Genetic Parameters Estimation of High Yielding and Large Seed Size of Soybean [Glycine max (L.) Merrill] Genotypes

In Indonesia, the soybean [Glycine max (L.) Merrill] seed yield and seed size  are two important agronomic traits needed by farmers Therefore,  genetic improvement through breeding activity to derive the intended lines or cultivars is necessary. Plant breeders need to identify the genetic diversity in soybean to select genotypes with high productivity supported by desirable yield components. The availability of desirable source genes and breeding method used highly determine the success of a soybean variety development for high productivity. To broaden the genetic base of soybean cultivars, it is necessary to exploite the availability of germplasm lines based on the mean performance having excellent source of genetic variability (Kumar et al. 2020).

The success of a variety development is influenced by the genetic parameters of  certain trait of the genotype. The genetic parameters include genotypic and phenotypic variances, heritability and genetic advance. Heritability is one of the important genetic parameters that is used to predict the progress of the selection in the breeding activity of a certain character. Based on the value of the heritability, a certain character could be controlled by genetic factors or influenced by environmental factors. Broad sense heritability is the proportion of genotypic variance (σ²_g) to phenotypic variance (σ²_p). The genotypic variance is a variance total of dominance (σ²_D), additive (σ²_A) and epistatic (σ²_I). The combination of the high heritability and high genetic advance provides the degree of selection progress for crop improvement programme (Jain et al. 2018; Sulistyo and Mejaya, 2018).

The improvement of seed size of existing varieties togetherly with other superior varieties having large seed size is necessarry. Some genetic criteria were estimated for agronomic traits that enable to obtain the effective improvement of the soybean genotypes. The objective of this study was to estimate the genetic advance of soybean genotypes to obtain the new large-seeded and high yielding varieties.

Experimental site
 
The trials were conducted in two locations in East Java Province, Indonesia, i.e. at Jambegede, Malang (-8°10’22” S; 112°33’40”E; 305 m asl) and Ngale, Ngawi (-7°24’56” S; 111°22’11”; 56 m asl) Experimental Farms during the 1^st dry season (1^st DS) 2018.

Thirty soybean homozygous lines and two national check cultivars (Anjasmoro and Dega 1 which were released in 2001 and 2016, respectively) were arranged in a randomized completely block design, with three replication (Table 1). Each genotype was planted in a plot of 5.6 m².     



The soybean in two locations was planted after rice, manual planting with spacing of 40 cm inter-row and 15 cm within row, two plants/hill. Fertilizer at the rate of 100 kg ha^-1 SP36 (36% P₂O₅), 250 kg/ha of Phonska (15-15-15) and 1.5 t/ha manure were applied to each trial. The fertilizers were applied at planting time in a line of 5 cm from the planting rows and the manure was used as planting hole cover.
 
Measurements on agronomic characteristics
 
Measurements on 10 random sample plants were taken on plant height, main branches number, fertile nodes number, filled pod number, seed weight/plant. Seed weight/plot, flowering and maturity days and 100 seed weight were observed on plot basis. The seed weight/plot (5.6 m²) was converted to t/ha using formula (1) and then converted to seed yield at 12% moisture content using formula (2). Potential yield was calculated based on seed weight of 10 plants which was converted to t/ha on the assumption full plant stand.

 

                                Y= (10/A)*X  .....(1)

 
Where
Y= Seed yield (t ha^-1).
A= Plot area (m²).
X= Seed yield in harvested plot (kg).
 

                         Y12= [(100-Wi)/88]*Y  .....(2)

 
Where
Y12 = Seed yield at 12% moisture content (t ha^-1).
Wi = Initial seed moisture content (%).
Y = Seed yield calculated using formula (1).
 
Analisis of variance
 
Estimation of variance components (genotypic variance, phenotypic variance and environmental variance) were calculated from the analysis of variance as described by Hallauer and Miranda (2010). Genotypic and phenotypic variance was calculated based on the following equation:

 

σ²g= (MSg-MSe)/r

 

σ²p= (σ²g + MSe)

 
Broad sense heritability values (h²) are classified as low criteria if the h² value is < 0.2, moderate criteria if 0.2≤ h²≤0.5 and high criteria if h²>0.5. Determination of heritability values using the following equation:

h²= σ²g/σ²p

 
The determination of the value of the expected genetic advance  was calculated using the following equation:

 

KGH= i × h² × σp

Combined variance analyses over the two locations showed the significant interaction on flowering days, maturity days, number of filled pods and 100 seed weights (Table 2). The existence of G × E interaction results in the response of the genotypes to environments (Morsy et al., 2016).     

       
 
Heritability
 
There were differences in genotypic variance of soybean between Ngawi and Malang locations, especially in plant height, filled pods number /plant, maturity time and  seed weight/ plant (Table 3). The genotypic variance for plant height in Ngawi (83.61) is higher than that in Malang (6.95). The same case occur on filled pods number /plant, maturity time and seed weight/plant. The phenotypic variance for plant height in Ngawi (103.79) is higher than that in Malang (26.61). The same case occur on filled pods number /plant, maturity time and seed weight/ plant.    

