High-temperature-resistant high-quality hybrid rice sterile line breeding method

Abstract

The invention relates to a breeding method of a high-temperature-resistant high-quality hybrid rice sterile line, which comprises the following steps of: hybridizing core xiangxiang S serving as a female parent and salt 416S serving as a male parent to obtain a hybrid F1; planting the F1 to obtain an F2 generation; and screening excellent single plants from each generation, and harvesting and planting the single plants to obtain the next generation. According to the method, rice quality identification is carried out under high-temperature and low-temperature conditions, the outcrossing maturing rate is identified through seed production under the high-temperature condition, and beneficial genes such as Badh2, Chalk5, WXb, ALKb and AAP6 are polymerized in combination with molecular marker-assisted selection; after multiple generations of breeding, the obtained high-grade high-quality sterile line with high temperature resistance has the advantages of high temperature resistance, outcrossing high temperature resistance and combined high temperature resistance, and breaks through the technical bottleneck in the aspect of breeding of the high-temperature-resistant high-quality sterile line in the prior art.

Description

Technical Field

[0001] The present invention relates to a method for breeding plant varieties, and particularly to a method for breeding a high-quality hybrid rice male sterile line. Background Art

[0002] The successful utilization and large-scale application of heterosis in rice have made significant contributions to food production increase. With the improvement of living conditions, people's demand for food has shifted from "having enough to eat" to "eating well". On the premise of ensuring basic requirements such as high yield and wide adaptability, eating quality has become a key factor determining the market competitiveness of hybrid rice varieties. However, the El Niño and La Nina phenomena caused by global climate change have led to frequent extreme weather events. In particular, the extreme high-temperature weather in July and August coincides with the maturity period of double-season early rice in the Yangtze River Basin and the booting and heading stages of middle rice, seriously affecting rice quality and yield formation, and bringing new challenges to rice production. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a method for breeding a hybrid rice male sterile line, which can breed a hybrid rice male sterile line with high temperature tolerance and high rice quality.

[0004] The technical solution adopted by the present invention to solve its technical problems is as follows: A method for breeding a high-quality hybrid rice male sterile line with high temperature tolerance uses the two-line male sterile line Xinxiang S as the female parent and the two-line male sterile line Yan 416S as the male parent, and hybridizes to obtain the hybrid F1; plants F1 to obtain the F2 generation; then, excellent individual plants are screened from each generation, and the seeds harvested from the individual plants are planted to obtain the next generation;

[0005] The screening method includes one or more of screening method A, screening method B, and screening method C; the same or different screening methods can be selected for different generations;

[0006] The screening method A includes: multiplying seeds under low temperature, and screening individual plants that simultaneously carry the Badh2, Chalk5, WX b genotypes in Xinxiang S and the Pita, ALK b and AAP6 genotypes in Yan 416S and pass the rice quality detection;

[0007] The screening method B includes: dividing the seed materials into two or more copies, and after sowing one of them, identifying the outcrossing seed setting under high temperature, and screening individual plants that simultaneously carry the Badh2, Chalk5, WX b genotypes in Xinxiang S and the Pita, ALK b and AAP6 genotypes in Yan 416S and pass the rice quality detection;

[0008] The screening method C includes: dividing the seed materials into two or more replicates. One replicate is sown and cross-fertilized under high temperature to screen out the lines with high cross-fertilization rates; the other replicate is multiplied under low temperature, and plants that simultaneously carry the Badh2, Chalk5, and WX b genotypes of Xinxiang S and the Pita, ALK b , AAP6 genotypes and pass the rice quality test are selected.

[0009] The high temperature refers to the temperature at which rice is under heat stress; the low temperature refers to below the sterility starting temperature of the sterile line.

[0010] Preferably, the screening method further includes: dividing the seed materials of the testcross combinations of different lines into two or more replicates. One replicate is sown at different times, and the rice quality is identified under high temperature to screen out the lines with excellent rice quality under high temperature; one or more of the other replicates are used to identify the rice quality in different ecological regions, and those with excellent rice quality are selected.

[0011] Preferably, the screening criteria further include: starting from the F3 generation, using leaf color as a marker and taking Xinxiang S as a control, the lines with light green leaves are selected.

[0012] Preferably, the screening criteria further include: the lines with strong tillering ability and fast tillering rate are selected.

[0013] Preferably, the criteria for the rice quality test are: head rice rate > 58%, chalkiness degree ≤ 1%, transparency grade 1, alkali spreading value ≥ 6.0 grades, gel consistency ≥ 60 mm, amylose content of 13% < amylose content ≤ 17%, and length-width ratio > 4.0.

[0014] Preferably, the high temperature refers to one or more of the following situations during the booting stage, heading stage, and filling and maturity stage: the daily maximum temperature is above 40°C, the daily maximum temperature is above 37°C for 5 consecutive days, and the daily average temperature is above 32°C.

[0015] Preferably, the low temperature is below 23.5°C.

[0016] Preferably, in the screening method C, the lines with cross-fertilization rates higher than those of the control heat-tolerant sterile line are selected.

[0017] Preferably, the screening criteria further include: the lines with sterility starting temperature below 23.5°C are selected.

