The definition of experimental reference sets for Zea
--Bird, RMcK

Part of a new project at CIMMYT, in which we are characterizing maize genebank accessions through DNA fingerprinting, will be the selection of several sets of materials to be made available for a wide range of studies as references or points of comparison. We feel there is need for such sets--much research has been based on materials chosen without regard for comparability to other studies or repeatability using the same stocks. How could one compare or even repeat studies if one study were of isozyme differences between maize and teosinte, the "teosinte" being a few landrace samples of Z. diploperennis and Z. mexicana from a U.S. genebank and the maize being from ears in a private collection, and the other study were of RFLPs, the teosinte being an accession of Z. luxurians from CIMMYT and the maize being a set of Peruvian lines supplied by a geneticist? Yet many studies are based upon such arrays of materials.

Previously I defined two reference sets -- 12 maize accessions in one, the other with seven teosinte accessions (Maize for Biological Research, W. F. Sheridan, ed., pp 341-350, 1982). Entries were listed in order of "utility". The criteria for selection were distinctiveness using current information, lack of evidence of inter-racial introgression, availability in a public genebank, and, to some degree, adaptation to U.S. conditions. Researchers at Pioneer Hi-Bred International have studied 30 inbred lines in many ways (Smith; et al., Maydica, 36:213-226, 1991 and three earlier papers). These form a reference set for Pioneer use, but several public lines, Mo17, B73 and A632, have been included, so these three can be compared using morphological, agronomic, isozyme and RFLP data, a small reference set.

The criteria above are those being used here except we will pay less attention to U.S. adaptation and will look for use of the entry in prior comparative studies. One set will sample the overall variation of the genus Zea increasing the 7-teosinte set to ca. 12 members. The second set may include the 12 maize races in the 1982 set, though checked for appropriateness of the member accessions and availability at CIMMYT. Another set might be inbreds such as the U.S. public lines listed above plus some CIMMYT, European, African and/or Asian inbred lines. Here an added criterion is the sampling of known and suspected heterotic groups. 

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