Soybean [
Crop breeding program requires a significant amount of time and labor. Among the various stages in crop breeding program, generation advancement is one of the bottleneck steps to decrease breeding period. There have been various approaches to reduce this, such as marker-assist selection (MAS) (Johnson 2003; Eathington
LED module manufactured by Wooree Bio (Ansan, Korea) was composed of blue, green, and red LEDs. LED growth shelf was made by alternately installing one lane consisting of red (630 nm), blue (440 nm), and green (530 nm) and the other lane consisting of red (660 nm), blue (440 nm), and green (530 nm). A total of 8 shelves were made, one controller to control 4 shelves were equipped, and one 24V 100A power supply was installed per two shelves (Fig. 1). And by connecting the controller and the computer with a data cable, it was possible to control light time and strength using the software provided by the manufacturer. The Photosynthetic photon flux density (PPFD) of maxi-mum output was measured at 732.2 ± 19.6 mmol/(m^{2}∙s) at 30 cm above the ground. For the stability of the LED, 80% of the maximum output was employed to the maximum condition.
A 50-seedling tray measuring 28 × 54 × 11.2 cm was employed in this study. And two planting densities were chosen: 10 cm × 10 cm (low density) and 5 cm × 5 cm (high density) (low density). Conditions of light separated using two sources, LED in the SB growth room and sodium lamp in the glass house (Fig. 2). LED growth shelves were installed in a room separated from the outside which was maintained at 25℃ ± 2℃ of temperature and humidity of 50% ± 10% using thermo-hygrostat, and a sodium lamp was equipped in the glass house with the air conditioner set to 25℃. PPFD was measured using a PG200N Spectral PAR Meter (UPRtek, Taiwan) at 30 cm above the ground of each growth floor. In the LED growing room, two settings of LED intensity (high; 80% of total output, and low; 40% of total output) were used.
As a result of measuring PPFD under various light conditions, it was measured to average 506.0 ± 7.4 mmol/(m^{2}∙s), 257.4 ± 10.4 mmol/(m^{2}∙s) at LED high and low intensity. At sodium lamp conditions, the average was 288.5 ± 6.9 during the day and 188.4 ± 10.8 at night, which was used in this experiment. More detailed information was indicated in Table 1.
Table 1 . Summary of photosynthetic photon flux density measurement results under various light conditions.
Condition | Point of measurement | PPFD (mmol/(m^{2}∙s)) | PFD-B (mmol/(m^{2}∙s)) | PFD-G (mmol/(m^{2}∙s)) | PFD-R (mmol/(m^{2}∙s)) |
---|---|---|---|---|---|
LED (High PPFD) | 30 cm above the ground | 506.0 ± 7.4 | 184.9 ± 4.8 | 126.1 ± 1.2 | 195.1 ± 3.6 |
LED (Low PPFD) | 257.4 ± 10.4 | 92.9 ± 3.8 | 63.4 ± 3.1 | 101.1 ± 4.0 | |
Sodium lamp (day) | 288.5 ± 6.9 | 35.4 ± 2.6 | 158.2 ± 4.2 | 94.5 ± 4.0 | |
Sodium lamp (night) | 188.4 ± 10.8 | 10.8 ± 6.7 | 126.2 ± 5.7 | 55.5 ± 5.6 |
Photosynthetic photon flux density was measured in a wavelength range of 400 to 700 nm, and photon flux density of blue, green, and red were measured in a range of 400 to 500 nm, 500 to 600 nm, and 600 to 700 nm.
PPFD: photosynthetic photon flux density, PFD: photon flux density.
A total of 29 soybean varieties were used in the experi-ment, and 4, 9, 7, 6, and 3 varieties were included in the early, middle, middle-late, late, and unknown maturity groups. Table 2 provided more comprehensive information.
Table 2 . List of varieties used in the experiment according to maturity group.
Maturity group | List of varieties |
---|---|
Early-maturity group | Hannam, Ilpumgeomjeong, Josaengseori, Yonpoong |
Mid-maturity group | Pungwon, Galchae, Haman, Williams82, Daewon, Hwangkeum, Cheongja, Socheong 2, Daeheuk |
Mid-late-maturity group | Daepung, Soho, Taekwang, Uram, Danbaek, Saedanbaek, Cheongja 3 |
Late-maturity group | Bangsa, Somyeong, Shinhwa, Pureun, Heukcheong, Seoritae |
Unknown maturity group | PI96983, 1000-al, PI84669 |
Two growth periods were measured at R1 stage, which is the beginning bloom, and R6, which is full-seed stage. The number of pods per plants were recorded at R8 stage, which is 95% of pods were mature in color. Three biological replicates were tested in each variety.
