Breeding of High Quality Indica CMS Line Xinlong A

LIU An, YU Min, HUANG Xiong, DENG Meng, LAN Sheng-ru, ZHONG Zhong, LIU Zhi-yong

1. Hunan Xinsheng Huafeng Seed Industry Technology Co., Ltd, Yueyang 414000, PRC;

2. Yueyang Jinsui Crop Research Institute, Yueyang 414000, PRC

Abstract Xinlong A was a high quality indica CMS line developed with early rice intermediate material 05Zao20 (Zhouyou 903/Zhong9B F6) as female parent and IR58025B/Q96 F4 as male parent, Jin23A was then used as female parent for test crossing with BC, and backcrossed and bred with complete fertility and abortion lines. The male sterile line had the characteristics of good agronomic characters, strong combining ability, good resistance, high yield and good quality which reaches gradeⅡstandard of national high quality rice. It showed broad prospects and was technically identified in Jiangxi Province in 2017.

Key words Xinlong A; Hybrid rice; CMS line; High quality; Breeding

1. Introduction

The breeding of sterile line and restorer line is critical to the breeding of three-line hybrid rice[1]. The breeding of sterile line also determines the quality of the first filial generation of rice[2-3]. Therefore, it’s natural for breeding experts to choose a CMS (cytoplasmic male sterile) line hybrid rice featured with excellent agronomic characters, strong combining ability, high rice quality, good resistance and easy-tobreed[4]. Xinlong A is a high quality early-maturing middle indica CMS line bred by Hunan Xinsheng Huafeng Seed Industry Technology Co., Ltd and Jiangxi Xiannong Seed Co., Ltd. Xinlong A has high and stable sterility, strong combining ability and high outcrossing rate, which is suitable for breeding fine quality late-maturing middle and late hybrid rice combination. The sterile line was identified in Jiangxi Province in February 2017, with identification number: Ganshendao 20170053.

2. Breeding Process

Xinlong A was developed in 2005 with high quality early rice intermediate material 05Zao20 (Zhouyou 903/Zhong9B F6) as female parent and IR58025B/Q96 F4as male parent using emasculation with hot water. Totally 20 hybrid seeds were obtained. In the winter of 2005, the F1generation was planted in Hainan, totally 12 plants; in 2006, F2was planted in Yueyang, Hunan, totally 1 200 plants. 20 short individual plants with strong tillering ability were selected; F3was planted in 2006 in Hainan, and 15 plants were selected; F4was planted in 2007 in Yueyang, Hunan, and individual plants with low plant height, strong tillering ability, short flag leaf and high stigma exsertion rate were selected as male parent, and Jin23A was used as female parent for test crossing. Totally 11 pairs of test crossing were completed; complete fertility and abortion lines were backcrossed in pairs for the test crossing seeds and corresponding male parent lines planted in 2007 in Hainan; for the BC1regularly planted in 2008 in Yueyang, cross breeding was continued for complete fertility and abortion lines; after three years (six growing seasons) of backcrossing and breeding of added generations in Yueyang and Sanya, some backcrossing lines in Hainan tended to be stable in 2011. Then test crossing was conducted between the sterile line and the three-line restorer line. The advantage identification on F1(Yueyang) indicated that BC108-3-5 showed good combining ability, and F1hybrid presented proper height, large panicle, long grains, high rice quality, good leaf shape, good parachrosis and high production; it was then officially named as Xinlong A in 2015 (Fig. 1).

3. Main Traits

3.1. Morphological characteristics

Xinlong A is compact in plant type. The flag leaf is medium and narrow, the leaf color is dark green, and the leaf auricle, ligule, sheath, apiculus and stigma are colorless; the variety has strong tillering ability and high panicle bearing tiller percentage (8～10 panicles for one individual plant); the panicle type is medium and the grain is slender and awnless. The plant height is 58 cm, the panicle length is 24.6 cm, the total grain number per panicle is 171～238, and the 1 000-grain weight is about 25.0 g.

3.2. Duration from seeding to heading (DSH)

The DSH in autumn sowing in Hunan is 74 d, and the DSH in winter sowing in Hainan is 80～85 d. In 2016, the DSHs in spring and autumn in Jiangxi were 83 and 74 d, respectively. The number of leaves on the main stem was 13.5～15.0. The DSH presented good stability between different years, and the DSH of Xinlong A was 20 d longer than that of Jin23A.