The phenotypic variances was found higher than the genotytic variances for all characters in both locations indicate the significant effect or important role of environment in the expression of the characters. In Ngawi, the phenotypic variance for plant height (103.79) is higher than the genotypic variance (83.61). In Malang, the phenotypic variance for plant height  (26.61) is higher than the genotypic variance (6.95) (Table 3).

The heritability estimation values in Ngawi ranged from 0.31 (seed weight/plant) to 0.81 (plant height) (Table 3). In Malang, the heritability ranged from 0.09 (seed weight/plant) to 0.61 (100-seeds weight). Two traits (maturity days and 100 seeds weight) consistently showed similar heritability values in both locations.



The closer differences between estimates values of phenotypic variances and genotypic variances, for certain traits (100-seeds weight) indicate that expression of this characters under study was less influenced by environmental factors. The high values of phenotypic variances and genotypic variances indicate the presence of sufficient genetic variability for selection of the traits (Baraskar et al., 2014). Narrow differences between phenotypic variances and genotypic variances of the characters revealed that less environmental influence on the expression of the characters (Malek et al. 2014).

The phenotypic variances was found higher than genotypic variances which indicates the significant effect or important role of environment in the expression of the characters (Kuswantoro et al., 2018). The high genotypic and phenotypic variances were exhibited by the seed weight and plant height (Jain et al., 2018; Jandong et al., 2020). High heritability with high genetic advance for seed yield/plant, number of pods/plant and 100-seed weight was observed by Kumar et al. (2020) which indicated the predominance of additive gene action in controlling these traits.
 
Expected genetic advance
 
Table 4 shows that soybean genotypes evaluated in Ngawi produced higher seed yield (2.59 t/ha) compared to that in Malang (1.98 t/ha). This was supported by a higher filled pod number/plant and larger 100-seed weight and seed weight/plant compared to the same traits measured in Ngawi. The difference in elevation and daytime temperature between the two sites could be responsible to the difference in maturity days. Elevation in Malang site is higher than in Ngawi site and temperatur in Malang site during the daytime is 1-3°C lower than that in Ngawi.

  

In selection intensity of 20%, the value of expected genetic advance in Ngawi varies from 0.78% (filled pod number/plant) to 27.22% (branches number/plant) (Table 4). In Malang, the value of expected genetic advance varies from 0.70% (filled pod number/plant) to 15.34% (plant height). In Ngawi, other agronomic traits that have a genetic advance above 10% are maturity days, fertile node number/plant, 100 seed weight/plant and seed yield. In Malang, there was no other agronomic trait that have a genetic advance above 10%.   

The highest genetic advance value of branches number/plant and plant height could be used as soybean selection criteia in Ngawi and Malang locations, respectively. The 100 seed weight had high both heritability and fertile node number/plant with genetic advance values in Ngawi suggested that this trait could be used as soybean selection criteria in Ngawi condition. The varied responses on vegetative and generative periods determine the seed yield which are attributed to pod number, seed number per pod and seed size (Hu and Wiatrak, 2012).

High heritability and genetic advance of a character indicates additive genes in controlling the character by inheritancing the genetic factor from parent to offspring. Combination of genetic variability, high heritability and genetic advance could be effective on selection based on phenotype traits (Singh et al., 2020; Baraskar et al., 2014; Osekita and Olorunfemi 2014). The number of filled pods, plant height and 100 seed weight were also considered an effective trait as a direct selection criteria to obtain high seed yield and large seed size in soybean breeding (Ghodrati 2013; Malek et al. 2014; Sulistyo et al., 2021; Mejaya et al., 2022; Putri et al., 2022;).
 
The selected lines
 
The seed weight/plant can be used as an indicator of  yield potential of a certain genotype. Potential seed yield of 32 soybean genotypes tested ranged from 1.73 to 3.48 t/ha in Ngawi and 4.82 t/ha and from 1.25 to 2.93 t/ha in Malang with average of two locations ranged from 1.96 to 3.06 t/ha (Table 5).

  

Average of two locations, 12 out of 30 soybean lines showed higher seed yield than the check variety Anjasmoro, by which 6 lines showed higher 100-seed weight than the check variety Dega 1. The soybean lines G 5 (Anjasmoro ×  MD6)-11 and G 21 (Grob × Argopuro) × (Pangrango)-41-10 showed the highest seed yield of 3.03 and 3.07 t/ha, respectively, which are significantly higher than the Anjasmoro (2.30 t/ha) (Table 6). 

 

The maturity time and 100 seeds weight traits have similar heritability values in both Ngawi and Malang locations. In Malang, the value of expected genetic advance was less than that in Ngawi, suggested that Ngawi is better location for soybean selection for high yield potensial and large seed size (100-seed weight). The soybean lines G 5 (Anjasmoro × MD6)-11 and G 21 (Grob × Argopuro) × (Pangrango)-41-10 have the highest seed yield of 3.03 and 3.07 t/ha, respectively, which is significantly higher than the check variety Anjasmoro (2.30 t/ha). G 21 also has larger 100-seed weight than the check variety Anjasmoro.

Thank you to the Directors of the Indonesian Legumes and Tuber Crops Research Institute (ILETRI), Ministry of Agricultural of the Republic of Indonesia for the financial support of this research. Our thanks to Mr. Abdullah Taufiq, Dr. Titik Sundari and Dr. Novita Nugrahaeni for their assistance in this research.