2. Capsules per plant exhibited significantly positive association (0.59**), while physiological maturity showed significantly negative association (-0.17**) with seed yield per plant. Correlation between capsules per plant and physiological maturity was significant negative (-0.20**). However, physiological maturity was associated significantly positive with reproductive period (0.74**), i.e. longer crop duration was associated with longer reproductive period. In contrast, correlation between vegetative and reproductive periods was significantly negative (-0.21**), implying that short vegetative duration is important for longer reproductive period. The association between capsule length and seeds per capsule was also significant positive (0.56**).
 
 
Table 2 Phenotypic correlation coefficients among components of crop duration and seed yield
*,**significant at 5% and 1% level, respectively
 
A perusal of the data presented in Table 3 revealed that the average seed yield of five top yielding germplasm lines was 2.3 g higher than the population mean. These top yielding germplasm lines were, on an average, 3 days earlier in maturity and 7 days shorter in reproductive period but showed more capsules per plant (7 no.) over population mean.
 
 
Table 3 Mean values for components of crop duration and seed yield of the highest yielding top five genotypes
 
2 Discussion
Knowledge of genetic control of physiological traits and traits related to reproductive efficiency offers good scope for improvement of yield and exploitation of heterosis in sesame (Krishna Devi et al. 2002; Menzir 2012; Rani et al. 2015). Major traits which are related to physiological process and also considered to be components of crop duration are vegetative period, reproductive period and crop maturity duration. These physiological traits are easy to measure and play a critical role in improving the overall efficiency of resource utilization and thereby yield. Alteration in lengths of durations may provide opportunity to improve yield if sizeable heritable differences exist for these traits. The present study generated the information on genetic variability for components of crop duration and seed yield using diverse germplasm lines of sesame (Table 1). The physiological maturity ranged from 74~104 days and reproductive period varied from 37~68 days. Both these parameters showed almost similar range but quite wider than that of vegetative period (33~45 days). Since vegetative period plus reproductive period make up the days to maturity, wide variation range of reproductive period indicated the importance of this character in determining earliness. Obviously this result suggests that possibility exists to develop early maturing sesame genotypes by cut down of reproductive duration with hastening the seed filling process without affecting vegetative period. Vegetative period is also an important phase of crop duration which provide the bases of floral structure and sink capacity on which the seed yield is dependent (Monpara, 2011).
 
Since sesame is a highly self-pollinated crop, additive genetic variation is essential by breeders aiming to improve quantitative traits (Singh et al., 2008). Heritability together with genetic advance is good predictors of genetic gain as they indicate the involvement of type gene actions governing the trait (Yirgalem et al., 2013). It is evident from the present study that genetic variability for reproductive period, capsules per plant, seeds per capsule and seed yield per plant was associated with additive gene action as these characters exhibited high magnitude of heritability as well as high genetic advance as percentage of mean. This complements other studies which have reported additive gene action for capsules per plant (Parameshwarappa et al., 2009) and seed yield per plant (Singh et al., 2008) in sesame. Beaver (1998) reported moderate to high narrow sense heritability for reproductive period in common bean. In sesame such studies are not reported. However, high heritability along with high genetic advance for capsule filling period have been reported (Yirgalem et al., 2013), while Jamie et al. (2002) noted that seed maturation duration rather than duration of reproductive/flowering period is useful to enhance sesame seed yield. High heritability was not always accompanied by high genetic advance for several characters. For instances, physiological maturity, plant height, primary branches per plant and capsule length revealed high heritability with moderate genetic advance, whereas high heritability coupled with low genetic advance was estimated for vegetative period. In such a case non-additivity may be the major cause of total variation and this situation makes the improvement of such important traits very difficult in sesame (Menzir, 2012). Among the crop duration components, predicted genetic advance was markedly higher for reproductive period than crop maturity and vegetative period (Table 1), suggests that improvement in this character is possible through selection.

A pronounced environmental effect for primary branches per plant was reflected by low estimate of heritability (Table 1). Actually, crop experienced moisture stress at plant growth phase and this moisture stress condition may have interfered with formation and development of primary branches. Phenotypic variation might be increased more rapidly than the genotypic variation for one of the moisture sensitive traits like primary branches and resulted into low heritability.

