
Wheat (
Dissecting the genetic loci underlying culm length and days to heading date (DHD) is also crucial to maximize yield, as the major genes controlling these traits affect yield components (Tshikunde
In Korea, wheat is mostly cultivated as a secondary crop in rice-wheat double cropping practices. Therefore, late heading causes wheat harvesting without sufficient grain filling in order to sow the main crop such as rice in an optimal planting season, resulting in a decrease in wheat yield and quality (Cho
A population of 94 doubled haploid lines was produced from the cross between Korean wheat cultivars, Keumkang and Olgeuru, using the wheat × maize system described by Inagaki and Mujeeb-Kazi (1995). Keumkang is a popular cultivar with good milling, end-use quality and early matu-rity (Song 1998). Olgeuru exhibits a higher yield than Keumkang (Nam 1994). The doubled haploid lines were grown at the Upland Crop Experimental Farm of the National Institute of Crop Science, Rural Development Administration (Iksan, Korea) for seed multiplication in 2009. Field trials were performed in upland condition at Jeonbuk National University (35°85΄N 127°13΄E) in Jeonju, South Korea, during three growing seasons (2017, 2018, and 2019). The seeds were sown in late October, and each plot consisted of three 2 m rows spaced 25 cm apart. The plots were combine-harvested in mid-June. The field management was conducted according to the standard wheat cultivation manual of Rural Development Admini-stration (RDA), South Korea (RDA 2012).
A total of eight yield-related traits were evaluated: DHD, culm length (CL), spike length (SL), kernels per spike (KPS), tiller number per m2 (TN), test weight (TW), thousand kernel weight (TKW), and yield (YD). DHD was recorded as the number of days from sowing date to heading date when 50% of the plants in each plot showed the emergence of spikes from the stem. CL was determined by measuring the length from the ground to the base of the spike and SL was measured as the length of the spike excluding awns. KPS was measured as the number of kernels per main spike. CL, SL, and KPS were measured from the main culms of ten plants randomly selected in each plot at maturity. TN was counted as the number of stems per m2. TW, TKW, and YD were measured after harvesting and drying the grains at 14% moisture content. TW and TKW were evaluated by weighing one liter of grain and 1,000 kernels, respectively. YD was recorded by weighing the grains from each plot and converting the value in kg/10a.
Genomic DNA was extracted from young leaf tissue using a DNA extraction kit (Solgent, South Korea) according to the manufacturer’s instruction. The 94 dou-bled haploid lines and the parental cultivars were geno-typed using AxiomTM 35K Wheat Breeder’s Genotyping Array (ThermoFisherScientific, Applied BiosystemsTM, US). QTL mapping was performed using IciMapping program version 4.2 (Meng
Distribution of the eight yield-related traits (DHD, CL, SL, KPS, TN, TW, TKW, and YD) in the 94 doubled haploid lines and their parents evaluated in three years are illustrated in Fig. 1 and Supplementary Table S1. The average KPS (33.6) and YD (437.3 kg/10a) of the doubled haploid lines were between the values of Keumkang (33.4 and 427.1 kg/10a) and Olgeuru (35.1 and 485.7 kg/10a) in three years, while the average SL (8.1 cm), TN (851.6/m2), TW (806.0 g/l), and TKW (39.7 g) were lower than the values of both Keumkang (8.4 cm, 940.3/m2, 815.7 g/l and 42.4 g) and Olgeuru (8.6 cm, 1008.4/m2, 827.0 g/l, 41.4 g) in three years. The parental values for DHD and CL showed inconsistent patterns (Keumkang headed earlier than Olgeuru in 2017 and 2019, while Olgeuru headed earlier in 2018; Keumkang was taller than Olgeuru in 2017 and 2018, while Olgeuru was taller in 2019). Transgressive segregation was observed for all investigated traits.
The correlations among the yield-related traits are sum-marized in Supplementary Figs. S1-S3. Thirteen pairs of traits showed sig-nificant correlations in all three years. While the DHD-CL (r = 0.33-0.45), DHD-SL (r = 0.36-0.46), DHD-KPS (r = 0.55-0.74), CL-SL (r = 0.22-0.45), CL-TKW (r = 0.31-0.46), SL-KPS (r = 0.44-0.48) correlations were signifi-cantly positive in all three years, the DHD-TN (r = ‒0.38 to ‒0.21), DHD-TW (r = ‒0.45 to ‒0.29), SL-TN (r = ‒0.31 to ‒0.25), SL-TW (r = ‒0.47 to ‒0.34), KPS-TN (r = ‒0.41 to ‒0.25), KPS-TW (r = ‒0.50 to ‒0.35), and TN-TKW (r = ‒0.40 to ‒0.27) correlations were significantly negative in all three years. However, YD did not exhibit such consis-tent correlation with any other trait across three years, reflecting its complex nature affected by different yield components and environmental factors.
