FAO-SUPPORTED ACTIVITIES

ACTIVITÉS DE LA FAO

ACTIVIDADES DE LA FAO

Hybrid rice: recent progress and challenges¹

D.V. Tran

Executive Secretary, International Rice Commission, Crop and Grassland Service, FAO Plant Production and Protection Division

INTRODUCTION

Hybrid rice technology emerged just 25 years ago and is relatively young when compared with that of hybrid maize. Since the 1980s many countries have become increasingly aware of the importance of hybrid rice to improve food security. China's successful programme is an example for other countries to replicate. Furthermore, international and regional efforts from FAO, the International Rice Research Institute (IRRI), the United Nations Development Programme (UNDP) and the Asian Development Bank (ADB) are providing strong and consistent support in improving national capacities in hybrid rice breeding, F1 seed production and research facilities in several countries.

In the last decade, progress in hybrid rice development and F1 seed production has been impressive in some countries, especially India and Viet Nam. However, promoting wide adoption of hybrid rice technologies and higher yields of the commercial hybrid combinations, and gaining adequate political support for national programmes, remain of the utmost importance. Many lessons learned from the implementation of hybrid rice programmes have not been well communicated to other countries. Therefore, an extensive interaction among breeders, seed production specialists, extension workers, policy-makers and senior government officials, at national and regional levels, is required.

PROGRESS AT THE NATIONAL PROGRAMME LEVEL

National capacity building

Several national hybrid rice programmes have gained substantial strength in both research and development. The number of rice scientists and seed specialists working on hybrid rice has continuously grown and their skills have been improved through effective, well-conducted national and international training programmes. More contract growers and farmers have accumulated experience in producing hybrid seed and growing hybrid rice under the guidance of extension workers. Several national hybrid rice programmes have been established with well-defined objectives and activities with support from their governments. An example is the Philippine hybrid rice programme, which is strongly supported by the government and now ranks third after the Indian and Vietnamese hybrid rice programmes.

The national hybrid rice programmes in Bangladesh, Indonesia and Sri Lanka have gradually improved through the efforts of their skilled human resources and research facilities and with support from their governments, FAO, IRRI and China. Recently, Egypt has given high priority to its hybrid rice programme with support from FAO and the United States Agency for International Development, IRRI and the University of California at Davis, United States.

However, it is well known that hybrid rice and hybrid seed production require enormous amounts of qualified human resources; hence a need for comprehensive training programmes to strengthen the progress.

Institutional level

In Viet Nam, the Hybrid Rice Research Centre (HRRC), which was established in 1994 under the supervision of the Vietnam Agricultural Sciences Institute (VASI), has relatively strong technical and staffing capacity to handle research and to supply nucleus, breeder and foundation seed of hybrid and parental lines to the national, provincial and district hybrid rice programmes. In 2000, its staff comprised 22 specialists (2 Ph.D., 3 M.Sc. and 17 B.Sc.); 4 contract specialists (3 M.Sc. and 1 B.Sc.) and 10 contract workers. The Centre has 5 ha of land for experimental purposes at its headquarters and 4.5 ha in the Ba-Vi area with good isolation conditions suited to cytoplasmic male sterile (CMS) line multiplication in the spring season. It also has a few F1 seed farms (10 ha) contracted with farmers at Hai Phong and an extension centre in Thai Binh Province in northern Viet Nam. This centre was strongly supported by project FAO/TCP/VIE/6614 (T), especially in staff training and in upgrading hybrid rice research facilities.

In India, the national hybrid rice programme has been strongly supported by the government with the active participation of the public and, especially, private seed sectors. In fact, the Indian Council of Agricultural Research (ICAR) identified hybrid rice technology as a top priority area and in December 1989 initiated a network project on hybrid rice in collaboration with IRRI. This project has been further strengthened with the assistance of UNDP and FAO since September 1991 until the present (DRR, 1996). The first phase of the project was completed in 1996 and its second three-year phase started in 2000. Its research network comprises two lead centres, Kapurthala in Punjab State for northern India and Mandya in Karnataka State for southern India, plus ten other research institutes and centres.

Strong extension support, improved grain quality for diversified local demands and reduced F1 seed production costs will give another boost to the Indian hybrid rice programme.

Recently, the Philippine Rice Research Institute (PhilRice) Hybrid Rice Centre, based in San Mateo, Isabel, has become totally devoted to hybrid rice research and development programmes.

