Advances in Maize Breeding through the Cumulative Complex Improvement of Sources
Maize breeding, on which the future of maize production is based, can be expected to undergo further important developments in the 21st century. Opportunities for development are latent in a more scientific approach to production methods and in the better exploitation of the available genetic resources. There is no lack of favourable gene combinations contributing to higher yield (e.g. 20–22 t/ha). However, the genes and gene combinations controlling the improvement and stabilisation of performance are unfortunately scattered over various different races, varieties and individual plants, where they occur at low frequency. Combination breeding and, more recently, cumulative source management are designed to collect these genes and concentrate them in special parental lines and heterosis sources.
The pure line method has been a basic procedure in maize breeding for the last 100 years, and is likely to remain so for the next 100 years. Combination breeding and cumulative source management are an integral part of this method. The concentration of favourable genes has been facilitated to an unexpected extent by the use of this method. When breeding open-pollinated varieties all the gene combinations required had to be collected into a single population, while in the case of heterosis breeding it is sufficient if the male and female parents each contain half the required gene combinations. These are then combined automatically in the course of crossing.
Over the last 20 years too little attention has been paid to the breeding of basic material, so the number of heterosis sources has declined and some have become eroded due to unsupervised mixing. There have been few reports on the development of new heterosis sources vying in quality with earlier sources. In the course of hybrid maize breeding, closely related pedigrees have been crossed to develop new elite lines in the hope of quick results. Due to the lack of substantial initial divergence this is unlikely to result in any great increase in yield. Authoritative opinions consider this to be the reason for the slower rate of yield increase, and for the very small differences now existing between the yield levels of rival hybrids.
There is no lack of genetic resources, but more attention should be paid to the careful breeding of basic materials. The future of maize breeding will depend on the discovery of new gene combinations more efficient than those currently available, and on their successful concentration in different sources of heterosis.
KeywordsZea mays diversity genetic resources heterosis sources
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- Gerdes, J.T., Behr, C.F., Coors, J.G., Tracy, W.F. 1994. Compilation of North American Maize Breeding Germplasm. Crop Sci. Mad., WI. 201 pp.Google Scholar
- Hadi, G., Marton, L.Cs., Szundy, T., Kovács, I., Pintér, J., Dolinka, B. 2004. Contribution made by the maize variety Mindszentpusztai Yellow Dent (MYD) to the birth of hybrid maize in Hungary and in Europe as a whole. Review. Cereal Res. Comm. 32:159–166.Google Scholar
- Jenkins, M.T. 1935. The effect of inbreeding and selection within inbred lines of maize upon the hybrid made after successive generation of selfing. Iowa State Coll. J. Sci. 3:425–450.Google Scholar
- Jones, D.F. 1918. The effects of inbreeding and cross-breeding upon development. Conn. Agric. Exp. Stn. Bull. 207:5–100.Google Scholar
- Lonnquist, J.H. 1974. Consideration and experiences with recombination of exotic and corn belt maize germplasm. Proc. Annu. Corn and Sorghum Ind. Conf. 29:102–107.Google Scholar
- Pollmer, G.W. 1971. Report of the Northern Maize Committee. In: Kovács, I. (ed.), Proc. of the Fifth Meeting of the Maize and Sorghum of Eucarpia. Akadémiai Kiadó, Budapest, pp. 19–29.Google Scholar
- Shull, G.H. 1908. The composition of a field of maize. Am. Breed. Assoc. Rep. 4:296–301.Google Scholar
- Shull, G.H. 1909. A pure line method of corn breeding. Am. Breed. Assoc. Rep. 5:51–59.Google Scholar
- Zuber, M.S., Darrah, L.L. 1979. 1979 U.S. corn germplasm base. Proc. Corn and Sorghum Ind. Res. Conf. 35:234–249.Google Scholar