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The Asian Maize Biotechnology Network: Achievements and Opportunities

Maria Luz C. George1, David Hoisington2 and Kevin Pixley2

1CIMMYT-Philippines, c/o IRRI, DAPO Box 7777, MetroManila, Philippines www.cimmyt.org
2
CIMMYT, Apartado Postal 6-641, Mexico, D.F. 06600 Mexico www.cimmyt.org

Abstract

The Asian Maize Biotechnology Network (AMBIONET), a collaborative research, training, and information network, aims to help national programs in China, India, Indonesia, Philippines, Thailand and Vietnam apply modern science and technologies for maize improvement. Network activities are geared towards building capacity through workshops and exchange visits, supporting collaborative research through the provision of funds and scientific/technical support, and promoting the sharing of research results, technologies and materials.

Collaborative research under AMBIONET is focused on the use molecular markers to more efficiently address maize production problems of national and regional importance. Characterization of a collection of inbred lines, including tropical and subtropical lines from the Asian national programs, showed that breeding activity in the region has not caused a decline in the overall amount of diversity. About half of the alleles observed in the Asian lines had frequencies of 0.10 or less, and only 2 % had frequencies > 0.80, indicating the presence of many alleles, and thus a high level of diversity. Quantitative trait loci with significant effects on resistance to the five downy mildew diseases in the region, including a strong and stable QTL on chromosome 6, were identified. The next steps that build on the existing momentum generated by the network are also discussed.

Media Summary

The value of a collective research effort for maize improvement is demonstrated by the Asian Maize Biotechnology Network, a network that fosters the integration of biotechnology in plant breeding.

Key Words

Network, molecular markers, maize, breeding,

Introduction

Maize is the third most important cereal crop in Asia, where it is mainly grown in marginal production environments, often in rainfed uplands characterized by shallow and infertile soils. With the exception of China, most maize farmers in Asia are resource-poor smallholders, and their yields are generally low. Maize demand in the region is projected to rise from 138 million metric tons in 1993 to 241 million metric tons in 2020. Meeting this rising demand is a pressing challenge.

Research to enhance productivity in the face of complex crop production problems requires a multidisciplinary approach that combines knowledge and methodologies from breeders, agronomists, biotechnologists, and other scientists. The substantial human and capital resources required underscore the need for networking and working effectively in collaborative relationships. This need is especially vital in many developing countries, where national programs seeking to incorporate biotechnology in agricultural research, cannot afford to build the necessary capacity by themselves, and thus remain unable to exploit the rapid advances being made in this field. In Asia there are several highly developed national programs, as well as others with varying levels of capacities and resources. Networking scientists from these different national programs to partner in addressing complex, common agricultural problems, creates synergies and economic efficiency at the regional level. agriculture

This paper provides an overview of the Asian Maize Biotechnology Network (AMBIONET) as an example of a regional network for crop improvement, including research results that demonstrate the value of a coordinated, collective effort. Further, we discuss the next steps and future directions to build on the existing momentum generated by the network.

The Asian Maize Biotechnology Network- A Case Study

The AMBIONET was launched in 1998 as a collaborative research, training, and information network whose goal is to help build an enabling environment for NARS in China, India, Indonesia, Philippines, Thailand and Vietnam to use modern science and biotechnology tools to address maize production problems. Co-financed by the Asian Development Bank (ADB), NARS of member countries and CIMMYT, the network emphasizes the application of molecular markers in the development of improved maize varieties. The network builds upon previous investments in the region by the Rockefeller Foundation’s International Rice Biotechnology Program, and the International Rice Research Institute’s Asian Rice Biotechnology Network. Activities are geared towards building capacity through workshops and exchange visits, supporting collaborative research through the provision of funds and scientific/technical support, and promoting the sharing of research results, technologies and materials.

