All 10 chromosomes of maize (Zea mays, 2n = 2x = 20) were recovered as single additions to the haploid complement of oat (Avena sativa, 2n = 6x = 42) among F1 plants generated from crosses involving three different lines of maize to eight different lines of oat. In vitro rescue culture of more than 4,300 immature F1 embryos resulted in a germination frequency of 11% with recovery of 379 F1 plantlets (8.7%) of moderately vigorous growth. Some F1 plants were sectored with distinct chromosome constitutions among tillers of the same plant and also between root and shoot cells. Meiotic restitution facilitated development of un-reduced gametes in the F1. Self-pollination of these partially fertile F1 plants resulted in disomic additions (2n = 6x + 2 = 44) for maize chromosomes 1, 2, 3, 4, 6, 7, and 9. Maize chromosome 8 was recovered as a monosomic addition (2n = 6x + 1 = 43). Monosomic additions for maize chromosomes 5 and 10 to a haploid complement of oat (n = 3x + 1 = 22) were recovered several times among the F1plants. Although partially fertile, these chromosome 5 and 10 addition plants have not yet transmitted the added maize chromosome to F2offspring. We discuss the development and general utility of this set of oat-maize addition lines as a novel tool for maize genomics and genetics.

Sexual inter-species hybridization is a powerful tool for understanding genome structure and interaction in higher plants. Breaking through inter-species incompatibility also enables chromosome engineering with horizontal (species-to-species) transfer of characters to which plant researchers and breeders have no access when utilizing only intraspecies gene pools. The more remotely related the parental genomes, the more the gene pool may be enriched.

Most of the favored host plants for chromosome engineering are allopolyploids or amphidiploids. Although in rare cases pure diploid species do tolerate alien chromosome additions, e.g. rye (Secale cereale; Kynast, 1986), the redundancy provided by homoeologs in polyploids is expected to better compensate for the loss of genetic information from alien substitution or translocation. Once stabilized as a disomic addition, the alien chromosome pair is transmitted consistently in the majority of the plants (Riley, 1960).