“Slow” and “Quick” S ‐Alleles without Dominance Interaction in the Sporophytic One‐locus Self‐Incompatibility System of Stellaria Holostea (Caryophyllaceae)

Six self‐sterile plants were collected in the neighbourhood of Lund in 1991. Four of these plants in crosses produced 7 F 1 families, totalling 52 plants (range 3–11 plants). Incompatibility interrelationships were assessed from seed‐setting data from the complex programme of sellings, F 1 sib intercrosses, crosses to parents, and crosses to non‐related plants that was conducted in 1992 and 1993. Data confirmed the presence of one S ‐locus acting sporophytically and with co‐dominance, 10 alleles being distinguished among the six plants, which were all heterozygotes, with the genotypical assignments consistently covering the whole set of 50 plants studied. A fraction of the pollen grains reacted as if one of the two S ‐gene imprints were absent, as indicated by slight but clearly significant elevations of seed‐set in intergroup matings with one allele matched. It was possible to exclude the presence of occasional recessiveness to a non‐matched S ‐allele, or allelic interaction leading to mutual weakening of the matched and the non‐matched alleles. Instead, the idea of “slow” and “quick” alleles was conceived. “Slow” S ‐alleles are visualized sometimes to produce insufficient amounts of S‐substances, and normally efficient “quick” alleles, sometimes to meet a barrier to the penetration of their S‐substances within the tetrad of microspores. Apparently, the S ‐alleles in family Caryophyllaceae do not exert their control of the pollen through tapetal cells in the anthers, but through S ‐gene messengers produced in the meiocyte itself. This may indicate not only an intrinsic difference but the origin of S ‐genes on more than one occasion.