Multi-environment trials (METs) are essential in plant breeding programs to evaluate crop productivity and adaptability in diverse environments. In this study, we demonstrated the practical use of METs to evaluate grain yield and yield-related traits using 276 Korean rice cultivars, divided into three maturity groups (81 early-, 90 medium-, and 105 medium–late-maturing cultivars) grown in three regions (Jeonju, Suwon, and Miryang) and two planting seasons (early and regular planting) for two years. Due to the narrow genetic variability of the commercial cultivars, which are cultivated in relatively similar environmental conditions, genotype-by-environment interaction (GEI) effects were not statistically significant. However, genotype and environment evaluation using GGE biplot analysis exhibited distinct patterns of mega-environment formation, winning genotypes, ranking genotypes, discriminating power, and representativeness according to the differences in planting seasons and regions. Moreover, the simultaneous selection of stable high-performance genotypes using a weighted average of absolute scores from the singular-value decomposition of the matrix of BLUPs (WAASB) and a multi-trait stability index (MTSI) revealed six recommended genotypes each for early-maturing (Manho, Namil, Unkwang, Odae 1ho, Sinunbong 1ho, and Jonong) and medium-maturing (Sobi, Cheongdam, Shinbaeg, Boramchal, Mimyeon, and Saemimyeon) cultivars, and four genotypes for medium–late-maturing cultivars (Hanmauem, Dami, Baegseolchal, and Hangangchalbyeo). The winning genotypes of each trait can be used as parents to develop regional specialty cultivars by fine-tuning favorable traits, and recommended genotypes can be utilized as elite climate-resilient parents that can aid breeders in improving yield potential and stability across the planting seasons and regions.

Optimizing flowering time in crop plants is critical for maximizing yield and quality under target environments. While there is a wide range of heading date variation in Korean rice cultivars, the underlying gene mechanisms are unclear. Here, we sequenced the protein coding regions of Hd1, the major rice heading date gene, from 293 Korean rice cultivars and investigated the associations between Hd1 allele types and major agronomic traits under four different environments. There were four functional Hd1 and five nonfunctional hd1 alleles distributed among the 293 Korean rice cultivars. The effects of the Hd1 allele types were highly significant for days to heading in all four environments, explaining 51.4–65.8% of the phenotypic variation. On average, cultivars carrying nonfunctional hd1 headed 13.7 days earlier than those carrying functional Hd1. While the Hd1 allele types exhibited highly significant effects on culm length and protein content under all four environments, the differences between cultivars carrying Hd1 and hd1 were minimal. The effects of the Hd1 allele types on amylose content were significant in only one of the four environments. Our results provide useful information for fine-tuning rice heading dates by utilizing different Hd1 alleles in rice breeding programs.

Understanding the gene mechanisms controlling days to heading (DH) is important in rice breeding for adaption in the target environment. Using a recombinant inbred line population derived from the cross between two japonica rice cultivars, Koshihikari and Baegilmi, we identified three consistent quantitative trait loci (QTLs) for DH for two years, qDH3, qDH6, and qDH7 on chromosomes 3, 6, and 7, respectively. While Baegilmi contributed the allele for early heading at qDH6 and qDH7 with the additive effect of five days each, Koshihikari contributed the allele for early heading at qDH3 with the additive effect of three days. Notably, pyramiding two or more alleles for early heading at these QTLs accelerated heading effectively. Sequencing of Hd16, Hd1, and Ghd7, the previously known heading date genes underlying qDH3, qDH6, and qDH7, respectively, revealed that Baegilmi and Koshihikari carry different alleles at the three genes. Molecular markers were developed to screen the allelic compositions of the three genes among 295 Korean commercial rice cultivars. The results showed that few cultivars carry alleles for early heading at the three genes, highlighting that DH can be further accelerated and fine-tuned in breeding programs by combining the desirable alleles of Hd16, Hd1, and Ghd7.

