Two strains ofMelampsora lini(flax rust) were identified that differed in their ability to produce a self-inhibitor of urediospore germination. Analysis of germination self-inhibitor production amongst 63 F2progeny derived from a sexual hybrid of these two strains revealed segregation of this trait. Segregation of urediospore germination self-inhibitor production was consistent with single-locus control with inhibitor production being recessively inherited.Key words: rust, germination, spore, inhibitor.