[0018] Preferably, starting from the F1 generation, the outcrossing habits are investigated generation by generation. The lines with stigma exsertion rate greater than 90% and stigma still having activity 10 days after flowering are selected.

[0019] Preferably, the screening for disease and pest resistance is carried out in an environment with a daily average temperature above 24°C and an average relative humidity above 55% in some generations.

[0020] Preferably, the F1 generation is used to identify rice blast, the F2 generation is used for mixed sowing to identify rice blast, and the F3 generation is used for line identification of rice blast, and those with moderate or above sensitivity are selected.

[0021] Preferably, the F1 generation is identified for powdery mildew, and the F3, F4, and F5 generation strains are identified for powdery mildew, and those with moderate resistance or above are selected.

[0022] Preferably, the F1 generation is identified for rice false smut; the F3 generation, F4 generation, and F5 generation lines are identified for rice false smut, and those with medium resistance or above are selected.

[0023] The present invention has the following beneficial effects: the method for breeding high-quality, high-temperature-resistant hybrid rice sterile lines of the present invention obtains high-quality, high-quality, high-temperature-resistant sterile lines with the advantages of high-quality quality, high-temperature resistance, outcrossing resistance and combined high-temperature resistance, breaking through the technical bottleneck of the existing technology in the breeding of high-temperature-resistant, high-quality sterile lines.

[0024] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Description of preservation:

[0026] The two-line sterile line Xinxiang S involved in the present invention is rice (Oryza Sativa L.), which was deposited in the China Center for Type Culture Collection (CCTCC, address: Wuhan University, Wuhan, China) on April 8, 2025, with the deposit number CCTCCNO: P202506.

[0027] The two-line sterile line Yan 416S involved in the present invention is rice (Oryza Sativa L.), which was deposited in the China Center for Type Culture Collection (CCTCC, address: Wuhan University, Wuhan, China) on April 8, 2025, with the deposit number CCTCCNO: P202507. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 This is a grain shape diagram of the high-temperature-resistant, high-quality hybrid rice sterile line Yuxiang 368S bred according to an embodiment of the present invention;

[0030] Figure 2 This is a comparison of grain shapes between the high-temperature-resistant, high-quality hybrid rice sterile line Yuxiang 368S and its parent Xinxiang S bred in accordance with an embodiment of the present invention;

[0031] Figure 3 This is a photo of a single plant of the heat-tolerant and high-quality hybrid rice sterile line Yuxiang 368S selected in the embodiment of the present invention; left: tillering stage; right: maturity stage;

[0032] Figure 4 This is a photo of the maturity stage of the population of the heat-tolerant and high-quality hybrid rice sterile line Yuxiang 368S selected in the embodiment of the present invention;

[0033] Figure 5 This is a comparison chart of the coverage of the heat-tolerant and high-quality hybrid rice sterile line Yuxiang 368S selected in the embodiment of the present invention and the control sterile line Li 68S planted in the same period; upper left: single plant of the control sterile line; upper right: single plant of Yuxiang 368S; lower left: population of the control sterile line; lower right: population of Yuxiang 368S;

[0034] Figure 6 This is a photo of the field performance of the combination Yuxiang Liangyou 1958 with the heat-tolerant and high-quality hybrid rice sterile line Yuxiang 368S selected in the embodiment of the present invention under high temperature;

[0035] Figure 7 This is a photo of the field performance of the combination Yuxiang Liangyou 001 with the heat-tolerant and high-quality hybrid rice sterile line Yuxiang 368S selected in the embodiment of the present invention under high temperature;

[0036] Figure 8 This is a photo of the rice samples of the heat-tolerant and high-quality hybrid rice sterile line Yuxiang 368S selected in the embodiment of the present invention and the combinations it forms; left: Yuxiang 368S; right: Yuxiang Liangyou 1958. Detailed implementation manners

[0037] In order to make the objectives, solutions and beneficial technologies of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and the accompanying drawings. It should be noted that the embodiments described in this specification are only for explaining the present invention and not for limiting the present invention.

[0038] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, although not explicitly recorded, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recorded.

[0039] In the description of this article, it should be noted that unless otherwise specified, "above" and "below" include the number itself, "multiple" in "one or more" means two or more, and "multiple" in "one or more" means two or more.

[0040] An embodiment of the present invention provides a method for breeding a high-temperature-resistant high-quality hybrid rice sterile line, using the two-line sterile line Xinxiang S as the female parent and the two-line sterile line Yan 416S as the male parent, and hybridizing to obtain the hybrid F1; planting F1 to obtain the F2 generation; then screening excellent individual plants from each generation, and harvesting and planting the individual plants to obtain the next generation;

[0041] The screening method includes one or more of screening method A, screening method B, and screening method C; the same or different screening methods can be selected for different generations;

[0042] The screening method A includes: multiplying seeds at low temperature, and screening individual plants that simultaneously carry the Badh2, Chalk5, and WX b genotypes in Xinxiang S and the Pita, ALK b and AAP6 genotypes in Yan 416S and pass the rice quality test;

[0043] The screening method B includes: dividing the seed materials into two or more copies, sowing one of them and identifying the outcrossing seed setting rate under high temperature, and screening individual plants that simultaneously carry the Badh2, Chalk5, and WX b genotypes in Xinxiang S and the Pita, ALK b and AAP6 genotypes in Yan 416S and pass the rice quality test;

[0044] The screening method C includes: dividing the seed materials into two or more copies, sowing one of them and having outcrossing seed setting under high temperature, and screening out the plant lines with a high outcrossing seed setting rate; sowing the other copy at low temperature to multiply seeds, and screening individual plants that simultaneously carry the Badh2, Chalk5, and WX b genotypes in Xinxiang S and the Pita, ALK b and AAP6 genotypes in Yan 416S and pass the rice quality test;

[0045] The high temperature refers to the temperature at which rice is under heat stress; the low temperature refers to below the sterile starting temperature of the sterile line.

