OAT-MAIZE CHROMOSOME ADDITION LINES - A NEW SYSTEM FOR MAPPING THE MAIZE GENOME

Novel plants with individual maize chromosomes added to a complete oat genome have been recovered via embryo rescue from oat (Avena sativa L ., 2n = 6x = 42) x maize (Zen mays L., 2n = 20) crosses. An oat-maize disomic addition line possessing 21 pairs of oat chromosomes and one m aize chromosome 9 pair was used to construct a cosmid library. A multi probe (mixture of labeled fragments used as a probe) of highly repetit ive maize-specific sequences was used to selectively isolate cosmid cl ones containing maize genomic DNA. Hybridization of individual maize c osmid clones or their subcloned fragments to maize and oat genomic DNA revealed that most high, middle, or low copy number DNA sequences are maize-specific. Such DNA markers allow the identification of maize ge nomic DNA in an oat genomic background. Chimeric cosmid clones were no t found; apparently, significant exchanges of genetic material had not occurred between the maize-addition chromosome and the oat genome in these novel plants or in the cloning process. About 95% of clones sele cted at random from a maize genomic cosmid library could be detected b y the multiprobe. The ability to selectively detect maize sequences in an oat background enables us to consider oat as a host for the clonin g of specific maize chromosomes or maize chromosome segments. Introgre ssing maize chromosome segments into the oat genome via irradiation sh ould allow the construction of a library of overlapping fragments for each maize chromosome to be used for developing a physical map of the maize genome.