Breeding of a New Fine Quality Fragrant Hybrid Rice Combination Taoxiangyoulijin

PENG Jian , LIU Jun , JIA Lin , ZHANG Chao-fu , LIU Jia , HUA Wen-jie , ZHOU Xiao-ping , WU He-zhou *

1. Changde Research Institute of Agriculture and Forestry, Changde 415000, PRC;

2. Hunan Taohuayuan Agricultural Science and Technology Co. Ltd, Changde 415000, PRC

Abstract Taoxiangyoulijing is a new fine quality fragrant hybrid combination bred by matching the fine quality indica sterile line Taoxiang A with the fine quality restorer line R Lijing by Hunan Taohuayuan Agricultural Science and Technology Co.Ltd, Changsha Zhulixiang Agricultural Science and Technology Co. Ltd and Hunan Zhihe Seed Technology Co., Ltd. The combination is featured with wide adaptability, high yield, strong resistance to rice blast, and GB class 2 high quality. In October 2019, Taoxiangyoulijing was approved by the National Crop Variety Certification Committee and it reached the second class standard of quality score according to the Standard for Fine Quality Rice, Ministry of Agriculture, China.

Key words Fine quality fragrant hybrid rice; Taoxiangyoulijing; Breeding

1. Introduction

Rice is one of the most important food crops in China. The annual production of rice accounts for about 43% of China’s total grain production, hence it is of great significance to raise rice yield to ensure food supply. In comparing with other crops, rice has distinct advantages in yield and resistance, whereas rice quality is a problem that needs special concerns. The demand of people for high quality fragrant rice is increasing with the development of their living standards. Therefore, the breeding of high quality fragrant hybrid rice has been one of the objectives of numerous breeders while guaranteeing the production of hybrid rice. Every superior rice variety is a rice population cultivated by human beings through certain breeding means including selection, breeding and reproduction. One of the basic means is to cultivate sterile lines and restorer lines with fragrance and good agronomic characteristics and then breed a new high quality fragrant hybrid combination. Taoxiangyoulijing performed noticeably well in multiple regional tests and multi-site demonstration tests in the past few years. The variety is featured with high yield, high quality and strong resistance. The rice grain is crystal clear and tastes good with impressive fragrance when cooked. Both the quality and appearance of Taoxiangyoulijing have reached the first class high quality late rice standard. As a strong-flavor hybrid rice, it was approved by the Crop Variety Certification Committee of Ministry of Agriculture in June 2019 (Approval Number: Guoshendao 20196030).

2. Parental origin and breeding process

Taoxiangyoulijing is a new three-line hybrid rice combination by matching the sterile line “Taoxiang A” with the restorer line “R Lijing”.

2.1. Breeding process of female parent Taoxiang A

Taoxiang B was a hybrid of Yinfeng B and 35B lines selected in 2007. 35B was a maintainer line media developed by Hunan Taohuayuan Agricultural Science and Technology Co. Ltd. The strain was “Guangye B///IR58025B/Zhe 8010//Fengyuan B”. Yinfeng B and 35B lines were used to select the stable progenies Fand T98A to backcross generation 6 in 2011, and the combination became stable in 2014 which were then named as Taoxiang A and Taoxiang B.

2.2. Breeding process of restorer line “R Lijing”

“R Lijing” was a hybrid of X469 (Thailand scented rice/Huazhan, hybrid of Thailand scented rice with Huazhan in the summer of 2010 in Qingyuan, Guangdong) and conventional rice R1125 F(Yuejingsimiao No. 2/Molixinzhan). Resistance screening and agronomic characters were performed at Fgeneration. Individual plants with high resistance to rice blast and good agronomic characters were selected. Pedigree selection and rice blast resistance examination were then conducted. After initial stabilization of Fgeneration, the pedigree was selected and determined the advantages by using the method of matching and stabilizing simultaneously until the hybrid was stable in 2014 which was called after “R Lijing”. The initial heading period of “R Lijing” was similar to Huazhan, but the plant height was 10 cm higher than Huazhan. Meanwhile, “R Lijing” had strong tillering ability. The leaf color was light green. Each ear contained 120 grains on average. The grain length to width ratio was 3.8, and the 1 000-grain weight was about 19.1 g. The glume tip, stigma and leaf sheath were colorless. The comprehensive resistance to rice blast was class 3.5.

