First pod height (FPH) is an agronomic trait for the mechanical harvesting of soybeans with combines. The seed loss could be minimized, if the FPH is higher than the height of the cutter bar in combines. Hence, developing soybeans with high FPH has become one of important breeding goals in current crop improvement programs. The objective of this study was to evaluate genetic and environmental variation of FPH in soybean and to analyze the effect of ratio of FPH to plant height (PH) on seed yield. Four genotypes were evaluated across six different environments to analyze environmental variation of agronomic traits including FPH. Three F2 populations were evaluated to analyze genetic variation and relationship between the ratio of FPH to PH and seed yield. The main effects of planting distance, genotype and seeding date were significant for FPH, but FPH is affected more by genetic factors than by environmental factors. The mean heritability value of FPH was 66% across three F2 populations. Seed yield was found to reduce with increase in the FPH/PH ratio. In conclusion, genetic factors have effect more than environments to the variation of FPH. While FPH is higher than cutting height, the smaller ratio can minimize seed yield decrease.
Harvesting is one of the most laborious operations in crop production (Ramteke
Compared to the other agronomic traits, FPH have received little attention of the breeders. Nevertheless, several researchers have analyzed the genetic and environmental variation among soybean genotypes and studied the correlation of FPH with other important traits. The genetic effects of FPH are estimated by determining the broad sense heritability. Martin and Wilcox (1973) evaluated three F2 populations for FPH variation to estimate the genetic effects of F2 plants and observed heritability estimates of 0.62. Similarly, Costa
FPH is positively correlated with plant height, but negatively correlated with number of pods, number of seeds per plant, number of seeds per pod and seed weight (Oz
Four genotypes, ‘Uram’ (Ko
The experiment was conducted in Daegu experiment station, Rural Development Administration (RDA) (Dalseong, 35°54′18″N, 128°26′42″E, Republic of Korea) in 2014. The experiments were designed in a split plot design with two replications in each seeding date. Main plots had three planting distances (7.5, 15, and 30 cm) and sub plots had four soybean genotypes. The plantings were made in 29th May and 27th June 2014. Plots of each genotype were planted in four-row plots 2 m long with spacing of 60 cm between rows, and hills within rows were spaced at 15 cm intervals with two seedlings per hill. The plants were phenotyped at R6 stage (Fehr
Four soybean genotypes, a cultivar Uram and ‘Chamol’ (Lee
The trait data were used for the analysis of variance (ANOVA) of seeding date, planting distance and interactions, and for the analysis of correlation coefficient. The ANOVA was performed using PROC GLM of SAS (SAS 9.2). The data were analyzed in a split plot design with two seeding dates. The differences among mean values were determined using Least Significant Difference at
The combined ANOVA indicated that planting distance (D), genotype (G) were significant for plant height, FPH, number of nodes, number of branches, number of pods and stem thickness. Seeding date (S) was also significant for all the traits except number of branches. Seeding date an effect on FPH and interaction between genotype and seeding date was also detected (Table 2 and 3). Early seeding date showed significantly higher FPH than late seeding date, however not all the genotypes showed significant decrease at late seeding date. FPH in Seonpung significantly decreased at late seeding date but the other genotypes were not significantly changed. Genotype was significantly interacted with seeding date and planting distance for plant height, number of nodes, and number of pods, but not for the number of branches (Table 2).
The FPH was decreased by increasing the planting distance. Mean values for FPH in planting distance 15, 17.5, and 30 cm were 16.1, 15.3, and 13.4 cm, respectively (Table 3). Furthermore, the results show that the four genotypes responded differently by planting distance. FPH did not differ significantly in all the 4 genotypes planted in 7.5 and 15 cm distances; however the genotypes except Uram planted in 30 cm distance showed significant reduction in FPH.
The mean value of FPH for Uram, Seonpung, Tawon, and Milyang 255 were 21.1, 19.5, 8.1, and 11.1 cm, respectively (Table 3). CV of four genotypes in planting distance and seeding date was different. CV for planting distance of Uram, Seonpung, Tawon and Milyang 255 was 6, 8, 18, and 16%, respectively. Uram was less affected by planting distance compared to other three genotypes. CV for seeding date of Uram, Seonpung, Tawon, and Milyang 255 were 4, 18, 1, and 10%, respectively and Tawon was found to be less affected by seeding date. The CVs in all six environments by three planting distances and two seeding dates for Uram, Seonpung, Tawon, and Milyang 255 were 27, 29, 39, and 45%, respectively. This result suggests that Uram is the most stable genotype across the seeding date and planting distance.