A linkage map covering 2639.0 cM was constructed using 641 SNPs with unique genetic positions out of the 3,325 polymorphic SNPs. The average chromosome length was 125.7 cM, ranging from 7.9 cM (6D) to 288.7 cM (5A). Chromosome 5B had the greatest number of markers (76), while chromosome 5D had the smallest number of markers (3). The overall SNP density was 4.39 cM, with the highest density on 6D (1.3 cM) and the lowest density on 7D (9.6 cM).
A total of seven QTLs, three for DHD and one each for CL, KPS, TKW, and TW, were detected in at least two of the three years (Table 1 and Fig. 2). Three QTLs for DHD,
Table 1 . QTLs for yield-related traits identified from the Keumkang/Olgeuru doubled haploid population
QTLz) | Year | Position (cM) | Left marker | Right marker | Interval (cM) | LODy) | PVEx) (%) | ADDw) |
---|---|---|---|---|---|---|---|---|
2017 | 117.0 | AX-95081398 | AX-95147328 | 6.0 | 16.1 | 40.9 | ‒2.2 | |
2018 | 106.0 | AX-94527403 | AX-95081398 | 9.0 | 6.3 | 17.4 | ‒1.1 | |
2019 | 117.0 | AX-95081398 | AX-95147328 | 5.0 | 18.9 | 18.0 | ‒1.7 | |
2017 | 124.0 | AX-94511377 | AX-94916148 | 5.0 | 6.5 | 12.8 | 1.2 | |
2018 | 124.0 | AX-94511377 | AX-94916148 | 5.0 | 4.7 | 12.2 | 0.9 | |
2019 | 119.0 | AX-94649598 | AX-94511377 | 3.0 | 27.2 | 33.1 | 2.2 | |
2017 | 89.0 | AX-94523269 | AX-94944119 | 9.0 | 4.6 | 8.7 | ‒1.0 | |
2019 | 91.0 | AX-94523269 | AX-94944119 | 10.0 | 8.1 | 6.0 | ‒1.0 | |
2017 | 75.0 | AX-94718756 | AX-94415763 | 8.0 | 10.3 | 27.5 | 4.0 | |
2018 | 75.0 | AX-94718756 | AX-94415763 | 4.0 | 6.1 | 25.6 | 3.2 | |
2019 | 72.0 | AX-94722330 | AX-94718756 | 10.0 | 4.7 | 13.8 | 2.8 | |
2017 | 117.0 | AX-95081398 | AX-95147328 | 6.0 | 8.6 | 30.6 | ‒2.6 | |
2018 | 117.0 | AX-95081398 | AX-95147328 | 7.0 | 5.5 | 20.8 | ‒1.6 | |
2019 | 117.0 | AX-95081398 | AX-95147328 | 8.0 | 3.9 | 15.6 | ‒1.1 | |
2017 | 73.0 | AX-94718756 | AX-94415763 | 8.0 | 5.0 | 21.9 | 1.6 | |
2018 | 73.0 | AX-94718756 | AX-94415763 | 9.0 | 3.3 | 15.2 | 1.3 | |
2019 | 73.0 | AX-94718756 | AX-94415763 | 7.0 | 5.3 | 22.7 | 1.6 | |
2018 | 5.0 | AX-94895904 | AX-94739433 | 7.5 | 3.9 | 17.9 | 6.1 | |
2019 | 4.0 | AX-94448644 | AX-94895904 | 7.5 | 3.7 | 13.2 | 5.7 |
z)QTLs stably identified at least two of the three years are listed in the table. QTLs were named according to Mcintosh et al. (2017). DHD: days to heading date, CL: culm length, KPS: kernels per spike, TKW: thousand kernel weight, TW:
test weight.
y)Logarithm of the odds.
x)Phenotypic variance explained.
w)Additive effect of allele substitution. The units are those of the corresponding traits. A positive sign indicates that the
Keumkang allele increased the trait value.