3. Main traits

3.1. Yield performance

The average yield per mu of Taoxiangyoulijing was 599.10 kg in the 2017 regional tests of the middle and late maturity indica group in upper reaches of the Yangtze River. The yield increased to 640.46 kg during the extended tests in 2018; the average yield per mu in the two-year regional tests was 619.78 kg, 3.0% higher than that of the control group “F You 498”; the average yield per mu was 589.80 kg during the production tests in 2018, 1.4% higher than that of the control group “F You 498”. During the 2017 regional tests of the middle and late maturity indica group in middle and lower reaches of the Yangtze River, the average yield per mu of Taoxiangyoulijing was 648.51 kg. In 2018, Taoxiangyoulijing made it through the extended tests and production tests of the 2018 green channel middle and lower reaches of the Yangtze River middle and late maturity indica group. The average yield per mu was 675.60 kg; the average yield per mu in the two-year regional tests was 662.10 kg, 2.74% higher than that of the control group “Fengliangyou 4”. In 2017, Taoxiangyoulijing attended the regional tests of the South China photosensitive late indica group, and the average yield per mu was 472.50 kg; in 2018, it attended the extended tests and the average yield per mu was 452.05 kg; the average yield per mu in the two-year regional tests was 462.30 kg, 3.02% higher than that of the control group “Boyou 998”; during the production tests in 2018, its average yield per mu was 471.40 kg, 4.20% higher than that of the control group “Boyou 998”.

3.2. Quality traits

Results of rice quality identification of the 2018 green channel middle and lower reaches of the Yangtze River middle and late maturity indica group: brown rice yield, 79.7%; milled rice rate, 68.8%; class 2 head yield, 63.8%; grain length, 7.2 mm; grain length-to-width ratio, 4.1; chalky grain percentage, 3%; chalkiness degree, 0.3%; amylose, 15.1%; gel consistency, 70 mm; alkali spreading value, level 6.8; transparency, level 1. The rice quality reached the national class 2 high quality standard. The seedlings, rough rice and cooked rice all had strong fragrant smell.

3.3. Resistance performance

Results of multi-site identification of the green channel middle and lower reaches of the Yangtze River middle and late maturity indica group in 2017 and 2018: rice blast composite index of Taoxiangyoulijing, 5.1; highest loss rate of neck blast, level 6; sheath blight resistance, level 7; ustilaginoidea virens resistance, level 4; bacterial blight, level 3.

3.4. Main agronomic traits

The combination was planted as middle rice in Wuling mountainous area. The whole growing period was about 130.2 d, similar to the control group. It was planted as late rice in South China area. The whole growing period was about 112.7 d, 2.5 d shorter than the control group Boyou 998. The plant height was 127.9 cm with good leaf shape and strong tillering ability. The ear length was 26.1 cm, the total number of grains per ear was 187.4, the setting rate was 83.7%, and the 1 000-grain weight was 23.4 g. The plant had strong growth potential, good tidiness and straight leaf orientation. The leaf color was green and the seed was yellow at the late period.

4. Cultivation techniques

4.1. Timely sowing and thin sowing for cultivating of strong seedings

Taoxiangyoulijing was an indica three-line hybrid rice. When planted as single-season middle rice in upper reaches of the Yangtze River, the optimal sowing time was from March 20to April 20, the seeding rate on seedling bed was 150~225 kg/hm, the field transplanting quantity was 15~22.5 kg/hm, the direct seeding quantity was 26.25~30 kg/hm, and the seedling age should not exceed 35 d; when planted as single-season middle rice in middle and lower reaches of the Yangtze River, the optimal sowing time was from May 20to June 15, the seeding rate was 225~300 kg/hm, the field transplanting quantity was 15~22.5 kg/hm, the direct seeding quantity was 26.25~30 kg/hm, and the seedling age should not exceed 30 d; when planted as double-season late rice in South China rice area, the optimal sowing time is from July 1to July 20, the seeding rate was 150~180 kg/hm, the field transplanting quantity was 15~22.5 kg/hm, the direct seeding quantity was 25.5~30 kg/hm, and the seedling age should not exceed 20 d.

4.2. Timely transplanting and rational close planting

When planted as single-season middle rice in upper, middle and lower reaches of the Yangtze River or as double-season late rice in South China rice area, the transplanting density should be 180 000~225 000 holes/hm, with each hole accommodating two seedlings to ensure that the density of basic seedlings can reach 360 000~450 000 holes/hm; field drying should be started when the maximum number of tillering seedlings reached 2.7~3 million holes/hm.

4.3. Rational application of fertilizer

Basic principle of fertilization: “apply sufficient base fertilizer, timely apply tillering fertilizer, topdress proper amount of booting fertilizer”and “control nitrogen, increase phosphorus, supplement potassium, and apply silicon, zinc, iron and other microelements.”The amount of base fertilizer depended on the specific fertility of the field. Apply 375 kg/hmof 45% compound fertilizer for fields with high fertility soil (N-P-K proportion: 15∶15∶15), apply 450 kg/hmof 45% compound fertilizer for fields with medium fertility soil (N-P-K proportion: 15∶15∶15), and apply 525 kg/hmof 45% compound fertilizer for fields with poor fertility soil (N-P-K proportion: 15∶15∶15). Do not apply nitrogen fertilizer as base fertilizer independently. After 5~7 d of seedling transplanting, apply green tillering fertilizer and 150~225 kg/hmof 40% compound fertilizer (N-P-K proportion: 20∶8∶12) with herbicides and paclobutrazol. The application amount of paclobutrazol was 2.25 kg/hm. Mix evenly and control the height. After rewatering the dried field, topdress 150 kg/hmof potassic fertilizer as the booting fertilizer. This variety was not resistant to nitrogen which could easily cause lodging of the plants. Therefore, it was forbidden to apply nitrogen at later period and do not break water off supply too early.

