Construction of 'compound' rust resistance genes in maize

The Rpl locus of maize is a complex rust resistance locus where multiple resistance genes are clustered. Rare recombination events between Rpl genes or alleles can produce two or more detectable genes linked in coupling phase. Such 'compound' genes can then be manipulated as a single gene in breeding programs. Several compound Rpl genes, each carrying two or three tightly linked resistance genes, were constructed to test their utility in controlling common rust. While none of the lines carrying single Rpl genes were resistant to all of the characterized North American P. sorghi biotypes, most of the two component and all of the three component Rpl complexes were resistant. The potential for utilization of compound resistance genes in other crop species is discussed.