‘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).

‘Seongsan’, an early multi-resistant japonica rice cultivar developed from a cross between ‘Jopyeong’ and ‘Jungmo 1012’, was developed by the rice breeding team of the National Institute of Crop Science, Rural Development Administration. The average heading date at the ordinary planting was July 25th in seven test spots. In response to physiological stresses, premature heading rate was very low and viviparous germination rate was relatively low (15.7%). In response to biotic stresses, ‘Seongsan’ showed resistance to bacterial blight pathogen K1 to K3, rice stripe virus, and blight leaf. The milled rice of ‘Seongsan’ was translucent with relatively clear non-glutinous endosperm and medium short grain. The cooked rice had good palatability compared with that of ‘Chucheong’. The milled rice yield of this variety was approximately 5.52 MT/ha in a three-year local adaptability test. ‘Seongsan’ was an early maturing multi-resistant rice with good grain quality, and it was expected to be used as a representative for maturity diversification of rice cultivation area (Registration No. 7277).

Rice blast caused by the fungus Magnaporthe grisea (anamorphic: Pyricularia oryzae) is an important disease in rice and development of resistant varieties to blast is one of the most important goals in rice breeding programs. A japonica rice variety, Palgong, has shown resistance to the Korean blast pathogen since it was developed in 1996. Nine blast resistance quantitative trait loci (QTLs) in Palgong alleles were identified on chromosomes 2, 4, 7, and 11. Four QTLs of qBn2.3, qBn4.2, qBn11.1, and qBn11.2 explained 28–56.7% of total phenotypic variation, while five QTLs of qBn2.2, qBn2.4, qBn4.1, qBn7.1, and qBn7.2 explained 9.7–18.8%. In a previous study, one to four resistance genes were located on the loci qBn2.2, qBn2.3, qBn4.2, qBn11.1, and qBn11.2, however, resistance genes were not located on the loci qBn2.4, qBn4.1, and qBn7.1. A major QTL, qBn11.2, explaining 56.7% of total phenotypic variation was related to the durable resistance of Palgong. Additionally, rice stripe virus resistance of Palgong was assumed to be based on the Stvb-i gene, which is located on a major QTL qBn11.2.

‘Sinjinbaek’ is a bacterial blight (BB)-resistant, mid-late maturing rice cultivar with high grain quality. To diversify the resistance genes and enhance the resistance of Korean rice cultivars against BB, ‘Sinjinbaek’ was developed from a cross between ‘Iksan493’ (cultivar name ‘Jinbaek’) and the F₁ cross between ‘Hopum’ and ‘HR24670-9-2-1’ (‘HR24670’). ‘Jinbaek’ is a BB-resistant cultivar with two BB resistance genes, Xa3 and xa5. ‘Hopum’ is a high grain quality cultivar with the Xa3 resistance gene. ‘HR24670’ is a near-isogenic line that carries the Xa21 gene, a resistance gene inherited from a wild rice species O. longistaminata, in the genetic background of japonica elite rice line ‘Suweon345’. ‘Sinjinbaek’ was selected through the pedigree method, yield trials, and local adaptability tests. Using bioassay for BB races and DNA markers for resistance genes, three resistance genes, Xa3, xa5, and Xa21, were pyramided in the ‘Sinjinbaek’ cultivar. ‘Sinjinbaek’ exhibited high-level and broad-spectrum resistance against BB, including the K3a race, the most virulent race in Korea. ‘Sinjinbaek’ is a mid-late maturing rice cultivar tolerant to lodging. It has multiple disease resistance against BB, rice blast, and stripe virus. The yield of ‘Sinjinbaek’ was similar to that of ‘Nampyeong’. ‘Sinjinbaek’ showed excellent grain appearance, good taste of cooked rice, and enhanced milling performance, and we concluded that it could contribute to improving the quality of BB-resistant cultivars. ‘Sinjinbaek’ was successfully introgressed with the Xa21 gene without the linkage drag negatively affecting its agronomic characteristics. ‘Sinjinbaek’ improved the resistance of Korean rice cultivars against BB by introgression of a new resistance gene, Xa21, as well as by pyramiding three resistance genes, Xa3, xa5, and Xa21. ‘Sinjinbaek’ would be suitable for the cultivation in BB-prone areas since it has been used in breeding programs for enhancing plants’ resistance to BB (Registration No. 7273).

