Teosinte crossing barrier1, a locus governing hybridization of teosinte with maize
A teosinte gene or gene cluster, Teosinte crossing barrier1 (Tcb1), that restricts crossability with maize mapped 6 centiMorgans distal to sugary-1 on chromosome 4. Tcb1 is loosely linked with the gametophyte-1 locus whose Ga1-s allele, present in many popcorns, confers nonreceptivity to the pollen of other maize varieties (ga1). Full-strength Tcb1 (positive modifiers present) was nonreceptive to Ga1-s as well as to ga1 pollen. Attenuated Tcb1 (positive modifiers absent) was detectably more receptive to Ga1-s than to ga1, suggesting cross recognition between the two systems of incompatibility. Reciprocally, homozygous Ga1-s was unreceptive both to Tcb1 and tcb1 pollen, but heterozygous Ga1-s/ga1 plants were somewhat more receptive to Tcb1 than to tcb1. Discrimination by Tcb1/− females against tcb1 pollen is prezygotic, accomplished without the loss of viable ovules. When introduced into maize, Tcb1 incompatibility may be useful for isolating one category of commercial varieties from another.