‘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.

‘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).