Phenotypic values, standard deviation (SD), CV, skewness, and kurtosis of FPH in three F2 populations for FPH are given in Table 4, and the frequency distribution are shown in Fig. 1. FPH of all the three populations showed transgressive segregation, suggesting the quantitative behavior of the trait. The range of FPH for Pop I, Pop II, and Pop III was 1–37, 4–50, and 4–67 cm, respectively. Mean values with SD were 14.7 ± 6.2, 24.0 ± 6.1, and 25.6 ± 9.1 cm, and CV values were 42.1, 25.5, and 35.6% for Pop I, Pop II, and Pop III, respectively. The skewness of Pop I, Pop II, and Pop III was 0.41, 0.58, and 0.92, respectively and distributions were right-skewed. The kurtosis of Pop I, II, and III was 0.01, 1.44, and 1.88 and those distributions were all positive and had sharper peak with fatter tails than a normal distribution.
The range of plant height for Pop I, Pop II, and Pop III was 19–105, 30–150, and 25–200 cm, respectively. Mean values with SD of plant height for Pop I, Pop II, and Pop III were 62.9 ± 17.6, 92.6 ± 13.4, and 108.0 ± 23.9 cm, respectively. CV values for Pop I, Pop II, and Pop III were 27.9, 14.5, and 22.1%, respectively. The skewness of Pop I, Pop II, and Pop III for plant height was −0.28, −0.22, and 0.39, respectively. The kurtosis of Pop I, Pop II, and Pop III for plant height was −0.54, 1.65, and 1.44, respectively. The skewness and kurtosis of plant height were tended to left skewed and wider peak compared with FPH.
Broad-sense heritability estimates for FPH and plant height in three populations are shown in Table 4. Heritability for FPH of Pop I, Pop II, and Pop III was 51, 79, and 67%, respectively. Mean heritability for FPH was 66%. Heritability for plant height of Pop I, Pop II, and Pop III was 90, 82, and 73%, respectively. Mean heritability for plant height was 81% and comparably higher than that of FPH. In correlation analysis, FPH showed positive and significant correlation with plant height (
Mean and range data obtained from the samples in Pop I and Pop II are given in Table 6. The data suggests that the increased FPH/PH affects number of pods per plant and yield negatively. When FPH/PH was more, the yield decreased significantly. In Pop I, the seed yield was significantly decreased from 32.0 g in 0.05–0.10 ratio to 5.5 g in 0.31–0.35. The number of pod that is a trait highly related to seed yield was also significantly decreased from 79 in 0.05–0.10 ratio to 45 in 0.31–0.35. In Pop II, similar variation of evaluated traits was recognized. The seed yield was significantly decreased from 48.3 g in 0.05–0.10 ratio to 0.26–0.30 and the number of pods was also significantly decreased from 109 in 0.05–0.10 ratio to 58 in 0.26–0.30. The variation of one-hundred seed weight in Pop I and Pop II was not shown meaningful tendency relating to FPH/PH. FPH in Pop I and Pop II was increased, but variation of plant height was not relating to variation of FPH/PH.
Phenotypic variation for a quantitative trait is influenced by the genetic and environmental factors. FPH is a quantitative trait (Fig. 1) and affected by the environments, such as seeding date and planting distance. In this study, decrease in the FPH was observed with increased planting distance and delayed the seeding date. These results were similar with the studies reported by Ibrahim (2012a, 2012b). Furthermore, significant D × S and G × S interactions, like those reported by Ibrahim (2012a, 2012b) and Karaaslan
Heritability analyses in the segregating populations are conducted to estimate the genetic effects of FPH. Martin and Wilcox (1973) evaluated three F2 populations for FPH and estimates of heritability were 63% (Beeson × L66-1085-1-270), 74% (Amsoy71 × L66-1085-1-239) and 50% (Wayne × L66-1085-1-251). Costa
The frequency distribution of FPH in three F2 populations (Pop I: Uram × Chamol, Pop II: Uram × Milyang 257 and Pop III: IT143195 × Uram) showed normal distribution in the F2 populations, indicating that FPH behave as a quantitative trait in these populations.
