| The assumptions for engineering-oriented seed production of hybrid rice were proposed and the related researches were conducted based on the knowledge of small grain and dwarf indica rice variety-Xiaoxiangai (XXA). The researches results indicated that the small grain and dwarf gene of XXA was linked and controlled by a pair of plant height recessive quality gene-rRH, and this gene located at 8.4 cM upstream from the-RM249 in the fifth chromosome; through improvement of XXA, a passel of photo-thermo-sensitive genic male sterile lines were selected, and the comprehensive characters of 171S were the best among them; using 171S to conduct mixed direct-sowing seed production experiment, and some restrictive factors were clear. To realize mechanized seed production, the small grain character of XXA was researched and the grains separating mechanism with great effect was designed. The main research results were showed as follows:1. Characters of XXA:XXA is kind of late maturity early rice; it sowing at early season in Changsha, and the duration from seeding to heading was about 90 days; the agronomic traits of XXA were similar to that of erect panicle rice varieties, which plant height was 55 cm,1000-grain weight was around 11.5 g, large panicle and many grains; the hybrid F1 that crossed by XXA and semi-dwarf and large grain variety showed as semi-dwarf and large grain; the hybrid F1that crossed by XXA and high stalk and large grain variety showed as high stalk and large grain; using wide compatibility testing variety to test cross, the setting percentage of F1 reached 75% or more, which wide compatibility was similar to Peiai 64's; the difference between seed weight for XXA and normal rice variety was large, it could been separated grains of XXA from mixed samples.2. The genetic regularity of small grain and dwarf characters of XXA:when XXA crossed with semi-dwarf and large grain variety-Xiangzaoxian 143, the proportion of semi-dwarf and large grain variety and dwarf and small grain variety that isolated from F2 colony was 3:1; when XXA crossed with high stalk and large grain variety-Liguzao, the proportion of high stalk and large grain variety, semi-dwarf and large grain variety, semi-dwarf and small grain variety and dwarf and small grain variety that isolated from F2 colony was 9:3:3:1; these results indicated that the characters of small grain and dwarf of XXA belonged to pleiotropism or linkage inheritance. When small grain and semi-dwarf mutant crossed with semi-dwarf variety, the progenies showed character of high stalk and large grain, it indicated that small grain and semi-dwarf mutant containing high stalk inhibitory gene. Theses results revealed that the characters of small grain and dwarf of XXA is kind of expression that a pair of inhibitory gene under sd condition, in other words, the characters of small grain and dwarf of XXA were linked and controlled by a pair of plant height recessive quality gene-rRH.3. Gene localization of small grain and dwarf characters of XXA:In order to locate rRH gene loci, partial SSR markers of 12 rice chromosomes were selected by PCR that based on BSA, and the semi-dwarf gene of XXA was located to the fifth chromosome. Through intercomparison and calculation, the semi-dwarf gene of XXA located at 8.4 cM upstream from- RM249 in the fifth chromosome, which was different from the sdg downriver from the RM249.4. breeding male sterile line:Using cross breeding method to transport character of photoperiod sensitive genic male sterile into XXA, then through multi-generation pressurized selecting, a passel of photo-thermo-sensitive genic male sterile lines were gotten; and using methods that backcross, hybrid with wild rice and ionizing radiation, etc. to improve shapes of plant and leaf of XXA and increase its stigma exsertion rate. A passel of male sterile lines with great comprehensive characters were obtained, which were 9sy220,9sy507 and 9d82, etc..5. Quality combinations with characters of high-yield could be selected:Taking 171S as research object match group widely to determine its combining ability, the results showed that 171S has great combining ability, and quality combinations with characters of high-yield and appropriate growth period could be selected.6. Preliminary Studies on mixed direct-sowing seed production:Taking 171S as research object and taking restorer line 440, which has similar growth period with 171S's, to conduct mixed direct-sowing seed production; direct sowing experiments were conducted with parents'grain proportion of 1:10,1:20 and 1:30 and repeated three times. The results showed that the average outcrossing rate of 171S was 13.71%, and the differences of outcrossing rates among three levels were not significant. Several factors for low outcrossing rate were analyzed as follows:first, the sensitive degrees of GA3 on parents are different, and the applying amount of GA3 is not easy to control; second, the flag leaves of 171S are long and wide, which affecting pollination; third, the florescence of 171S is not concentrated.7. Separating machine on the design:Taking XXA as small grain sample to conduct separating experiment for grains and seeds. The results showed that using 3.5 mm circular screen to sift over three times, the small grain and normal large grain (1000-grain weight is around 25 g) could be separated, and the purity of separated seeds reached over 99% that accord with national standards of rice commercial seeds. Based on the separating theory of indented mold-hole, the separating machine had been made by utilizing the different lengths between seeds to ensure the characteristics of mold hole and perfecting related designs, and it has great separating effect.
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