Occurrence of Two Homozygous Self‐incompatibility Genotypes in I1 Segregates of Red Clover, <i>Trifolium pratense</i> L.¹

Intercrosses within three I 1 families of red clover ( Trifolium pratense L.) established that two families possessed both of the gametophytic homozygous S‐allele classes (S 1 S 1 and S 2 S 2 ) along with the heterozygous class (S 1 S 2 ). The other family segregated only one homozygous class (S 1 S 1 ) indicating the possibility of differential growth rates of pollen tubes. Reciprocal backcrosses of 15 I 1 progenies to their I 0 clones revealed a deficiency of the sum of the two homozygous classes. The inference is that the deficiency may have resulted from heterozygotic advantage or from zygotic lethality. We conclude that the gametophytic type of S‐allele system is common in red clover, but segregation of S‐alleles is influenced by the interaction of alleles with temperature and possibly other environmental factors.