Cross-incompatibility between maize and wild teosinte
 Figure 10. The pollen of domesticated maize does not function on the silks of some strains of teosinte, its wild progenitor, but teosinte pollen functions on maize silks. In collaboration with the laboratory of Jerry L. Kermicle (University of Wisconsin-Madison) we are studying factors that prevent the pollination of wild teosinte by domesticated maize. The compatibility of maize with its closest relatives, the annual Mexican teosintes, depends on the direction of the cross. Used as ovule parent, maize pollinated with these teosintes produces a full set of kernels and highly to fully fertile F1 plants. For many strains of teosinte however the cross in the opposite direction often fails (Figure 10). The available data concerning the collections of mexicana that block pollination by maize suggested they derive from regions where teosinte grows exclusively as a weed and flowers in synchrony with the local maize.
 Figure 11. Ears from crosses designed to distinguish between incompatibility genes segregating in a W22 backcross lineage of Z. m. spp. parviglumis (collection 104). Pollen from a true breeding Ga1-m Tcb1 strain was mixed with ga1 tcb1 pollen that confers kernel color and placed on silks of plants in the test strain (A, D). Pollen from each of the test plants was used in crosses to Ga1-s (B,E) and Tcb1 (C,F) silks. Two classes of plants were present: (i) A-C those whose silks did not discriminate against the colored tracer pollen and whose pollen was unreceptive on both testers; and (ii) D-F those whose silks were unreceptive to the tracer pollen and whose own pollen was unreceptive on the Ga1-s tester but receptive on Tcb1. Plants of category (i) lack both Ga1 and Tcb1 whereas those of category (ii) lack Ga1 but carry Tcb1. Unilateral compatibility presents a unique opportunity to characterize barriers to crossing genetically. Crosses in the compatible direction provide material for analysis; the reciprocal cross assays for incompatibility. Obviously, bilateral incompatibility precludes this approach and partly accounts for the dearth of genetic evidence concerning IC. These circumstances prompted us to undertake study of maize teosinte compatibility with the general, long-term goals of identifying the major genes involved, incorporating them singly into maize lines and there determine their actions (Figure 11). We have identified and are characterizing a major crossing barrier complex on maize chromosome 4 (Figure 12).
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TAIR
