In the present study, we conducted a detailed analysis of the genetic diversity and structural organization of 96 domestic Korean rice varieties (Oryza sativa L.) using 2,565 high-resolution TCS-based single nucleotide polymorphism (SNP) markers. Genetic structural variations were investigated using diversity indices, PCA, genetic similarity, and network analysis. Genetic diversity analysis revealed a significant expansion of the genetic foundation after the 1980s, marked by a sharp increase in the number of alleles (Na) from the 2000s. Despite this, high genetic homogeneity was maintained, with an average similarity of 77.7%. The observed 10% difference among same-cross varieties suggests that critical genetic variations are fixed by strong selection pressures for quality traits. Network analysis (85% similarity threshold) confirmed that the Korean rice breeding population followed a distinct core-periphery model (eight communities). The connected 84 varieties had a centrality range of 0.01 0.39. Core Variety Groups (e.g., ‘Junam’ and ‘Sindongjin’) exhibited the highest centrality (up to 0.39), indicating their extensive use as key breeding parents and their function as the central axis of the genetic network. Bridge Variety Groups (e.g., ‘Hwayeong’ and ‘Samkwang’) played an intermediary role linking clusters. Crucially, 12 ‘isolated accessions’ showed zero centrality (0.00), representing a genetic disconnect from the main pool. This quantitative network-based assessment provides essential fundamental data for breeders to select appropriate germplasms. Furthermore, the findings suggest that the current cultivar naming system, which inadequately reflects genetic relationships, requires reassessment, and that the establishment of objective management standards based on this research is warranted.

‘Amissal’ is a regionally specialized rice cultivar developed to strengthen the competitiveness of local rice and is characterized by its distinct long-grain japonica type. It was bred through a single backcross between ‘Boramchan’—a high-yielding japonica cultivar with excellent cultivation stability used as the recurrent parent—and ‘HR30198-AC33’ (DGS79), a breeding stock with extra-long and spindle-shaped grains used as the donor parent for japonica grain shape diversification. Population and pedigree breeding methods were used during the breeding process. During the selection stage, molecular marker-assisted selection targeting the major grain shape genes, GS3 and qSW5 was applied, enabling the identification of lines carrying the gs3-qSW5 allele combination associated with long grain shape. ‘Amissal’ was developed through yield trials, local adaptability tests, selection trials addressing regional needs, and on-farm research aimed at developing long-grain japonica rice for export. The heading date of ‘Amissal’ was August 17, two days later than that of ‘Nampyeong’. Compared to ‘Nampyeong’, ‘Amissal’ exhibited greater biomass due to longer culms, more spikelets per panicle but fewer panicles per hill, and a heavier 1,000-grain weight. It demonstrated strong resistance to bacterial blight (races K1, K2, and K3) but was susceptible to viral diseases and insect pests. In terms of yield, it outperformed ‘Nampyeong’. The average brown rice grain length was 6.14 mm, classifying it as long-grain type. The length-to-width ratio was 2.43, corresponding to a semi-spindle shape, which clearly distinguishes it from existing Korean japonica cultivars. While its milling recovery rate was similar to that of ‘Nampyeong’, a high proportion of broken rice due to its long grain shape resulted in a lower head rice. ‘Amissal’ had low protein content and provided the sticky and soft texture typical of japonica rice, with excellent scores in sensory evaluation tests. As a differentiated, regionally specialized rice cultivar featuring a long-grain japonica type and superior eating quality, ‘Amissal’ is expected to contribute to the advancement of the local rice industry, particularly through applications in rice export and the utilization of broken rice and rice straw (Registration No. 10167).

To diversify the grain quality characteristics of Korean varieties of japonica rice (Oryza sativa japonica), recombinant inbred lines were developed from a cross between the Korean cultivar “Boramchan” and the tropical japonica cultivar “Pecos” from the United States. Quantitative trait locus (QTL) analysis was performed to investigate the traits related to grain quality. Sixteen traits were evaluated, including five related to grain appearance, six associated with pasting properties and glossiness of cooked rice, and four related to eating texture. QTLs were detected on chromosomes 3, 5, 6, and 10, and candidate genes, including Hd1, qLTG3-1, GW5, and qGS10 were identified. The heading date-related gene Hd1 was associated with the following traits: head rice (HR), opaque rice (OR), damaged rice, pasting temperature, peak viscosity (PV), breakdown viscosity (BD), and glossiness. Most quality-related traits were influenced by allelic variation at Hd1, and the Hd1⁺ allele from “Boramchan”, which delays heading, positively affected both grain appearance and eating quality. The low-temperature germinability gene qLTG3-1 was identified as a candidate gene for broken rice and several pasting properties, including trough, final, and breakdown viscosities, and was shown to influence pasting characteristics depending on allelic variation. The grain shape gene GW5 was a candidate gene for HR and whiteness, whereas qGS10 was associated with OR, PV, BD, and setback viscosity. The GW5⁺ and qGS10^P alleles, derived from the slender grain shape of “Pecos,” contributed positively to both grain appearance and eating quality, indicating their potential as favorable alleles for improving grain shape and diversifying quality traits in Korean japonica rice. The results of this study demonstrate that key agronomic trait-related genes, such as heading and grain shape, significantly affect various quality-related traits, highlighting the potential of introducing and combining novel alleles to enhance grain quality in Korean japonica rice.

