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

Abstract

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, S1S5, 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.