1. P. Suit’, S.N. Ahn1, H.P. MOON’ and H.S. SUB2
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 eta!. 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 a!. 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)/IMilyang 23lHapcheonaengmi
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 (Suhetal. In preparation). BC1F2
seeds from each 98 BC,F, 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 genninability
for the backcross progenies, along with the parents is shown in Fig. I
and the backcross progeny averaged 53 % for germinability ranging from
3 to 100 %. The distribution of the population is with transgressive varialion
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 a!. (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-1l. 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 YJ. 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. Appi. 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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