The correlation analysis (Table 2) indicated that a long reproductive period was associated with a later maturity and a shorter vegetative period. Correlation effect of capsules per plant was significant positive (Parameshwarappa et al., 2009) and of physiological maturity was significant negative (Singh et al., 2008) on seed yield per plant. Correlation effect of vegetative and reproductive periods showed to be independent with seed yield per plant. This indicates that selection for an optimal duration of vegetative and reproductive periods to improve seed yield would not seem to be a deserving objective in sesame. Further, it implies that combine selection for capsules per plant and maturity duration would enable more gain in yield improvement and earliness without affecting the length of reproductive period. Capsule length and seeds per capsule were correlated significantly to each other but not with seed yield. These results are akin to those reported by (Parameshwarappa et al. 2009; Yirgalem et al. 2013).
 
The average yield of top ranking five genotypes (Table 3) showed the yield difference over population mean by increment of 62%, which is little bit higher to predicted gain of 59.56% (Table 1) at 5% selection intensity. The marked difference between average and population mean values was also observed for reproductive period, physiological maturity and capsules per plant. Accordingly high yielding plants are characterized by a high number of capsules per plant, shorter length of reproductive period with early maturity, showing the relation among these traits.
 
Variation in seed yield was largely associated with variation in capsules per plant and reproductive period. Thus, it is evident that in addition to the capsules per plant breeders could better tailor reproductive period and physiological maturity through selection for earliness. Early maturity is very important trait in sesame as it allows plants to suit in different agronomic environments and management practices, escapes the crop from terminal moisture/heat stress, well fits in multiple cropping systems and helps in spreading the area of adaptation.

3 Materials and Methods
The field trial was conducted at the Agricultural Research Farm of the Junagadh Agricultural University, Amreli (21`36 N; 71`13 E), Gujarat State, India, during rainy season of 2010. The site was well drained with medium black soil having pH 7.5 to 8.3, Available N 2 175 to 210 kg/ha and C/N ratio 8 to 12. The average annual rainfall for the 2010 was 750 mm. Mean temperature ranged from 270 C to 330 C during experimental period.

Seventy sesame genotypes sourced from the germplasm available at the Agricultural Research Station, Amreli, representing the diversity with respect to growth habit, yield, crop duration and other traits were used for this study. The experiment was arranged in a randomized block design with three replications. Each genotype was grown in single row plot of 4 meter length keeping row to row distance of 60 cm. Sowing of sesame seeds after mixing with sand was done through hand-drill. The seedlings were thinned with 10 cm plant to plant spacing at three weeks after sowing. The soil of experimental area was fertilized at the rate of 25 kg·N·ha-1 and 25 kg·P·ha-1 as basal dose. The same quantity of nitrogen, i.e., 25 kg·N·ha-1 was applied as topdressing at 30 days~35 days after sowing. The recommended agronomical practices were followed to raise the good crop. All care was taken to minimize any variation due to environmental and cultural conditions.

Biometric observations commenced when the plants began to bloom. In each plot, five plants were randomly selected, tagged and used as representative sample. Data were collected on days to flower initiation, days to 50% anthesis, days to maturity, plant height (cm), primary branches per plant, capsules per plant, capsule length (cm), seeds per capsule, 1000-seed weight (g) and seed yield per plant (g). Days from date of sowing to date on which flowers appeared open on the fifty per cent plants in a plot was considered as days to anthesis. Days to maturity were the duration between date of sowing and date of physiological maturity. Physiological maturity was judged when approximately 75% of the capsules turned yellow. Vegetative period was measured as duration between sowing date and the date of anthesis. Reproductive period was determined as days from date of anthesis till when plant attained physiological maturity.

The data collected on nine characters were subjected to statistical analysis of variance using SAS version 9.2 (SAS Institute, 2008). The genotypic (GCV) and phenotypic (PCV) coefficients of variation, broad sense heritability and the genetic advance as percentage of mean assuming the selection intensity of 5%, and correlation coefficients were estimated for all the traits according to the formulae described by Menzir (2012).

Acknowledgement
The authors are very grateful to Junagadh Agricultural University for providing facilities to conduct this research work.

Authors’ contributions
BA Monpara designed the study, managed the literature searches, wrote the protocol and wrote the first draft of the manuscript. SS Khairnar carried out data collection and performed the statistical analysis. All authors read, edited and approved the final manuscript.

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