Rice is a staple crop in South Korea and globally. The era of global boiling, characterized by rising temperatures and abnormal climatic conditions, significantly impacts crop production worldwide. This study examines the effects of high temperatures and rainfall on early maturing rice varieties, focusing on enhancing heat tolerance during the ripening stage and preharvest sprouting resistance. Utilizing ‘Milyang247,’ a progeny line from ‘Nampyeong,’ we developed the intermediate line ‘MY362VP.’ During 2020–2022, regional adaptability tests were conducted at five locations across Korea. Results showed that ‘MY362VP’ had a viviparous germination rate of 1.9% compared to 19.0% in the control variety ‘Jopyeong.’ Furthermore, ‘MY362VP’ maintained a head rice rate of 90.6% under high temperature conditions, outperforming ‘Jopyeong,’ which has a rate of 62.1%. ‘MY362VP’ produced an average yield of 529 kg/10a, comparable to the control’s 518 kg/10a. This study offers valuable insights for breeding climate-resilient early-maturing rice varieties, positioning ‘MY362VP’ as a promising candidate for future cultivation.

Bakanae disease, also known as the foolish seedling disease, caused by Gibberella fujikuroi, is a serious issue in Korea. Since 2007, there has been a rapid increase in the occurrence of bakanae disease; this has caused severe yield loss to rice farmers every year. The most reliable and economical solution for managing bakanae disease is to cultivate resistant varieties; however, there are only a few rice varieties in Korea that can withstand this disease. Therefore, this study aimed to evaluate the resistance of 61 major rice varieties which account for 89% of the total rice cultivation area. Only six varieties showed intermediate or higher resistance to bakanae disease; this included Anpyeong and Samkwang. The genetic inconsistency between the bioassay results and the allele types of 12 molecular markers (associated with four QTLs) ranged from 4.7% to 48.7%. Therefore, more accurate markers, such as gene-based markers, are essential for monitoring general breeding programs or gene pyramiding.

A total of 285 Korean rice cultivars were used for amylose content and genetic analyses using KASP markers related to the amylose content. We used three polymorphic KASP markers targeting the Waxy (Wx) gene and compared the genotyping efficiency with previously reported molecular markers. The rice cultivars were raised in Miryang, Korea, for one period. Genetic analysis of the rice cultivars revealed that the three KASP markers on the Wx gene were functional for genomic selection of SNPs related to amylose content variation. Therefore, the three KASP markers targeting different Wx alleles can be used for genomic selection. In addition, KASP markers were more efficient than previously reported molecular markers that target the same alleles. These findings can be beneficial for the breeding and genomic selection of high-quality rice in Korea.

Consumer demand for Triticale cultivars as a winter forage crop in Korea has been increasing because of its ability for high and stable yield. However, more than 10 years are required to develop new varieties with conventional breeding programs. A speed breeding system using long-day photoperiodic treatment has recently been suggested and applied in wheat and barley, but not in the triticale breeding program in Korea. To evaluate the availability of the established speed breeding system for triticale breeding programs in Korea, we used nine domestic triticale cultivars to investigate their growth characteristics under a 22 h photoperiod. The average days to heading (DTH) of the nine cultivars was 38 days, and Gwangyoung and Minpung showed the most delayed DTH at 42 days. Therefore, all nine triticale cultivars were able to shorten the growth duration under the tested photoperiod condition. One productive tiller and more than 10 seeds were obtained from each cultivar. The germination percentage was over 82% when the spikes were harvested 20 days after heading, dried, and chilled for a week to break dormancy. These results suggest that in Korea, the rapid generation advancement system with simple long-day photoperiodic treatment can be applied to triticale breeding programs to reduce the breeding time.

The rice variety ‘Youngjin’ is a japonica rice (Oryza sativa L.) with good eating quality, lodging tolerance, and resistance to the rice stripe virus (RSV) and bacterial blight disease (BB). It was developed by the rice breeding team of the Department of Southern Crop, NICS, RDA, in 2016. This variety was derived from a three-way cross between ‘Iksan486’, ‘YR22722-B-B-B-25-1’, and ‘Chengmu,’ with good eating quality, in the summer of 2007. The pedigree of ‘Youngjin’ was YR27874Acp46-1, and was designated as ‘Miyang283’ in 2012. After local adaptability tests at five different locations from 2014 to 2016, it was released under the name ‘Youngjin’ in 2016. ‘Youngjin’ is a mid-late maturing ecotype with a short culm length of 67 cm. This variety was found to be resistant to the K1, K2, and K3 races of BB, and RSV, and moderately resistant to leaf blast disease. The milled rice kernels of ‘Youngjin’ were translucent and clear, without white core and belly, and had good eating quality, according to a panel test. This variety showed a lower percentage of cracked kernels compared to other susceptible cultivars. The milled rice yield of ‘Youngjin’ was 568 kg/10a, under normal levels of fertilization, determined by the local adaptability tests. This cultivar is adaptable to the Yeongnam plain area (Registration No. 7653).

