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Recent Advances in Crop Improvement in China

Ming Lu, Zhiyong Xin, Shihua Cheng, Zhonghu He, Xinhai Li, Tianfu Han, Shuxun Yu and Hanzhong Wang

The Crop Science Society of China Email duj@mail.caas.net.cn

Abstract

China has made some outstanding achievements in crop improvement. Rice breeding is highlighted by the discovery of the “wild abortive rice” and the development of hybrid rice and super rice. Wheat breeding for yield potential, resistance to stripe rust, powdery mildew and scab, and high gluten quality is practised. Hybrid maize breeding is characterized by the development of elite inbred lines, construction of improved populations and classification of heterotic groups. Cotton cultivars with good resistance to Fusarium and Verticillium wilts, high yielding and good fibre quality, and Bt transgenic cottons are released. Soybean breeding focuses on yield, high oil content and resistance to SMV and SCN. Rape breeding emphasizes on high yield potential, low erucic acid and low glucosinolates and resistance to stem rot, and hybrid rapes are released.

Media summary

Recent advances in breeding of rice, wheat, maize, cotton, soybean and rape in China are summarized.

Key Words

Crop breeding, rice, wheat, maize, cotton, soybean, rape

Introduction

The Chinese crop breeding system has been established since mid-1950s. 90% of the crop acreage is sown with newly improved varieties which have a yield increase around 7~10% over the old ones. Plant introduction, reselection, hybridization, wide cross, anther culture and mutation breeding have been employed, hybridization as well as utilization of heterosis being the predominate one.

Rice

Rice is the biggest crop in China. About 33 million hectares are grown annually with an average yield of about 6 tons/ha, and the total output is approximately 200 million tons. More than 400 varieties/ combinations were grown annually in recent years.

“Three-line” hybrid rice

L.P.Yuan and others found the “wild abortive rice” (O.rufipogon) in 1970. A complete set of “three-lines” was first accomplished in 1973 and the first hybrid indica rice was released in 1975. Hybrid rice is characterized by its broad adaptation, good tolerance to biotic stresses, strong tillering ability, and high yield potential. In 2000 hybrid rice covered 15.5 million hectares which was about half of the total rice acreage, and its output occupied about 60% of the total production. More than 200 hybrid combinations are grown each year. Among them Shanyou 63 is the most popular one with a highest annual acreage of 6 million hectares, and Shanyou 64 and Weiyou 64 come next, covering 1.33 million ha each year separately.

“Two-line” hybrid rice

Studies on the “two-line method” of hybrid rice development began in 1980 as M.S.Shi observed for the first time that ordinary rice plants were fertile under long-day and high temperature, and became male-sterile at short-day and low temperature. So the same line could be used as both the male-sterile line and the maintainer line when sown at different times or locations. A genetic male-sterile japonica rice Nongken 58S was then developed. The “two-line” hybrid rice combinations such as Liangyoupei 9, Xiangliangyou 68 and others were released for commercial production and their total acreage was nearly 1 million ha in 2000.

Super rice

Super rice refers to those new varieties/combinations having a very high yield potential around 12 tons/ha and about the average level of disease resistance and quality as the ordinary cultivars. More than 10 super rice varieties/combinations were released and the accumulated acreage was about 1 million hectares in 2002. Among them Yeyou 9308, Shanyouming 86 and II You 162 were developed from the “three-line method”, Liangyoupei 9 was bred from the “two-line method”, and Shennong 265, a japonica rice variety in Northeast China with erect spike, was developed from the conventional method.

Wheat

Wheat is the second biggest crop in China. Recently about 24 million hectares are grown yearly with an average yield of about 3.8 tons/ha. The total output is about 90 million tons. About 300 varieties are grown annually.