The intermediate breeding material ‘JJ625LG’ was developed to diversify the grain shape characteristics of Korean japonica rice cultivars. ‘JJ625LG’ was derived from a cross between ‘HR30198-AC33 (DGS79),’ a japonica breeding material with extra-long and spindle-shaped grains, and ‘Boramchan,’ a high-yielding japonica cultivar with excellent cultivation stability and medium-short and semi-round grains. By employing both bulk and pedigree breeding methods, strong selection pressure was applied to eliminate undesirable traits inherited from ‘DGS79,’ such as very late heading, long awns, and susceptibility to lodging. Consequently, elite lines with long spindle-shaped grains on a japonica background were selected. These lines subsequently underwent yield performance and local adaptability tests, during which their agronomic traits were comprehensively evaluated, leading to the final selection of ‘JJ625LG.’ The heading date of ‘JJ625LG’ was August 16th, three days later than that of ‘Nampyeong’. Its culm length was similar to ‘Nampyeong.’ ‘JJ625LG’ exhibited a higher number of spikelets per panicle, fewer panicles per plant, and heavier 1,000-grain weight than brown rice. Additionally, it showed strong resistance to bacterial blight (races K1, K2, and K3) but was susceptible to viral diseases and insect pests, indicating the need for further improvement in these areas. Its grain yield was comparable to that of ‘Nampyeong.’ With a brown rice grain length of 6.34 mm, ‘JJ625LG’ was classified as a long-grain type and had a grain length-to-width ratio of 2.64, reflecting a spindle-shaped morphology. It carried the GW2-gs3-qSW5 allele combination associated with grain shape, which is a genetic profile not found in existing Korean japonica cultivars. Although its milling recovery rate was similar to that of ‘Nampyeong,’ the presence of many broken rice due to its long grain shape resulted in a lower percentage of head rice. The eating quality of ‘JJ625LG’ was excellent, with its grains exhibiting the sticky and soft texture typical of japonica rice and receiving high scores in sensory evaluation. As the first intermediate breeding material in Korea with long and spindle-shaped grains in a japonica background, ‘JJ625LG’ is expected to contribute significantly to diversifying the traditionally narrow grain shape spectrum of Korean japonica rice cultivars (Registration No. 10166).

‘Boramchan’ is a high-yielding, mid-late maturing temperate japonica rice cultivar developed in Korea, while ‘Pecos’ is an early-maturing tropical japonica cultivar from the United States with medium-grain shape characteristics. In this study, quantitative trait loci (QTL) analysis was conducted on yield- and grain-related traits using recombinant inbred lines derived from a cross between ‘Boramchan’ and ‘Pecos’ in order to broaden the genetic diversity of these traits in Korean japonica rice varieties. QTLs for heading date were identified on chromosomes 3 and 6, with Hd6 and Hd1 proposed as candidate genes for this trait. The major heading date gene Hd1 exhibited pleiotropic effects, influencing not only the heading date (HD) but also multiple yield components, including culm length, panicle length, number of spikelets per panicle (NS), 1,000-grain weight (TGW), ratio of ripened grain (RRG), brown/rough rice ratio, and grain yield per plant. The minor heading date gene Hd6 showed a masking effect on HD and NS, depending on the allele type of Hd1. Allelic combinations of Hd1 and Hd6 allowed HD regulation for approximately 30 days. As more functional alleles associated with delayed heading accumulated, the values of yield-related traits gradually increased. Three QTLs for grain-related traits–qGL2, GW5, and qGS10–were identified on chromosomes 2, 5, and 10, respectively. GW5 was confirmed as a major gene with significant effects on phenotypic variation, influencing all grain-related traits, including grain length (GL), width (GW), thickness (GT), length to width ratio, and TGW. qGL2 was associated with GL and colocalized with qNS2, a QTL related to NS. qGS10 was identified as a QTL that affected GW, GT, and TGW. Allelic combinations of qGL2, GW5, and qGS10 influenced not only grain-related traits but also variation in yield-related traits. Combinations carrying the gw5^- allele from ‘Boramchan’ generally exhibited favorable characteristics in terms of yield potential. Furthermore, the introduction of qGL2^P and qGS10^P alleles from ‘Pecos’ contributed to the diversification of grain shape and showed positive effects on NS, RRG, and yield. Novel allele combinations, such as qGL2^P-gw5^--qGS10^B and qGL2^P-gw5^--qGS10^P are expected to enhance the genetic diversity of yield- and grain-related traits in Korean japonica rice varieties.

Risotto is an Italian rice dish cooked in broth until it reaches a creamy consistency. This is one of the most common rice preparation methods in Italy. The famous rice varieties for risotto are ‘Carnaroli,’ ‘Arborio,’ and ‘Vialone Nano.’ This study was conducted to provide essential data for breeding risotto rice varieties suitable for Korea by analyzing the agricultural traits of three risotto varieties and ‘Cheolweon96’ (Carnaroli SA-mutant line) under Korean environmental conditions. The risotto varieties and the mutant line showed early maturation, similar to ‘IS592BB.’ They had longer culm lengths and fewer panicles per hill and spikelets per panicle than to the Korean rice varieties, ‘i.e., Sindongjin’ and ‘IS592BB.’ They also exhibited lower ratios of ripened grains, brown/rough rice ratios, and lower yields. The risotto rice varieties and the mutant line other than ‘Vialone Nano,’ represented longer, wider, and heavier grain characteristics. The rice varieties and the mutants line had high levels of chalky rice, which absorbs water rapidly during cooking. Because broth absorption is important in risotto preparation, chalkiness can be considered an important characteristic of risotto rice varieties. In the analysis of pasting properties, ‘Carnaroli,’ ‘Cheolweon96,’ and ‘Vialone Nano’ showed similar characteristics, whereas ‘Arborio’ was grouped with ‘IS592BB.’ The cooked rice of ‘Carnaroli,’ ‘Cheolweon96,’ and ‘Vialone Nano’ exhibited a hard and non-sticky texture, while that of ‘Arborio’ was softer and stickier than that of the Korean rice varieties. The risotto rice varieties showed a larger grain size, higher chalkiness, pasting temperature, setback viscosity, and harder texture than the Korean rice varieties. These characteristics are expected to be useful selection indicators for breeding Korean risotto rice varieties.