‘Haepum’ is a bacterial blight-resistant, medium maturing rice cultivar with high grain quality. It was derived from a cross between ‘Iksan493’ (cultivar name ‘Jinbaek’) and the F₁ cross between ‘Iksan495’ (‘Dacheong’) and ‘Iksan496’ (‘Jungmo1005’). Of these three cultivars, ‘Jinbaek’ is a bacterial blight-resistant mid-late maturing rice cultivar with high grain quality, ‘Dacheong’ is a mid-late maturing rice cultivar with multiple resistance to disease and insects, and ‘Jungmo1005’ is a mid-late maturing rice cultivar with lodging tolerance. To develop fixed lines, the anther culture method was applied to F₁ plants. The cultivar ‘Haepum’ was selected using the pedigree method, yield trials, and local adaptability tests. The heading date of ‘Haepum’ was August 11^th, three days earlier than that of ‘Nampyeong’ cultivar. Haepum’ is a cultivar tolerant to lodging and it has short culms. Due to its low rate of viviparous germination, ‘Haepum’ could be useful for preventing pre-harvest sprouting in cultivation of medium maturing rice in the southern plain area of Korea. ‘Haepum’ carries two bacterial blight resistance genes (Xa3 and xa5), and in our study, it exhibited high-level and broad-spectrum resistance against bacterial blight, including K3a, the most virulent race in Korea. ‘Haepum’ is also resistant to the rice stripe virus and moderately resistant to rice blast. The yield of ‘Haepum’ was similar to that of ‘Nampyeong’. ‘Haepum’ showed excellent grain appearance and good taste of cooked rice, and therefore it could contribute to the development of bacterial blight-resistant rice cultivars of improved quality. ‘Haepum’ would be suitable for cultivation in the southern plain area of Korea as well as in bacterial blight-prone areas. (Registration No. 6068)

Joil’ is a multiple disease resistant early maturing rice cultivar with high grain quality. ‘Joil’ was derived from a single cross between ‘Unbong37’ (cultivar name ‘Unmi’) and ‘HR23156-26-2-3-5’. ‘Unmi’ is an early maturing rice cultivar with high grain quality and resistance to rice blast and stripe virus. ‘HR23156-26-2-3-5’ is an early maturing elite rice line with lodging resistance and cold tolerance. ‘Joil’ was selected through the pedigree method, yield trials, and local adaptability tests. ‘Joil’ was an early maturing rice. The heading date of ‘Joil’ was July 16 in early transplanting cultivation, which was 2 days later than that of ‘Jopyeong’. ‘Joil’ was a lodging resistance rice with a short culm and showed better tolerance to viviparous germination than that of ‘Jopyeong’. ‘Joil’ was a multiple disease resistant rice with resistance against rice blast, bacterial blight, and stripe virus. ‘Joil’ showed higher yield in both early and late-transplanting cultivations than those of the standard rice cultivars ‘Jopyeong’ and ‘Geumo’. ‘Joil’ had enhanced grain quality under high temperature ripening conditions in early transplanting cultivation. The cooked rice had good grain appearance and taste attributes, and this cultivar had a higher head rice ratio than that of ‘Jopyeong’. ‘Joil’, a multiple disease resistant early maturing rice cultivar with high grain quality, would be suitable for early transplanting cultivation in the southern plain area (Registration No. 6792).

To enhance rice yield and diversify grain quality of Korean japonica rice, we developed japonica rice line with long and spindle-shaped grain. Korean japonica rice cultivars have narrow genetic background of grain size and shape. Most of cultivars show medium-short and semi-round grain. To diversify the genetic background for grain, we developed Jeonju625, japonica rice line with long and spindle-shaped grain, derived from a cross between DSG79, the breeding material with extra-long and spindle-shaped grain, and Boramchan, japonica super high-yielding cultivar with medium-short and semi-round grain. Jeonju625 had GW2gs3qSW5+qGL3 allele type for grain-related genes, which conferred extra-long and spindle-shaped grain. The grain length and ratio of length to width of brown rice of Jeonju625 was 7.06 mm and 2.72, respectively. Jeonju625 was improved the deteriorated traits of DGS79, very late heading, long culm, long awn, droopy flag leaves, and susceptibility to lodging, by strong selection pressure focused on field breeding. The milled rice yield of Jeonju625 was 559 kg/10a, which was similar level of Boramchan (552 kg/10a) and 29% enhanced yield compared to DSG79. Jeonju625 had suitable characteristics for cooked rice. Jeongju625 showed lower protein contents and better glossiness and palatability of cooked rice than Boramchan and Hanareum2. Elite japonica rice line, Jeonju625, with extra-long and spindle-shaped grain showed good characteristics for rice yield and grain quality. Jeonju625 could be utilized practical cultivar and breeding material for enhancing rice yield and diversifying grain quality.