Breeding for high yield potential and good quality

Breeding for high yield in wheat emphasized reducing plant height and increasing kernel weight in the past 40 years. Rht 1, Rht 1S, Rht 2, and Rht 8 are the dwarfing genes commonly used in wheat breeding. Most of the cultivars now used in the main growing areas are about 80cm in plant height with stiff straw and the nation-wide thousand kernel weight has been raised from 30g to 40g in 50 years. In the past 10 years Yumai 18, Yumai 21, Lumai 14, Mianyang26, and Jinan 19 were among the top leading varieties. Breeding wheat for good processing quality was not put on the agenda until mid-1980’s. Some good quality stocks, such as Zhongzuo 8131 and Linfen 5046 with CIMMYT pedigrees were used as parents and hybrid progenies carrying HMW-GSs 1 or 2*, 5+10, and 17+18 were screened in breeding programs. Some good quality varieties, for example, Jinan 17, Zhongyou 9507, Longmai 26, Yumai 34, Liaochun 10, Zhengmai 9023 and others, have been released for bread baking and noodle making in recent years. The total acreage planted to good quality varieties was about 3 million hectares in 2003.

Breeding for disease resistance

Development of resistant varieties has basically controlled the epidemic of stripe rust in the main winter wheat region of the Yellow and the Huai River Valleys, although the disease still causes severe damage in some years in the high altitude areas of Southwest and Northwest China. Head scab is the most severe disease in lower and middle reaches of the Yangtze River Valley. Sumai 3 is the best source of resistance to scab. Among the many varieties with moderate resistance released for production, Yangmai 5, Yangmai 158, E’en 1, and Huamai 8 were grown extensively in large areas. Powdery mildew is getting serious since more fertilizer and irrigation practices are applied to wheat fields. Several Pm genes such as Pm2+6, Pm4 and Pm21, were pyramided recently for controlling the disease.

Biotechnological breeding

Some important resistance genes to powdery mildew, scab, stripe rust and barley yellow dwarf virus (BYDV) were mapped with molecular markers and some PCR markers were developed for screening resistance to powdery mildew and BYDV. Thus the marker-assisted selection for disease resistance has primarily been established. Several genes such as Nib8, GCE and GNA, relevant to the resistance to virus, fungus or aphid, have been successfully transferred into wheat.

Maize

Maize is the third biggest crop in China. About 23 million hectares are grown yearly with an average yield of about 5.2 tons/ha. The total output of maize is about 120 million tons. 90% of maize acreage is sown with hybrid corn and 88% of hybrid corn is from single crosses.

Germplasm improvement and development

By the end of 2000, more than 3000 elite inbred lines had been developed, of which Huangzao 4, Dan 340, Zi 330, Ye 478, Shen 5003, S37, 48-2, E28, Qi 319, P 138, Zong 31 and X 178, characterized with good resistance to several diseases, tolerance to drought and high level of combining ability, played a very important role in hybrid breeding programs. Fifteen populations including CA-Syn3, Jilin-SynF, Liaoning-Syn, Shannxi-Syn1, Henan-Syn2, Guanxi-Syn2, Hubei-Syn, WBM, etc. had been composed and improved. Four QPM (CA-pop13, CA-pop 14, CD, R) and 5 high oil populations (BHOC14, AIHO C8, etc.) had also been synthesized. Some QPM inbreds (CA375, Qi205, etc) with more than 0.4% lysine content of whole kernel and high oil lines (By804, 815, 830, etc.) with more than 11% had been developed.

Hybrid maize breeding

The genetic diversity of over 400 inbred lines has been studied with molecular markers, pedigree analyses and quantitative genetics approaches, and 5 to 6 heterotic sub-groups (Sipingtou, Luda Red Cob, Lancaster, Reid, PA, PB) and 2 heterotic patterns (Sipingtou/Luda Red Cob Lancaster, Sipingtou/Luda Red CobPA) were defined. For the QPMs a heterotic pattern Qi 205CA 375 has been established. By the end of 2000, more than 500 hybrids had been released, of which Zhongdan 2, Danyu 6, Danyu 13, Nongda 108, Yedan 2, Yedan 13, Zhengdan 14, Shendan 7, Ludan 50, Yuyu 22, Zhengdan 958, Jidan 180, Yandan 14, Sidan 19, Zhongdan 9409 QPM, High-oil 115, etc. played a very important role in maize production.

