| LTG (low temperature germinability) and AG (anoxia germinability) in 521 rice varieties were evaluated. The mechanism of low temperature germination was discussed about content of endogenous ABA and GA, and the type of amylase during germination at low temperature. Mapping of quantitative trait loci (QTLs) controlling LTG and AG had been carried out in a RIL population using molecular markers. A linkage map including 114 SSR markers was constructed using USSR5/N22 F2 as a mapping population, and QTLs for LTG and AG were identified. The results were as follows:1. The evaluation of LTG and AG in rice varietiesIn this study, seed LTG and AG in 521 varieties were detected. The result showed there was significant difference in LTG and AG between japonica and indica. LTG in indica cultivars was higher than that in japonica. While AG in japonica cultivars was stronger than that in indica.Regional difference existed in LTG and AG in rice varieties. Some varieties from Yunnan had stronger AG. LTG of Varieties from Southern China was stronger than that from other regions.The correlate coefficient between LTG and AG was significant at 0.1 level, which indicate correlation degree of two traits was low.2. The physiological mechanism of low temperature germinationGerminating at low temperature, the level of ABA content in rice seeds kept high. Comparing with strong LTG variety, USSR5, poor LTG variety, N22 was more sensitive to ABA. Moreover, the result of exogenous ABA treatment also supports this conclusion.The results of amylase electrophoresis indicated that the type of amylase have no variation in germinating seeds at low temperature, but its expression lowered and delayed.3. Identification of QTL controlling LTG and AG in rice81 Rl lines from Kinmaze/DV85 were analyzed genetically using 137markers. Five putative LTG QTLs, qLTG-2, qLTG-6, qLTG-7, qLTG-11 and qLTG-12 were detected on chromosome 2, 6, 7, 11 and 12, respectively. PVE ranged from 8.8% to 27.1%. Two pairs of epistatic QTLs were detected on chromosome 3, 5 and 7 with significant epistatic effects.Five putative QTLs for AG linking with XR2635, R418, G260, XI05, X3 79 , whose PVE ranged from 12.05% to 19.56% , were detected on chromosome 1 , 2, 5, 7. There were two QTLs for LTG on chromosome 5. Three pairs of epistatic QTLs were detected on chromosome 2, 3, 5 and 11 with significant epistatic effects.4. Construction of a SSR linkage map and QTL analysis of LTG and AGA linkage map including 114 SSR markers, which covered 2115.4cM of 12 rice chromosomes, was constructed using 189USSR5/N22 p2 plants as a mapping population. The average distance between two markers was 18.56cM. Using this map, QTLs controlling LTG and AG were identified.LTG was evaluated day by day were analyze genetically. 12QTLs controlling LTG were detected. QTLs for LTG on chromosome 7, 8, 10, 12 played an important role at early germinating stage. PVE ranged from 7.1% to 70.2%. QTLs on chromosome 3, 4, 5, 9, 11 were expressed stably during the whole germination stage.AG was evaluated at 30 C and 0.003588g/100g H2O for 5days. Four putative QTLs for AG on chromosome 3, 5 , 11, respectively, were identified, and the LOD value ranged from 2.78 to 4.89, and PVE ranged from 6.70% to 14.50%.QTLs for LTG and AG detected in different population always changed, but main QTL was stable. Main QTL for LTG existed on chromosome 11. Main QTL for AG was found on chromosome 3, 5. The result of phenotype evaluation and QTL mapping showed LTG correlated with AG at some extent.
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