Inheritance of a Self-Compatibility Response to Temperature and the Segregation of S Alleles in Diploid Alsike Clover, Trifolium hybridum L.1
- C. E. Townsend2
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 (S5S6), 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 ✕ S3S4, S1S1 ✕ 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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