Adoption of hybrid rice

In Viet Nam, farmers grew hybrid rice on 11 000 ha in 1992, 102 000 ha in 1996 and 340 000 ha in 2000, reaching nearly 70 percent of its goal. The country intends to grow 1 million ha of hybrid rice in northern and central Viet Nam, where arable lands are very limited (Nguyen, 1997). This rapid increase in annual hybrid rice area meant that local F1 seed multiplication was insufficient to meet farmers' demands. At present, Viet Nam is only able to produce enough F1 seed to meet 10 percent of farmer demands, although it plans to reach 60 percent by 2005. The country therefore has to import a large quantity of hybrid seed and parental lines from southern provinces of China. It is believed that the government's willingness and appropriate organization of a rational seed multiplication programme will soon achieve its goal of self-sufficiency.

In India, during the dry season 1995/96, 1 300 tonnes of F1 seed were produced, of which 91 percent were produced by the public sector. During 1997, it was estimated that about 3 000 tonnes of hybrid seed were produced by the public and private sectors for growing about 125 000 ha (Ahmed, 1997). In 2000, hybrid rice was grown on between 150 000 and 200 000 ha, or about 10 percent of the targeted 2 million ha (FAO, 2000a).

INTERNATIONAL AND REGIONAL SUPPORT

FAO's hybrid rice programme

In compliance with the International Rice Commission's recommendations, FAO has given its highest priority to promoting the wide adoption of hybrid rice outside China. In the past ten years, it has provided support to various national rice programmes worldwide. The relevant activities are listed in Table 1.

The major objectives of these FAO-supported projects are:

1. to assist interested member countries in strengthening national capacity in hybrid rice breeding, F1 seed multiplication and production;
2. to improve the facilities for supporting the hybrid rice programme; and
3. to assist in formulating a medium-term hybrid rice development programme.

IRRI/ADB-funded project

The project "Development and Use of Hybrid Rice in Asia", funded by the ADB and coordinated by IRRI, was initiated in March 1998, under the framework of the International Task Force on Hybrid Rice (INTAFOHR). The project's objective is to expedite the development and use of hybrid rice in Asia. Its activities have been implemented by six countries, namely, Bangladesh, India, Indonesia, the Philippines, Sri Lanka and Viet Nam in the first phase, and the collaborating agencies, such as IRRI, FAO and the Asia and Pacific Seed Association (APSA). As a consequence, the project has made a major contribution to the dissemination of hybrid rice technology in the region. Phase II has been approved by the ADB for three years.

Major technological progress

F1 seed production
The seed yield of hybrid rice has progressively increased in China, India and Viet Nam (Table 2). In China, F1 seed yield increased from 410 kg/ha in 1976 to 669 kg/ha in 1981, 2 252 kg/ha in 1991 and 2 500 kg/ha in 1995 (Yuan, 1998). At the same time, Viet Nam produced 320 kg/ha of F1 seed in 1992, 1 751 in 1996 and 2 200 kg/ha in 1998 (MARD, 1999). In India, during the 1995/96 dry season, F1 seed yields varied from 1 072 to 1 925 kg/ha (DRR, 1996). Because other countries lack experience in hybrid rice seed production, they have lower F1 seed yields - around 1 000 kg/ha. High F1 seed yields are important to reduce the costs of seed production.

CMS lines

Several hundred CMS lines and hybrid combinations were developed by IRRI and national research institutes for different agro-ecologies, acceptable grain quality (including basmati), early maturity, resistance to major insect pests and diseases and tolerance to adverse soils and water stresses. It is believed that the number of CMS lines and hybrid combinations will increase exponentially in the near future because there are now more experienced hybrid rice specialists. However, low and inconsistent seed yields in hybrid production fields are still observed.

Two-line hybrids

Research on two-line hybrids has advanced considerably in China, IRRI and other national agricultural research centres. This technology would further boost wider adoption of hybrid rice in view of its yield advantage of 5-10 percent over the commercially cultivated three-line hybrid varieties. In the two-line system, there is no need for maintainer lines. The field area ratio between CMS line multiplication, hybrid seed production and commercial production of two-line hybrids is therefore much higher than that of three-line hybrid varieties (1-100-15 000 for two-line varieties compared with 1-50-6 000 for three-line hybrids). Consequently, this technology would lower the cost of F1 seed production (Yuan, 1996). However, more time is required to perfect the two-line hybrid rice technology before introducing it to farmers outside China.