‘Chamdongjin’ is a rice cultivar with a distinctively large grain size and good palatability, similar to ‘Sindongjin,’ which is a mega-cultivar in Korea. ‘Younghojinmi’ is a rice cultivar known for having the highest taste value among premium quality cultivars. In this study, we conducted quantitative trait loci (QTL) analysis of quality-related traits using recombinant inbred lines (RILs) derived from a cross between ‘Chamdongjin’ and ‘Younghojinmi’ to elucidate their genetic interactions. We analyzed 20 traits, including protein content, amylose content, glossiness of cooked rice, 7 traits related to grain appearance, 6 traits related to pasting properties, and 4 traits related to texture. Quality-related QTL were primarily detected on chromosome 3. In particular, GS3, one of the candidate genes for QTL, significantly influenced quality by affecting 14 different traits, including appearance traits such as head rice and the texture of cooked rice. Furthermore, RILs with the gs3 allele, which exhibited the large grains of ‘Chamdongjin,’ showed a lower protein content and higher amylose content than RILs with the GS3 allele. These lines also had lower head rice percentages and higher percentages of whiteness, opacity, and broken rice, indicating an inferior appearance quality. In terms of pasting properties, RILs with the gs3 allele showed a lower pasting temperature, peak viscosity, and breakdown, but a higher setback than RILs with the GS3 allele. Although the gs3 allele did not affect the glossiness, hardness, or toughness of the cooked rice, it resulted in higher adhesiveness and stickiness. Allelic alteration of the preharvest sprouting gene qLTG3-1 was found to affect seven quality-related traits, including pasting properties. Genes related to heading date (Hd18), culm length (SD1), and tiller number (OsTB1) were also associated with quality-related QTL. Alterations in the alleles of these genes caused variations in quality-related traits. Our identification of the association between quality-related traits and key agronomic genes is expected to support the effective development of rice cultivars with improved quality.

Rapid climate change has diversified the dynamics of brown planthoppers, necessitating the development of rice cultivars with enhanced resistance. Brown planthoppers contribute to reduced grain yield and quality, and the rapid ecological changes caused by global warming are expected to exacerbate this damage. In Korea, rice cultivars resistant to brown planthoppers have primarily been bred using Bph1, bph2, and Bph18. Despite the known resistance of Bph3 to brown planthoppers, this gene is underutilized in rice breeding programs. Therefore, in this study, we aimed to analyze the association between brown planthopper resistant genes and rice agronomic traits by breeding segregated populations incorporating Bph3, Bph18, and BPH26. Segregated populations were derived from crosses between ‘Jeonju686’ (carrying Bph3 and BPH26) and ‘JJ621MR’ (carrying Bph18). Our analysis revealed that Bph18 was significantly associated with a reduced fertility rate. However, Bph3 did not significantly affect fertility-related traits. As Bph3 has been reported to confer strong resistance to brown planthoppers, it is expected to be actively utilized in future resistance breeding programs. Ultimately, maximizing the efficiency of molecular breeding techniques is expected to provide valuable insights into the development of rice cultivars with enhanced resistance to brown planthoppers.

The rice cultivar ‘JJ644wx’ was developed to improve disease resistance and lodging tolerance of Korean japonica glutinous rice cultivars. ‘JJ644wx’ was derived from a cross between ‘HR27814-B-47-1-1’ (‘Sinjinbaek’), a multiple disease-resistant mid-late maturing elite line, and ‘HR29676-AC29’, a medium-maturing glutinous line with lodging tolerance. To shorten the breeding period, an anther culture method was applied to F₁ plants. ‘JJ644wx’ was selected through the pedigree method, yield trials, and local adaptability tests, with high selection pressure for disease resistance and lodging tolerance. The heading date of ‘JJ644wx’ was August 11th, four days later than that of ‘Sinseonchal’. ‘JJ644wx’ exhibited strong tolerance to lodging with a short culm length. The 1,000-grain weight of brown rice of ‘JJ644wx’ was heavier than that of ‘Sinseonchal’, and its yield was 553 kg/10a, which was 10% higher than that of ‘Sinseonchal’. ‘JJ644wx’ had a higher milling performance than ‘Sinseonchal’, but a lower head rice ratio due to a higher percentage of broken rice. ‘JJ644wx’ tended to be situated between ‘Sinseonchal’ and ‘Dongjinchal’ in terms of pasting and texture characteristics. ‘JJ644wx’ is the only Korean japonica glutinous rice cultivar resistant to the most virulent bacterial blight race, K3a; it also showed resistance to rice blast and stripe virus. ‘JJ644wx’ is expected to be a valuable resource that could contribute to improving the cultivation stability of Korean japonica glutinous rice in response to climate change (Registration No. 9606).

Recently, crossbreeding between Asian rice (O. sativa) and African rice (O. glaberrima) has become an important solution for hunger refugees and food problems in Africa by improving grain yield. O. glaberrima exhibits important traits such as stress tolerance, and genetic diversity evaluation and structural analysis of agronomic traits have been conducted. In this study, 11 yield-related agricultural traits were analyzed in 45 lines of O. sativa and 28 lines of O. glaberrima under Korean climatic conditions. Through cluster analysis using the investigated yield-related traits, O. sativa and O. glaberrima were grouped into clusters by characterizing the remaining traits, except for the number of spikelets, grain width, and grain thickness. The number of spikelets was highly influenced by the environment and had the greatest variation, whereas grain width showed the least variation. In addition, rice yield components are quantitative traits, and in breeding to improve yield, it is important to analyze the interaction of agricultural traits and the influence of the environment to maintain an optimal balance and improve plant potential. Although O. sativa was found to exhibit different agricultural traits depending on its ecotype, it still belonged to the same group when clustered. The results of this study provide basic information on the yield-related agronomic characteristics of O. sativa and O. glaberrima under Korean climatic conditions, suggesting that O. glaberrima can be used as breeding material to diversify Korean rice genetic resources.

