Genetic Control of Floral Morph In Tristylous Pickerelweed (Pontederia cordata L.)

Pickerelweed (Pontederia cordata L.) is a diploid (2n=2x=16) tristylous wetland perennial native to Florida. Populations usually comprise three floral morphs that differ reciprocally in style length and anther height. All flowers are perfect and bear a single style and two sets of three anthers in one of three positions (long, mid and short). Plants bearing flowers with a style in the long position are referred to as L-morphs, while plants that produce flowers with a style in the mid or short position are called M- and S-morphs, respectively. This floral polymorphism promotes disassortative mating among the three floral morphs. The goal of this study was to determine the number of loci, number of alleles and gene action controlling floral morph in pickerelweed. Three parental lines (one each of the L-, M- and S-morph) were used to generate S₁ and F₁ populations. F₂ populations were produced through self‑pollination of F₁ plants. Progeny ratios of S₁, F₁ and F₂ generations revealed that tristyly is controlled by two diallelic loci (S and M) with dominant gene action and expression is influenced by epistasis. The S locus is epistatic to the M locus, with the S‑morph produced by plants with the dominant S allele (genotype S _ _ _). Plants with recessive alleles at the S locus were either L-morph (ssmm) or M-morph (ssM_). The results of this experiment demonstrate that the inheritance of tristyly in pickerelweed is the same as previously reported for several tristylous species in the Lythraceae and Oxalidaceae.