MAJOR AREAS OF CONCERN FOR FUTURE HYBRID RICE PROGRAMMES

Genetic impurity

The area of most concern for the future hybrid rice programme is the long-term maintenance of the genetic purity of F1 seed and parental lines (A, B and R lines). Several reports have recently indicated that the purity of these lines is deteriorating in certain countries, thus affecting the heterotic characteristics and the yield advantage of rice hybrids. According to Mao (1988) and Yin (1997), each percentage of genetic impurity in F1 seed could reduce paddy yield by approximately 100 kg/ha. Genetic impurity of parental lines of hybrid rice has recently been reported in India (FAO, 2000a), Indonesia (FAO, 2001a, 2001b) and the Philippines (FAO, 2000b). Dr C.X. Mao, IRRI, in his message dated 11 March 2001, addressed to the FAO Regional Office for Asia and the Pacific, reported that: "Most of the parental lines of hybrid rice in the tropical countries such as Indonesia, Sri Lanka and the Philippines are facing the serious problem of genetic purity, which may kill the hybrid rice programme in these countries in the near future." Likewise, Dr Viraktamath, Rice Breeder at the Directorate of Rice Research in Hyderabad, during his FAO mission to Indonesia from February to April 2001, reported that: "The major problem at present is the purity of parental lines and the hybrids. Unless this problem is tackled on warfooting, prospects for hybrid rice are rather bleak."

These alarming statements should be taken seriously by national and international hybrid rice programmes because the yield advantage of hybrid rice will continue to decrease drastically if no appropriate or timely action is taken to maintain the genetic purity of parental lines and F1 seeds.

The purification of parental lines is fundamental to obtaining good hybrid rice seed, and it is the most important step in determining the success or failure of a national hybrid rice programme. Mao (1988) suggested the following activities to ensure the quality of F1 hybrid seed:

• purification of parental lines;
• strict isolation;
• thorough roguing;
• field sanitation and quarantine;
• stricit adherence to procedures to avoid mechanical admixture;
• regular purity tests (field, laboratory, nursery test if suspected and isozyme test).

Aggressive training programmes and the dissemination of information on techniques for purification and maintenance of parental lines should be urgently conducted by international and national agricultural research centres and international agencies to ensure good heterosis and to avoid the latent negative trend in the application of hybrid rice technology.

OTHER ISSUES RELATED TO LARGE-SCALE HYBRID RICE PRODUCTION

Heterosis

The promotion of large-scale hybrid rice production will be facilitated by the introduction of highly heterotic combinations of parental lines of hybrid rice. Considerable progress has been achieved in areas of hybrid development other than heterosis. The present intervarietal hybrids, within indica cultivars, can only outyield the commercial rice varieties by 15-20 percent. The scarcity of maintainer lines is a major problem in current hybrid rice breeding. The most promising area is the deployment of intersubspecific hybrids, especially indica-japonica crosses. China, India and IRRI have exerted strong efforts in this area. Ikehashi (FAO, 2000a), in his mission to India, suggested that the heterosis of rice hybrids could be improved by the following means:

• use of wide compatibility genes (S-5n);
• development of the genetic basis of maintainers by utilizing javanica or japonica-like materials;
• expansion of the basis for restorers by utilizing partial restorers, as hybrid sterility genes can be recombined towards accumulation of neutral alleles (i.e. wide compatibility genes);
• intensification of test-crossing for a higher-level heterosis;
• selection of traits for high out-crossing rate in composite crosses (e.g. using O. longistaminata).

High and consistent productivity

In the field, the yield of rice hybrids and F1 seeds has been inconsistent over time and space owing to variable technology and crop management. Insect and disease resistance should be incorporated in parental lines. A complete package of hybrid technology should be developed and tested for specific locations. Suitable locations for hybrid rice seed and hybrid rice production should be identified for each country.

Lower costs of F1 seed production

As the cost of hybrid rice seeds has recently risen to five or six times higher than normal, increasing hybrid seed yield and/or supporting seed costs would encourage farmers to adopt hybrid rice on a large scale. Chinese rice specialists have spent 20 years improving their skills in F1 seed production, resulting in an increase of F1 seed yield from 0.3 tonnes/ha to 2.25 tonnes/ha.

This has enabled them to cut the cost of seed production from US$5.96/kg to US$0.79 (Table 3) (Mao, Virmani and Kumar, 1998). Other countries could only obtain between 1 and 1.5 tonnes/ha or less and their seed costs vary between US$1.5/kg and US$2.5/kg. These seed costs would be reduced by half if the technical gap between China and other countries were to be significantly narrowed and if the present seed yield could be doubled.

