Yangdao 6: Breeding and Utilization of a New Medium Indica Rice Variety with High Quality, High Yield and Disease Resistance

Yangdao 6 is a new medium indica variety bred by the Institute of Agricultural Sciences of the Lixiahe Region of Jiangsu, using Yangdao 4 as the female parent, crossed with "Yan 3021", with the F1 seeds subjected to 60CO-gamma ray irradiation mutagenesis, and then developed through continuous directional selection. This variety combines high quality, high yield, disease resistance and wide adaptability, and is an ideal seed source for developing high-quality rice; it has already been demonstrated and promoted on a large scale in Jiangsu, Anhui, Hubei, Shanghai and other provinces and municipalities. Yangdao 6 is also a high-quality restorer line for two-line hybrid rice and three-line Honglian-type hybrid rice, and the two-line hybrid rice and three-line Honglian-type hybrid rice formulated with it, such as "Liangyou Peijiu" and "Yueyou 938", have also been widely applied in production. In April 1997, August 2000 and January 2001, it passed the approval of the crop variety approval committees of Jiangsu, Anhui and Hubei provinces respectively.

I. Breeding Process

1. Parental crossing. Using the principle of complementary traits and aggregation of superior genes, the parents were selected. One parent, "Yangdao 4", has the advantages of slender grain shape, relatively low chalkiness rate, gelatinization temperature and gel consistency reaching the ministerial first-class standard, upright plant shape, clean and elegant growth, and resistance to bacterial blight, rice blast, sheath blight and rice planthopper; its disadvantage is a relatively high amylose content. The second parent, "Yan 302", has the advantages of good appearance quality, low amylose content, resistance to bacterial blight and rice blast, large panicles and heavy grains; but its leaves are wide and thin, and it is prone to premature senescence in the later stage. In 1986 the two parents were sexually crossed, and in 1987 the F1 generation was obtained.

2. Radiation mutagenesis. Using the principle of expanding the range of variation through 60CO-gamma ray irradiation mutagenesis, dry seeds of the F1 generation were irradiated, and the M1 generation was obtained in 1988.

3. Resistance screening. Using the principle of segregation of resistance among individuals in early generations, screening for pest and disease resistance was strengthened. The M2-M5 generations were subjected to inoculation identification for bacterial blight; for rice blast, inoculation identification was carried out with the main physiological races of Jiangsu Province, ZA49, ZE3 and ZG1, and at the same time natural induction identification was carried out in rice blast-prone areas such as Hainan, Hubei and Anhui; resistance to rice planthopper was identified by multi-point induction; and resistance to sheath blight was identified by a combination of artificial inoculation identification and field induction identification.

4. Quality identification. The selection of quality followed the principle of gradual deepening: the M2-M3 generations mainly observed and screened appearance quality traits such as grain shape, chalkiness and transparency; the M4-M5 generations were identified line by line for indoor appearance quality and processing quality; the MO7 generation was subjected to palatability tasting; and finally the selected and fixed M8 generation lines were subjected to physicochemical quality analysis.

5. Plant type selection. Adopting the viewpoint of coordinated symmetry, the upper and lower parts of the plant were examined as a whole, so that traits appeared symmetrical from the individual plant perspective and the distribution appeared coordinated from the population perspective. In low generations, emphasis was placed on comprehensive traits, and selection for economic traits was appropriately relaxed; in high generations, attention was paid to the unified examination of the stem system, leaf system and panicle system, with strict selection especially for late-stage ripening appearance, and consideration was given to the coordination performance of the population. Selection for the root system was mainly carried out through observation and identification screening of ratooning ability after cutting and bleeding sap volume.

6. Shuttle breeding. For the selection of adaptability, the principle of shuttle breeding in different ecological regions was adopted, with alternate planting and screening between the local area and Hainan. From 2000 plants in the M1 generation, 300 plants were selected; superior plants were continuously selected in the M2-M4 generations; in the M5 generation, 36 excellent individual plants were obtained; in the M6 generation, 36 lines were established in Yangzhou; in the M7 generation, 10 lines; in the M8 generation, 3 lines; and the fixed line 92-108 was decisively selected, fixed and numbered 93-11 in 1993.

7. Regional trials. In 1994 it participated in the Jiangsu Provincial Joint Identification Trial; in 1995 it participated in the Jiangsu Provincial Regional Trial; in 1996, while participating in the Jiangsu Provincial Regional Trial, it also exceptionally participated in the Jiangsu Provincial Production Trial; in April 1997 it passed the Jiangsu Provincial Variety Approval and was named; in 1999 it participated in the Hubei and Henan Provincial Regional Trials and the Anhui Provincial Production Trial respectively; in August 2000 it passed the Anhui Provincial Variety Approval and was named; and in January 2001 it passed the Hubei Provincial Variety Approval and was named.

