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Occurrence of Two Homozygous Self-incompatibility Genotypes in I₁ Segregates of Red Clover, Trifolium pratense L.¹

Intercrosses within three I₁ families of red clover (Trifolium pratense L.) established that two families possessed both of the gametophytic homozygous S-allele classes (S₁S₁ and S₂S₂) along with the heterozygous class (S₁S₂). The other family segregated only one homozygous class (S₁S₁) indicating the possibility of differential growth rates of pollen tubes. Reciprocal backcrosses of 15 I₁ progenies to their I₀ 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.

Key Words: Zygotic lethality • gametophytic homozygous classes

² Graduate assistant, Professor of Agronomy, University of Kentucky, and Plant Physiologist, Crops Research Division, ARS, USDA, Lexington 40506, respectively.

Received for publication February 4, 1968.