Grain quality

Grain quality is a major factor limiting the adoption of hybrid rice. Although the grain quality of hybrid rice has been improving in China, India and Viet Nam, greater efforts are still needed to address this aspect. Economic conditions are improving in the region, and diverse grain quality is demanded by consumers in different regions even within a country, especially in India. A lower price of hybrid rice will add greater leverage to the yield advantage of hybrids.

Large-scale seed production

A large quantity of hybrid seed should be produced to support large-scale production. The scarcity of skilled human resources and the complicated nature of the technologies have, however, hampered such efforts in some countries. For these reasons, the national capacity in the seed industry, the linkage of research, seed production and extension and policy support to the national hybrid rice programme are essential requirements to ensure large-scale seed production.

Government commitment

A lesson learned from the green revolution is that the process of developing and disseminating technologies requires a conducive institutional and policy environment. The goodwill of governments is essential to initiate and develop hybrid rice programmes and to promote effective coordination and intervention to solve problems that may arise. Several success stories have been reported in Bangladesh, Egypt, Indonesia and Viet Nam.

Thus, strong commitment and support from senior government officers, policy-makers, senior research management and scientists are essential to promote national hybrid rice research and development programmes as well as the wide adoption by farmers of this new technology. Specifically, it is suggested that the following main policy areas be focused on (Costales, 1999):

Technology development:

• Government policy for the development of hybrid rice technology within the food security framework.
• Commitment to allocate significant public research and development (R&D) resources to the development of hybrid rice technology.
• Commitment to focus R&D efforts and resources to meet specifications and preferences of ultimate users of hybrid rice technology.
• Commitment to seek international funding to support physical infrastructural requirements for national hybrid rice programmes.

Seed production, processing and distribution

• Governmetn policy to liberalize the seed industry in order to create a competitive seed market environment.
• Government policy to share, at the early stages of this technology, the risk and costs of seed production with the private sector.
• Adoption of a seed quality-control policy of "truthful labelling" rather than mandatory registration, seed testing and seed certification.
• Government policy to set hybrid seed prices in accordance with competitive market prices, coupled with government subsidy on hybrid seed for the purpose of introducing hybrid rice seed technology to farmers.
• A clearly defined government policy on the temporary role of the public sector in seed production, processing and distribution.

LESSONS LEARNED FROM EXPERIENCE

It is worth reiterating the main lessons, as discussed in the Workshop on "Progress in the Development and Use of Hybrid Rice outside China", held on 28-30 May 1997 in Hanoi, Viet Nam, as follows:

1. Strong government commitment and support to the hybrid rice programme, in terms of human resources, resources, coordination and monitoring. A functional national steering committee is crucial to coordinate research, seed production, extension and other related issues.
2. The preparation of a national medium-term hybrid rice programme with clear, specific and achievable goals, objectives, strategies and plan of action.
3. The establishment of appropriate research and seed multiplication on a full-time basis at each research network centre.
4. Active participation of seed production agencies, the private sector, non-governmental organizations and international agencies.
5. Active participation of the provisional, district and local extension agencies to promote wide adoption by farmers.
6. The development of an effective network of research, F1 seed production systems, extension services and other agencies involved, with clearly defined roles and responsibilities, under the coordination of the Steering Committee (Figure 1).
7. The free exchange of germplasm and technologies related to hybrid rice.
8. An intensive training programme for hybrid breeding and F1 seed production for the staff concerned and farmers. A large number of seed production personnel in the public and private sectors and progressive farmers should be trained in various aspects of hybrid seed production.
9. The need to establish pilot regions/provinces/areas where concerted efforts could be made for the wide adoption of hybrid rice.

FIGURE 1

CONCLUSION

Hybrid rice technology has provided farmers with high yields, saved land for agricultural diversification and created rural employment opportunities. Although this technology is still new, many rice-producing countries have expressed their interest in applying this technology to improve their food security. Government commitment and support are fundamental for initiating hybrid rice programmes and promoting rapid large-scale adoption. At the same time, technology should be further improved for higher heterotic advantage in the hybrid combination, better grain quality that is acceptable to markets and reduced cost of seed production. The second generation of hybrid rice, or super hybrid rice, which has been developed by China, together with the two-line hybrid system, should give another thrust to farmers' adoption of hybrid rice technology in the near future.

REFERENCES

Ahmed, M.I. 1997. Development and use of hybrid rice technology: Lessons learnt from the Indian experience. In Proceedings of the Workshop on Progress in the Development and Use of Hybrid Rice Outside China. Hanoi, 28-30 May 1997. 178 pp. Hanoi, Ministry of Agriculture and Rural Development.

