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This paper discusses alternatives for improving the maize plant. While maize hybrids dominate in the developed world, open-pollinated varieties mostly are grown in the developing countries. The importance of population improvement in maize has been emphasized. Population improvement procedures not only improve the population for developing superior varieties but also increase the chances of extracting superior lines that will result in better hybrid combinations. The accomplishments in the development of population improvement methods in maize are discussed. Some of the important population improvement schemes, such as mass selection, modified ear-to-row selection, and several recurrent selection schemes, are briefly discussed. In addition, mating design-1 and some family selection schemes such as full-sib, half-sib, and S1 have been mentioned. CIMMYT's maize improvement program, including the research activities of the Advanced Unit, Back-Up Unit, Quality Protein, and Special Projects, is discussed. The structure and function of these units are presented. The Back-Up Unit handles the germplasm bank and the gene pools. A total of 29 gene pools are being improved continuously by the half-sib selection procedure. The handling of gene pools is discussed along with information on population size, selection in male and female rows before and after flowering, among- and within-family selection intensity, stresses to diseases and insects, adaptation, and introgression of new germplasm in the pools. The various operations in the Advanced Unit are described both with normal and quality protein maize (OPM) populations. The full-sib system of family improvement is used in each population. Various stages in population improvement, such as progeny regeneration, progeny evaluation, and within-family improvement during the intervening cycles, are discussed. In addition to population improvement, site-specific and across-site experimental varieties are developed using approximately 10 top-performing families. The experimental varieties are evaluated in experimental variety trials (EVTs). The top performing EVs are designated as elites for further testing in elite experimental variety trials (EL VTs). The breeding effort concentrating on special attributes such as earliness and resistance to downy mildew, stunt, and streak is described. Breeding for resistance to fall armyworm, borers, and earworm also is being practiced in the gene pools and populations. The technique utilizing larvae instead of egg masses has been presented and the field execution of insect resistance work is briefly described. The problems encountered in OPM and the breeding strategy used in the accumulation and exploitation of genetic modifiers are discussed. The germplasm development effort and the breeding methodology used in breeding OPM has been presented. The salient features of the conversion process are given. The objective of OPM pools and their formation and handling have been discussed. The experimental evidence showing progress in pools and the performance of OPM materials in the international tests has been presented.

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