[0046] The outcrossing seed setting rate refers to the percentage of successfully set seeds to the total pollinated flowers after the hybrid of the rice sterile line and the restorer line.

[0047] The breeding method provided by the embodiments of the present invention has the following advantages: The breeding method of high-temperature-resistant high-quality hybrid rice sterile lines of the present invention, the obtained high-grade high-quality sterile lines with high-temperature resistance have the advantages of high-temperature resistance in quality, high-temperature resistance in outcrossing and high-temperature resistance in combinations, breaking through the technical bottleneck in the breeding of high-temperature-resistant high-quality sterile lines in the prior art.

[0048] In some embodiments of the present invention, the screening method further includes: preparing two or more copies of the seed materials of the test-cross combinations of different strains, sowing one copy at different times, identifying the rice quality at high temperature, and screening the strains with excellent rice quality at high temperature; and identifying the rice quality of the other copy or two or more copies in different ecological regions, and selecting the ones with excellent rice quality.

[0049] In some embodiments of the present invention, F2 uses screening method A to obtain F3 generation seeds.

[0050] In some embodiments of the present invention, F3 uses screening method C to obtain F4 generation seeds.

[0051] In some embodiments of the present invention, F4 uses screening method A to obtain F5 generation seeds.

[0052] In some embodiments of the present invention, F5 uses screening method C to obtain F6 generation seeds.

[0053] In some embodiments of the present invention, FVI uses screening method A to obtain F7 generation seeds.

[0054] In some embodiments of the present invention, F7 uses screening method B to obtain F8 generation seeds.

[0055] In some embodiments of the present invention, the screening criteria further include: starting from the F3 generation, using leaf color as a marker, taking Xinxiang S as a control, and selecting the strains with light green leaves.

[0056] In the embodiments of the present invention, the screening criteria further include: selecting the strains with strong tillering ability and fast tillering rate.

[0057] In some embodiments of the present invention, the standards for rice quality detection are: head rice rate > 58%, chalkiness degree ≤ 1%, transparency level 1, alkali spreading value ≥ 6.0 levels, gel consistency ≥ 60 mm, 13% < amylose content ≤ 17%, and length-width ratio > 4.0.

[0058] In the embodiments of the present invention, the high temperature refers to one or more of the following situations during the booting stage, heading stage and filling and maturity stage: the daily maximum temperature is above 40°C, the daily maximum temperature is above 37°C for 5 consecutive days, and the daily average temperature is above 32°C.

[0059] In the embodiments of the present invention, the low temperature is below 23.5°C.

[0060] In some embodiments of the present invention, shuttle breeding is carried out in Baoshan, Yunnan; Sanya, Hainan; and Changsha, Hunan.

[0061] Baoshan, Yunnan belongs to the subtropical monsoon climate, being warm throughout the year, without extreme high or low temperatures, with sufficient sunlight, uniform rainfall, moderate humidity, and a long frost-free period, providing ideal conditions for the reproduction of two-line sterile lines of hybrid rice. It meets the requirements of meteorological factors for the three safe periods of rice fertility sensitivity, heading and flowering, and harvesting and ripening.

[0062] In Sanya, Hainan, seeds can be sown in mid-November for seed multiplication and in mid-January for seed production. The high-temperature and high-humidity environment in Hainan is prone to causing diseases and pests, and screening for disease and pest resistance can be carried out.

[0063] In Changsha, Hunan, due to high temperatures in summer, seed production can be carried out, as well as screening and identification for high-temperature tolerance.

[0064] In some embodiments of the present invention, in screening method C, the lines with outcrossing seed-setting rate higher than that of the control high-temperature-tolerant sterile line are selected.

[0065] In the embodiments of the present invention, the screening criteria further include: the lines with a sterile starting temperature below 23.5 °C are selected.

[0066] In some embodiments of the present invention, single plants with good rice quality are screened by making test crosses.

[0067] In some embodiments of the present invention, starting from the F1 generation, the outcrossing habits are investigated generation by generation. The lines with a stigma exsertion rate greater than 90% and the stigma still being active 10 days after flowering are selected.

[0068] In the embodiments of the present invention, screening for disease and pest resistance is carried out in an environment with an average daily temperature above 24 °C and an average relative humidity above 55% for some generations.

[0069] In some embodiments of the present invention, rice blast is identified in the F1 generation, rice blast is identified by mixed sowing in the F2 generation, and rice blast is identified for the lines in the F3 generation. Those with medium susceptibility or above are selected.