As shortening DHD with maintaining productivity is one of the most important goals of Korean wheat breeding programs, we focused on the three DHD QTLs for further analyses. To characterize the effects of the three DHD QTLs and their interactions, we conducted three-way ANOVAs of
Table 2 . Three-way ANOVAs of
Traitz) | Allele | Main effecty) | Interaction | ||||||
---|---|---|---|---|---|---|---|---|---|
DHD (d) | Keumkang | 181.0 | 183.8 | 182.0 | |||||
Olgeuru | 184.1 | 181.8 | 183.7 | ||||||
*** | *** | *** | ns | ns | ns | ** | |||
PVE (%) | 27.7 | 13.1 | 9.5 | 1.2 | |||||
CL (cm) | Keumkang | 74.8 | 78.4 | 76.4 | |||||
Olgeuru | 78.7 | 75.8 | 78.2 | ||||||
*** | * | ns | ns | ns | ns | ns | |||
PVE (%) | 4.2 | 1.9 | |||||||
SL (cm) | Keumkang | 7.8 | 8.3 | 8.1 | |||||
Olgeuru | 8.2 | 7.8 | 8.1 | ||||||
*** | *** | ns | ns | *** | ns | ns | |||
PVE (%) | 7.4 | 7.4 | 3.9 | ||||||
KPS (no.) | Keumkang | 31.7 | 34.3 | 33.0 | |||||
Olgeuru | 35.2 | 33.0 | 34.4 | ||||||
*** | *** | *** | ** | ns | * | * | |||
PVE (%) | 22.2 | 4.4 | 3.6 | 2.2 | 1.3 | 1.3 | |||
TN (no./m2) | Keumkang | 873.0 | 819.8 | 854.8 | |||||
Olgeuru | 835.5 | 883.8 | 847.0 | ||||||
** | *** | ns | ns | ns | ns | ns | |||
PVE (%) | 2.9 | 9.6 | |||||||
TW (g/l) | Keumkang | 811.1 | 801.9 | 807.5 | |||||
Olgeuru | 803.4 | 810.8 | 803.8 | ||||||
*** | *** | ** | ** | ns | ns | * | |||
PVE (%) | 5.6 | 9.2 | 2.4 | 2.0 | 1.5 | ||||
TKW (g) | Keumkang | 39.9 | 40.4 | 39.7 | |||||
Olgeuru | 39.2 | 38.7 | 39.6 | ||||||
ns | *** | ns | ns | ns | * | ns | |||
PVE (%) | 5.7 | 1.4 | |||||||
YD (kg/10a) | Keumkang | 421.5 | 440.8 | 436.3 | |||||
Olgeuru | 449.4 | 434.6 | 438.7 | ||||||
*** | ns | ns | ns | ns | ns | ns | |||
PVE (%) | 8.7 |
z)DHD: days to heading date, CL: culm length, SL: spike length, KPS: kernel per spike, TN: tiller number per m2, TW: test weight, TKW: thousand kernel weight, YD: yield.
y)
Although the two-way and three-way interactions bet-ween the three DHD QTLs were significant for a few traits (i.e.,
This study identified seven stable QTLs for yield-related traits using the doubled haploid lines derived from the two Korean wheat cultivars, Keumkang and Olgeuru. As early heading is especially important in Korean wheat breeding programs, we focused on the three DHD QTLs (i.e.,
Heading date is an important trait to secure stable yield under target environments and cropping system. In Korea, developing early heading wheat cultivars is especially important to allow the optimum transplanting period of rice in the wheat-rice double cropping system while maintain-ing stable yield and quality of wheat. As Korean wheat breeding programs have focused on developing early-heading cultivars since the 1970s, most recent commercial cultivars already carry the alleles for early heading at the major heading date genes such as
However, caution is required because early heading is often associated with decreased spikelets per spike and kernels per spike, thus reduces the yield potential (Muterko
The datasets generated from this research are available from the corresponding author upon reasonable request.
This work was carried out with the support of the “Cooperative Research Program for Agriculture Science & Technology Development (RDA PJ0159652023)”, Rural Development Administration, Republic of Korea.
Sumin Hong performed the experiments, analyzed the data and wrote the first draft. Kyeong-Min Kim, Changhyun Choi, and Seong-Woo Cho conducted field trials and analyzed the data. Chul Soo Park designed the experiments and supervised the project. Youngjun Mo analyzed the data, supervised the project, and wrote the final draft.
The authors declare that they have no conflicts of interest.
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