4.4. Scientific irrigation, especially for main ear and big ear

Basic principle of water management: “deep water irrigation to promote seedling rooting, tillering promotion in shallow water, enough seedling field drying, flowering at inch of water, alternate dry and wet grouting.”After transplanting, the plants need to resume green in deep water and then tiller in shallow water with topdressing of tillering fertilizer; when the number of seedlings reaches 2.7~3 million holes/hm, dry the field until cracks show up and the soil surface turns white. When the color of plant leaves start to fade and the small tillers are effectively controlled, start the irrigation as appropriate. In the later period, apply alternate wetting and drying water management, control the number of tillers to increase the grains, ensure a good ventilation and low humidity, and reduce the occurrence of diseases and pests. Drain and dry the field one week before harvest to get a good yield.

4.5. Timely prevention and control of diseases and insects

Use trichloroisocyanuric acid or prochloraz for seed soaking, apply higher effective and lower toxic pesticide for chemical control, prevent chilo suppressalis walker during tillering stage, prevent banded sclerotial blight and cnaphalocrocis medinalis during booting stage, and prevent chilo suppressalis walker, rice planthopper, rice blast and ustilaginoidea virens during the breaking and heading stage. After grain-filling, pay attention to the cnaphalocrocis medinalis and rice planthopper. For specific disease and pest control methods, refer to the guidance of local plant protection departments.

5. Seed production techniques

5.1. Select a suitable production base

The seed production base should have good physical geographical space isolation, broad terrain, fertile soil, good drainage and irrigation conditions, and convenient transportation, without local quarantine diseases and pests. The spatial isolation should be at least 100 m, and the temporal isolation should be at least 20 d from the initial heading stage of adjacent rice varieties.

5.2. Arrange a reasonable parent sowing time

Select the best heading and flowering stage for female parent according to local meteorological data, and try to avoid continuous high temperature period and cold dew wind weather at the late period. Arrange a reasonable sowing time for the parent based on its growth periods and characteristics to ensure their flowering stages were consistent. In Changde area, the summer male parent was sown in early June, the difference of leaf age was 4 leaves and sowing interval was 5 d. The heading stage was around the middle of August. The initial heading of female parent was suggested to be 1~2 d earlier than that of the male parent.

5.3. Determine the number of parents seedlings and the ration of male and female parents

Breed multi-tiller strong seedings, strengthen field management, and determine the number of highyield parents seedlings: the sowing quantities for male parent and female parent were 7.5 and 30 kg/hm, respectively. During transplanting period, plant sufficient basic seedlings for female parent in a 16.5 cm ×16.5 cm area. The ration of male and female parents was 2∶12~2∶14. Apply sufficient base fertilizer in the rice seedling bed and the paddy field with topdressing as a supplement. Apply topdressing early, conduct wetting irrigation, dry the field in time, strengthen water and fertilizer management of the male parent, and prevent plant diseases and pests and rice kernel smut of the female parent.

5.4. Spray “920” in time to adjust parents' flowering stage

Spray a proper amount of “920” timely according to the weather, flowering and seedling growth to ensure a good head sprouting of the female parent. It was recommended that the male parent was 10~20 cm higher than the female parent, and the total amount of “920” was 0.39 kg/hmunder normal circumstances. Apply the first round of “920” when the heading index of the female parent is 5%~10%, apply the second round when the heading index reaches 30%, and apply the third round when the heading index reaches 60%~70%; after each round, apply “920” (0.03~0.06 kg/hm) on the male parent.

5.5. Ensure the purity of seedlings and the harvest time

Control the quality of parent seeds from the original. The purity of female parent should be at least 99.5%, and the purity of male parent should be at least 99.9%; the parent seeds should be single-soaked and single-sown, and the seedlings should be separately pulled and transplanted; in both the seedling stage and the field stage, remove the impurity plants timely and ensure no impurity plants exist in the field. Harvest the seeds on sunny days for the convenience of drying when the maturity of seeds reaches 85%; thresh, dry and store the seeds separately to ensure the purity and clarity of the seeds; carefully control the process of threshing, carrying, drying and delivering to make sure that the moisture and germination rate of the seeds can reach the standard, prevent mixture with impurity seeds and ensure their quality