[0070] In some embodiments of the present invention, false smut is identified in the F1 generation, and false smut is respectively identified for the lines in the F3 generation, F4 generation, and F5 generation. Those with medium resistance or above are selected.

[0071] In some embodiments of the present invention, false smut is identified in the F1 generation; false smut is respectively identified for the lines in the F3 generation, F4 generation, and F5 generation. Those with medium resistance or above are selected.

[0072] Example

[0073] The following examples describe more specifically the content disclosed by the present invention. These examples are only for illustrative purposes, as various modifications and variations within the scope of the present invention are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples can be obtained through conventional commercial channels or synthesized according to conventional methods, and can be used directly without further treatment. Unless otherwise stated, the instruments used in the examples can be obtained through conventional commercial channels.

[0074] Since 2017, shuttle breeding has been carried out continuously for many years in Baoshan, Yunnan; Sanya, Hainan; and Changsha, Hunan. An indica two-line sterile line "Yuxiang 368S" with an ideal plant type, strong tillering ability (early and rapid growth), high yield in propagation and seed production, strong combining ability, good resistance, rich fragrance, quality reaching the first-class standard of the Ministry of Agriculture, stable fertility, and a low sterility starting temperature (23.5°C) has been developed. The breeding time, location, and process of each generation are as follows:

[0075] In winter 2017, in Sanya, F0 generation: Sowed in mid-November. Using Xinxiang S as the female parent and Yan 416S as the male parent, 95 F1 hybrid seeds were obtained by hybridization.

[0076] In summer 2018, in Baoshan, F1 generation: Sowed in early April. 63 individual plants were planted, and 40 true hybrid plants were selected and harvested together to obtain F2 generation seeds.

[0077] In winter 2018, in Sanya, F2 generation: Sowed in early November. 10,000 plants were planted. Through molecular marker-assisted selection, individual plants containing the Badh2, Chalk5, WX b genotypes in Xinxiang S and the Pita, ALK b , AAP6 genotypes in Yan 416S were screened. Natural low-temperature seed multiplication was carried out. Combining with rice quality detection, 1,000 excellent individual plants with rice quality reaching above grade 1 were selected, and seeds were harvested from each individual plant to obtain F3 generation seeds.

[0078] In summer 2019, in Changsha and Baoshan, F3 generation: 1,000 seed materials were in duplicate. Sowed in early April in Baoshan and in early June in Changsha, and 1,000 plant lines were planted in each place; In Changsha, the outcrossing seed setting rate was screened and identified with R8029 as the male parent under high temperature; Based on the screening of the outcrossing seed setting rate of the plant lines in Changsha (higher than that of the control heat-tolerant sterile line Shuang 1S), combined with the molecular marker selection results of Badh2, Chalk5, WX b , Pita, ALK b and AAP6 genes, natural low-temperature seed multiplication was carried out. 500 individual plants with rice quality reaching grade 1, excellent fertility, morphology, and resistance were selected, and seeds were harvested from each individual plant to obtain F4 generation seeds.

[0079] In the winter of 2019, in Sanya, F4 generation: Sowed in early November, planted 2,000 plants, selected individual plants carrying Badh2, Chalk5, WX b , Pita, ALK b and AAP6 by molecular markers, propagated seeds under natural low temperature, combined with rice quality detection, selected 135 excellent individual plants, harvested seeds from each individual plant, and obtained F5 generation seeds;

[0080] In the summer of 2020, in Changsha and Baoshan, F5 generation: 135 seed materials were in duplicate. Sowed in early April in Baoshan and in early June in Changsha, and planted 135 plant lines each; Conducted screening and identification of outcrossing seed setting rate under high temperature with R8029 as the male parent in Changsha; Based on the screening of outcrossing seed setting rate of Changsha plant lines (higher than the control thermo-sensitive genic male sterile line Shuang 1S) in Baoshan, combined with the molecular marker selection results of Badh2, Chalk5, WX b , Pita, ALK b and AAP6 genes, propagated seeds under natural low temperature, selected 43 individual plants with rice quality reaching grade 1, good fertility, morphology and resistance, harvested seeds from each individual plant, and obtained F6 generation seeds;

[0081] In the winter of 2020, in Sanya, F6 generation: Sowed in November, planted 43 plant lines, selected 41 excellent individual plants, harvested seeds from each individual plant, and obtained F7 generation seeds;

[0082] In the summer of 2021, in Changsha and Baoshan, F7 generation: The seed materials were in duplicate. Sowed in early April in Baoshan and in early June in Changsha, and planted 41 plant lines each; Conducted outcrossing under high temperature with R8029 as the male parent in Changsha, combined with the molecular marker selection results of Badh2, Chalk5, WX b , Pita, ALK b and AAP6 genes, simultaneously carried out laboratory detection of fertility, plant type, resistance and rice quality, and selected plant line No. 2WSH368; According to the screening results in Changsha, Baoshan selected ideal individual plants and propagated seeds under natural low temperature to obtain F8 generation seeds; So far, the screening was basically completed, and then continued to expand propagation and test cross combinations;

