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Inheritance of a Self-Compatibility Response to Temperature and the Segregation of S Alleles in Diploid Alsike Clover, Trifolium hybridum L.¹

Inheritance of a self-compatibility response to temperature and the segregation of S alleles were investigated in I₂, F₁, F₂, and BC₁ progenies of diploid alsike clover, Trifolium hybridum L. I₁ clones, 6-5 (S₃S₄) and 7-1 (S_{5S6), were the temperature-sensitive parents and I1 clone 1-5B (S1S1) was the temperature-insensitive parent. Percentage of selfed florets setting seed after 3 to 5 days at 32 C was used to measure temperature-sensitivity. The S alleles in the self-progeny of clone 6-5 segregated in a 1 S3S3:2 S3S4:1 S4S4 ratio. The S6S6 genotype was absent in the self-progeny of clone 7-1, but the other two genotypes (S5S5 and S5S6) segregated in a 1 : 1 ratio. The expected S genotypes (S1S3, S1S4, S1S>sub>5}, and S₁S₆) were obtained equal frequencies in the F₁ progenies (S₁S₁ x S₃S₄, S₁S₁ x S₅S₆, and reciprocals). In all F₂ progenies, one homozygous and one heterozygous class (S₃S₃, S₁S₃; S₄S₄ S₁S₄; S₅S₅, S₁S₅ and S₆S₆, S₁S₆) were obtained in equal frequency. Only five of 202 F₂ plants were S₁S₁.

Although other gene models were considered, the temperature-sensitive data were interpreted best by a twogene model with an interaction between S allele genotype and temperature-sensitivity. The proposed temperature-sensitive genotypes of clones 6-5 and 7-1 were T₁T₁T₂t₂S₃S₄ and T₁t₁T₂t₂S₅S₆, respectively. The T gene(s) suppressed the action of the S alleles in the style when the plants were held at a 32 C temperature for 3 to 5 days. Dominance at one T locus was sufficient to give a temperature-sensitive reaction with the S₃, S₅, and S₆ alleles, but dominance at both T loci was required for such a reaction with the S, allele. Also, there was evidence for the interaction among certain S alleles in the presence of the T loci. The expression of the T loci was influenced by polygenes.

Apparently these data are the first from any species to establish the role that specific temperature-sensitive genes have on the expression of specific S alleles and interactions thereof.

Key Words: Self-incompatibility • Selective fertilization • Temperature-sensitivity

² Research Geneticist, Crops Research Division, ARS-USDA and Faculty Affiliate, Department of Agronomy, Colorado State University.

Received for publication May 7, 1970.