Rice cultivars with floury endosperm provide a useful raw material for producing dry-milled rice flour, helping to enhance the processed rice food industry. To expand the genetic resources for breeding floury endosperm rice cultivars, we developed Samkwang(SA)-flo3 (SK-flo3), a floury endosperm mutant line derived from the chemical mutagenesis of Samkwang, an elite Korean japonica rice cultivar. Compared with Samkwang, SK-flo3 showed significantly lower grain hardness, which is suitable for producing dry-milled flour without the soaking and drying processes required in regular wet rice milling. The dry-milled flour of SK-flo3 exhibited excellent physicochemical properties with less damaged starch and finer flour particles relative to Samkwang. Genetic analyses revealed a G-to-A point mutation in exon 7 of cyOsPPDKB, substituting glycine with aspartic acid as a causative mutation for the floury endosperm of SK-flo3. We named this allele flo4-6 and developed a molecular marker to efficiently transfer it to commercial rice cultivars. Our results provide useful genetic resources and information for developing specialty rice cultivars for high-quality rice flour production with reduced milling costs.

Purpose Rice (Oryza sativa L.) production is threatened by bacterial leaf blight (BLB), particularly from the virulent K3a strain. Reliableand efficient phenotyping is essential for breeding resistant cultivars, but traditional manual methods are time-consuming and prone to subjectivity. Methods This study assessed the accuracy of smartphone-based image analysis for measuring lesion length (LL) and lesion ratio (LR) in BLB-infectedrice. A total of 102 recombinant inbred lines (RILs) derived from Chamdongjin and Sindongjin were evaluated using both manual methods and imageanalysis. Images were captured in the field using a smartphone (12MP, 4000×3000 pixels), without any auxiliary equipment. The images were analyzedusing ImageJ and Python-based tools and compared with manual measurements. Results Image-based data showed strong correlation with manual results(r = 0.84–1.00), and principal component analysis (PCA) explained 94.14% of the variance, effectively distinguishing resistant and susceptible lines.Statistically significant differences were observed between groups (p < 0.01), confirming reliability. Images taken at 3x magnification showed highaccuracy (r = 0.88–0.92), while those at 1x magnification showed reduced accuracy (r = 0.76–0.79), likely due to the inclusion of surrounding plants—highlighting the importance of proper field design and image framing. Conclusion This study suggests that smartphone-acquired images, even withoutauxiliary equipment, may serve as a feasible and sufficiently accurate source for image-based phenotyping. This accessible approach has the potential tosupport rapid, low-cost data collection in field settings, which could contribute to breeding and disease resistance research.

The acceleration of global warming poses a serious threat to food security, particularly affecting rice production. High temperatures during the grain-filling period deteriorate the grain quality and appearance of brown and milled rice. This study investigated meteorological changes in Korea in 2023 and 2024 and analyzed key factors influencing rice grain appearance quality. The grain appearance quality of brown rice was influenced by whole grain and immature grain levels, whereas milled rice quality was determined by perfect grain, chalky grain, and broken grain levels. In 2024, the number of days with average temperatures exceeding 30 °C increased by 12 compared to 2023, and the number of days with maximum temperatures above 35 °C increased by 8. These climatic changes significantly affected the grain appearance quality of Dongjin2, Boramchan, Sugwang, and Hwanggeumnuri. However, Asemi6 and Nampyeong showed consistent grain appearance-related traits across 2023 and 2024, identifying stable expression despite climatic changes The negative impact of high temperatures during the grain-filling period resulted in reduced 1000-grain weight and grain quality, weakening market competitiveness and decreasing farmer income. These findings highlight the increasing need for research to address the effects of climate change on rice production. This study provides a systematic analysis of the relationship between temperature variations and rice grain appearance quality. Also, we identified rice cultivars that exhibited stable grain appearance-related traits despite environmental variations. These selected resources are expected to serve as valuable parental materials for breeding high-yield cultivars with stable trait expression under future climate change.