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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.
References
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).
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