Rice doubled haploid (DH) lines derived from crosses of the indica cultivar 93-11 and japonica line Milyang352 were used in genetic mapping and QTL analysis studies of days to heading (DTH), an important trait that controls rice yield and biomass. QTL mapping was conducted using the inclusive composite interval mapping method. We used 234 single-nucleotide polymorphic markers in the whole-genome region, including 100 KASP markers and 134 Fluidigm markers, to construct a genetic map. DH populations were raised in Milyang, Korea, over three different periods. Two major DTH QTLs, qDTH3-1 and qDTH7, were detected under natural conditions in Milyang, and explained 14.88%~24.56% and 24.20%~37.39% of the phenotypic variation, respectively, in 93-11×Milyang352 DH populations. During three different rice cultivation periods, qDTH3-1 and qDTH7 were repeatedly detected with significant logarithm of the odds scores and phenotypic variability explained. The findings of this study will make a valuable contribution to breeding high-yielding and early-maturing rice in Korea.

AbstractThe high-molecular-weight glutenin subunit (HMW-GS) composition of wheat is the main factor controlling gluten strength related to bread baking quality. Reported molecular markers for HMW-GS were validated and selected for improved breeding efficiency in South Korean wheat breeding programs. Sodium dodecyl sulfate polyacrylamide gel electrophoresis, lab-on-a-chip electrophoresis, sequence-tagged site (STS) markers, and Kompetitive Allele-Specific PCR were performed to re-evaluate the known HMW-GS of 14 wheat cultivars. Glu-A1b and Glu-A1c alleles were separated by the STS marker, UMN19, and KASP marker, namely Glu-Ax1/2*_SNP, at Glu-1 loci. At the Glu-B1 locus, Glu1-By8 and Glu1-By9 could be distinguished from Glu-B1b and Glu-B1c alleles by two STS markers, namely ZSBy8 and ZSBy9a, respectively. Glu1-Bx17 and Glu1-7^OE could respectively be separated from non-Glu-B1i and non-Glu-B1al alleles by cauBx642 and BX7^OE_866_SNP. The Glu-D1d allele, used to determine bread baking quality, could easily be distinguished from other alleles by Glu-D1d_SNP at Glu-D1 loci. Validated molecular markers in this study could therefore be used to select wheat lines for good bread baking quality in South Korean wheat breeding programs.

Limitation of genetic diversity in japonica rice breeding populations is often identified as a potential obstacle for the development of high yielding cultivars. The use of diverse germplasm in rice breeding has been suggested as one way of combating this problem. This study was conducted to improve the genetic diversity for rice, by developing an advanced backcross population derived from a backcross ‘Junam’ as recurrent parent and ‘IR72’ as a donor parent. Among them, we selected a promising line ‘YR24438-B-B-B-B-132’ containing bacterial blight resistance gene Xa4. Testing in the replicated yield trial in 2009, the ‘YR24438-B-B-B-B-132’ line was selected, and it was designated as ‘Milyang298’. The local adaptability test of ‘Milyang298’ was carried out at three locations from 2014 to 2016 and it was named ‘MY298BB’. The average culm length in the replicated yield trials was 87 cm, which is 15 cm taller than recurrent parent ‘Junam’. Number of spikelets per panicle was significantly lower than in ‘Junam’ but the number of tillers per hill was higher. This variety is resistant to bacterial blight race K1, K2, K3, and K3a.However ‘MY298BB’ showed early leaf senescence at the mature stage and the chlorophyll content of ‘MY298BB’ was significantly lower than that of the recurrent parent ‘Junam’. Moreover the grain filling ratio and yield were significantly lower in ‘MY298BB’ than those of recurrent parent ‘Junam’. Therefore, understanding the leaf senescence mechanism would be useful for improving yield potential in rice.

A speed-breeding system using photoperiod characteristics has recently been developed to reduce the entire growth period in wheat. In this study, the entire growth period of four Korean varieties was examined to investigate whether this speed-breeding system would be beneficial for our wheat breeding program. When four varieties were cultivated under a 22-hour light/2-hour dark cycle in a glasshouse, the number of days to heading of Jokyoung and Baekkang was 44 and 43, respectively, and the number for Keumgang and Joongmo2008 was more than 75. Around twelve seeds per plant were obtained from Jokyoung and Baekkang, and the seeds of these varieties completely germinated when harvested at 20 days after heading. These results suggest that this speed-breeding system can be a reliable method of reducing the growth period in Korean wheat breeding.