The rice cultivar ‘Chamdongjin’ exhibits a distinctively large grain size and excellent eating quality but is weak with regard to pre-harvest sprouting (PHS), requiring genetic improvement. In contrast, the premium-quality rice cultivar ‘Younghojinmi’ exhibits strong PHS tolerance. This study conducted quantitative trait loci (QTL) analysis on PHS and low-temperature germinability (LTG) using recombinant inbred lines derived from a cross between ‘Chamdongjin’ and ‘Younghojinmi’ to elucidate the genetic factors. Thus, an elite line with improved PHS tolerance was selected. QTL analysis revealed that qPHS3 and qLTG3 were associated with PHS and LTG, respectively, and the candidate gene was identified as qLTG3-1. The loss-of-function allele qltg3-1 in ‘Younghojinmi’ enhanced PHS tolerance compared to the functional allele qLTG3-1 in ‘Chamdongjin,’ but it also showed a trade-off relationship by decreasing LTG. CY_RILs carrying qltg3-1 exhibited lower PHS and LTG rates of 17.9% and 41.6%, respectively, compared to 44.1% and 55.7%, respectively, for CY_RILs with qLTG3-1. The elite line, CY_RIL79, carrying qltg3-1, was selected from CY_RIL. This line was recognized for its PHS tolerance while maintaining the key agricultural traits of ‘Chamdongjin,’ thus designated ‘Jeonju697.’ ‘Jeonju697’ is expected to be utilized as a practical alternative for addressing the issue of enhancing PHS tolerance in ‘Chamdongjin’; however, considering its weak LTG, it is desirable to improve this trait through further breeding efforts.

‘Saebonghwang’ was developed as a mid-late ripening rice variety with good cultivation stability and yield in transplanting and under direct seeding cultivation. It was bred by backcrossing ‘Hopum’, which has excellent cultivation stability and adaptability to direct seeding, as a repeat parent, and ‘Hitomebore,’ a Japanese rice variety with excellent taste, as a donor. The heading date of ‘Saebonghwang’ was August 11 under ordinary planting, which is two days earlier than that of ‘Nampyeong’, and August 13 under wet-direct seeding cultivation, which is the same as that of ‘Dongan’. ‘Saebonghwang’ had a culm length of 74 cm under wet-direct seeding cultivation, which is larger than that of ‘Dongan’ (69 cm), and had good cultivation stability, including lodging resistance. ‘Saebonghwang’ is resistant to bacterial leaf blight and rice stripe virus and shows moderate resistance to rice blast. Furthermore, ‘Saebonghwang’ has better grain appearance, superior taste and better milling characteristics than ‘Nampyeong’. The yield of ‘Saebonghwang’ when cultivated under ordinary planting, wet-direct seeding, and double cropping was 5.65, 5.37, and 5.37 MT/ha, respectively. Under wet direct sowing by drone cultivation, ‘Saebonghwang’ showed good initial survival rate and cultivation stability. The yield was 4.49 MT/ha, slightly lower than that obtained under transplanted cultivation (5.03 MT/ha), but was not statistically different; therefore, ‘Saebonghwang’ was adjudged to be adaptable to drone wet-direct seeding. ‘Saebonghwang’ can be used in various ways to suit the working conditions of farms, increase farm work efficiency, and expand the area of wet direct-seeding cultivation (Registration No. 9171).

‘Chamdongjin’ is a near-isogenic line with enhanced disease resistance compared to ‘Sindongjin,’ a mega-cultivar in Korea. ‘Younghojinmi’ is the rice cultivar with the highest taste quality among the premium cultivars. This study conducted quantitative trait loci (QTL) analysis on yield-related traits using the recombinant inbred lines derived from a cross between ‘Chamdongjin’ and ‘Younghojinmi’ to elucidate genetic interaction. We utilized KASP markers and a target-capture sequencing SNP genotyping platform to address the insufficient genetic diversity of the population using Korean japonica cultivars. A QTL associated with heading date (HD), qHd8, was detected, and the candidate gene Hd18 was identified. The hd18 allele delayed HD by 3 days and reduced the brown/rough rice ratio (BRR) by 0.3%. QTLs associated with culm length (CL), panicle length (PL), and yield (g/plant), namely qCL1, qPL1_2023, and qYield1_2023, respectively, were detected, and the candidate gene SD1 was identified. The sd1 allele shortened CL and PL by 11 and 0.8 cm, respectively, and reduced the yield by 2.3 g. It also reduced the number of spikelets per panicle (NS) by 10 and decreased the ratio of ripened grains (RRG) by 2.6 %. QTLs associated with 1,000-grain weight (TGW), NS, and BRR, namely qTGW3, qNS3, and qBRR3_ 2023, respectively, were detected, and the candidate gene GS3 was identified. The gs3 allele increased TGW and BRR by 3.8 g and 0.4%, respectively, and reduced NS by 12. It also reduced RRG content by 1.9% and increased the yield by 1.7 g. The QTL associated with the number of panicles per hill (PN), qTN3, and the candidate gene, OsTB1, were identified. The OsTB1^TGTG allele reduced PN by 1.3 and affected the increase in NS and RRG by 10 and 1.4%, respectively. The allele combinations of SD1, GS3, and OsTB1 were analyzed to assess their effects on yield-related traits. NS and RRG were influenced by trait variations, depending on the combination background of other alleles during allele substitution. ‘Jeonju 697,’ an elite breeding line exhibiting improved lodging resistance with shortened CL, was selected by substituting SD1 with sd1 while maintaining the Hd18-gs3-OsTB1^TGTG allele combination of ‘Chamdongjin.’ This is expected to be a practical alternative for addressing the lodging problem in ‘Chamdongjin.’

The rice cultivar ‘Namchan’ was developed to achieve high yields under low-nitrogen fertilizer conditions and enhance cultivation stability. ‘Namchan’ was derived from a cross between ‘Nikomaru’, a Japanese rice cultivar known for its excellent ripening ability in high-temperature conditions, and ‘Saenuri’, a Korean mega rice cultivar renowned for its high cultivation stability. To shorten the breeding period, anther culture was applied to F1 plants. ‘Namchan’ was selected through the pedigree method, yield trials, and local adaptability tests, with high selection pressure for ripening ability and cultivation stability. The heading date of ‘Namchan’ was August 16, four days later than that of ‘Nampyeong’. ‘Namchan’ exhibited strong tolerance to lodging and preharvest sprouting, indicating high cultivation stability. Despite having more grains and panicles compared to that in ‘Nampyeong’, ‘Namchan’ exhibited excellent ripening ability, presumed to be inherited from ‘Nikomaru’. ‘Namchan’ showed intermediate resistance to rice blast and resistance to bacterial blight and rice stripe virus. ‘Namchan’ had excellent grain appearance, improved milling performance, and superior taste compared to ‘Nampyeong’. ‘Namchan’ exhibited a yield of 6.34 MT/ha under normal nitrogen fertilizer conditions, and its index at 115%, when compared to that of ‘Nampyeong’, is the highest among Korean japonica rice varieties. It exhibited a high yield of 5.45 MT/ha even under low-nitrogen fertilizer conditions. ‘Namchan’ is promising as an outstanding cultivar that can contribute to carbon neutrality through the reduction of nitrogen fertilizers and greenhouse gases (Registration No. 8134).