‘Jungmo1045’, a multi-resistant japonica rice cultivar developed from a cross between ‘Hanggeumnuri’ having a good eating-quality and high yield and ‘SR30071’ having brown planthopper (BPH) resistance, was developed by the rice breeding team of NICS, RDA in 2015. This cultivar has about 121 days growth duration from transplanting to harvesting in west-southern coast, Honam and Youngnam plain of Korea. It has 73cm culm length and 22cm panicle length. In reaction to biotic and abiotic stresses, it shows resistance to bacterial blight pathogen races from K1 to K3, stripe virus and brown planthopper. The milled rice of ‘Jungmo1045’ exhibits translucent, relatively clear non-glutinous endosperm and medium short grain. It has good palatability of cooked rice compared with ‘Nampyeongbyeo’. The milled rice yield performance of this variety is about 5.74 MT/ha in local adaptability test for three years. ‘Junngmo1045’ would be useful genetic resources for multi-resistance breeding program against disease and insect and eco-friendly cultivation.

To diversify the grain size and shape of japonica rice, we developed the Breeding Materials with Diverse Grain Size and Shape (BM_DGS) and characterized the grain and yield-related traits. We used the donor parents Jizi1560 and Jizi1581, japonica germplasm with extremely large grain size. Four cross combinations between the each donor parents and Korean high yielding japonica rice cultivars, Deuraechan and Boramchan, were constructed and anther culture method was applied. Among 290 doubled haploid lines, we selected 91 elite lines with diverse grain size and shape and designated to the BM_DGS. The grain size and shape of BM_DGS exhibited beyond the characteristics of previously developed Korean rice cultivars. The alleles of major grain-related genes, GW2, GS3, and qSW5, in BM_DGS showed two types, wild type or loss-of-function mutant type. The loss-of-function mutant alleles, gw2, gs3, and qSw5, had an effect on increasing grain size. The phenotypic variation of grain length was mostly controlled by GS3 alleles, and grain width and thickness were influenced by the combinations of GW2 and qSW5 alleles. 1,000-grain weight was determined by the combinations of GW2, GS3, and qSW5. The grain-related genes influenced the phenotypic variation of yield-related traits. The result of this study could be useful to elucidate the relationship between the grain-related genes and agronomic traits. And the BM_DGS are being utilized in the breeding programs to diversify the grain size and shape in japonica rice.

‘Manbaek’ is a bacterial blight resistant mid-late maturing rice cultivar with high grain quality. ‘Manbeak’ was derived from anther culture using the backcross combination, Hopum*2/SR30075. ‘Hopum’ is a mid-late maturing rice cultivar with high grain quality and ‘SR30075’ is a pyramid line carrying three bacterial blight resistance genes. ‘Manbaek’ was selected through the pedigree method, yield trials, and local adaptability tests. ‘Manbeak’ carrying two bacterial blight resistance gene Xa3 and xa5 showed high-level and broad-spectrum resistance against bacterial blight. ‘Manbaek’ was resistant to K3a, mostly virulent race in Korea, and exhibited resistance reaction against 16 Korean bacterial blight isolates. ‘Manbaek’ was a mid-late maturing rice. The heading date of ‘Manbaek’ was August 19th, which was 5 days later than that of ‘Nampyeong’. Manbaek’ was a lodging-tolerant rice with short culm and dark green leaf. Due to the low viviparous germination, ‘Manbaek’ could be a useful material to prevent pre-harvest sprouting. ‘Mabeak’ was resistant to bacterial blight and rice stripe virus, but susceptible to other virus diseases and insect pests. The yield of ‘Manbaek’ was similar to ‘Nampyeong’. ‘Manbaek’ showed excellent grain appearance and good tastes of cooked rice, so that it could contribute to improving the quality of bacterial blight resistant cultivars. ‘Manbaek’, bacterial blight resistant cultivar with high grain quality, is suitable for the cultivation at bacterial blight prone area and has been utilized in the breeding programs for enhancing the resistance against bacterial blight (Registration No. 6069).

‘Ondami’, a japonica rice cultivar developed from a cross between Hitomebore having a high grain quality and Sangju27 adaptable to southern mid-mountainous area was developed by the rice breeding team of Sangju Substation, NICS, RDA in 2013. The heading date of ‘Ondami’ is july 27 which is same with ‘Odae’ in Southern mid-mountainous area, mid mountainous, southern alpine area and north-east coastal area of South Korea. ‘Ondami’ has 70cm culm length, 19cm panicle length which is 2cm shorter than those of ‘Odae’ and 78 spikelets per panicle. In reaction to biotic and abiotic stresses, it shows strong resistance to blast, but is susceptible to bacterial blight, virus diseases, and insect pests. The milled rice of ‘Ondami’ exhibits translucent and, relatively clear non-glutinous endosperm, and medium short grain shape. This variety has a higher head rice milling recovery ratio(73.1%) and lower amylose content(18.8%) than that of ‘Odae’. The milled rice yield performance of this variety was about 5.29 MT/ha in ordinary cultivation of local adaptability test for three years. ‘Ondami’ could be adaptable to Southern mid-mountainous area, mid mountainous, southern alpine area and north-east coastal area of South Korea.

