Chapter 5 - Maize Genetic Resources and Pre-Breeding

Abstract

Maize is one of the plant species with the greatest genetic variability. This large diversity is expressed in maize cultivated in different environments and used for many purposes, as well as in maize maintained in the germplasm banks (GB). Maize is originated from the Mesoamerican Diversity Center, which was widespread and formed thousands of races and landraces adapted to many environmental conditions. Great breeding effort has been carried out in maize, in which hybrid technology was available since 1920s in the United States of America, as a good breeding strategy. The genetic improvement carried out in the maize collections generated the elite or improved germplasm, which is genetically distant from the collections maintained in the GBs (unimproved germplasm). Thus, the elite germplasm has high yield performance, uniformity, and narrow genetic basis whereas the accessions of GBs in general have low productivity, high stalk and root lodging, high plant and ear height, large variability between individuals and broad genetic basis. Due to these differences, accessions of GBs are scarcely used in breeding programs. Pre-breeding links these both collections developing populations by the introgression of favorable alleles from unimproved germplasm into improved germplasm. These activities lead to better understand and to increase the use of GBs. In this context, this chapter will focus on: characteristics of maize genetic resources, demands of maize breeding programs, integration between genetic resources and breeding, knowledge of the variability maintained in maize GBs, and development of new elite populations and activities in maize pre-breeding.