3.3. Fertility performance

In the autumn of 2016, 51 panicles of clusters planted in Liantang of Nanchang County were tested. The samples were stained with I2-KI solution and observed under 10×10 fold microscope (each slice with two fields). Totally 3 129 pollen grains were observed. The microscopic examination showed 100% abortion rate. The percentage of self-fruited was 0. The pollen abortion rate was 100%, including 94.41% typical abortion type, 4.76% spherical abortion type and 0.83% stained abortion type.

3.4. Outcrossing characteristics

Xinlong A has tidy heading. It blooms the day after the heading. The heading period of a single panicle is 4 d, the blooming period is 6 d, hence the flowering period is 9～11 d. On sunny and warm days, it starts to bloom at 9:00～9:30 am and fully blooms at 10:00～11:30 am. The flowering rate by noon is 82.3%, and the glume opening and closing of a single flower lasts for 155 min. Xinlong A has small stigma. The stigma exsertion rate without application of “920” is 67.5%, including 23.1% double exsertion and 25.4% panicle-enclosure glume grain. Xinlong A is sensitive to “920”. Full heading of Xinlong A can be realized with an application of 0.015 kg/hm2of “920”, with good closure of glumes and low high-temperature glume closure rate. A survey of well-cultivated fields for seed production showed an average outcrossing setting rate of 58.4% with good outcrossing traits. The yield of large area seed production can reach 2 250～ 3 000 kg/hm2.

3.5. Rice quality and resistance

Fig. 1 Breeding process of Xinlong A(B)

According to the test results of Inspection Center of Food Quality (Wuhan) of Ministry of Agriculture in 2016, the brown rice rate, milled rice rate and head rice rate of Xinlong A were 78.2%, 67.9% and 43.1%, respectively. The grain length was 7.0 mm, the lengthwidth ratio was 3.5; the chalky rice rate and chalkiness were 26% and 3.1%, respectively. The transparency was in Level 3, the alkali spreading value was in Level 5.5, the amylase content was 13.8%, and the gel consistency was 67 mm.

The induced identification in the infected field of the Institute of Plant Protection of Xiangxi Academy of Agricultural Sciences (Hunan) showed that the seeding blast and leaf blast of Xinlong A were in Level 3, and the neck blast was in Level 5; the inoculation identification with representative strains (IV type) in the Yangtze River Basin of Hunan Rice Research Institute showed that the bacterial blight was in Level 7 and the ustilaginoidea virens was in Level 5.

3.6. Combining ability and restorability

The hybrid rice combination bred with Xinlong A grew luxuriantly with good plant and leaf type, abundant tillers, big panicles, large grain number per panicle, small 1 000-grain weight, good parachrosis in late period, large yield potential, and fine rice quality. Four representative male parents, namely R207, Chenghui 727, Yuehui 9113 and Huazhan, were selected for the test of combining ability in 2014, and Yueyou 9113 was the control group. The setting rates of the F1generation of Xinlong A crossed with the four restorers were 90.2%, 85.3%, 81.1% and 84.4% respectively, 1.6%～10.2% higher than those of the control group, showing good restorability. Its crossing with Yuehui 9113 and Huazhan presented excellent heterozygous advantages, especially the crossing with the self-selected restorer P656. In 2017, Xinlong A/P656 (Xinlongyou 3) prepared by Hunan Xinsheng Huafeng Seed Industry Technology Co., Ltd participated in Hunan Combined Variety Test. The whole growth period was 123.8 d, 1.2 d longer than the control group; the average yield was 9 531.0 kg/hm2, an increase of 3.67% compared with the control group of Tianyouhuazhan (9 193.5 kg/hm2). The rice quality is good and has reached the national secondclass quality standard of rice. In the 12thHigh Quality Rice Selection of Hunan Province, Xinlong A was rated as second-class high quality medium rice. In 2018, the variety group won the first in production during Hunan Combined Variety Test; in 2019, it gained qualification to the regional test of the Chuyue Association in the Middle and Lower reaches of the Yangtze River; the next year, it gained qualification to the continuous trial synchronous production test of the Chuyue Association. In 2019, the new bred Xinlongyousizhan had an excellent performance and was promoted to the national regional test.

4. Key Breeding Techniques

4.1. Time and leaf differences in male and female parents

In Jianning County, Fujian Province, during spring multiplication in Northern Hunan, the female parent was sown at the end of March and the male parent was sown at the beginning of April; the time difference was 6 d and the leaf difference was 1.3～1.5 leaves; the DSH of the female parent was 83～90 d. During the autumn multiplication in Northern Hunan, the female parent was sown in late June and the male parent was sown at the end of June; the time difference was 6 d, and the DSH of the female parent was 74 d.

