‘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.

96 BC3F5 introgression lines derived from a cross between Hwaseong and O. rufipogon were genotyped with 131 simple sequence repeat (SSR) markers to identify and characterize quantitative traits loci (QTLs) associated with grain quality traits in rice. 96 BC3F5 lines displayed a wide range of variation for days to heading and agronomic traits. Results indicated that one major QTL (qDTH6) on chromosome 6 was associated with significant variation for days to heading. 83 lines without the O. rufipogon segment at qDTH6 were selected and analyzed for grain quality traits. QTL analysis was conducted for two groups, 96 and 83 introgression lines, and a total of 25 QTLs were detected for rice quality traits. 16 QTLs were detected in a group of 93 lines, 11 QTLs detected in a group of 83 lines, and 2 QTLs were commonly identified in both groups. Most of the QTLs detected in this study were located on the same or adjacent regions as those reported by the previous studies, and the wild alleles negatively affected quality traits. In contrast, the wild allele at qGCR9 for the glossiness of cooked rice on chromosome 9 contributed to an increase in glossiness which is positively correlated with rice eating quality. Three ILs with the wild allele at qGCR9 displayed better eating quality than the recurrent parent, Hwaseong. To confirm the effect of qGCR9, high density mapping of the qGCR9 with a series of NILs will be conducted.

While a wealth of genetic diversity can be found from traditional rice varieties, wild rice species and wild relatives of rice, transfer of useful genes to modern varieties are often hampered by linkage drag. In this study, the previously identified blast resistance locus Pi45(t) from a cross between ‘Ilpumbyeo’ and ‘Moroberekan’ was showed to be linked with the spreading-type panicle caused by the SPR3 locus. Using InDel4 and RM17579 linked to the Pi45(t) and the SPR3, respectively, the distance between the two loci was estimated to be 6.9cM. This suggests a tight, yet incomplete linkage and provides the opportunity to utilize Pi45(t) in breeding programs without including SPR3. Two groups based on the genotype at the SPR3 locus were assembled; the CLosed Panicle (CLP) and SPReading panicle (SPR) groups with lines, which were homozygous for the Ilpumbyeo and Moroberekan alleles, respectively. A comparison between the traits of CLP and SPR groups revealed a decrease in 1000-grain weight and length and an increase in spikelets per panicle and secondary branches in the SPR group. This complicates selection against SPR3 as it is not clear whether these quantitative trait loci are linked to either SPR3 or Pi45(t). Re-evaluation of these traits using lines recombinant at the two loci would be necessary to clarify this issue.

Grain size is a major determinant of grain yield in rice. In a previous study, a QTL for grain width(GW), qgw1 was detected on chromosome 1 using 96 BC3F8 lines derived from a cross between ‘Hwaseongbyeo’ as a recurrent parent and ‘O. rufipogon’ as a donor parent. At this locus, the O. rufipogon allele increased GW. Among the 96 introgression lines, three ILs with the O. rufipogon qgw1 locus showed significantly increase in grain width compare to the recurrent parent. One of the three lines, CR572 was selected and crossed to ‘Hwaseongbyeo’. A total of 494 F2:3 were evaluated for grain width and agronomic traits in the field. QTL analysis in 494 F2:3 lines indicated that QTL for grain width was located in the interval RM495–RM5443. To narrow down the position of qgw1, substitution mapping using F4 lines with different cross-over breakpoints in the region is underway. The result will be discussed.

In previous studies, we reported that a QTL for 1000-grain weight (TGW), qTGW3 was located in the interval between RM60 and RM523 (1.2Mb) on chromosome 3 using advanced backcross lines derived from a cross between Oryza sativa ssp. Indica cv. Milyang 23 and O. glaberrima. The O. glaberrima alleles at this locus increased TGW and GL in the Milyang 23 background. To further confirm and narrow down the position of the QTLs on chromosome 3, twenty lines with different O. glaberrima segments in the target region were selected. Twenty lines were evaluated for seven agronomic traits including 1,000 grain weight and grain length and also genotyped with ten SSR markers. Sixteen lines(A, B, C groups) with the O. glaberrima segment flanked by SSR markers, RM60 and RM7332 displayed significantly higher values than Milyang 23 in TGW and GL whereas four lines(D, E groups) without the O. glaberrima segment displayed no difference in TGW and GL. The result indicates that two QTL, qTGW3 and qGL3 are located near RM60 and RM7332.

The objective of this study were to identify QTLs for agronomic traits using a set of introgression lines carrying wild rice (Oryza rufipogon) segment in cultivated rice (ssp. japonica cv. Hwaseongbyeo). Ninety-six ILs were evaluated for seven agronomic traits, amylose and protein contents. The proportion of the recurrent genome in ILs ranged from 87.8 to 100%, with an average of 96.7%. The mean number of homozygous and heterozygous donor segments were 2 (ranging 0-7) and 1.7 (ranging 0-6), respectively, and the majority of these segments had size less than 10 cM. A total of 22 quantitative trait loci were identified for 9 traits and each QTL explained 7.2% to 56.6% of the phenotypic variance. Some QTLs were clustered in a few chromosomal regions. A first cluster was located near RM527 on chromosome 6 with QTLs for culm length, panicle length, days to heading, 1000-grain weight and protein content. Three ILs with high spikelets per panicle compared to the recurrent parent were selected to detect and fine map the wild segments responsible for this variation. The results will be discussed.