Biotechnological breeding

The techniques of molecular mapping and marker-assisted selection have just been established for maize breeding. Some important genes, such as resistance to sugarcane mosaic virus, maize dwarf mosaic virus, southern rust, corn borer and drought, S-CMS, etc. have been mapped with molecular markers. With the adoption of marker-assisted selection approach, some novel breeding materials with specifically improved traits have been produced.

Cotton

Cotton is the most important fiber crop in China. About 4.2 million hectares are grown annually with an average yield (lint cotton) of about 1.2 tons/ha. The total output of cotton is about 5 million tons.

Breeding conventional cotton for high yield, good quality and wide adaptation

On the basis of identifying cotton germplasm resources for resistance to Fusarium and Verticillium wilts, efforts have been made in the development of resistant cultivars with high yielding ability and good fiber quality. The following cultivars such as Zhongmiansuo 12, Jimian 14, Yumian 4, Yanmian 48, Sumian 1 and others, were then released for commercial production in different regions. Short-seasoned cultivars such as Zhongmiansuo 16, Lumian 10, E’mian 13, and Xinluzao 2, etc, were recommended for areas of double cropping or intercropping with wheat. In 1990’s, nearly all the cultivars with low fibre quality were substituted by the good ones. Recently the main cultivars raised in the Yellow River Valley were Zhongmiansuo 41, SGK 321, Zhongmiansuo 37, Lumian 16, etc.; in the Yangtze River Valley were Zhongmiansuo 29, Zhongmiansuo 38, Nankang 3, Xiangzamian 2, Xiangzamian 3, etc.; and in the northwest inlands were Zhongmiansuo 35, Zhongmiansuo 36, etc. Some long staple cottons were also released in the northwest, Xinhai 16, Xinhai 17 and Xinhai 18 being the most outstanding ones. In northwest inland cotton growing region the lint yield usually maintains at a level over 1.8 tons/ha, and the highest lint yield of 3.46 tons/ha appeared in a field of Zhongmiansuo 19 in 1998. In southern parts of Xinjiang Autonomous Region in 2001, lint yield of Zhongmiansuo 35 in a farmer’s field of 3.3 hectares reached to a level of 3.45 tons/ha.

Development of transgenic cotton

Breeding transgenic cotton with Bt or Bt + CpTi gene began in 1991. A series of Bt transgenic insect (bollworm) resistant cottons were developed, namely, Zhongmiansuo 29, Guokangmian 1, Jimian 26, Jiza 66 and Lumianyan15, etc. Up to now, 22 Bt transgenic cultivars are released for production. Putting the introduced insect resistant cultivars from USA together, the total acreage of Bt transgenic cotton reached 2.8 million hectares in 2003, which occupied more than half the total cotton acreage in China.

Soybean

Soybean, mainly grown in the northeast provinces but scattered all over the country, is the most important oil as well as protein crop in China. About 8 to 9 million hectares were grown annually with an average yield of about 1.7 to 1.9 tons/ha in recent years. The total output of soybean in 2002 was 16.5 million tons.

Breeding for high yield and better quality

From 1949 to 2003, a total about 1000 improved soybean varieties had successively been released in the country, of which 651 were released before the end of 1995. Compared with landraces, the improved varieties were superior in earliness, lodging resistance, yield potential, disease resistance, and quality. The highest yield record occurred in Xinjiang Autonomous Region where cultivar Xindadou 1 yielded 5.96 tons per hectare in 2001. Since late 1990’s the improvement of oil content has been emphasized. Some high-oil (21.5% or above) varieties were then developed and rapidly released for commercial production. In the national soybean variety trials, the oil content of 35 varieties from the northern spring-sowing region averaged 20.4% in 2001 and 20.9% in 2002, respectively.