The cultivated area of glutinous rice in the Homan Plain of Korea is increasing to diversify the cropping system. Depending on the time of transplanting, glutinous rice can be divided into early, ordinary, and late cultivation. Eight glutinous rice cultivars (Baegseolchal, Baekogchal, Boramchal, Boseogchal, Dongjinchal, JJ644wx, Nunbora, and Sinseonchal) were used to evaluate yield, pasting properties, and texture according to cultivation time and to analyze the genotype-environment relationship. There were nine yield-related, six pasting-related, and four texture-related traits studied. Heading date and culm length were shortened as cultivation time increased, while panicle length, number of spikelets, and 1,000-grain weight increased. Furthermore, late cultivation time also reduced pasting properties, peak viscosity, trough viscosity, and final viscosity. Hardness and adhesiveness among the texture properties increased with cultivation time, but stickiness decreased. The variation in 1,000-grain weight is mostly dominated by genotype, whereas heading date and yield are heavily influenced by environmental factors. All pasting property characteristics varied with environment changes, and genotype variation was dominant for all texture properties. Boramchal yielded the most in early and ordinary cultivation and Sinseonchal, together with Boramchal, yielded the most in late cultivation. Cultivars with excellent grain quality were Sinseonchal in early cultivation and Baegseolchal and Baekogchal in ordinary and late cultivation. A comparative analysis of characteristics based on cultivation time can assist in the selection of glutinous rice suitable for the Honam Plain and in the breeding of cultivars with improved yield and excellent grain quality.

The rice cultivar ‘Chamdongjin’ was developed to enhance the disease resistance of ‘Sindongjin’. ‘Sindongjin’, developed by the RDA in 1999, is a mega-variety with a unique grain size and excellent taste, and has been cultivated in the largest area in Korea since 2018. As ‘Sindongjin’ has been cultivated in a large area recently, problems such as pest damage are increasing, and the necessity to develop alternative cultivars is emerging. Accordingly, the multiple disease-resistant, mid-late maturing rice cultivar ‘Chamdongjin’, carrying the bacterial blight resistance gene Xa21 into the genetic background of ‘Sindongjin’, was developed. ‘Chamdongjin’ was developed by the backcrossing method using the donor parent ‘HR27195-59-3-5-5’, harboring the bacterial blight resistance genes Xa3+Xa21 and the recurrent parent ‘Sindongjin’. ‘Chamdongjin’ was selected through the pedigree method, yield trials, and local adaptability tests, with a high selection pressure for agronomic trait similarities with ‘Sindongjin’. In order to effectively improve the disease resistance, marker-assisted selection for disease resistance genes and bioassays for bacterial blight, blast, and stripe virus were performed in parallel. ‘Chamdongjin’ was confirmed to have three disease-resistance genes, Xa3+Xa21+Stvb-i. Most of agronomic traits of ‘Chamdongjin’ were similar to ‘Sindongjin’, while ‘Chamdongjin’ showed enhanced disease resistance against bacterial blight and panicle blast compared to ‘Sindongjin’. ‘Chamdongjin’, like ‘Sindongjin’, possessed a grain size-related gene, the gs3 allele, and exhibited larger grains than general Korean japonica cultivars. In addition, ‘Chamdongjin’ showed a similar or higher level of palatability compared to ‘Sindognjin’, indicating the excellent quality characteristics. In the genetic background analysis using 787 KASP markers, ‘Chamdongjin’ showed 96.3% homozygosity with ‘Sindongjin’, indicating that it had a more similar genetic background to ‘Sindongjin’ than to other existing cultivars. ‘Chamgdongjin’ is expected to be widely cultivated as an alternative to ‘Sindongjin’, which could maintain the brand value while preventing the disease damage caused to ‘Sindongjin’ (Registration No. 9310).

“JJ603Balck” is a mid-late maturing high-yielding black rice having multiple-disease resistance. It was developed to increase the yield and disease resistance of Korean black rice. “JJ603Black” was derived from a cross between “Heughyang” and BC₂F₁ plants (Hopum*3/SR30075-1-12-6-1-1-1). “Heughyang” is a mid-late black rice with a short culm, while “Hopum” is a mid-late maturing rice cultivar with high yields and premium quality, and “SR30075” is a pyramid line carrying three bacterial blight resistance genes. “JJ603Black” was selected through the pedigree method, yield trials, and local adaptability tests, with a high selection pressure for black pericarp, resistance to bacterial blight K3a race, and high yield performance. The heading date of “JJ603Black” was August 19, 8 d later than that of “Heugnam,” which is the standard cultivar for black rice. “JJ603Black” is a cultivar tolerant to lodging with erect plant architecture. It showed multiple-disease resistance against bacterial blight and rice stripe virus owing to introgression resistance genes, Xa3+Xa21+Stvb-I; moreover, its yielding performance was high. The average brown rice yield of "JJ603Black" from 2016 to 2018 was 6.02 MT/ha, which was 14% more than that of “Heugnam” (5.30 metric/ha). Further, the anthocyanin content of “JJ603Black” (58 mg/100 g) was higher than that of “Heugnam” (51 mg/100 g). Therefore, “JJ603Black,” a high-yielding black rice cultivar with multiple-disease resistance, can be utilized for enhancing the disease resistance and yield of Korean black rice (Registration No. 7274).

