The performance of agronomic characters
Variation among genotypes was found in the performance of the agronomic characters of 50 soybean genotypes (Table 2). The days to maturity varied from 75 to 81 days (average of 78 days). In Indonesia, days to maturity is an important character in soybean development, since soybean is cultivated in a yearly planting pattern of paddy-paddy-soybean. In this study, most of the tested genotypes have early days to maturity (<80 days) (Fig 2A).
The growth characters of plant height, number of branches and number of nodes (Fig 1B, 1C, 1D) generally become the mutually agronomic supporting characters
(Li et al., 2020). The average plant height, number of branches, and number of nodes were 57.32 cm, 1.49 branches/plant and 10.25 nodes/plant. The number of pods consisted of filled and empty pods (Fig 1E, 1F). The average of filled pods was 29.27 pods/plant, meanwhile the average of empty pods was low (1.06 pods/plant). The yield characters, namely 100 seed weight and seed yield/plant were 15.59 g/100 seeds and 18.10 g/plant (Fig 1G, 1H), respectively. In Indonesia, large-seeded soybean is important for industrial raw material for tempeh. According to
Sulistyo et al., (2021), the length, width, thickness, the ratio of the three characters and the weight of 100 seeds can be used as selection criteria in a soybean breeding program to obtain large-seeded soybeans with a round or elliptical shape.
In this study, the range of seed yield of 50 genotypes was 6.18-18.10 g/plant. A total of 24 genotypes produced yield above the general mean (range of 10.23-18.10 g/plant).
Ige et al., (2021) evaluate the combining ability for seed yield, obtain several genotypes as the best combiners for the number of pods/plant and seed yield/plant in soybean. In black gram, the grain yield was associated with the performance of plant height and the number of primary branches per plant
(Priya et al., 2021).
Pod-shatter resistance
Pod shattering resistance of 50 soybean genotypes varied among genotypes (Table 1). The use of gradual temperature in the oven-dry method showed that the soybean pods were remaining unshattered after subjected to 30°C dan 40°C. Pods began to shatter after subjected to 50°C and were increased after 60°C.
This study showed that the use of the oven-dry method of 60°C provides a higher pressure than 50°C, thus the selected resistant genotypes have a chance of being resistant in the field condition.
Interrelationship among characters
The interrelationship among yield, yield components, and pod shattering was evaluated using the genotype by trait (GT) biplot. The GT biplot of mean performance of soybean genotypes explained 52% of the total variation. The low goodness of fit reflects the complexities of the relationships among characters (
Yan and Rajcan, 2002;
Sharifi and Ebadi, 2018). Nevertheless, the biplot could still capture the fundamental patterns among the characters
(Atnaf et al., 2017).
In the GT biplot (Fig 3), an acute angle (90°) indicates a positive correlation, an obtuse angle (>90°) indicates a negative correlation and a right angle indicates no correlation (
Yan and Tinker, 2006). Thus, the pod shattering (PSH) was positively correlated with 100 seed weight (SWG) and plant height (PHG), but negatively correlated with other agronomic characters. A larger seed size and a higher plant height causing an increase on the pod shattering percentage. The positive association between pod shattering and seed size was also reported in previous studies
(Bara et al., 2013; Krisnawati et al., 2020). On the other hand, seed yield was positively correlated with seed weight per plant (SWP), number of branches (NOB), number of filled pods per plant (NFP) and number of nodes per plant (NON). In this study, the days to maturity was positively correlated with NEP, NOB, NFP and NON. The interrelationship between yield and yield components and the use of for selection criterion in soybean have been extensively studied (
Yahaya and Ankrumah, 2016;
Kumar et al., 2020).
Character profiles of genotype
In Fig 4, a set of perpendicular lines divides the biplot graph into several sectors to characterize the genotypes. In Fig 4, only two quadrants in the biplot containing genotype points and agronomic character points. The genotypes located in the biplot vertex (vertex genotypes) perform best in one or more characters. Accordingly, in the first quadrant, G33, G16 and G50 as vertex genotypes demonstrated the best performance on the NEP, DTF, NON, NFP, NOB and SWP characters. In the second quadrant, G36 as the vertex genotype indicates that the genotype has the highest value for SWG, PHG and PSH characters. The genotypes located at the biplot vertices are very useful as candidates for parents in the breeding programs to develop varieties responsive to the traits of interest (
Yan and Rajcan, 2002;
Paramesh et al., 2016).
In the evaluation of the pod shattering character, genotypes that formed an acute angle with the pod shatteringector revealed genotypes with an above-average performance (high pod shattering). The genotype that forms an obtuse angle with the character vector (located in the opposite direction to the character’s position) is the genotype with lower performance for the character. Based on Fig 4, G20 (Grob/G100H-1-588) and G33 (G100H/Mhmr-4-993) were identified as high shatter-resistant and high yield. These genotypes have the potential to be developed as superior varieties as well as a source of genes to improve soybean pod shattering resistance.
