A winter wheat (Triticum aestivum L.) cultivar, ‘Taejoong’, was developed by the National Institute of Crop Science, Rural Development Administration in 2016. It was derived from a cross between ‘Xian83(104).11’ and ‘Keumkang’ in 2005. It was generated through the bulk and pedigree methods for six years, and then designated as ‘Iksan370’ after a two-year advanced yield trial test. This variety was designated the name ‘Taejoong’ after a regional yield trial test in eight locations throughout Korea for three years from 2014 to 2016. Its heading date was April 27 in upland and paddy filed conditions, and its maturity date was June 7 in uplands and June 4 in paddy fields, which were late compared to that of ‘Keumkang’. ‘Taejoong’ had 417 spikes per m², which was 300 less than that of ‘Keumkang’. However, the spike length was 13.4 cm and the number of kernel per one spike was 48, which was 5.8 cm longer and 19 higher than those of ‘Keumkang’, respectively. ‘Taejoong’ showed strong resistance to lodging and moderate resistance to Fusarium head blight, but was susceptible to powdery mildew. ‘Taejoong’ flour yield (71.8%) and flour lightness (91.90) were similar to those of ‘Keumkang’, but its protein content (11.1%), gluten content (8.8%), and sodium dodecyl sulfate-sedimentation volume (34.2 ml) were lower. These result showed that the flour dough strength of ‘Taejoong’ was weaker than that of ‘Keumkang’. The high-molecular-weight gluten subunit compositions of ‘Taejoong’ were Glu-A1 (N), Glu-B1 (7+9), and Glu-D1 (2+12). The granule-bound starch synthase compositions were Wx-A1, Wx-B1, and Wx-D1. The puroindoline compositions were Pina-D1 (a type) and Pinb-D1 (b type). The average grain yield of ‘Taejoong’ in a regional yield trial was 5.3 ton/ha in uplands and 4.6 ton/ha in paddy fields, which were 21% and 13% higher than that of the reference cultivar, ‘Keumkang’, respectively. (Registration No. 7378).

Association analysis was conducted to identify quantitative trait locus (QTL) of yield potential traits, days to heading date, culm length, spike length and kernels per spike in the genetic mapping population (94 F₁₀ recombinant inbred line) produced from a cross between two Korean wheat cultivars, Taejoong which has a large kernel number line, a longer spike length, and a higher kernel number per spike and Keumkang. Yield potential traits, days to heading date, culm length, spike length and kernels per spike were evaluated in 2017 and 2018 under upland conditions. Days to heading date were biased toward late heading date (skewness=-0.3), and spike length was biased toward short spike length (skewness=0.7). A genetic map was constructed with 57 microsatellite marker loci and two QTLs were detected for spike length. The first QTL on chromosome 2A, qSL-1 was detected by Xcfd5 and Xpsp3050 and explained 20.7% of phenotypic variation. The second QTL on chromosome 5B, qSL-2 was detected by Xwmc656 and Xwmc415 and explained 40.8% of phenotypic variation. These QTLs were applied to validate the relationships between genotypes of QTLs and 29 Korean wheat cultivars cultivated for nine years, from 2010 to 2018. The Korean wheat cultivars were classified into 6 types according to the genotypes of Xcfd5-Xpsp3050 and Xwmc656-Xwmc415. The same genotypes as Keumkang showed a higher frequency and shorter spike length than that of Taejoong in Korean wheat cultivars.

Molecular markers related to flour qualities of long spike wheat lines were evaluated. Ash, wet gluten and protein content of long spike wheat lines were higher than Keumkang(Korean wheat cv.) but SDS-sedimentation volume(SDSF) was lower. Particle size and lightness of flour of long spike wheat lines showed similar to Keumkang. The high positively correlation was presented between protein content and SDSF, wet gluten and particle size, respectively. However, negatively correlation was between protein content and lightness. Through the analysis of molecular markers, we identified the genotypes of four genes, Glu-A3c, Wx-A1a, Wx-B1a and Wx-D1a. These genes had same genotypes with Keumkang. Six genes, Glu-A1c, Glu-B1c, Glu-D1a, Glu-B3g, Pina-D1and Pinb-D1b, were presented in most of the lines. Two genes, Glu-A1 and Glu-B1b, were related to higher protein contents and wet gluten. The lines containing three genotypes, Glu-D1d, Glu-B3h and Pinb-D1b, had higher ash, protein contents, SDSF and wet gluten, and lightness was darker. Through the results, we expect that long spike type wheat lines are necessary to breed wheat having high yield productivity.

One hundred sixty four wheat (Triticum aestivum L.) lines expressing the long spike were developed by the National Institute of Crop Science, Rural Development Administration. Six of 11 genes showed allelic variation among 164 lines and they were highly related to yield traits containing spike and kernel number, kernel length, 1000-kernel weight and grain yield. Analysis of allelic variation of each gene showed high correlation between allelic variation and agricultural characteristics. Coefficient of correlation between culm length and spike length was the highest 0.436. The heading date of the lines expressed Vrn-D1 allele was late and the lines expressed Vrn-D1 allele had longer spike length and higher number of kernel per spike than other lines. There was no significant difference in agronomic characteristics of analysis of Vrn-B1. Ppd-D1b was related to heading date and higher number of spike/m². Ppd-D1a was corresponded to number of kernel per spike and 1000-kernel weight. Three haplotypes, Hap-L, Hap-6A-G and TaCwi-A1a, were related to 1000-kernel weight.