Rice blast is one of the most serious agricultural diseases in the world. Rice blast can be managed using low nitrogen fertilizers, treatment with chemical fungicides, and the most effective resistant varieties. Many genetic resources have been investigated and used along with molecular markers to breed blast-resistant rice varieties. In this study, the genetic diversity of blast resistance genes using 27 functional/linked markers and rice blast incidence over three years was investigated in 296 Korean rice varieties. Blast incidence was determined using a 0-9 scoring system (0=no lesions to 9=dead leaves) in nursery tests. The blast incidence of 296 rice varieties showed a significant correlation between years (r>0.64, p<0.001). The 261 Japonica varieties showed blast resistance compared to 114 mid-late maturing varieties or 96 medium-maturing varieties. 35 Tongil-type varieties also exhibited greater resistance than Japonica varieties. DNA marker-trait association analysis was conducted using 27 DNA markers linked to 19 blast resistance genes. Twelve DNA markers showed significant associations with the average blast incidence over 3 years. The ‘9871.T7E’ marker linked with Pi40 was strongly associated with blast disease, with a phenotypic variance of 24% over 3 years (p<0.001). Among the varieties harboring the Pi40 allele, early maturing varieties accounted for 87%. These results imply that the blast resistance of early maturing Korean varieties is associated with the Pi40 gene. These results will be beneficial for breeding blast-resistant rice in Korea.

Temperate japonica is used as the parent for crossing in the breeding of new rice cultivars in Korea, and the grain shape of the developed lines or cultivars is a semi-round and medium-short grain length. To overcome the current low quantity of japonica cultivar germplasm and deterioration in quality caused by climate change, it is necessary to diversify the grain characteristics of japonica. Most of the United States (US) cultivars are classified as medium, long, extra-long, and half spindle- and spindle-shaped grains. The qSW5 allelotype, a major gene involved in grain width, is found in all US cultivars. In addition, the US cultivar ‘Saber’ has both qgl3 and GS3_B alleles, which have low allele frequencies among Korean rice cultivars, and ‘A020’ had gw8, an allele with a reduced grain width. The pasting properties and texture of medium-grain length and half-spindle-shaped cultivars were relatively similar to those of the Korean rice cultivar, but different from those of long-grain and long spindle-shaped cultivars. Therefore, grain shape is associated with pasting properties and texture traits. Among the rice cultivars in the US, tropical japonica belongs to the same japonica as the Korean rice cultivar; however, its grain shape is similar to that of indica. As grain shape is also related to grain quality, US cultivars can be used as a useful genetic resource for diversifying the grain characteristics of Korean japonica cultivars and breeding new cultivars.

Interspecific and intersubspecific crosses have been an important strategy for rice breeding programs to obtain useful characters by expanding genetic diversity. However, the wide cross routinely causes undesirable characters in rice, such as spikelet sterility and poor quality. In this study, we developed near-isogenic lines of R-gene (Xa4+xa5+Xa21+Pi40+Bph18) introgression population to investigate the genetic relationship between the occurrence of poor characters and R-genes induced by MAS. The ANOVA analysis revealed that Pi40, Bph18, and Xa4 were associated with spikelet fertility (SF), ratio of ripened grain (RRG), third internode length (TIL), panicle extraction (PE), and protein content (Pro), whereas others showed no association with the 14 traits tested. In the three-way ANOVA, the impact of two R-genes (Pi40 and Bph18) on the poor characters was independent, with no interaction with others. Quantitative trait locus (QTL) analysis identified QTLs for PE and TIL traits near Pi40, and in particular, QTLs for five traits (SF, RRG, TIL, PE, and Pro) were negatively affected around Bph18. The occurrence of a poor character in R-gene pyramiding lines could be associated with linkage drag caused by the Bph18 gene. We speculate that the development of DNA markers that effectively eliminate poor characters will not only improve breeding efficiency using MAS, but will also help improve traits of japonica rice through wide crossing.

‘Jonong’ is an early maturing whole crop silage (WCS) japonica rice cultivar characterized by a short growth duration and numerous spikelets. It was developed to enhance the adaptability of WCS rice to double-cropping systems. ‘Jonong’ is derived from a cross between ‘Binhae Col.#1’ and ‘Deuraechan’; ‘Binhae Col.#1’ is a semi-early maturing China rice germplasm with numerous spikelets on dense panicles, whereas ‘Deuraechan’ is a high-yielding japonica rice cultivar with numerous spikelets on long panicles. To diversify the genetic variation and shorten the breeding period, an anther culture method was applied to the F₁ plants. ‘Jonong’ was selected through the pedigree method, yield trials, and local adaptability tests, with a high selection pressure for short growth duration and high biomass. The average heading date of ‘Jonong’ was August 1^st, which is 11 days earlier than that of ‘Nokyang’, the standard cultivar for WCS rice. Moreover, the growth duration of ‘Jonong’ is the shortest among all Korean WCS rice cultivars. The culm length of ‘Jonong’ is 88 cm, which 4 cm longer than that of ‘Nokyang’ and the highest among all Korean early maturing rice cultivars. ‘Jonong’ has 149 spikelets per panicle, which is 30 more than that of ‘Nokyang’, and is the highest among all Korean early maturing rice cultivars. ‘Jonong’ exhibits stable premature heading and is tolerant to lodging. It is moderately resistant to leaf blast and resistant to the rice stripe virus. The feed value of ‘Jonong’ in terms of total digestible nutrients is good and comparable to that of ‘Nokyang’. Furthermore, compared with ‘Nokyang’, ‘Jonong’ shows a similar level of dry matter yield and a higher rough rice yield. Therefore, ‘Jonong’, an early maturing WCS japonica rice with short growth duration and numerous spikelets, would be suitable for cultivating in winter forage crop-rice double cropping systems (Registration No. 7274).

