Sources of Useful Germplasm

Latin American countries are a very important source of maize for gene banks since the crop originated in this area. The largest germplasm accessions are in

INIFAP in Mexico and ICA in Colombia. The germplasm bank in Mexico is holding accessions from Mexico, Central America and the Caribbean; some of the foreign accessions are not duplicated in any other germplasm bank. Colombia is holding accessions from Colombia, the Caribbean and South America; again some of the foreign accessions are not duplicated in other gene banks. The other Latin American countries are holding the germplasms that was collected in their own country. The concern is that the equipment for these cold storage facilities is very old, and since a large number of these accessions are not duplicated in another storage facility, they could be lost forever.

Under the support of International Plant Genetic Resources Institute (IPGRI), new accessions were collected in several countries of Central and South America. In most of the countries the number of accessions collected is known, but there are a few that are unknown.

According to the reports presented by the maize curators of Latin American countries (CIMMYT, 1988) the total number of accessions held in these gene banks is 31,159. The number of duplicate accessions is 3996, so the total number of unique accessions is 27,163.

More than 27,000 accessions exist in the germplasm bank of America, classified into about 250 races, with some overlap (Goodman, 1983; Goodman and Brown, 1988). Most recent estimates following critical re-examination of morphological, cytogenetic and molecular marker data are that maize germplasm of the western hemisphere can be classified into about 130 racial complexes.

In areas below 1800 m of elevation, some examples of non-native usage of maize germplasm are: Bolivia is using Caribbean material; Brazil is using Cateto, Tuxpeno and Caribbean germplasm; Colombia is using Tuxpeno, Caribbean Flints and ETO; Mexico, Central America and the Caribbean area form their hybrids on the basis of Tuxpeno, ETO, Cuban Flint and Coastal Tropical Flint; Paraguay is using Caribbean germplasm; Peru based its hybrids on crosses between Perla (the formerly predominant flint variety) and the exotic Caribbean flint-dent complex; Venezuela is successfully working the Tuxpeno X ETO, in addition to the formation of native varieties (Salhuana, 1995).

In contrast, Goodman (1985) estimated that only 1% of the genetic material in US commercial hybrids traced to exotic sources. 'Fewer races have been identified in the United States and many of the open-pollinated varieties that constituted the Corn Belt Dents were discarded during the first half of this century before it became apparent that they might still harbor useful germplasm for future corn improvement'. However, the origin of the Corn Belt Dents from two races (the Southern Dents and Northern Flints), which differ genetically very significantly (Doebley et al., 1988), resulted in the Corn Belt Dents encompassing a broad range of genetic diversity. Furthermore, some, perhaps much, of the genetic diversity that was present in the open-pollinated varieties was carried into numerous private and public breeding programmes. This diversity is now sequestered in breeders stocks and is pyramided into new, more productive varieties.

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