FPH was found to show positive correlation with plant height, number of nodes and stem thickness, but negative correlation with the number of pods. Similar correlations were observed by Oz
The number of pods is one of the most important traits determining seed yield (Oz
Although the highest yield was achieved in the two populations when the FPH/PH ratio was between 0.05–0.10, the FPH for the Pop I and Pop II was in the range 2–7 and 4–5, respectively. Therefore, it is difficult to select FPH around 15cm for combine harvest in this ratio. However, when the FPH/PH ratio range was 0.16–0.25, the seed yield per plant was 8–58 g with FPH ranged 4–17 cm in Pop I. In case of Pop II, when the FPH/PH ratio range was 0.11–0.20, the seed yield per plant was 4–96 g with FPH ranged 9–24 cm. These results indicated that soybean yield and FPH were different by cross combination and FPH/PH ratio range 0.16–0.25 had proper range for FPH and seed yield in both population.
In conclusion, high FPH prevents harvesting losses, but seed yield in a plant could be decreased. Seed yield was found to reduce with increase in the FPH/PH ratio. The adequate FPH/PH ratio for a plant was found to be 0.16–0.25 in the present study. FPH is a trait which can be selected by phenotype in the field because genetic variation of FPH is higher than environmental variation. However, genetic information (e.g., QTLs and related genes) of FPH is not analyzed at this time. Knowledge of genetic background of agricultural trait is important for breeders. Therefore, further research for identifying detailed genetic information should be conducted in the future.
This research was supported by the National Institute of Crop Science (NICS), Rural Development Administration (RDA) of South Korea (No. PJ011225022017).
Agronomic traits of four genotypes, Uram, Seonpung, Tawon and Milyang 255 evaluated in regional yield trials conducted across eight regions in Korea for 3 years (2011–2013).
|Flowering date (month day)||Maturity date (month day)||Plant height (cm)||First pod height (cm)||Number of nodes||Number of branches||Number of pods||100-seed weight (g)|
|Uram||Aug. 1||Oct. 9||79az)||19a||14b||3.1a||47b||25.8a|
|Seonpung||Aug. 5||Oct. 19||67b||18a||16a||3.0a||43b||25.9a|
|Tawon||July 21||Sep. 29||51c||7b||13c||2.7a||69a||9.7b|
|Milyang 255||July 27||Oct. 9||44c||7b||13bc||3.1a||71a||9.4b|
z)Means followed by the same letter within columns are not significantly different according to DMRT at 0.05 level.
Mean square value and degree of freedom for analysis of environmental variation for plant height, first pod height, number of nodes, number of branches, number of pods and stem thickness for four soybean genotypes grown in three planting distances and two seeding date in Daegu experiment station at 2014.
|Source||dfz)||Plant height||First pod height||Number of nodes||Number of branches||Number of pods||Stem thickness|
|Seeding date (S)||1||23,166.3***||280.1***||406.1***||4.3||27,592.9***||390.3***|
|Block (in seeding)||1||3894.0***||130.7*||2.0||3.3||1188.3||25.2***|
|D × S||2||113.6*||123.2***||2.3||3.6||571.2||1.7|
|G × S||3||479.8***||73.3*||7.9***||0.5||2,394.3***||0.6|
|D × G||6||163.2***||14.9||4.9***||2.3||3,664.2***||2.5*|
|D × G × S||6||169.7***||34.3||1.9||1.7||614.2||1.3|
*, **, and ***stand for significantly different at 0.5, 0.01, and 0.001 level, respectively.
z)Degree of freedom.
Evaluation of first pod height and coefficient of variation in different planting distance and seeding date.
|Treatments||First pod height (cm)|
|Planting distance (cm)||7.5||21.0||21.2||9.1||13.0|
|Seeding date||May 29 2014||21.7||21.9||8.1||11.9|
|June 27 2014||20.4||17.1||8.0||10.4|
z)CV(%) was calculated across planting distance and seeding date.
y)Mean FPH calculated across planting distance and seeding date.
Mean with standard deviation (SD), range, coefficient variance (CV), skewness, kurtosis, and heritability of plant height and first pod height of three cross combinations in three F2 populations.