[0083] In the winter of 2021, in Sanya, F8 generation, the seed materials were in duplicate. One was sowed in November, propagated under low temperature isolation, and harvested seeds at the end of March to obtain F9 generation seeds; The other was sowed in early February and conducted test cross with other male parents;

[0084] In the summer of 2022, in Changsha, F9 generation, conducted artificial cold water pool identification, eliminated individual plants with higher sterility starting temperature, selected individual plants with sterility starting temperature lower than 23.5°C and harvested seeds to obtain F10 generation seeds; At the same time, conducted heterosis identification on the combined seed materials test crossed in Hainan the previous year;

[0085] In the winter of 2022, in Sanya, for the F10 generation, the seed materials were in duplicate. One was sown at the beginning of November, and after low-temperature isolation, multiplication and seed harvesting; the other was sown at the beginning of February 2023 and was used for test crossing with other male parents.

[0086] From 2023 until now, in Changsha: Superiority identification was carried out to determine the core strain lines. An indica two-line sterile line with stable and consistent agronomic traits, ideal plant type, strong tillering ability, high yield in propagation and seed production, strong combining ability, good resistance, strong rice fragrance, and rice quality reaching the first-class standard of the Ministry of Agriculture was basically developed. The sterility starting temperature is low (lower than 23.5°C), and it is named "Yuxiang 368S".

[0087] In this example, the standards for rice quality detection were: head rice rate > 58%, chalkiness degree ≤ 1%, transparency level 1, alkali spreading value ≥ 6.0 levels, gel consistency ≥ 60 mm, amylose content 13% < amylose content ≤ 17%, and length-width ratio > 4.0.

[0088] In this example, rice quality identification was carried out under high-temperature and low-temperature conditions respectively. The outcrossing seed-setting rate was identified under high-temperature conditions for seed production, and combined with molecular marker-assisted selection, favorable genes such as Badh2, Chalk5, WX b , ALK b , AAP6, etc. were aggregated; through the selection of multiple generations, a high-temperature-resistant and high-quality hybrid rice sterile line with high-quality rice was obtained.

[0089] Identification of the obtained high-quality hybrid rice

[0090] 1. Fertility performance

[0091] Yuxiang 368S was sown on February 4 in Sanya, Hainan, and began to panicle on April 20; sown on May 24 in the Changsha area, it began to panicle on August 6, and sown on June 2, it began to panicle on August 12, all showing sterility. After preliminary identification by the Hunan Hybrid Rice Research Center and Hunan Agricultural University in the artificial cold water pool, the fertility conversion starting temperature of Yuxiang 368S is lower than 23.5°C, and the sterility is stable.

[0092] 2. Growth period

[0093] Yuxiang 368S was sown on May 24 in Changsha, Hunan, and began to panicle on August 6, sown on June 2, it began to panicle on August 12, and sown on February 4 in Sanya, Hainan, it began to panicle on April 20, all showing sterility, and the sowing-to-heading duration was 71 - 75 days. When sown in different years and different locations, the sowing-to-heading duration is relatively stable.

[0094] 3. Morphological characteristics and agronomic traits (early growth and rapid growth characteristics)

[0095] Figure 1 This is the grain shape diagram of Yuxiang 368S. The grains are slender and plump, with a 1000-grain weight of about 23.2 g, a grain length of 10.6 mm, a grain width of 2.2 mm, and a length-width ratio of about 4.79.Figure 2 Figure showing the grain shape comparison between Yuxiang 368S and its parental line Xinxiang S. Compared with Xinxiang S, Yuxiang 368S has a smaller grain width and a larger length-width ratio.

[0096] The plant height of Yuxiang 368S is about 87.4 cm. It has a moderately compact and loose plant type, a moderately thick stem, light green leaves, and the leaves are generally upright as a whole. The flag leaf is 35 cm long, 1.5 cm wide, and the included angle is about 20 - 30°. The leaf sheath and lemma tip are both colorless (see Figure 3 Left: Photo of a single plant of Yuxiang 368S at the tillering stage; Figure 3 Right: Photo of a single plant of Yuxiang 368S at the maturity stage; Figure 4 : Photo of the Yuxiang 368S population at the maturity stage). It has a fast tillering rate, an early appearance of the tillering peak, showing the characteristics of "early and rapid growth", and strong tillering ability. Generally, the number of effective panicles per single plant is 11.2 - 15.6, with an average of 13.4 panicles. The panicle length is about 28.8 cm, the panicle grain density is relatively large, with about 3 rings of the total spikelets per panicle on average, about 245 grains per panicle on average, a seed setting rate of about 85.9% during high-yield reproduction, and the highest yield per mu can reach 603.2 kg.

[0097] Figure 5 Figure showing the coverage comparison between Yuxiang 368S and Li 68S (control sterile line) planted in the same period (upper left: single plant of the control sterile line; upper right: single plant of Yuxiang 368S; lower left: population of the control sterile line; lower right: population of Yuxiang 368S); it can be seen that Yuxiang 368S has a fast tillering rate, an early appearance of the tillering peak, showing the characteristics of "early and rapid growth", strong tillering ability, and high population coverage.

