Abstract

Media summary

Key words

Rice breeding, high yield, good quality

Introduction

Since 1981, new rice varieties with erect panicles, such as Liaojing 5, Shennong 91 et al., have been released in Liaoning Province of China. The experimental and productive results indicated that the grain yield of rice varieties with erect panicles not only exceeded that of the cultivars with curved panicles but also rivaled that of the hybrid rice (Gao et al., 1988). Guided by this, the process for breeding new high-yielding and good quality rice varieties began in 1987.

Methods

Crossing and selection

Shennong 91 was a high-yielding rice variety with erect panicles. It was a derivative of Liaojing 5 and had the genetic material of indica. S22 was a new line with curved panicles and good quality, but its yield potential was normal. In 1987, Shennong 91, S22 and other cultivars were planted. Used as a key parent, Shennong 91 was crossed with S22. In 1988, the F₁ progeny of Shennong 91/S22 were crossed with the qualitative variety Toyonishiki. Since that time, only a few crosses between different varieties, or subspecies, have been made each year. In the F₁ progeny, unvalued crosses were eliminated. In the F₂ progeny, some desirable plants with short culms and resistance to diseases and cold were selected from the population. Then 3-10 seeds per plant with short culms and resistance to diseases and cold were taken from the progeny to form a mixed population, while other plants were discarded. In this way, multiple crosses were made and the selection was conducted.

The rice strain test

In F₃ to F₆, strain tests combined with examination in the early generation were conducted. Some new lines were involved and the check varieties were Akihikari, Liaojing 5 or other varieties. In general, four replicates were arranged for the strain test and the examination. At the same time, new lines and the mixed population selected from the crosses were planted.

The regional test and productivity test

In 1993 and 1994, Shennong 8801 was involved in regional tests in Liaoning Province. The check variety in the regional test was Akihikari. Four replicates were set up in the tests. In 1995 and 1996, Shennong 8801 underwent productivity tests. The check variety was Akihikari. The acreage planted for Shennong 8801, or for Akihikari, was 667 m² per test site. Afterwards, other new lines took part in the test too.

Results

Objectives of the rice breeding

Toyonishiki and Akihikari were semi-dwarf rice varieties introduced from Japan. They were planted on large scale in Liaoning Province for many years because of their high yield and quality. Toyonishiki and Akihikari were used as the check variety in the medium-late and in the medium maturing rice strain tests, respectively. Grain yields of them were about 7-8 t per ha. For new lines or combinations to pass the regional tests and become varieties, their grain yields should be over 8 t per ha, i.e. 5% above that of the check varieties. Grain quality properties are very important in the future. The grain quality properties of new lines, such as the brown rice rate, milled rice rate, grain shape, chalkiness, gel consistency, amylose content etc., should reach the second-grade of the national standard for high quality rice in China. Meanwhile, the new rice varieties should be resistant to lodging, cold and diseases (Wang et al., 2000).

Strategy for increasing the yield potential of rice

In Liaoning province, 1980 was a turning point in rice breeding because the hybrid rice Liaoyou 1 passed the variety examination. During 1971-1979 and 1980-1990, the average yields of rice varieties released were 6.58 t and 7.50 t per ha, the average heights of the varieties were 97.5 cm and 96.6 cm, the average numbers of panicles per square meter of the varieties were 465 and 447, and the average numbers of ripened grains per panicle of the varieties were 66.3 and 88.2, respectively. The yield potential and actual yields of the varieties were increasing. Although the number of panicles per unit area decreased nevertheless the number of ripened grain per panicle increased significantly as time went on. Only the average plant height changed very little. The semi-dwarf varieties can produce higher grain yields because they have far greater numbers of panicles than the traditional rice cultivars they replaced. Hybrids and varieties with erect and semi-erect panicles can produce higher yields because they have either more or bigger panicles (about 100 ripened grains per panicle), or both (Shao et al., 1995). In general, the grain quality of variety with semi-erect panicles is appreciative (Wang et al., 1992, 2002). So the key is to select semi-dwarf plants with semi-erect and erect panicles and to increase ripened grains per panicle.

Effectiveness of selection for new rice varieties

Rice breeding for high yield and good quality is complicated work. It is necessary to optimize the traits of the plants, to identify selection results and to make strategic decisions with the aid of computer (Wang et al., 2000). The breeding process is presented in Fig.1. With this method, some superior lines have been selected.

