Isoenzymatic Variation in Zea (Gramineae)

Abstract

An average of 14(7-34) plants each for 61 different collections of Zea (maize and its wild relatives, the teosintes) were studied for 12 enzyme systems coded for by 21 loci. Principal component and cluster analyses based on allele frequencies showed Zea can be divided into two major groups: 1) sect. Luxuriantes, including Z. perennis, Z. diploperennis, and Z. luxurians; and 2) sect. Zea (in part), including Z. mays subsp. mays, var. parviglumis, and subsp. mexicana. Zea mays var. huehuetenangensis (Huehuetenango teosinte) is isoenzymatically distinct from both sections, but shows its closest relationship to Z. mays var. parviglumis of sect. Zea. Populations of Z. mays subsp. mexicana and var. parviglumis grade isoenzymatically from one into the other without any clear break, but without any overlap either. Five populations of Z. mays subsp. mays are all isoenzymat- ically very similar to Z. mays var. parviglumis. The isozyme data are consistent with the theory that Mexican annual teosinte is the ancestor of maize. With the exception of the unusual isoenzymatic nature of Z. mays var. huehuetenangensis, the isoenzymatic data agree with previous studies of tassel morphology and cytoplasm DNAs. A comparison of sympatric populations of maize and teosinte suggests that teosintes are not greatly affected by introgression from maize. Zea mays var. parviglumis and Z. diploperennis have considerable within and among population variation; Z. luxurians has much less. Race Central Plateau of Z. mays subsp. mexicana has greater among population variation than any other taxon in Zea. Zea tends to show greater within population heterozygosity and more variance within species and subspecies than most other plants that have been studied isoenzymat- ically.