[0098] 4. Outcrossing Habit

[0099] When Yuxiang 368S is heading and flowering, it is slightly arc-shaped. The 3 - 5 days after heading is the full-bloom stage. The flowering time is relatively early, and the full-bloom stage is from 10:00 to 12:00. The flowering peak is obvious, and the pre-noon flowers account for more than 90%. The flowering time coincidence rate is high. The length of the panicle neck envelopment during the sterile period is about 1.1 cm, and the percentage of panicle neck envelopment grains is about 5.1%. The stigma exsertion rate is high. Without spraying "920", the total stigma exsertion rate is 79.8%, among which the bilateral exsertion rate is 51.7%. The stigma vitality is strong, and the outcrossing seed setting rate can reach more than 72.0%, making it easy to achieve high yields in seed production. It is relatively sensitive to "920". When 15 - 20% of the plants are heading, spraying 15 g of "920" per mu can relieve the panicle neck envelopment.

[0100] 5. Rice Quality

[0101] After rice quality analysis and testing, the rough rice rate of Yuxiang 368S is 81.1%, the milled rice rate is 67.5%, the head rice rate is 59.5%, the rice grain length is 8.9 mm, the length-width ratio is 4.7, the chalky grain rate is 0.8%, the chalkiness degree is 0.4%, the transparency is Grade 1, the alkali spreading value is Grade 7.0, the gel consistency is 82 mm, the amylose content is 15.8%, the protein content is 6.9%, and the fragrance type is popcorn fragrance. When planted under multiple ecological conditions in Changsha, Yunnan, and Hainan, the rice quality of Yuxiang 368S reaches the first-class standard of the Ministry of Agriculture. Through molecular marker detection, Yuxiang 368S contains the fragrance gene Badh2 and excellent genotypes of rice quality-related genes Chalk5, ALK b , WX b , and AAP6.

[0102] 6. Identification of high temperature tolerance of Yuxiang 368S

[0103] 6.1 Identification of high temperature tolerance of outcrossing seed setting rate of male sterile lines

[0104] The identification test of high temperature tolerance of outcrossing seed setting rate of male sterile lines was carried out at a certain base in Liuyang, Changsha in 2022. Yuxiang 368S and the high temperature tolerance male sterile line control material Shuang 1S (control) were sown on June 5. The male parent R8029 was sown in two phases with an interval of 8 days, and the first phase was sown on May 10. According to the traditional hybrid seed production method, the first phase and the second phase of the male parent were planted alternately, with a transplanting leaf age of 5.0 - 5.5 leaves and a transplanting specification of 20 cm × 20 cm; the female parent was transplanted in the middle of the male parent, with 8 rows planted for each variety, 8 hills in each row, and 1 grain of rice seedling planted in each hill. Record the sowing date, transplanting date, initial heading date, full heading date, and maturity date. Place a temperature and humidity automatic recorder in the field to record the daily maximum temperature, daily minimum temperature, daily average temperature, and rainfall during the whole growth period of the experimental field. According to the weather forecast, when high temperature weather occurs, that is, when the daily average temperature is above 32°C and / or the daily maximum temperature is above 37°C, more than 40 panicles of the rice varieties to be identified that start heading on the same day are marked and sampled to investigate their seed setting rate. The standard for male sterile lines to tolerate extreme high temperature: when encountering high temperature during the booting / heading and flowering period, the outcrossing seed setting rate of male sterile lines is greater than that of Shuang 1S.

[0105] In this example, the high temperature tolerance of rice male sterile lines during the booting / heading and flowering period is identified by sowing in different periods in the field and encountering natural high temperature, and the evaluation criterion is the outcrossing seed setting rate. Large-scale variety high temperature identification can be carried out in the field, with simple operation, close to the actual field situation, reliable results, and low cost; the test results can be directly applied without field verification, and it has strong practicability. A control variety is set, marked at the initial heading stage, and the seed setting rate of the marked panicles is investigated. The evaluation is carried out according to the outcrossing seed setting rate being higher than that of the control Shuang 1S, and the effect is easy to evaluate. Shuang 1S is a variety selected by the Hunan Hybrid Rice Research Center and has applied for plant variety right protection, CNA027163E.

[0106] The results are shown in Tables 1 - 3. From July to August 2022, in a certain base in Liuyang, there were 33 days with a daily maximum temperature ≥ 37°C, 2 days with a temperature ≥ 40°C, and 24 consecutive days with a temperature exceeding 37°C. From August 7th to 25th, 2022, for 19 consecutive days, the daily maximum temperature was ≥ 37°C, and the daily average temperature was above 30.7°C (Tables 2 and 3). Under high temperature (heading stage from August 7th to 25th), Yuxiang 368S began heading on August 17th, and the outcrossing seed - setting rate under high temperature was 67.3, higher than that of the heat - tolerant control sterile line Shuang 1S (Table 1).