|Cross combination||Plant height (cm)||First pod height (cm)|
|Mean ± SD||Range||CV (%)||Skewness||Kurtosis||Heritability (%)z)||Mean ± SD||Range||CV (%)||Skewness||Kurtosis||Heritability (%)z)|
|Pop I (Uram × Chamol)||P1 (n = 22)||83.4 ± 9.0||72–120||10.8||−0.81||1.24||17.5 ± 4.8||12–35||27.6||2.11||6.66|
|P2 (n = 24)||43.7 ± 3.6||37–52||8.2||0.35||0.02||90||10.6 ± 3.9||3–18||15.1||0.29||−0.43||51|
|F2 (n = 704)||62.9 ± 17.6||19–105||27.9||−0.28||−0.54||14.7 ± 6.2||1–37||42.1||0.41||0.01|
|Pop II (Uram × Milyang 257)||P1 (n = 25)||91.7 ± 4.2||81–98||4.6||−0.63||−0.08||21.6 ± 2.2||16–25||10.3||−0.49||0.17|
|P2 (n = 23)||88.0 ± 7.9||71–100||9.0||−0.87||−0.03||82||24.6 ± 4.2||15–33||17.1||−0.12||0.32||79|
|F2 (n = 679)||92.6 ± 13.4||30–150||14.5||−0.22||1.65||24.1 ± 6.1||4–50||25.5||0.58||1.44|
|Pop III (IT143195 × Uram)||P1 (n = 11)||126.8 ± 18.6||81–162||14.7||−0.79||3.42||30.9 ± 5.4||20–38||17.4||−0.48||−0.30|
|P2 (n = 25)||86.4 ± 8.4||63–101||9.7||−0.78||0.88||73||20.2 ± 5.1||10–31||25.2||−0.17||−0.06||67|
|F2 (n = 538)||108.0 ± 23.9||25–200||22.1||0.39||1.44||25.6 ± 9.1||4–67||35.6||0.92||1.88|
z)Broad sense heritability.
Correlation coefficient among agronomic traits of four genotypes evaluated in two seeding date and three planting distance.
|Agronomic traits||Plant height||First pod height||Number of nodes||Number of branches||Number of pods||Stem thickness|
|No. of nodes||0.66***||0.49***||1|
|No. of branches||−0.06NS||−0.18***||0.25***||1|
|No. of pods||−0.29***||−0.47***||0.06NS||0.58***||1|
NS and ***stands for none significant at 0.05 level and significant different at 0.001 level, respectively.
Mean value of seed yield per plant, number of pods, one hundred weight, first pod height and plant height by the ratio of FPH to plant height which calculated from randomly sampled plants in two F2 populations in Daegu experiment station in 2014.
|Cross combination||Traitsz)||Ratio of first pod height to plant height|
|Pop I (Uram × Chamol)||YP (g/plant)||32.0ay) (8–50)x)||26.3ab (2–62)||21.7bc (8–54)||21.0bc (6–58)||23.3abc (4–56)||15.5c (4–32)||15.2c (4–28)|
|NP||79a (25–148)||59abc (10–130)||49bc (21–111)||50bc (19–124)||64ab (8–160)||45bc (6–128)||40c (12–94)|
|HSW (g)||29.5ab (16.0–38.9)||30.9a (24.0–37.0)||30.1a (17.1–36.0)||30.9a (22.0–37.8)||25.5b (16.0–33.9)||25.9b (12.1–40.0)||29.6ab 14.3–40.0)|
|FPH (cm)||4d (2–7)||7d (4–11)||11c (8–17)||16b (7–25)||21a (8–31)||21a (9–31)||22a (9–37)|
|PH (cm)||52cd (26–89)||49d (27–73)||62abcd (46–96)||66ab (29–101)||74a (26–105)||64abc (29–95)||56bcd (22–92)|
|No. of samples||11||16||18||21||26||22||12|
|Pop II (Uram × Milyang 257)||YP (g/plant)||48.3a (46–51)||38.3ab (4–96)||26.1bc (10–50)||25.2bc (2–72)||15.2c (2–28)||18.3c (6–38)||15.1c (2–30)|
|NP||109a (103–114)||110a (17–227)||78ab (34–138)||81ab (18–157)||58b (10–89)||61b (27–96)||46b (11–81)|
|HSW (g)||23.8a (22.0–25.5)||20.1ab (10.0–30.0)||21.0ab (12.0–26.0)||18.7ab (8.7–28.6)||16.9b (9.6–26.5)||18.7ab (11.7–24.7)||18.8ab (9.5–28.0)|
|FPH (cm)||5f (4–5)||13e (9–17)||17d (11–24)||22c (17–28)||28b (22–35)||30b (24–38)||35a (29–45)|
|PH (cm)||70b (65–75)||95a (77–126)||92a (60–122)||93a (78–113)||98a (80–117)||88a (70–113)||92a (76–111)|
|No. of samples||2||15||15||15||15||16||10|
z)YP: seed yield per plant, NP: number of pods, HSW: 100-seed weight, FPH: first pod height, PH: plant height.
y)Within rows, means followed by the same letter are not significantly different according to DMRT at 0.05 level.
x)Value in parenthesis indicate the range of evaluated traits in each ratio of first pod height to plant height.