Genes conferring specific plant disease resistance.

Genes conferring host resistance to an obligate parasite, grouped together in complex loci provide opportunities to study their structure. By means of an appropriate operational definition of these genes, a modified cis-trans test was used to interpret the position effects of codominant genes mutually recombined within each of two complex loci of flax, with the use of a specially developed method of analysis among F(2) segregants. The different behavior of genes in the M and L groups may reflect a difference in their structure sufficient to raise important implications in the theory of specific host-parasite interactions.