The Gametophyte-1 locus and reproductive isolation among Zea mays subspecies

Fourteen paired populations of annual teosinte and an associated maize landrace were characterized for allelic composition of the potential crossing barrier locus gal. The four populations of subspecies parvighumis teosinte carried predominately gal or Ga1-m, both of which are receptive to gal pollen. The sole population of subspecies huehuetenangensis was polymorphic for Ga1-m, and for Ga1-s, which is unreceptive to gal pollen. Ga1-s predominated among the six weedy populations of subspecies mexicana whereas the three ruderal/weedy populations of this subspecies contained gal or Ga1-m. This distribution Suggests a role for Ga1-s enabling weedy populations to grow in intimate association with maize. However, the predominant allele in sympatric maize landraces proved to be Ga1-m, which regularly fertilized Ga1-s in controlled crosses. The Ga1-s pistil barrier thus would seem unable to prevent teosinte from being fertilized by sympatric maize. Nevertheless, Ga1-s pollen fertilized Ga1-s Ga1-s plants somewhat more effectively than Ga1-m when both were present. This preference may be strengthened by modifier gene differences between teosinte and maize, thereby providing partial reproductive isolation between the two.