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 selfings, 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.