Analysis of correlation coefficient between 4 maturity groups and 18 phenotypes were performed using R Statistical Software (V4.1.2; R Core Team 2021) and COR R package (Ihaka and Gentleman 1996).
Under the condition of High PPFD and low density, the mean period to R1 was 27.0 days and the standard deviation was 1.3 days. The shortest period was 26 days for 15 varieties and the longest period was 30 days for one variety. The mean of the period to R6 was 52.5 days and the standard deviation was 5.3 days. The shortest period was 47 days for 7 cultivars, and the longest period was 64 days for 1 cultivar. In the condition of high density, the mean period to R1 was 29.1 days and the standard deviation was 1.4 days. The shortest period for 14 varieties was 28 days, and the longest period for one variety was 32 days. The mean period to R6 was 52.5 days and the standard deviation was calculated as 4.6 days. The shortest period was 49 days for 15 varieties, and the longest period was 63 days for one variety.
At low PPFD and low-density conditions, the mean period to R1 was 27.7 ± 1.7 days. The shortest period was 26 days for 12 varieties, and the longest period for 2 varieties was 31 days. In R6, the mean of the period was 51.0 days and the standard deviation was 4.8 days. The shortest period was 47 days in 10 cultivars, and the longest period was 61 days in 2 cultivars. In the condition of high density, the mean period to R1 was 30.2 days, and the standard deviation was 2.9 days. The shortest period was 28 days for 12 varieties and 41 days for one variety. The mean duration to R6 was 51.0 days and the standard deviation was 4.8 days. The shortest period was 47 days in 10 cultivars, and the longest period was 61 days in 2 cultivars.
Under the conditions of a sodium lamp and a greenhouse of low density, the average cycle to R1 was 37.3 days and the standard deviation was 4.9 days. The shortest period was 30 days for 2 varieties, and the longest period for 4 varieties was 47 days. The mean time to R6 was 74.5 days, and the standard deviation was 5.2 days. The shortest period was 65 days for one cultivar and the longest period was 84 days for one cultivar. The average period from high-density greenhouse to R1 was 41.0 days and the standard deviation was 4.1 days. The shortest period for the two varieties was 35 days, and the longest period for the two varieties was 49 days. The mean of the period to R6 was 75.9 days, and the standard deviation was 4.0 days. The shortest period was 67 days in the second variety, and the longest period was 84 days in the first variety.
Under the high PPFD and high-density conditions, the average number of pods per plant was 4.5 ± 1.9, and under the same light and low-density conditions, the average number was 2.8 ± 1.3. The average number of pods per individual was 2.6 ± 2.0 in the low PPFD and high-density conditions. Under the same light conditions and low- density conditions, the average number was 3.4 ± 1.4. Under sodium lamp conditions, the average number was 2.1 ± 1.6 in high-density and 1.9 ± 1.1 in low-density.
There was no significant correlation between phenotypes and maturity group, according to the Pearson correlation coefficient. The highest positive and negative correlation were 0.23 and ‒0.42, respectively (Supplementary Table S1).
Through this study, it was feasible to compare the period of time from planting to harvest as well as the number of pods caused by differences in light source type, intensity, and planting density. According to planting density, there was no apparent change between R1 and R6. The average number of pods per plant, however, differed according to planting density, with 4.5 ± 1.9 being the highest value observed in the high-density, high PPFD condition. Overall, it was determined that growing conditions utilizing LEDs in a closed environment were faster growing than those using sodium lamps in a greenhouse, taking an average of 10.7 days less to reach R1 and 22.6 days less to reach R6 (Fig. 3).
A further study, studies dealing with different ratios of red and blue LEDs and measuring the phenotypes that appear will be conducted. The results of flowering time and plant height according to three ratios of red and blue LEDs have already been published (Jahne
We developed the growth conditions for reducing the period of soybean generation progression based on speed breeding. Developed conditions are as follows. (1) 506 mmol/(m^{2}∙s) of PPFD at 30 cm from the ground, (2) Planting density of 5 cm × 5 cm, (3) irradiation using LED light source for 9 hours, (4) temperature of 25℃ ± 2℃ and (5) humidity of 50% ± 10%. If this condition is used, soybeans can be advanced by one generation within 73 days. It is possible to advance five generations a year using only SB, and if it includes the advancement of breeding lines in the field, it is possible to advance three generations indoors and one generation in the field, for a total of four generations (Fig. 4).
This research was supported by the project “Develop-ment of a large set of molecular markers associated with major environmental stresses in soybean (No. PJ01577 12022)” in Rural Development Administration (RDA) of Rep. Korea.
The authors declare that they have no conflict of interest.