Breeding for disease and stress resistance

Soybean mosaic virus (SMV) and soybean cyst nematode (SCN, Heterodera glycines) are two major diseases in the country, while frog-eye spot (Cercospora sojina) and soybean rust (Phakospora pachyrhizi) are important in Northeast China and South China, respectively. Some SMV-resistant varieties such as Bayuehuang, Kefeng 1, Jindou 23 and others were bred. Several materials resistant to SCN were screened and some resistant varieties such as Kangxian 1 and Qihuang 25 were released. Scientists in Nanjing Agricultural University found that resistance of soybean to soybean stemfly (Melanagromyza sojae) was controlled by a pair of dominant genes without cytoplasmic effect. The insect resistant variety Jilin 3 developed in Jilin province reduced considerably the damage caused by pod borer (Legumininora glycinivorella) and thereby improved the commercial quality. Some drought resistant varieties such as Jindou 21 etc. were developed and released in Shanxi province and the Loess Plateau.

Biochemical Breeding

Scientists in CAAS have engaged in breeding soybean varieties with null or reduced anti-nutritional factors. Cultivars with deletion of lipoxidases, trypsin inhibitor, or both and with high isoflavones were developed separately or jointly. For example, Zhonghuang 28 is a variety with deletion of lipoxidase (lx2lx2) and low beany flavor, Zhongdou 28 is free from trypsin inhibitor (titi) and Zhongdou 27 contains high content of isoflavones. They are released for production in North China.

Rape

Rape is one of the important oil crops in China. In recent years rape acreage increased quickly. In 2000, 7.4 million hectares were grown with an average yield of about 1.5 tons/ha. The total output was about 11 million tons which occupied about 30% of the world’s total output. In 1972 T.D. Fu and others of Huazhong Agricultural University found firstly the valuable polima cytoplasmic male-sterile material in rape (Brassica rapa L.). In 1980 D.R. Li found another source of CMS known as “Shan 2A” and then the first hybrid rape Qinyou 2 was released in 1983. Its acreage in 1992 was about 1.33 million hectares, occupying about 1/4 of the national winter rape acreage, with an average yield of 2.4 tons/ha. Meanwhile Zhongyou 821, a conventional cultivar with high yield and good adaptation developed by the Institute of Oil Crops, CAAS in 1987, was recommended for production with an acreage of about 1.8 million hectares, occupying 1/3 of the national total from late 1980’s to early 1990’s.

Zhongshuang 4, the first “double-low” (low erucic acid and low glucosinolates) conventional rape variety, was released for commercial growing by CAAS in 1993. Its average yield in a series of variety trials was 2.1 tons/ha and the seedstock contained 0.06% erucic acid, 12.2 μmol/g glucosinolates, and 42% oil. The accumulated acreage of Zhongshuang 4 reached 2 million hectares. During the period of 1991-1995, Huaza3, the first “three-line” hybrid rape with low erucic acid and low glucosinolates, and 12 other “double-low” rape varieties/hybrids were released. After that, more than 50 high yield, high quality and “double-low” rape varieties/hybrids, such as Zhongyouza 2, Zhongshuang 9, Huaza 4, Youyan 7, Xiangyou 15, Chuanyou 21, Zheshuang 72 etc. were successfully released for production. Among them, Zhongyouza 2 and Zhongshuang 9 are the most outstanding ones. Zhongyouza 2, a hybrid rape, contains 0.9% erucic acid, 20.7 μmol/g glucosinolates, and 41.5% oil. It performs high yield potential and wide adaptation with an accumulated acreage of 1.3 million hectares. Zhongshuang 9 contains 0.23% erucic acid, 22.7 μmol/g glucosinolates, and 42.0% oil; it is resistant to stem rot (Sclerotinia sclerotiorum) and high in yield potential. The estimated annual acreage of “double-low” rape varieties/hybrids is about 5.1 million hectares, which occupies about 70% of rape acreage in the whole country.

References

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Xin ZY, He ZH, Ma YZ and Zhuang QS (1999). Crop breeding and biotechnology in China. Journal of New Seeds Vol.1:67~80.

Liu JL(2002) Hybrid maize breeding. In:Maize Breeding, Beijing:China Agriculture Press 114~200 (in Chinese).

Zhang SH, Peng ZB, Li XH and Yuan LX. (2000). Heterotic patterns and germplasm enhancement in maize breeding of China. In: Proceedings of International Conference on Engineering and Technological Sciences, Beijing: New Wold Press 418~419.

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