A doubled haploid (DH) lines derived from the cross between high-yielding japonica rice cultivars ‘Deuraechan’ and ‘Boramchan’ was developed to increase diversity of panicle and yield-related traits and select high-yielding lines. Panicle and yield-related traits of DH population consisting of 163 lines and 13 selected high-yielding lines were analyzed using correlation, principal component, and path analysis. Among panicle-related traits, number of spikelets on secondary rachis-branches (SRBs) was more highly correlated with and had more positive effect on number of spikelets (NS) than number of spikelets on primary rachis-branches (PRBs) per panicle. In the DH population, NS had the most positive effect on yield, whereas panicle number per hill (PN) was in the selected lines. PN was significantly positive correlated with ratio of ripened grain (RGG) in both case. The enhancement of ripening and increase of total spikelets number by increasing PN had more effect on yield than increase of total spiekelts number by increasing NS in the selected lines. Among 13 lines, four lines, AC60, AC152, AC156, and AC161 showed higher yield than Deuraechan (481 kg/10a) and Boramchan (558 kg/10a). Deuraechan exhibited panicle-weight type with low tiller and heavy panicles and Boramchan was slightly panicle-number type with more PN and higher RGG. Selected high-yielding lines showed medium characteristics of parents with improved yield potential. These elite lines could be utilized to develop high-yielding japonica rice.

This study was conducted to develop the early maturing rice lines with genes conferring resistance to bacterial blight and rice stripe virus to enhance the adaptability in plain area. Unkwang carrying Xa3 was used as a recurrent parent and SR30075 carrying Xa4+xa5+Xa21+Stvb-i was used as a donor parent. RL1(Resistant Line, BC₁F₇), RL2, RL3, RL4, and RL5(BC₂F₆) were bred through bio-assay of K3a race inoculation and phenotypic selection of agronomic traits. The presence of introduced genes was confirmed by testing the resistance levels against bacterial blight and rice stripe virus and then double-checked by using DNA marker. RL1 has all target genes, Xa3+xa5+Xa21+Stvb-i. RL2, RL3, and RL5 have Xa3+Xa21+Stvb-i whereas RL4 has only Xa21. Rice lines carrying Stvb-i showed resistance reaction to rice stripe virus. The combinations of bacterial blight resistant genes(Xa3+xa5+Xa21 and Xa3+Xa21) were found to be promising, as the rice lines carrying these genes enhanced a strong resistant reaction against 16 bacterial blight isolates. Also, the inoculation of K3a race did not alter the brown rice yield, ripened grain ratio and kernel quality of brown rice compared to control. Although RL1 containing all the target resistance genes showed excellent resistance performance, it is not suitable to cultivate in plain area due to instability to lodging, 80% yield level than Unkwang, and low grain quality. RL5 backcrossed twice with Unkwang was found to be a promising line due to its effective resistance gene combination, Xa3+Xa21+Stvb-i and good agronomic traits such as stability to lodging, higher yield and quality compared to Unkwang.

‘Chindeul’, a new japonica rice cultivar developed from a cross between HR22538-GHB-36-4 having brown planthopper (BPH) resistance and Iksan471 having a good eating-quality and high yield, was developed by the rice breeding team of Department of Rice and Winter Cereal Crop, NICS, RDA in 2012. This variety has about 124 days growth duration from transplanting to harvesting in west-southern coast, Honam and Youngnam plain of Korea. It has 83 cm culm length and tolerance to lodging. In reaction to biotic and abiotic stresses, it shows resistance to bacterial blight pathogen races from K1 to K3, stripe virus and brown planthopper. The milled rice of ‘Chindeul’ exhibits translucent, relatively clear non-glutinous endosperm and medium short grain. It has lower protein content of 5.9% and good palatability of cooked rice compared with Nampyeongbyeo. The milled rice yield performance of this variety is about 5.61 MT/ha in local adaptability test for three years. ‘Chindeul’ would be useful genetic resources for multi-resistance breeding program against disease and insect.