Costales, A.C. 1999. Policy and institutional constraints to the development and use of hybrid rice technology in member countries of the IRRI/ADB Hybrid Rice Project. Paper presented at the Regional Meeting on Seed Policy and Programmes for Asia and the Pacific, Bangkok, 2-6 May 1999.

DRR. 1996. Final report 1991-96. ICAR/UNDP/FAO Project on Development and Use of Hybrid Rice Technology (IND/91/008). Hyderabad, India, Directorate of Rice Research. 87 pp.

FAO. 2000a. Consultancy mission report on Project UNDP/FAO/IND/98/140 "Development and Large-Scale Adoption of Hybrid Rice Technology", by H. Ikehashi. Mission undertaken from 28 August to 16 September 2000. Rome. 19 pp.

FAO. 2000b. Mission report on hybrid seed production of technical cooperation project, by X.G. Pan. Mission undertaken from 15 September to 28 October 2000. Rome. 27 pp.

FAO. 2001a. Mission report on strengthening the development and use of hybrid rice in Indonesia, by B.C. Viraktamath. Mission undertaken from 24 February to 24 April 2001. Rome. 42 pp.

FAO. 2001b. Mission report on strengthening the development and use of hybrid rice in Indonesia (TCP/INS/8921), by K. Krishnaiah. Mission undertaken from 24 February to 10 March 2001. Rome. 40 pp.

Mao, C.X. 1988. Hybrid rice seed production in China. In Seed Health. pp. 177-282. Manila, International Rice Research Institute.

Mao, C.X., Virmani, S.S. & Kumar, I. 1998. Technological innovations to lower the costs of hybrid rice seed production. In S.S. Virmani, E.A. Siddiq & K. Muralidharan, eds. Advances in hybrid rice technology. pp. 111-128. Manila, International Rice Research Institute.

MARD. 1999. Report on agricultural production in 1999, dated 2 November 1999. Hanoi, Ministry of Agriculture and Rural Development. 15 pp.

Nguyen, C.T. 1997. Opening address delivered at the Workshop on "Progress in the Development and Use of Hybrid Rice Outside China", Hanoi, 28-30 May 1997. pp. 10-11. Hanoi, Ministry of Agriculture and Rural Development.

Yin, H.Q. 1997. Strategies and procedures used for nucleus, breeders and foundation seed production. In Proceedings of the Workshop on Progress in the Development and Use of Hybrid Rice Outside China. Hanoi, 28-30 May 1997. pp. 52-58. Hanoi, Ministry of Agriculture and Rural Development.

Yuan, L.P. 1996. Hybrid rice in China. In Hybrid rice technology. pp. 51-54. Hyderabad, India, Directorate of Rice Research.

Yuan, L.P. 1998. Hybrid rice development and use: innovative approach and challenges. IRC Newsletter, 47: 7-14.

Riz hybride: progrès récents et défis

Au cours de la dernière décennie, les progrès réalisés dans le développement du riz hybride et la production de semences F1 ont été impressionnants dans certains pays, surtout en Inde et au Viet Nam. Au Viet Nam, le Centre de recherche sur le riz hybride a été créé en 1994. Les agriculteurs ont cultivé le riz hybride sur 11 000 ha en 1992 et sur 340 000 ha en l'an 2000, soit près de 70 pour cent de l'objectif fixé. Le pays entend cultiver du riz hybride sur un million d'hectares dans le nord et le centre du Viet Nam où les superficies arables sont restreintes. En Inde, le programme national pour le riz hybride a été fortement soutenu par le Gouvernement avec une participation active du secteur semencier public, mais surtout privé. En l'an 2000, le riz hybride a été cultivé sur 150 000-200 000 ha, soit environ 10 pour cent de l'objectif prévu, fixé à 2 millions d'hectares.

