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Cytology of Backcross Offspring Derived from a Maize-Tripsacum Hybrid¹

Hybrids combining 10 Zea (Zm) and 36 Tripsacum (Tr) chromosomes are produced when diploid Zea mays L. (2n = 20) is crossed with tetraploid Tripsacum dactyloides (L.) L. (2n = 72). In these hybrids the 36 Tr chromosomes pair, while the 10 Zm chromosomes remain as univalents and are usually eliminated during meiosis. Backcrossing with maize frequently reconstitutes the 2n = 46 hybrid. After four generations of backcrossing, the frequency of multivalents increased while the frequency of univalents decreased in 2n = 46 individuals, suggesting that segmental chromosome exchanges between genomes of Zea and Tripsacum had taken place. In the third and fourth backcross generations, individuals with 36 Tr + 6, 10, 12, 14, 16, 18, or 20 Zm chromosomes were obtained. Chromosome pairing in these individuals suggests that an extensive amount of gene transfer is feasible from Tripsacum into maize.

Key Words: Tripsacum dactyloides (L.) L. • Zea mays L. • Gametophytic apomixis • Homoeologous pairing • Autosyndetic pairing • Introgression

² Research assistant, and Professors, respectively, Crop Evolution Laboratory Agronomy Department, University of Illinois, Urbana, Illinois 61801.

Received for publication May 25, 1973.