Rice is the most important staple food in Korea. Rice blast, caused by Magnaporthe oryzae, is one of the most devastating diseases in the rice-growing world and in Korea. Eighteen major blast resistance genes were screened in 33 leading Korean japonica varieties using 44 DNA markers. The 33 leading japonica varieties are cultivated in 659,642 ha (90.4%), and a variety of Samkwang is cultivated widely on a nation-wide scale. Four resistance genes, Pia, Pib, Pi19, and Pb1, were detected in 10-21 varieties, and the R-genes of Pii, Pish, Pita/Pita-2, Piz/Piz-t, Pi35, and Pi65(t), were present in 2-5 varieties. Five R-genes, Pit, Pi5, Pi9, pi21, and Pi40, were not detected in the Korean japonica rice varieties. A total of six varieties, two mid-late flowering varieties, Ilmi and Saeilmi, a medium flowering variety Gopum; and three early flowering varieties Jopyeong, Haedamssal, and Haedeul; were resistant to blast nursery screening over 12 years. A variety of Gopum harbored alleles for Piz/Piz-t, and three early flowering varieties, Jopyeong, Haedamssal, and Haedeul, had extensive loci of the multiple-gene family Piz/Piz-t, Pi9, and Pi40 on chromosome 6. Two mid-late flowering varieties, Ilmi and Saeilmi, harbored the Pita-2 gene, and Gopum had Pita. In the japonica rice breeding program, an effective means for enhancing stable resistance to blast would be introduced to 2-3 R genes among resistance genes Pit, Pi5, Pi9, pi21 and Pi40 which were not identified in Korean japonica rice varieties, and resistance genes Pita/Pita-2, Piz-t/Piz-5, to 2-3 R genes among and Pi20 that showed stable resistance in monogenic IRBL lines.

The damage caused by typhoons to rice production has been increasing. To reduce this damage, wind-tolerant rice breeding programs have been conducted at the Yeongdeok substation (YS) of the National Institute of Crop Science (NICS). This study was conducted to examine the effects of these wind-tolerant rice breeding programs. Under the wind-tolerance screening facility (WTSF), the wind-tolerance of 17 rice varieties bred at NICS (usual rice) and 20 rice varieties bred at YS (wind-tolerant rice) were analyzed by evaluating six traits: white spikelet (WS), white panicle (WP), degree of wind damage (DG), ratio of ripened grain (RRG) at control (RRG_C) and treatment (RRG_T), and reduction rate of RRG between control and treatment (RRG_R). Wind-tolerant rice showed more wind-tolerant characteristics than usual rice, such as lower WS, WP, DG, and RRG_R and higher RRG_T and RRG_C. In the principal component analysis, wind-tolerant rice showing a similar direction for RRG_T and RRG_C were located separately from the usual rice. The adaptability tests of wind-tolerant rice were conducted by evaluating eight yield-related traits in the wind-prone areas. Wind-tolerant rice was divided into three clusters by K-means clustering analysis using WP and RRG_T with the WTSF, RRG, and yield in the wind-prone areas. Among the three clusters, YC2 had the strongest wind tolerance performance, followed by YC3 showing moderate wind tolerance, and YC1 the weakest wind tolerance. ‘Sinbo’, a variety belonging to YC2, exhibited the strongest wind tolerance and high yield potential among all varieties. The wind-tolerant rice varieties bred at YS could be used practically to prevent wind damage and utilize breeding materials to enhance the wind tolerance of rice varieties.

Early maturing rice is widely utilized to diversify cropping systems in the Honam Plain, Korea. It is based on the principle of a short growth duration. There is concern regarding quality deterioration of early maturing rice owing to the high temperature during the ripening stage as compared to that for mid and mid-late maturing rice. This study was conducted to analyze six pasting property-related and eight quality traits of six early maturing rice varieties (Jopyeong, Odae, Unkwang, Haedamssal, Jinkwang, and Haedeul) on early, ordinary, and late cultivations, and to interpret the relationships between genotypes and environments. As the cultivation time increased, the ratio of head rice (HR) and glossiness of cooked rice (Toyo value, TY) increased. The cumulative mean temperature of the ripening stage showed a strong negative correlation with HR and TY at all cultivation times. Pasting temperature, peak viscosity (PV), trough viscosity, final viscosity, and breakdown (BD) decreased, whereas setback (SB) increased as the cultivation time was delayed. Pasting properties were affected more by climate conditions in the ripening stage than during the growth stage. Additive main effects and multiplicative interaction analysis revealed that pasting property-related and quality traits were affected more by environment than genotype. Jinkwang and Haedamssal in early and ordinary cultivation and Jinkwang and Haedeul in late cultivation exhibited higher HR and TY and a lower protein content. They also showed higher PV and BD and lower SB, which are characteristics of good eating quality japonica rice. Jinkwang, Haedamssal, and Haedeul are premium-quality, early maturing rice varieties that were recently developed. The cultivation of these varieties could improve the grain quality of early maturing rice at high temperatures during the ripening stage in the Honam Plain.

The cultivation of early maturing rice in the plain areas in Korea is increasingly diversifying its cropping systems. Early maturing rice cultivars are usually vulnerable to bacterial blight (BB) and rice stripe virus (RSV) compared to mid- and mid-late maturing rice cultivars. To enhance the resistance of early maturing rice against BB and RSV, ‘IS592BB’ was developed by introgression of resistance genes, Xa3, Xa21, and Stvb-i into the genetic background of ‘Unkwang’, an early maturing rice cultivar with excellent agronomic characteristics. ‘IS592BB’ was derived from a backcross between ‘Unkwang’ and the F1 cross between ‘Unkwang’ and ‘SR31206-12’ (‘Unkwang’/‘SR30075’) and selected through the pedigree method, yield trials, and local adaptability tests. Using bioassay and marker-assisted selection to BB and RSV, Xa3, Xa21, and Stvb-i were pyramided in ‘IS592BB’. ‘IS592BB’ exhibited high-level and broad-spectrum resistance against BB, including the K3a race, the most virulent race in Korea, and also showed a resistance reaction to RSV. ‘IS592BB’ was found to be an early maturing rice cultivar with similar agronomic characteristics to ‘Unkwang’ such as early maturing, lodging tolerance with short culm, erect plant architecture, blast resistance, and high-yielding performance. In the genetic background analysis using 771 KASP (Kompetitive Allele-Specific PCR) markers, ‘IS592BB’ was confirmed to be the near-isogenic line (NIL) of ‘Unkwang’ with a 93.6% recovery rate. ‘IS592BB’ was successfully introgressed with the Xa3+Xa21+Stvb-i genes into ‘Unkwang’ without linkage drag negatively affecting its agronomic characteristics. ‘IS592BB’ would enhance the adaptability of early maturing rice in the plain area through its multiple disease resistance (Registration No. 7648).

