The inheritance of tristyly in Decodon verticillatus (Lythraceae)

Abstract

The inheritance of tristyly is generally thought to be governed by two diallelic loci, S and M, with complete dominance and epistasis between the loci. Significant departures from the two-locus model have, however, been recently reported in species of Oxalis. This study presents a genetic analysis of tristyly in the eastern North American monotypic perennial Decodon verticillatus (L.) Ell. (Lythraceae). Crosses conducted on plants from six natural populations in Ontario resulted in patterns of segregation consistent with the two-locus model. The L morph is homozygous at both loci (ssmm). Crosses among F1 progeny identified two F1 individuals of the M morph homozygous for the dominant allele at the M locus (ssMM) and an F1 individual of the S morph homozygous for the dominant allele at the S locus (SSmm). Crosses between these genotypes demonstrated epistasis of the S locus over the M locus and produced putative double heterozygotes (Sm/sM). Five of these F2 genotypes were both self-fertilized and crossed as pollen donors to individuals of the L morph. Segregation in F3 and backcrossed progenies confirmed the two-locus model and provided no evidence for linkage between the loci. The results support the model of inheritance established for distantly related Lythrum salicaria, suggesting that the genetic control of tristyly may be uniform throughout the Lythraceae. © 1993 The Genetical Society of Great Britain.