Rice stripe virus (RSV) is one of the major constraints in rice production which is transmitted by the small brown plant hopper, Laodelphax striatellus. Identifying new resistance genes from diverse sources is important for rice breeding programs to enhance the resistance level and/or to overcome the breakdown of resistance genes. This study was conducted to identify novel sources of resistance against RSV. We used five RSV resistant varieties that do not harbor Stv-bⁱ. The presence of known genes for RSV resistance was identified using the InDel7 marker for Stv-bⁱ, two Indel (Sid primer set) markers for Stv-b, and DNA sequence analysis for OsSOT1. We revealed that two varieties, 02428 (IT236925) and Tung Ting Wan Hien 1, are novel RSV resistance sources.

Rice tungro disease is a serious threat to rice production in South and Southeast Asian countries. Rice production in these countries has been intensified, often through continuous cultivation of rice. We conducted a screen of the resistance to tungro virus disease in Korean japonica rice. Dongjin, Hwaseong, and Sangju were varieties resistant to Rice tungro spherical virus (RTSV) but susceptible to Rice tungro bacilliform virus (RTBV). RTSV-resistant variety Sangju was crossed with RTSV-susceptible variety Unkwang to conduct a genetic analysis for RTSV resistance originating from Sangju. Evaluation of 201 F2 plants from the cross between Unkwang and Sangju showed that there were 85 plants showing resistance, and that 116 plants were susceptible, indicating a ratio fitting a 7:9 ratio ratio (χ² = 0.54; p = 0.46). Thus, the resistance to RTSV in Sangju might be controlled by two recessive genes. This result indicates that Sangju might serve as a useful genetic source for diversification of RTSV resistance and stabilization of resistance through gene pyramiding.

Rice production is largely affected by various environmental conditions such as cold, heat and flooding. Here, to identify cold tolerant QTLs at seedling stage in rice, we generated RIL population derived from a cross between Hanareum 2 and Unkwang which are a highly cold sensitive and cold tolerant, respectively. We observed cold phenotype of this population in the growth chamber conditions and natural field conditions. For observation of cold tolerant phenotype of RIL population in the growth chamber, we treated cold stress (5~13°C) for 14 days and recovery for 4 days. When we examined the phenotype of RIL in the field conditions, temperature range in the field conditions was about 6 to 25°C in 2015~2016. We named QTLs as Seedling Cold Tolerant (SCT) in growth chamber and Cold induced Yellowing Tolerant (CYT) in the field, respectively. Three QTLs for SCT and 5 QTLs for CYT were detected on chromosome 1, 6, 7, 8, 10, 11 and 12. Among these QTLs, qSCT12 on chromosome 12 showed 26.3 LOD score with 25.5% of phenotypic variation. When qSCT11.1 and qSCT12 were combined, cold tolerant was most strongest in our experimental conditions. qCYT10 on chromosome 10 was identified in field experiment on both 2015 and 2016. These results may provide useful information for a marker-assisted breeding program to improve cold tolerance in rice.

The amylose contents of rice determine eating quality which is one of the major traits in rice breeding program. To identify the low-amylose gene of the japonica rice cultivar Baegjinju, genetic analysis was conducted using 200 F₂ population derived from a cross between the japonica cultivars, Saeilmi and Baegjinju. Individual F₂ plants were classified as wild type (translucent grain) and mutant type (dull grain) based on the grain appearance of brown rice. Two hundred F₂ plants were segregated into 155 wild type plants and 45 mutant type plants, which fit the 3:1 ratio (x² = 0.667, df = 1, p = 0.414) and this result indicated the low-amylose gene of Baegjinju is a single recessive gene which controls the amylose contents. Linkage analysis was conducted to localize the low-amylose gene of Baegjinju and fine mapped within an 800-kb interval between 17.5 to 18.8Mb on short arm of chromosome 10. Co-segregated SSR marker, RM25648 was developed and it could be useful for marker-assisted selection and determination of the genetic resource related with amylose contents in rice breeding.

Bakanae (foolish seedling) disease caused by Gibberella fujikuroi creates serious problems in the foremost rice growing countries. This study was conducted to identify new resistance genetic sources to Bakanae disease. Bioassay showed that 11 varieties including Gwangmyeongbyeo, Hawn, Wonseadaesoo, Erguailai etc. were resistant to bakanae disease among 254 rice germplasm. Mismatch ratio between phenotype on bakanae disease bioassay and allele type of RM9, a SSR marker closely linked the bakanae disease resistant QTL, qBK1, were 38.3%. These results suggest that RM9 might be used for selecting qBK1, but it cannot be used for wide range of rice germplasm. Resistant germplasm in this study might be have resistant genes different from qBK1. The eleven varieties resistant to selected in this study will be used to identify new resistant alleles or genes to improve bakanae disease resistance in rice.