Recent advances in high-throughput sequencing technologies have enabled large-scale cost-effective genotypic analyses, and consequently, obtaining reliable phenotypic data has now become a major bottleneck in data-driven plant breeding. In order to construct a phenotype database for commercial rice varieties released by the National Institute of Crop Science, Rural Development Administration, we initiated a systematic phenotype evaluation project, with the aim of investigating the major agronomic traits of Korean rice varieties released during the period between 1979 and 2017. Despite the narrow genetic background, we found that the days to heading (DTH) and culm length (CL) of the 297 Korean rice varieties assessed exhibited wide phenotypic variation under different environments. Under normal planting cultivation in 2018, the DTH ranged from 48 to 104 days in Suwon, 46 to 111 days in Wanju, and 39 to 97 days in Miryang, with CL values ranging from 59 to 134 cm, 55 to 122 cm, and 57 to 106 cm, respectively. During early planting cultivation in 2019, the DTH ranged from 56 to 113 days (Suwon), 58 to 109 days (Wanju), and 58 to 100 days (Miryang), with corresponding CL values ranging from 63 to 119 cm, 55 to 93 cm, and 51 to 115 cm. Despite the difference of one month in planting dates in 2018 and 2019, DTH in the different years and regions showed highly significant positive correlations (r=0.90-0.98), whereas CL showed positive but weaker correlations (r=0.45-0.82). Furthermore, we detected a weak, although significant, correlation between DTH and CL in each environment (r=-0.18-0.35). Analyses of additive main effects and multiplicative interaction (AMMI) were conducted for DTH and CL to identify rice varieties with stable phenotypes under different environments. We anticipate that the findings of this study will provide a useful rice phenotype database to facilitate genotype-phenotype association studies and data-driven rice breeding.

The cultivation of early maturing rice in the Honam plain area of Korea is increasing to diversify the cropping systems. The cropping systems of this rice are usually classified as early, ordinary, and late cultivations based on transplanting time. The characteristics of varieties vary depending on the cultivations. To evaluate the performance of varieties and interpret the relationships between genotype and environment, nine yield and 17 panicle-related traits of six early maturing rice varieties (Jopyeong, Odae, Unkwang, Haedamssal, Jinkwang, and Haedeul) were characterized on early, ordinary, and late cultivations. Heading date was longer in order of early, ordinary, and late cultivations. The cumulative mean temperature of growth stage was similar for all cultivations. The variation in the number of spikelets per panicle (NS) was mainly due to the variety and the traits related with secondary rachis-branch were affected more by variety than the traits related to primary rachis-branch. The varieties with the highest yield were Haedamssal on early maturing cultivation and Unkwang on ordinary and late cultivations. Haedamssal displayed a panicle-number type plant architecture with relatively higher number of panicles per hill (PN) and average NS. Unkwang exhibited panicle-weight type with many NS and less PN. Additive main effects and multiplicative interaction analysis revealed that, NS and HD were mostly affected by genotype and environment, respectively. Among yield-related traits, NS contributed the most to enhanced yield of varieties in all cultivations. NS could be the target trait of breeding programs intended to improve the yield potential of early maturing rice adaptable to the Honam plain area. However, proper PN should be considered because PN, which was negatively correlated with NS, also affected the yield.

Rice research in Korea during the past 100 years has gone through tremendous changes and improvements as the country underwent a turbulent history of transformation. Full-scale R&D modernization began in the 1970s, when the government focused policy on achieving self-sufficiency in rice in order to establish the foundation for national economic growth. A major landmark was reached by the development of the rice variety “Tongil” and its cultivation technology, which was at the core of the unprecedented Korean “Green Revolution”. Since achieving self-sufficiency in rice, the breeding goal of Korea moved from increasing yield to improving grain quality as more consumers began to seek high quality food products in the 1980s. This change led to the establishment of the high quality rice breeding platform for enhancing the global competitiveness of Korean rice to cope with the opening of domestic rice market in the 2000s. Currently, the major breeding goals in rice are developing premium quality cultivars for table rice and specialized cultivars for boosting processed food industry. To date, the National Institute of Crop Science has released a total of 300 rice cultivars, including 202 table rice and 98 specialized usage cultivars. Diverse technologies have been developed and utilized for breeding new rice cultivars to meet changing needs. In the next 100 years of rice breeding, the convergence of traditional crop improvement technologies and the new breeding technologies utilizing recent advances in biotechnology will play a crucial role in enhancing breeding efficiency.

‘Yechan’ is a high grain quality mid-late maturing rice cultivar with lodging tolerance and multiple disease resistance. It was a derived from a cross between ‘Hopum’ and ‘Iksan537’ (cultivar name ‘Haepum’). ‘Hopum’ is a high grain quality mid-late maturing rice cultivar with strong lodging tolerance and ‘Haepum’ is a high grain quality medium maturing rice cultivar with multiple disease resistance. To shorten the breeding period, another culture method was applied to the F₁ plants. ‘Yechan’ was selected through the pedigree method, yield trials, and local adaptability tests, with a high selection pressure for grain quality, lodging, and disease resistance. The heading date of ‘Yechan’ was August 14, one day later than that of ‘Nampyeong’. ‘Yechan’ is a cultivar tolerant to lodging and it has short culms. It has multiple disease resistance against rice blast, rice stripe virus, and bacterial blight, including the K3a race, the most virulent race in Korea. The yield of ‘Yechan’ was similar to that of ‘Nampyeong’. ‘Yechan’ showed excellent grain appearance, superior taste when cooked, and enhanced milling performance; thus, we concluded that it could contribute to the improvement of Korean japonica rice cultivar quality. ‘Yechan’, a high grain quality mid-late maturing rice cultivar with lodging tolerance and multiple disease resistance, would be suitable for cultivation in the southern plain area in Korea and has been utilized in the breeding programs aimed at enhancing the grain quality and stability for the cultivation of Korean japonica rice (Registration No. 7647).