[0107] Table 1 Identification results of outcrossing seed - setting rate of heat tolerance for Yuxiang 368S and Shuang 1S

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[0109] Table 2 Statistics of high - temperature weather in July and August 2022 in Liuyang, summer

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[0111] Table 3 Statistics of meteorological data from August 7th to 25th, 2022 in a certain base in Liuyang

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[0113] 6.2 Identification of heat tolerance for the combinations of test - crossing sterile lines

[0114] The high temperature tolerance identification of the sterile line's crossed combinations was carried out at a certain base in Liuyang, Changsha in 2024. Using the method of sowing in stages, the combinations crossed with Yuxiang 368S (Yuxiang Liangyou 1958, the parental sources are Yuxiang 368S and 1WH1958; Yuxiang Liangyou 001, the parental sources are Yuxiang 368S and 8X001) and the control variety were sown in the first stage on April 10th, with a 10-day interval between each stage, and sown for 5 stages. When the seedling age reached 25 days, they were transplanted, and the transplanting specification was 20cm×20cm. Single-plant transplantation was adopted, with 8 rows planted for each variety, and 8 hills in each row. Protection rows should be set around the test, and the protection rows should be no less than 3 rows. Record the initial heading date, full heading date, maturity date, and heading and flowering stage of each stage. Place temperature and humidity recorders in the field to record the field temperature, humidity, and light from July to September. When the daily maximum temperature is above 40℃ (extreme high temperature), or the daily average temperature is above 32℃ or the daily maximum temperature is above 37℃ (ordinary high temperature), select single plants at the 6th stage of young panicle differentiation (booting stage), the panicles on the day of initial flowering (heading and flowering stage), and the panicles 10 days after heading (filling stage) for hanging tags. The evaluation of high temperature tolerance is measured by the relative high temperature tolerance seed setting coefficient (the ratio of the average seed setting rate of the rice material to be identified and the high temperature tolerance control variety under high temperature conditions) and the rice quality index, and the high temperature tolerance of the rice material to be identified at the heading and flowering stage is graded and evaluated according to the grading standard in Table 4. The detection and evaluation of rice quality are carried out according to the evaluation standard of "Agricultural Industry Standard NY / T593-2013", divided into first-class, second-class, and third-class. The rice quality of varieties that do not reach the high-quality level is all ordinary.

[0115] Table 4 Grading and evaluation standard for high temperature tolerance [[ID=~]]

[0116] Evaluation level Relative high-temperature resistant strength coefficient (r1) High-temperature resistance 1 r1≥1.10 Strong / high-temperature resistant 3 0.90≤r1＜1.10 Relatively strong / relatively high-temperature resistant 5 0.70≤r1＜0.90 Average / average high-temperature resistant 7 0.50≤r1＜0.70 Relatively weak / low high-temperature resistant 9 r1＜0.50 Weak / extremely low high-temperature resistant

[0117] The results are shown in Tables 5-7. According to the records of the temperature and humidity recorder in the field spike layer at a certain base, there were two high temperature weather conditions from July 1st to August 20th, 2024. The first high temperature weather was from July 14th to July 25th, the daily maximum temperature in the field spike layer was 37.3-41℃, the daily average temperature was 30.7-32.8℃, the daily minimum temperature was 26.9-28.8℃, and the air humidity was 73.4-85.1%; the second high temperature weather was from August 2nd to August 10th, the daily maximum temperature in the field spike layer was 37.4-40℃, the daily average temperature was 30.3-32.4℃, the daily minimum temperature was 24.9-27.6℃, and the air humidity was 75.8-84.3%, meeting the requirements of high temperature weather. The identification results show that the seed setting rates of the combinations Yuxiang Liangyou 1958 and Yuxiang Liangyou 001 crossed with Yuxiang 368S are greater than 85% under high temperature, and the chalkiness degree is lower than 1% and the transparency reaches the first level under high temperature, indicating that these two combinations have strong high temperature tolerance.

[0118] Figure 6 and Figure 7They are the field performances of the combinations Yuxiang Liangyou 1958 and Yuxiang Liangyou 001, which are made with Yuxiang 368S, under high temperature; the seed setting is not affected under high temperature, the spikelet density is relatively large, and the yield is high.

[0119] Table 5 Temperature and Humidity of the Spike Layer in a Certain Base Field from July 10th to August 10th, 2024

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[0122] Table 6 Results of the Identification of the High Temperature Resistance of the Milling Quality of the Test Materials

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[0124] Table 7 Results of the Identification of the High Temperature Resistance of the Test Materials

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[0126] 6.3 Identification of the Milling Quality of the Combinations Made with Yuxiang 368S

[0127] The experiment was carried out in Lingshui, Hainan in 2023. To evaluate the performances of multiple rice varieties in the dry season in Lingshui, Hainan. 48 varieties were demonstrated, with Yexiangyou Lisi and Zhenliangyou Yuzhan (CK) as the controls. The sowing and transplanting method was adopted. All varieties were sown on December 30th and transplanted on January 29th; they were planted in the wide-narrow row method, with a narrow row of 6 inches, a wide row of 12 inches, a plant spacing of 6 inches, and 2 grain seedlings transplanted per hill. Protection rows should be set around the experiment, with no less than 3 rows of protection rows, and the varieties corresponding to the plots were planted. The spacing between large plots and between large plots and protection rows was 40.8 cm. The milling quality detection and evaluation of the demonstrated varieties were carried out according to the evaluation standard of "Agricultural Industry Standard NY / T 593-2013", which was divided into first-class, second-class, and third-class. The milling quality of the varieties that did not reach the high-quality level was all ordinary.

