SLOW AND QUICK S-ALLELES WITHOUT DOMINANCE INTERACTION IN THE SPOROPHYTIC ONE-LOCUS SELF-INCOMPATIBILITY SYSTEM OF STELLARIA-HOLOSTEA (CARYOPHYLLACEAE)
A. Lundqvist, SLOW AND QUICK S-ALLELES WITHOUT DOMINANCE INTERACTION IN THE SPOROPHYTIC ONE-LOCUS SELF-INCOMPATIBILITY SYSTEM OF STELLARIA-HOLOSTEA (CARYOPHYLLACEAE), Hereditas, 120(3), 1994, pp. 191-202
Six self-sterile plants were collected in the neighbourhood of Lund in
1991. Four of these plants in crosses produced 7 F-1 families, totall
ing 52 plants (range 3-11 plants). Incompatibility interrelationships
were assessed from seed-setting data from the complex programme of sel
fings, F-1 sib intercrosses, crosses to parents, and crosses to non-re
lated plants that was conducted in 1992 and 1993. Data confirmed the p
resence of one S-locus acting sporophytically and with co-dominance, 1
0 alleles being distinguished among the six plants, which were all het
erozygotes, with the genotypical assignments consistently covering the
whole set of 50 plants studied. A fraction of the pollen grains react
ed as if one of the two S-gene imprints were absent, as indicated by s
light but clearly significant elevations of seed-set in intergroup mat
ings with one allele matched. It was possible to exclude the presence
of occasional recessiveness to a non-matched S-allele, or allelic inte
raction leading to mutual weakening of the matched and the non-matched
alleles. Instead, the idea of ''slow'' and ''quick'' alleles was conc
eived. ''Slow'' S-alleles are visualized sometimes to produce insuffic
ient 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 tape
tal cells in the anthers, but through S-gene messengers produced in th
e meiocyte itself. This may indicate not only an intrinsic difference
but the origin of S-genes on more than one occasion.