Self‐Compatibility Studies with Diploid Alsike Clover, Trifolium hybridum L. IV. Inheritance of Type II Self‐Compatibility in Different Genetic Backgrounds1

Abstract

Inheritance of a type of self‐compatibility, possessing sporophytic and gametophytic characteristics, was studied in different genotypes of diploid alsike clover, Trifolium hybridum L. This type of self‐compatibility was referred to as Type II. The original hypothesis stated that the A1 allele of the A locus in a heterozygous condition suppressed the action of only the S1 allele of the S locus in the pollen to give self‐compatibility. Results from a series of crosses between self‐compatible (SC) and self‐incompatible (SI) plants showed that this postulate must be modified. In some crosses, the A1 allele was found to suppress the action of other S alleles. In other crosses the A1 allele did not suppress the action of any S alleles because all F1 plants were SI. When four of these SI F1 plants were backcrossed to a SC plant, only two of the 46 backcross plants were SC. Thus, the action of the A1 allele was variable. The number of SI and SC plants obtained in some progenies agreed with those expected according to the hypothesis that the A1 allele suppressed the action of only the S1 allele. The frequency of SI and SC plants from two F1 progenies with the same SC male parentage, differed from the frequency obtained in the progenies of the reciprocal crosses. The reason for the discrepancy is not known. In general, the deviation of the results obtained from those expected, and the complete absence of SC plants in some progenies, can be explained by the presence of modifying genes. Consequently, genetic background had considerable influence on the expression of Type II self‐compatibility.