Les rendements en semences du riz hybride a progressivement augmenté en Chine, en Inde et au Viet Nam. En Chine, le rendement des semences F1 a augmenté, passant de 669 kg/ha en 1981 à 2 500 kg/ha en 1995. Au cours de la même période, le Viet Nam a produit 320 kg/ha de semences F1 en 1992 et 2 200 kg/ha en 1998 (Ministère de l'agriculture et du développement rural, 1999). En Inde, au cours de la saison sèche 1995-96, les rendements des semences F1 ont oscillé de 1 072 à 1 925 kg/ha. Les autres pays, qui manquent d'expérience pour la production de semences de riz hybride, ont des rendements inférieurs: autour de 1 000 kg/ha. Plusieurs centaines de lignées de stérilité mâle cytoplasmique et de combinaisons d'hybrides ont été mises au point par l'IRRI et les instituts de recherche nationaux pour diverses zones agroécologiques, et pour obtenir une qualité acceptable des grains (y compris le basmati), une maturité précoce et une résistance aux principaux ravageurs. La recherche sur les hybrides à lignée double a progressé considérablement en Chine, à l'IRRI et dans d'autres Services nationaux de recherche agricole (SNRA). Toutefois, il faut encore perfectionner la technologie du riz hybride à lignée double, et donc attendre encore, avant de procéder à l'introduction auprès des agriculteurs, hors de Chine.

La question la plus intéressante, dans le cadre du programme futur sur le riz hybride concerne le maintien à long terme de la pureté génétique des semences F1 et des lignées parentales A, B et R. Plusieurs rapports ont récemment relevé que la pureté de ces lignées se détériore dans certains pays, affectant donc les caractéristiques hétérotiques et les aptitudes productives des riz hybrides. Actuellement, les spécialistes du riz sont confrontés aux défis suivants: augmentation de l'hétérosis et du rendement des semences F1, maintien à un niveau élevé et uniformité de la productivité des hybrides, et réduction des les coûts de production des semences de F1.

Arroz híbrido: Progresos y desafíos recientes

Durante el último decenio, los progresos en el desarrollo del arroz híbrido y la producción de semillas F1 han sido impresionantes en algunos países, especialmente en la India y Viet Nam. En Viet Nam, se estableció en 1994 el Centro de Investigaciones sobre Arroz Híbrido. Se producía arroz híbrido en 11 000 ha en 1992 y en 340 000 ha en el año 2000, habiéndose alcanzado casi el 70% del objetivo. El país trata de cultivar un millón de hectáreas de arroz híbrido en el Norte y Centro, donde las tierras de labranza son muy limitadas. En la India, el gobierno ha apoyado decididamente el programa nacional de arroz híbrido con la participación activa del público y especialmente del sector privado de las semillas. En el 2000, se cultivó arroz híbrido en unas 150 000-200 000 ha, es decir, alrededor del 10 por ciento del total de 2 millones de hectáreas fijado como objetivo.

El rendimiento de las semillas de arroz híbrido ha aumentado progresivamente en China, India y Viet Nam. En China, el rendimiento de las semillas F1 aumentó de 669 Kg/ha en 1981 a 2 500 en 1995. Al mismo tiempo, en Viet Nam se pasó de un rendimiento de 320 Kg/ha de las semillas F1 en 1992 a 2 200 Kg/ha en 1998 (Ministerio de agricultura y de desarrollo rural, 1999). En la India, durante la estación seca de 1995-96, los rendimientos de las semillas F1 variaron de 1 072 a 1 925 Kg/ha. Como otros países carecen de experiencia en la producción de las semillas de arroz híbrido, han obtenido menores rendimientos con las semillas F1: alrededor de 1 000 Kg/ha. El IRRI e institutos nacionales de investigación desarrollaron varios centenares de líneas de esterilidad masulina citoplásmica y combinaciones híbridas para distintas agroecologías, una calidad del grano aceptable (incluido el Basmati), madurez temprana y resistencia a las principales plagas. La investigación sobre híbridos en dos líneas ha avanzado mucho en China, en el IRRI y en otros Servicios nacionales de investigación agrícola. Sin embargo, se necesita más tiempo para perfeccionar la tecnología del arroz híbrido de dos líneas antes de ofrecérsela a los agricultores de fuera de la China.

No obstante, la esfera de mayor preocupación para el futuro programa de arroz híbrido es el mantenimiento duradero de la pureza genética de la semilla F1 y las líneas parentales: A, B y R. Varios informes recientes indican que la pureza de estas líneas está empeorando en unos pocos países, lo que afecta a las características heteróticas y a las ventajas de rendimiento de los híbridos del arroz. Actualmente, los principales desafíos para los científicos arroceros consisten en el modo de incrementar la heterosis y el rendimiento de la semilla F1, mantener una productividad elevada y constante de los híbridos y reducir los costos de la producción de semillas F1.

¹ Excerpts from the paper presented at the Workshop on Policy Support for the Rapid Adoption of Hybrid Rice on Large-scale Production in Asia, held in Hanoi, Viet Nam, 22-23 May 2001.