II. Characteristics and Traits

1. Main characteristics. Yangdao 6 is short and sturdy at the seedling stage, with good luxuriance and medium tillering ability; plant height is 115 cm, the culm is thick and strong, there are 5 elongated internodes above ground, the total number of leaves is 17-18, the panicle length is 24 cm, the panicle layer is neat, and the ripening appearance is quite good. Generally, the number of productive panicles is about 2.25 million/hm2, the total number of grains per panicle is more than 165, the seed-setting rate is more than 90%, and the 1000-grain weight is about 319. The whole growth period is about 145 days, and it is a late-maturing medium indica type.

2. Main traits

(1) Excellent quality. According to the 1996 determination by the Rice and Rice Products Quality Monitoring Center of the Ministry of Agriculture, of the 12 quality measurement indicators of Yangdao 6, 10 reached the ministerial first-class rice standard: brown rice rate 80.9%, milled rice rate 74.7%, grain length 7.0 mm, grain length-to-width ratio 3, chalkiness 5%, transparency grade 2, amylose content 17.6%, alkali spreading value grade 7, gel consistency 94 mm, protein content 11.3%; the cooked rice is loose and soft, does not harden after cooling, and has good palatability.

(2) Strong resistance. According to the 1996 identification by the Institute of Plant Protection of the Jiangsu Academy of Agricultural Sciences, the disease grades against the representative bacterial blight strains KS-6-6, Zhe 173, GD1358 and JS49-6 were all grade 3. It showed resistance to the rice blast physiological races of Jiangsu Province, ZA49, ZE3 and ZGI, with disease grade R. According to the sheath blight resistance identification trial by the College of Agriculture of Yangzhou University, the resistance of Yangdao 6 to the RH9 sheath blight strain was grade 2.2. Yangdao 6 has resistance to bakanae disease and basal rot; no disease occurred in many years of demonstration and trial planting, late-stage leaf diseases were mild, cloud-shaped disease and leaf tip blight rarely occurred, and three green leaves were still retained at maturity. Yangdao 6 has field resistance to rice planthopper. In 1997, when rice planthopper broke out severely in Jiangsu and Anhui, the hybrid rice Shanyou 63 and Xiedai 63 lodged and died in patches, while only Yangdao 6 had green stems and yellow grains, standing upright without lodging. Yangdao 6 is highly resistant to lodging. According to the 1996 determination by this institute, the breaking resistance of the second internode from the base at the yellow-ripe stage of Yangdao 6 was 1.1158 kg/cm, while that of the control Shanyou 63 was 0.722 kg/cm, and its breaking strength was 54.54% higher than that of Shanyou 63. In the 1995-1996 Jiangsu Provincial Regional Trial and Jiangsu Provincial Production Trial, no lodging occurred at any trial site, and large-scale planting also showed high lodging resistance.

(3) High yield. Yangdao 6 showed outstanding yield performance in the variety comparison trial of this institute, the Jiangsu Provincial Regional Trial, the Production Trial, and the regional trials of Anhui, Henan and Hubei provinces. In 1993-1994, in the variety comparison trial and high-yield cultivation trial of this institute, the yield per 667 m2 was 652 kg and 698.1 kg respectively, increasing by 6.4% and 16.72% respectively compared with the control Shanyou 63. In the 1995-1996 Jiangsu Provincial Variety Regional Trial, the average yield was 614.1 kg/667 m2, 7.21% higher than the control Yangfuxian 2 (extremely significant), ranking first among the participating varieties (lines). In 1996 it exceptionally participated in the Jiangsu Provincial Production Trial ahead of schedule, with an average yield of 571.93 kg/667 m2, 7.47% higher than the control Yangfuxian 2, ranking first. In the 1997-1998 Anhui Provincial Medium Indica Regional Trial, it increased yield by 3.0% and 8.16% respectively compared with the control Yangdao 4, reaching an extremely significant level. In the 1998 rice improved variety regional trial in the southern rice region of Henan Province, it increased yield by 4.86% compared with the control Yuxian 3, reaching a significant level. In the 1999 Hubei Provincial Hybrid Medium Rice (Introduced Variety) Regional Trial, it increased yield by 2.64% compared with the control Shanyou 63 (CK).