Fig.1 The breeding process

In the regional tests, the average yields of Shennong 8801, Shennong 8718, Shennong 315, Shendao 2, Shendao 3, Shendao 4, Shendao 5, Shendao 6 and Shennong 7 were 5.9%, 5.0%, 2.8%, 7.1%, 4.2%, 8.4%, 4.3%, 3.1% and 0.8% higher than those of the CK varieties (Table 1). In the productivity tests, the average grain yields of the new varieties were 8.95, 9.18, 8.13, 9.63, 8.82, 8.83, 8.46, 9.46 and 8.14 t per ha, which were 12.8%, 15.3%, 2.6%, 12.4%, 2.9%, 7.3%, 8.1%, 6.3% and 0.8% higher than those of CK varieties, respectively. The plant height and the number of panicles per unit area of the new varieties were similar to those of the CK varieties. But the number of ripened grains per panicle, the percentage of effective tillers, the percentage of ripened grains and the weight of 1000 grains of the new varieties were higher than those of the CK varieties. Qualities of seven new varieties reached the second-grade of the national standard for high quality rice in China and another came to the third-grade (Table 2). Shennong 8718 and Shennong 7 had passed the variety examination and were named accordingly by the National Crop Variety Examination Committee and others passed the examination in Liaoning.

Table 1 Comparison of grain yields between new varieties and CK

Table 2 Quality of the new varieties

Conclusion

In order to create new variations, crossing between indica and japonica, between javanica and japonica, or between different types of japonica rice is important (Yang S J et al., 1987). To improve the quality, the progeny should be crossed multiply with a qualitative japonica variety. The varieties with erect panicles were used as key parents. In view of the partial sterility and unordinary segregation of the progenies of crossing between indica and japonica, mass selection was used as the main method and purity selection as the supplementary. The process of purity selection was combined with the examination in early generation to increase selection accuracy. Superior lines were determined with the computer program and selected for the strain performance test and the regional test. Desirable strains were chosen for productivity test. To sum up, the strategies for achieving high yield are to create variation by crossing between indica and japonica, to combine mass selection with pedigree selection, to seek for ideal plant type and to determine optimum characteristics (Wang et al., 2002). The practice proves this breeding process to be effective.

To increase yield potential and actual yield, plant type should be improved (Donald, 1968; IRRI, 1996). The upper leaves are erect, thick and still vigorous in the late growth period. The panicles are semi-erect or erect. The plants are tolerant of cold and drought, and resistant to diseases and lodging. This plant type is efficient to light utilization (Wang et al., 1989, 1997). But the plant type is associated with grain quality. After optimizing the characteristics of the plants, the traits of ideal plants were initially identified. The traits should include grain quality (Wang, 1992). In Liaoning Province of China, breeding for rice plant with semi-erect panicles could increase the yield and improve the quality easily.

Acknowledgements

The National 863 project (2001AA241015) and the Liaoning Science Foundation project (99101002) of China

References

Donald C.M., 1968. The breeding for crop ideotypes. Euphytica. 17, 385-403.

Gao P.W., Wang B.L. et al., 1988. Studies on physiology and ecology for rice with high yield. Liaoning Agricultural Science. 1, 7-11.

International Rice research Institute, 1996. Rice research in Asia. IRRI. 1-70.

Shao G.J. et al., 1995. Summarization and discussion on rice breeding research and development in Liaoning Province. Liaoning Agrirultural Science. 6, 28-33.

Wang B.L. et al., 1989. Incident light distribution over the population with high yield in rice. Liaoning Agricultural Science. 6, 27-30.

Wang B.L., 1992. The Trail and method of rice breeding for super high yield. The Proceedings of Rice Research. Chinese Science and Technological Press. 97-104.

Wang B. L. et al., 1997. Studies on genetic activities of semi-dwarfism and erect-panicle in rice. Journal of Shenyang Agricultural University. 28(2), 83-87.

Wang B.L., 2000. Studies on rice breeding for high yield, good quality and multiple resistance. Prospects of Rice Genetics and Breeding for the 21^st Century. China Agricultural Scientech Press. 191-195.

Wang B.L. et al., 2002. Analysis of rice breeding in Liaoning Province in 1949-2000. Liaoning Agricultural Science. 5, 5-8.

Yang S.J., et al 1987. Research on rice breeding through crossing indica and japonica and its evolution in the past thirty six years. Journal of Shenyang Agricultural University. 18(3), 3-9.