Collaborative Research under AMBIONET

Collaborative research under AMBIONET is focused on the application of molecular marker technology to problems of national and regional importance, such as the molecular characterization of locally important maize lines, mapping of quantitative trait loci (QTLs) for resistance to major diseases – downy mildews, Sugar Cane Mosaic Virus and Banded Leaf and Sheath Blight –, tolerance to abiotic stresses (drought and low nitrogen conditions), and the integration of marker-assisted selection (MAS) in the national breeding programs. AMBIONET teams engage in country-specific research at the same time that they work collaboratively with others in network-wide research involving common research areas. Two examples of such collaboration are given below.

Fingerprinting and Genetic Diversity of Maize Germplasm

DNA fingerprinting and genetic diversity analyses facilitate the efficient management of germplasm collections (Warburton and Hoisington, 2001). Accurate assessment of genetic diversity is helpful in maize breeding for maintaining/broadening the genetic base of elite germplasm; for assigning lines to heterotic groups; and for selecting appropriate parental lines for hybrid combinations. As a predictive tool, genetic distance between inbred lines can be valuable in crops like maize, where substantial resources are devoted to field-testing lines in various cross combinations to identify those with superior combining ability.

A network-wide effort was made to fingerprint and characterize the genetic diversity of maize germplasm in Asia using simple sequence repeats (SSRs) or microsatellites. Molecular profiling of 102 inbred lines, including tropical and subtropical lines from the national programs in China, India, Indonesia, Philippines, Thailand, Vietnam and CIMMYT (Asian Regional Maize Program and Maize Program), as well as temperate lines from the US and Europe, revealed that breeding activity in Asia has not caused a decline in the overall amount of diversity in the region. About half of the alleles observed in the Asian lines had frequencies of 0.10 or less, and only 2 % had frequencies > 0.80, indicating the presence of many alleles, and thus a high level of diversity. Cluster analysis produced a dendrogram that distinguished lines from the US, Germany, and China comprising three distinct clusters of temperate maize, and those from India, Indonesia, Philippines, Thailand, Vietnam and CIMMYT comprising seven indistinct clusters of tropical and subtropical maize (George et al., 2004a). Studies in China (Yuan et al. 2001), India (Pushpavalli et al. 2001), and Indonesia, Philippines, Thailand and Vietnam (unpublished data) provided valuable information about genetic relationships of breeding materials in the individual countries. A high level of SSR heterozygosity in some lines, possibly due to inadequate cycles of inbreeding, uncontrolled pollination, contamination of seed stocks, mutations at diverse SSR loci, or amplification of similar sequences in different genomic regions, was observed in these studies.

To obtain a picture of the relationships between local lines and those in the regional and international breeding programs, a coordinated effort was made to develop and use a standardized methodology for genetic diversity studies to yield reproducible results across laboratories. This allowed multiple datasets to be compared and combined into a common database, and the wide-scale analysis of maize diversity (George et al., 2004b). It is now possible for breeders to make more informed choices in making crosses between their local lines and CIMMYT materials. An example is presented in the dendrogram in Figure 1, showing the relationship of Vietnam testers with lines carrying traits for downy mildew resistance (DMR) and high quality protein (QPM).

Figure 1. UPGMA dendrogram of maize inbred lines consisting of testers and lines with high protein content and downy mildew resistance, based on 34 SSR markers. Data from AMBIONET-Vietnam (tester and QPM lines), CIMMYT Applied Biotechnology Center (DMR lines) and the AMBIONET Service Lab were combined and analyzed to produce this dendrogram. Two US Corn Belt lines (Mo17 and B37) were included for comparison

Mapping of QTLs for resistance against downy mildews

A major emphasis in maize breeding in Asia has been the improvement for resistance to the downy mildews, a serious disease that causes significant yield losses. A network-wide effort to map resistance genes for the different downy mildews, with CIMMYT contributing seeds and genotype data, and the AMBIONET teams contributing the phenotype data, resulted in the identification of resistance QTLs.

The QTL mapping study was based on a multi-environment evaluation of a set of recombinant inbred lines (RILs) derived from Ki3 x CML139 cross. The RIL families were evaluated at Mandya in southern India against sorghum downy mildew (P. sorghi); at Udaipur in western India against Rajasthan downy mildew (P. heteropogoni); in Indonesia against Java downy mildew (P. maydis); in Thailand against sorghum downy mildew (P. zeae); and in the Philippines against Philippine downy mildew (P. philippinensis). Composite interval mapping was carried out for joint analysis of data across environments to map QTL and estimate their genetic effects (George et al., 2003).