[0128] The identification results are shown in Table 8. Among them, Mengxiang A / SNR6, Xinxiang Liangyou 1958, Xinxiang Liangyou 2020, and Xinxiang Liangyou 3998 had lower alkali digestion values. Except for the positive control Yexiangyou Lisi, among all varieties, the milling quality trait indicators of Yuxiang Liangyou 1958 were ranked first comprehensively and individually. The grain length was 7.5 mm, the length-width ratio was 4.1, the chalky grain rate was 2%, the amylose content was 15.3%, the gel consistency was 85 mm, and the alkali digestion value was 6.0.

[0129] Figure 8 They are the rice samples of Yuxiang 368S and the combinations made with it (left: Yuxiang 368S; right: Yuxiang Liangyou 1958); the chalkiness degree and chalky grain rate of Yuxiang 368S and Yuxiang Liangyou 1958 are low, and the rice quality reaches the first-class of the national standard, being high-grade and high-quality.

[0130] Table 8 Results of the Identification of the Milling Quality of the Test Materials

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[0132]

Claims

1. A method for breeding a high-quality thermo-tolerant hybrid rice sterile line, characterized in that, Using the two-line sterile line Xinxiang S as the female parent and the two-line sterile line Yan 416S as the male parent, hybridize to obtain the hybrid F1; plant F1 to obtain the F2 generation; then screen excellent individual plants from each generation, and harvest and plant the seeds of the individual plants to obtain the next generation; The screening methods include one or more of screening method A, screening method B, and screening method C; the same or different screening methods can be selected for different generations; The screening method A includes: multiplying seeds at low temperature, screening individual plants that simultaneously carry the Badh2, Chalk5, WX b genotypes in Xinxiang S and the Pita, ALK b , AAP6 genotypes and pass the rice quality test; The screening method B includes: dividing the seed materials into two or more duplicates, sowing one of them and identifying the outcrossing seed setting under high temperature, screening for individual plants that simultaneously carry the Badh2, Chalk5, and WX b genotypes in Xinxiang S and the Pita, ALK b , AAP6 genotypes and passing the rice quality test; The screening method C includes: dividing the seed materials into two or more copies, sowing one copy and carrying out outcrossing and seed setting under high temperature, and screening out the lines with high outcrossing seed setting rate; carrying out seed multiplication of the other copy under low temperature, and screening the individual plants that simultaneously carry the Badh2, Chalk5, WX b genotypes in Xinxiang S and the Pita, ALK b , AAP6 genotypes and pass the rice quality test; The high temperature refers to the temperature at which rice is under heat stress; the low temperature refers to below the sterility starting temperature of the sterile line.

2. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1, characterized in that The screening methods also include: preparing two or more copies of the seed materials of the test-cross combinations of different plant lines, sowing one copy at different times, identifying the rice quality under high temperature, and screening the plant lines with excellent rice quality under high temperature; identifying the rice quality of the other copy or two or more copies in different ecological regions, and selecting the ones with excellent rice quality.

3. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1 or 2, characterized in that, The screening criteria also include: selecting the plant lines with strong tillering ability and fast tillering rate; the screening criteria also include: starting from the F3 generation, using leaf color as a marker, with Xinxiang S as the control, selecting the plant lines with light green leaves.

4. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1 or 2, characterized in that The criteria for rice quality detection are: head rice rate > 58%, chalkiness degree ≤ 1%, transparency level 1, alkali spreading value ≥ 6.0 levels, gel consistency ≥ 60 mm, amylose content 13% < amylose content ≤ 17%, length-width ratio > 4.

0.

5. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1 or 2, characterized in that, The high temperature refers to one or more of the following situations during the booting stage, heading stage, and filling and maturity stage: the daily maximum temperature is above 40°C, the daily maximum temperature is above 37°C for 5 consecutive days, and the daily average temperature is above 32°C; the low temperature is below 23.5°C.

6. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1, characterized in that In screening method B, select the plant lines with outcrossing seed-setting rate higher than that of the control heat-tolerant sterile line.

7. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1, characterized in that, The screening criteria also include: selecting the plant lines with sterility starting temperature below 23.5°C.

8. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1 or 8, characterized in that Starting from the F1 generation, investigate the outcrossing habits generation by generation. Select the plant lines with stigma exsertion rate greater than 90% and stigma still having activity 10 days after flowering.

9. The method for breeding high-temperature resistant and high-quality hybrid rice male sterile lines according to claim 1, characterized in that Screen the disease and insect resistance in the environment where the daily average temperature is above 24°C and the average relative humidity is above 55% for some generations.

10. The method for breeding a high-temperature resistant and high-quality hybrid rice sterile line according to claim 1 or 9, characterized in that, Identify rice blast in the F1 generation, identify rice blast by mixed sowing in the F2 generation, identify rice blast for the plant lines in the F3 generation, and select the ones with medium susceptibility or above; identify false smut in the F1 generation, identify false smut for the plant lines in the F3, F4, and F5 generations respectively, and select the ones with medium resistance or above; identify false smut ball in the F1 generation; identify false smut ball for the plant lines in the F3, F4, and F5 generations respectively, and select the ones with medium resistance or above.

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