‘Huimangchan’ is a new japonica rice variety developed and registered by the rice breeding team of Department of Rice and Winter Cereal Crop, NICS, RDA in 2011. This variety was derived from the three-way cross of ‘Milyang165’, ‘Shindongjin’ and ‘YR19105-Acp222’. This variety has about 126 days of growth duration from transplanting to harvesting in Honam and Youngnam plain of Korea. It is about 91 cm in culm length and tolerance to lodging. In reaction to biotic stresses, it shows moderate resistance to blast, resistance to bacterial blight pathogen races from K1 to K3, and rice stripe virus, but susceptible to other major diseases and insect pests. The milled rice of ‘Huimangchan’ has high quality, midium short grain. The milled rice yield of this variety is about 6.18 T/ha in local adaptability test for three years. ‘Huymangchan’ would be adaptable to Middle plain, Honam plain and Youngnam plain area of Korea.

‘Sanhomi’, a new japonica rice cultivar developed from a cross between Sangmibyeo and F₁ plant derived from the cross between Sangju24 and Hwayeongbyeo having bacterial blight and rice stripe virus resistance was developed by the rice breeding team of Sangju Substation, NICS, RDA in 2012. This variety has about 114 days of growth duration from transplanting to harvesting in southern mid-mountainous area of South Korea. It has 70 cm culm length and tolerance to lodging. In reaction to biotic and abiotic stresses, it shows multiple resistance to blast, bacterial blight and rice stripe virus. The milled rice of ‘Sanhomi’ exhibits translucent and, relatively clear non-glutinous endosperm, and medium short grain. This variety has a higher milled rice recovery (67.3%), better palatability of cooked rice and similar amylose content (19.9%) compared with Odaebyeo. The milled rice yield performance of this variety was about 5.60 MT/ha in local adaptability test for three years. ‘Sanhomi’ would be adaptable to southern mid-mountainous of South Korea.

This study was conducted to develop breeding lines carrying bacterial blight resistance genes, Xa2, Xa3, xa5, and Xa21 for enhancing the resistance of early maturing glutinous japonica rice. Resistant lines were developed by backcrossing into early maturing glutinous elite cultivar, Sangjuchalbyeo and phenotypic selection for bacterial blight resistance and agronomic traits. Selected lines were confirmed the incorporation of the resistance genes using DNA markers and evaluated the resistance reaction against four Korean and eleven Philippine bacterial bight races. HR24465 line carrying Xa2 was resistant to Korean races K1, K2, and Philippine race 9a. HR24666 line carrying Xa3 was moderately resistant or resistant to races except for Korean race K3a and Philippine race 6. Resistant lines carrying xa5 were resistant to all races except for Philippine race 6. HR24669 line carrying Xa21 was moderately resistant or resistant to races except for Korean race K1 and Philippine race 10. Yield-related traits of breeding lines exhibited similar characteristics to Sangjuchalbyeo. These resistant lines could be useful breeding materials for improving the resistance of early maturing glutinous japonica rice against Xanthomonas oryzae pv. oryzae.

This study was conducted to develop multi-resistant lines to brown planthopper, bacterial blight, and rice stripe virus using anther culture in rice. A total of 213 double haploid lines were developed the cross between HR26234-12-1-1 conferring resistant to bacterial blight and rice stripe virus and SR30071-3-7-23-6-2-1-1 conferring resistant to brown planthopper, bacterial bight, and rice stripe virus. Using DNA molecular marker, HR26234 and SR30071 were confirmed to have Xa3+xa5+Stvb-i and Bph18+Xa4+Stvb-i, respectively. All double haploid lines carried Stvb-i, and Bph18+Xa3, Bph18+Xa4, Bph18+Xa3+xa5, Bph18+Xa4+xa5, bph18+Xa3, bph18+Xa4, bph18+Xa3+xa5, and bph18+Xa4+xa5 combinations were identified. Segregation distortions such as no combinations carrying Bph18(or bph18)+xa5+Stvb-i and fewer lines carrying Bph18 than bph18 were occurred in DH population. Brown planthopper resistant lines carrying Bph18 showed longer culm length than susceptible lines. Selected Bph18+Xa4+xa5+Stvb-i combination lines with short culm conferred resistant to brown planthopper, bacterial blight, and rice stripe virus, while showed deleterious effects such as spikelet sterility, lower yield, and vulnerable to lodging than standard and comparative varieties. Using anther culture, we rapidly developed multi-resistant lines to brown planthopper, bacterial blight, and rice stripe virus. However, distorted segregation in DH population and linkage drag with Bph18 were obstacles to develop practical multi-resistant cultivars.