‘Hwaweon 6’ was developed from a cross between ‘Hwaseongbyeo’ and a wild species, Oryza minuta L. (Acc. No. 101154) based on marker-assisted selection and backcrossing. The recurrent parent ‘Hwaseongbyeo’ is a high grain quality cultivar with medium maturity. Hwaweon 6 is nearly isogenic to Hwaseongbyeo except a small O. minuta introgressed segment on chromosome 7 harboring genes related with spikelets per panicle. The preliminary and replicated yield trial was conducted at Chungnam National University and Chungcheongnamdo Agricultural Research & Extension (CARES), Yesan in 2009 and 2010. The local adaptability test was carried out by the National Seed Management Office (NSMO) in 2011 and 2012. This cultivar was registered to NSMO with a cultivar designated as Hwaweon 6. This cultivar averaged 80cm in culm length and has a medium growth duration. Milled rice of Hwaweon 6 is translucent and the grain quality traits are comparable to those of the recurrent parent. The average yield potential of Hwaweon 6 in grain was about 6.57 MT/ha at the ordinary fertilizer level for two years about 3.0% higher than that of Hwaseongbyeo due to an introgression of the quantitative trait locus (QTL) for spikelets per panicle (qSPP7) from O. minuta. This variety is comparable to Hwaseongbyeo in low temperature germinability and cold tolerance. The qSPP7 QTL would be useful in enhancing yield potential in rice breeding program.

‘Hwaweon 7’ was developed from a cross between the African upland cultivar, ‘Moroberekan’ and ‘Ilpumbyeo’ based on marker-aided backcross selection. The recurrent parent, Ilpumbyeo is a high grain quality cultivar with medium to late maturity. Hwaweon 7 is nearly isogenic to Ilpumbyeo except a small Moroberekan introgressed segment on chromosome 6 harboring genes related with spikelets per panicle and internode diameter. The preliminary and replicated yield trial was conducted at Chungnam National University and Chungcheongnamdo Agricultural Research & Extension (CARES), Yesan in 2010 and 2011. The local adaptability test was carried out by the National Seed Management Office (NSMO) in 2012 and 2013. This cultivar was registered to NSMO with a cultivar designated as “Hwaweon7”. This cultivar averaged 80cm in culm length and has a medium growth duration. Milled rice of “Hwaweon7” is translucent and the grain quality traits are comparable to those of the recurrent parent. The average yield potential of Hwaweon 7 in grain was about 6.48 MT/ha at the ordinary fertilizer level for two years about 5.1% higher than that of Ilpumbyeo due to increase in spikelets per panicle. This variety is tolerant to lodging and the tolerance is due to the APO1 gene controlling the base internode diameter on chromosome 6 introgressed from the donor parent, Moroberekan. The Apo1 gene would be useful in enhancing resistance to lodging in rice breeding program.

Grain size has a great impact on rice grain yield and is controlled by quantitative trait loci (QTL). Daeribbyeo 1 with big grain is widely used for genetic materials to develop varieties with diverse grain size. This study was conducted to identify genes controlling grain size traits of Daeribbyeo 1. An F_2:3 population derived from a cross between two japonica cultivars, Boseogheugchal and Daeribbyeo1, was used to identify QTL controlling grain shape traits. A total of 284 F₂ plants were measured for grain shape traits, grain length (GL), grain width (GW), grain thickness (GT), 1,000 grain weight (TGW), and two morphological traits, pericarp color and waxy endosperm. Sixty F₃ lines were selected based on the grain shape traits and marker genotypes and evaluated for grain shape traits. For marker analysis, SSR markers tightly linked to five known grain size genes and two QTLs were selected and used for genotyping. A total of 11 QTLs detected on chromosomes 2, 3, 4 and 6 explained phenotypic variation from 3.9% to 59.3%. qTGW2, qGW2 and qGT2 were detected in the same region between RM12811-RM12837 that are tightly linked with GW2 gene. qTGW3 and qGL3 were detected near GS3 gene. To know whether Daeribbyeo 1 has the same mutations in GW2 and GS3 as the various grain-size genotypes, GW2 and GS3 of two parents were sequenced. Daeribbyeo 1 had the same one base (A) deletion at a position 316 as ‘WY3’ in GW2 which results in the loss of function of GW2 gene. Boseogheugchal showed a C-to-A nonsense mutation in the second exon of GS3 gene that increased grain length. Interaction between GW2 and GS3 was not significant indicating that two genes controlled grain-size traits in additive pathway. The results from this study indicate that three QTLs GW2, qGT4 and qGL6 are associated with the grain size variation in Daeribbyeo 1 with GW2 as the major QTL.

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.

‘Hwaweon3’ was developed from an interspecific cross between Hwayeongbyeo and a wild species, Oryza rufipogon L. (W1944) based on marker-aided selection and backcrossing. The recurrent parent ‘Hwayeongbyeo’ is a high grain quality cultivar with medium-maturity. ‘Hwaweon3’ is nearly isogenic to Hwayeongbyeo except a small O. rufipogon introgression on chromosomes 1, 8 and 12 harboring the QTL gene for cold tolerance. The preliminary and replicated yield trial was conducted at Chungnam National University in 2006 and 2007. The local adaptability test was carried out by the National Seed Management Office (NSMO) in 2008 and 2009. This cultivar was registered to NSMO with a cultivar designated as ‘Hwaweon3’. This cultivar averaged 78 cm in culm length and has a medium growth duration. This variety is resistant to stripe virus as the recurrent parent, and moderately resistant to leaf blast disease with durable resistance. Milled rice of ‘Hwaweon3’ is translucent and the grain quality traits are comparable to those of the recurrent parent. it has low protein content. The yield potential of ‘Hwaweon3’ in grain is about 7.23 MT/ha at the ordinary fertilizer level comparable to that of Hwayeongbyeo. ‘Hwaweon3’ performed better than Hwayeongbyeo in cold tolerance-related trait in the cold water-irrigated plot in the Chuncheon sub-station. This is mainly due to the introgressed segment from O. rufipogon on chromosome 1 harboring pe1.2 for panicle exsertion. ‘Hwaweon3’ could be used as a bridging line to enhance cold tolerance of japonica breeding lines.