QTLs with significant effects on resistance to the five downy mildew diseases were identified. Three QTL, two on chromosome 2 and one on chromosome 7, significantly influenced resistance only to specific pathogen populations, while the other two, one each on chromosome 6 and 10, were nonspecific. The most important genomic region, having a strong and stable expression against all five downy mildews, was found on chromosome 6. Interestingly, this QTL is located in a region holding clusters of resistance genes in maize (George et al., 2003).

AMBIONET: Next Steps

Prior to AMBIONET, national programs in Asia had made isolated efforts to integrate biotechnology in maize improvement. Collaboration in AMBIONET has resulted in the systematic and region-wide application of molecular markers and their integration into the maize breeding programs. Significant factors that contributed to this enabling environment are a growing culture of sharing and interactions fostered in the network, capacity building activities, and regional scientific and technical support provided through the network. .

The synergies created by AMBIONET must now be harnessed and expanded to reach the resource-poor farmers in Asia. The next steps should involve two broad components: First, AMBIONET partners must further apply research findings to date, while beginning to address additional priority research areas,such as tolerance to abiotic stresses (drought, acid soils) and improvement of the nutritional quality of maize (QPM). Secondly, new partnerships must be built to add an essential dimension of technology dissemination, involving farmer participatory technology evaluation, and links to seed/technology producers and retailers. CIMMYT will be proud to be a partner in developing and implementing this strategy: To create and use synergies among regional partners to strengthen and empower individual partners to make greater impact on the livelihoods of farmers in their respective countries.

Acknowledgements

The Asian Maize Biotechnology Network is supported by funds from the Asian Development Bank, NARS partners, and CIMMYT. The research was done by the AMBIONET teams led by S. Zhang, X. Li, G. Pan and W. Li (China); B.M. Prasanna and NN Singh (India); F. Kasim, Sutrisno and M. Dahlan (Indonesia), A. Salazar and E. Sales (Philippines); P. Grudloyma and K. Sripongpangkul (Thailand) and P.X. Hao and V.D. Quang (Vietnam) in collaboration with the AMBIONET Service lab (E Regalado) and CIMMYT Scientists (M. Warburton, D. Jeffers, and J M. Ribaut).

References

George, MLC, W. Li, C. Moju, M. Dahlan, M. Pabendon, E Regalado, M Warburton, XC Xia, and D Hoisington. 2004. Molecular characterization of Asian maize inbred lines by multiple laboratories. Theor Appl Genet (in press)

George, MLC, E Regalado, M Warburton, S. Vasal, and D Hoisington. 2004. Genetic Diversity of Maize Lines in relation to downy mildew. Euphytica 135: 145-155.

George, MLC, BM Prasanna, RS Rathore, TAS Setty, F Kasim, M Azrai, S Vasal, O Balla, D. Hautea, A. Canama, E. Regalado, M. Vargas, M. Khairallah, D. Jeffers, and D. Hoisington. 2003. Identification of QTL conferring resistance to downy mildews of maize in Asia. Theor Appl Genet 107: 544-551.

Pushpavalli S N C V L, Sudan C, Singh N N & Prasanna B M, 2001. Differentiation of elite Indian maize hybrids using simple sequence repeat markers. Indian J Genet 61, 304-308.

Yuan L.X., J.H. Fu, S.H. Zhang, X. Liu, Z. Peng, X.H. Li, M.L. Warburton & M. Khairallah. 2001. Heterotic grouping of maize inbred lines using RFLP and SSR markers. Acta Agronomica Sinica, 27: 149-156.

Warburton, M L & Hoisington D, 2001. Applications of molecular marker techniques to the use of international germplasm collections. in Plant Genotyping: The DNA Fingerprinting of Plants, edited by R J Henry. CABI Publishing, Wallingford, UK. Pp 83-93..

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