4.2. Sparse and uniform seeding of male and female parents, and cultivation of strong seedlings

As the saying goes: “Good seedlings are half of the basis for a good harvest of rice.” Cultivation of strong seedlings is critical to the high yield of hybrid rice production[5]. Paddy fields with good irrigation and drainage conditions, fertile soil, and sunny exposure without cold soak were selected as rice seedling bed. 525 kg/hm2of high-efficacy fertilizer were applied as the base fertilizer for the seedling bed. The seedling box was flattened before seeding. The seeding rate was 90～120 kg/hm2; the sowing quantity of the female parent and the male parent was 45 and 9 kg/hm2respectively, both sparsely and uniformly seeded. The paddy field was exposed to sun during the budding period, and maintained shallow water with frequent irrigation when one leaf and one sprout were seen; 75 kg/hm2of urea was applied during the 3-leaf stage. The seedlings were healthily cultivated. Diseases and pests such as rice thrips should be prevented. Pesticides were sprayed and 60 kg/hm2of urea was applied 4～5 d before transplanting[6].

4.3. Timely transplanting and rational close planting

The ration of male and female parents in the breeding field was 2 ∶12; the distance between male and female parents was 16.5 cm; the plant and row spacing of the male parent was 20 cm×33.3 cm; the plant and row spacing of the female parent was 13.3 cm×16.5 cm; the seedling age of the male and female parents was 20～25 d. Two seedlings were planted in each hole. Make sure 1.8 million female parent basic seedlings and 450 000 male parent basic seedlings be planted in each hectare.

4.4. Reasonable fertilizer, water management and enhanced pest control

Follow the fertilization principle of “heavy application of base fertilizer, proper application of organic fertilizer and topdressing according to the growth of seedlings at later stage”. Apply 525 kg/hm2of compound fertilizer as the base fertilizer at one time when plowing the field; apply 150 kg/hm2of granular fertilizer mixed by quick acting nitrogen fertilizer and organic fertilizer for topdressing 3 d after planting of male parent; apply 150 kg/hm2of urea for topdressing 4 d after planting of female parent to turn the seedlings green and promote tillering; apply 15 bags/hm2of herbicide (Paoyangjing) to clear barnyard grass or dropped grains; as the flag leaf of the female parent sprouts out, apply 75 kg/hm2of potash fertilizer as the seedling robust fertilizer; spray 1.5 kg/hm2of potassium dihydrogen phosphate during filling period to improve the 1 000-grain weight. In the early stage, adopt shallow water irrigation, and leave the root stumps above the soil. In the medium stage, expose the paddy field to morning sun according to the condition of the sprouts. During the heading stage, maintain an 8～10 cm water layer, and dry-wet seed robust method after pollination. Meanwhile, prevent stem borers, planthoppers, sheath blight, rice blast, smut disease and other pests and diseases.

4.5. Make flowering prediction and improve outcrossing setting rate

Track the growth of young panicles, adopt the method of “controlling by nitrogen and promoting by potassium” method to adjust flowering time to make their flowering time meet. When the heading index of the female parent reaches 10%, spray “920” in sunny morning, totally 0.375 kg/hm2for three times: 0.105 kg/hm2for the first time, 0.120 kg/hm2for the second time, and 0.150 kg/hm2for the third time; in the fulling heading time, apply 0.030 kg/hm2of “920” for flower growing; the application should be in fine uniform sprays, and one more spray is needed each time for male parent to adjust the heading height. Apply artificial double bars pollination, 2～3 times a day. The first pollination is applied when massive flowering occurs to the female parent every day.

4.6. Remove impunities to guarantee seed quality

Under the premise of time and space isolation of seed production fields, we should remove impunities carefully, improve management measures related to impunity removal and purity conservation, establish or improve seed production archives, and control the seed purity from the source. Impurities should be carefully removed during the first heading stage of the female parent and before the harvesting. During the ripe and harvest period, we should pay close attention to the medium and long term weather forecast, reap and dry the seeds (85% ripeness) in sunny days to avoid preharvest sprouting during cloudy and rainy weather which would influence the purity and germination rate of seeds; in order to ensure the purity and clarity, the seeds should be thrashed, dried in the sun and preserved separately after reaping, and the process of stripping, transporting, drying and delivering also should be strictly controlled. Meanwhile, make sure the water content and germination rate meet the standards and prevent mix of different levels of seeds to guarantee the quality of seeds.