18. QTL analysis of low temperature germinability in a Korean weedy rice (Oryza sativa L.)
J. P. SUH1, S.N. AHN1, H.P. MOON1 and H.S. SUH2
1)Rice Breeding Division, National Crop Experiment Station, Rural Development
Administration, Suwon 441-100, Korea
The adoption of direct seeding methods for rice crop establishment in place of transplanting has continuously increased in Korea because of increased labor costs and improvement of direct seeding technology (Park et al. 1997). However, poor germinability at low temperature is still one of the major problems in the adoption of direct seeding methods in Korea. Genotypic variation in germinability at low temperature has been reported and some Korean weedy strains were observed to have a high degree of germinability at low temperature and a high degree of shoot-emergence ability in deep water (Suh et al. 1997). This study was conducted to identify quantitative trait loci (QTL) related to germinability at low temperature (15°C) from a japonica weedy accession, Hapcbeonaengmi 3.
A backcross population (98 BC1F1 plants) derived from a Milyang 23 (Tongil - type)//Milyang 23/Hapcheonaengmi 3 cross was developed and used for QTL analysis. A total of 135 markers including morphological, isozyme, RFLP (restriction fragment length polymorphism), RAPD (randomly amplified polymorphic DNA), microsatellite or SSR (simple sequence repeat) markers spanning 1,640 cM of the rice genome with an average interval length of 12.2 cM were mapped for QTL analysis and details of map construction are reported elsewhere (Suh et al. In preparation). BC1F2 seeds from each 98 BC1F1 plants, along with their parents were treated for 7 days at 50°C to break the dormancy and tested for germinability at 15°C. Thirty seeds for each entry were sown 2mm-deep in sterilized soil in plastic trays with two replications. The trays were kept in a growth chamber (15°C, dark condition) for 30 days and germinability was scored as the number of emerged seedlings (%). Means over replications were calculated and used in data analysis.
Frequency distribution of germinability for the backcross progenies, along with the parents is shown in Fig.1 and the backcross progeny averaged 53 % for germinability ranging from 3 to 100 %. The distribution of the population is with transgressive variation toward the Hapcheonaengmi 3 type and some BC1F1 plants showed two-fold higher values than that of Hapcheonaengmi 3. This result is in good agreement with the result of Jun et al. (1987) that F2 progeny derived from the Milyang 23/Seolakbyeo (japonica) cross displayed the transgressive distribution toward the better parent type (Seolakbyeo) for germinability at low temperature.
Interval mapping of QTL using the QGene (Nelson 1997) with threshold LOD »=2.00, identified three QTLs affecting low temperature germinability on chromosomes 5, 6, and 11, respectively (Fig. 2). Individual QTLs accounted for 11.4 -18.6% of the phenotypic variation and the three QTLs explained 37.9 % of the total phenotypic variation in the backcross population (Table 1). Direction of additive gene effect coincided with that predicted by phenotypes of the parents at two loci , qLTG-5 and qLTG-11. At these two loci, the Hapcheonaengmi 3 alleles increased the germination ratio but the Hapcheonaengmi 3 allele decreased the germination ratio at qLTG-6. No significant interaction among three QTLs was observed. The identification of QTLs underlying the low temperature germinability may be useful in selecting lines with enhanced germinability at low temperature in the breeding program.
Jun. B.T., J.I. Kim and S.Y. Cho, 1987. Studies on the inheritance of quantitative characters in rice. VIII. Analysis on the low temperature germination in diallel cross of F2 generation. Korean J. Breeding 19(3): 240-244.
Nelson, J.C., 1997. Qgene manual. Electronic address:greengenes. Cit. Cornell. Edu. Port 70; directory "Software for genetics/qGene."
Park, S.T., S.C. Kim and Y.J. Oh, 1997. Yield stability technology of direct seeded rice in Korea. Discussion paper, National Yeongnam Agricultural Experiment Station, Milyang 627-130. Korea.
Suh, H.S., Y.I. Sato and H. Morishima, 1997. Genetic characterization of weedy rice (Oryza sativa L.) based on morpho-physiology, isozymes and RAPD markers. Theor. Appl. Genet. 94: 316-321.
Suh, J.P., S.N. Ahn, H.P. Moon and H.S. Suh, 1999. QTL analysis of cold tolerance-related traits in a Korean weedy rice (in preparation).