Drought stress is one of the major stresses affecting growth and productivity in rice. Drought tolerance is a complex trait governed by quantitative trait loci(QTLs) making it difficult to understand mechanisms underlying it. We generated a set of 55 introgression lines via backcrosses using Milyang23, the Korean Tongil-type rice variety as the recurrent parent and Oryza glaberrima (IRGC Acc. No. 103544) as a donor parent. 139 SSR markers were used to genotype 55 introgression lines. The 55 introgression lines with Milyang23 were evaluated for physiological traits such as fresh shoot weight (FSW), fresh root weight (FRW) and dry shoot weight (DSW) under the control and 30% PEG-treated condition. Three lines (IL9, IL12, and IL55) showing significant difference with Milyang23 were selected for further analysis. Genotyping revealed that three lines had four, four and two O. glaberrima homozygous segments, respectively. IL9 performed better than Milyang23 in all traits measured in the 30% PEG-treated condition. IL9 possessed four O. glaberrima introgressions on chromosomes 1, 2, 6 and 7. IL12 performed better than Milyang23 in FSW and FRW and contains four O. glaberrima introgressions on chromosomes 3 and 6. IL55 contains two O. glaberrima introgressions on chromosomes 2 and 6. Three lines shared the O. glaberrima segment delimited by markers RM133-RM225 at chromosomes 6. This region corresponds to the QTL region for drought tolerance reported by other previous studies. Although IL9 and IL12 showed improved drought tolerance at the seedling and vegetative stage, they performed poor under the drought stress at the reproductive stage implying that the level of drought tolerance differs according to the growth stage in rice. IL55 was not significantly different from Milyang 23 in SPP and FER and had significantly higher no. of the total grain than Milyang 23. This result seems to indicate that IL55 will be a good resource for drought tolerance breeding. The population would be useful not only in developing drought tolerant lines in the breeding program but also in fine-mapping the genes/QTLs for drought tolerance.

본 연구에서는 밀양23호의 배경에 O. glaberrima의 특정 염색체단편을 가지는 55 이입계통의 내건성 관련 형질을 조 사하여 변이를 검정하고 내건성이 향상된 4 계통을 선발하였 다. 특히 IL55는 유묘기, 영양생장기 그리고 생식생장기에서 반복친인 밀양23호에 비해 조사된 내건성 형질에서 우수한 특성을 보였으며 내건성 관련 유전자의 분석 및 교배모본으 로 이용될 수 있을 것이다. 이입계통들은 밀양23호의 유전적 배경에 각 계통마다 서로 다른 O. glaberrima 단편이 이입된 계통으로, 이 집단은 O. glaberrima에서 유래된 내재해성 및 작물학적으로 유용한 유전자의 탐색에 효율적인 도구가 될 것이다.

Drought stress is one of the major stress affecting growth and productivity in rice. Drought tolerance is a complex trait governed by quantitative trait loci (QTLs) making it difficult to understand mechanisms underlying it. We generated a set of 55 introgression lines via a backcrossing using Milyang23, a Korean Tongil-type rice variety as the recurrent parent and O. glaberrima (IRGC Acc. No. 103544), an exotic collection from Mali, West Africa as donor parent. 141 SSR markers were used to genotype 55 introgression lines. The 55 introgression lines with the Milyang23 were evaluated for physiological traits such as Fresh shoot weight (FSW), Fresh root weight (FRW) and Dry shoot weight (DSW) under control and 20% PEG-treated condition. Three lines (IL9, 12, 55) showing significant difference with Milyang23 were selected. The genetic background of the three lines were similar to Milyang23 and it has four, four and two O. glaberrima homozygous segments, respectively. IL9 performed better than Milyang23 in all traits measured in the 20% PEG-treated condition. IL9 possessed four O. glaberrima introgressions on chromosomes 1, 2, 6 and 7. IL12 performed better than Milyang23 in FSW and FRW. IL12 contains four O. glaberrima introgressions on chromosomes 3 and 6. And IL55 contains two O. glaberrima introgressions on chromosomes 2 and 6. O. glaberrima segment delimited by markers OSR19-RM225 at chromosomes 6 was commonly present in these three lines. This region corresponds to the QTL region for drought tolerance reported by other previous studies. A set of introgression lines are being developed containing only few chromosomal segments from O. glaberrima in the Milyang23 background. These would be useful not only in developing drought tolerant lines in the breeding program but also in fine-mapping the genes/QTLs for drought resistance.

In the previous study, 141 BC3F2 lines from a cross between the Oryza sativa cv. Milyang 23 and O. glaberrima were used to identify favorable wild QTL alleles for yield component traits. In this study, we carried out QTL analysis of four grain morphology as well as four yield component traits using 141 BC3F5 lines from the same cross and compared QTLs detected in two different generations. The mean number of O. glaberrima segments in the 141 BC3F5 lines ranged from 1 to 13 with 2.69 and 5.71 of the average means of homozygous and heterozygous segments, respectively. There was a three-fold difference in the number of QTLs detected for four traits commonly evaluated in two generations (seven QTLs in the BC3F5 vs 21 in the BC3F2 population). The percentages of the phenotypic variance explained by QTLs in the BC3F5 population were similar to or less than those in the BC3F2 population. This is probably due to the difference in the genetic composition of two populations and the environmental effects. The locations of the QTLs commonly detected in both generations were in good agreement except for one QTL for spikelets per panicle. The yield QTL, yd3 was colocalized with the spikelets per panicle, spp3. Yield increase at this locus is due to the increase in spikelets per panicle, because both traits were associated with increase in spikelets per panicle and yield due to the presence of an O. glaberrima allele. Clusters of QTLs for grain morphology traits were observed in two chromosome regions. One cluster harboring five QTLs near SSR markers RM106 and RM263 was detected on chromosome 2. This population would serve as a foundation for development of the introgression line population from a cross between Milyang 23 and O. glaberrima.

In this study, a 141 BC3F4 lines from across between the O. sativa cv. Milyang23 as there current parent, and O. glaberrima as the donor parent was used to identify favorable QTL alleles from O. glaberrima for yield and yield components. To detect the introgressions, 198 microsatellite markers of known chromosomal position were used for the parental survey. Of the 178 markers, 128 (64.6%) showed polymorphism. Among them, 115 SSR markers were used to construct a genetic linkage map with average interval length of 12.7 cM based on the previous rice molecular genetic map. The mean number of O. glaberrima segments in the population was 1.84 ranging from 0 to 7. The average length of the segments was 16.6 cM and ranged from 0.5 to 232.5 cM. This population consisting of 141 lines was used to evaluate for six traits of agronomic importance and genotypes were determined for 141 BC3F5 using SSR markers. A total of 22 QTLs for 6 traits were detected on chromosomes 1, 2, 3, 4, 5, 6, 7 and 9. Phenotypic variance associated with each QTL ranged 9.5% ~ 58.2%. For 26 of the QTLs identified in this study, the O. glaberrima alleles contributed a desirable agronomic effect despite the over all undesirable characteristics of the wild phenotype. Favorable wild alleles were detected for culm length, panicle length, yield, panicles per plant and 1000-grain weight. When compared with previous studies involving interspecific crosses, it can be concluded that O. glaberrima is useful asa source of valuable alleles for rice improvement. There sults will be discussed.