David S. Wofford

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

Pickerelweed (Pontederia cordata L.) is a diploid (2n = 2x = 16) tristylous aquatic perennial. Populations usually contain 3 floral morphs that differ reciprocally in style length and anther height (referred to as the long-, mid-, and short-styled morphs, hereafter L-, M-, and S-morphs). The floral polymorphism promotes disassortative mating among the 3 floral morphs and is maintained in populations by negative frequency-dependent selection. The objective 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 create 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 2 diallelic loci (S and M) with dominant gene action. 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.

Potential of RAPD analysis of the promiscuous nodulation trait in soybean (Glycine max L)

Inoculation of soybean with cowpea-type rhizobia results in either a promiscuous type of nodulation which produces a plant with functional nodules capable of N fixation and has green leaves without N fertilization or nonpromiscuous type of nodulation which forms nonfunctional (or no nodules) and develops yellow leaves without N fertilization. Promiscuous soybean types are desirable in production regions where the availability of commercial inoculants is limited. Plant breeding efforts to develop improved promiscuous cultivars particularly in developing countries require inexpensive molecular tools for laboratory-based germplasm selection in order to reduce lengthy conventional breeding cycles. The objective of this study was to evaluate the potential of random amplified polymorphic DNA (RAPD) method in identifying promiscuous soybean genotypes. Segregating plant populations created by reciprocal crosses of promiscuous × nonpromiscuous soybean lines were evaluated for useful RAPD markers for promiscuous nodulation. One hundred and sixty random decamers of arbitrary sequences were used in screening for polymorphic loci between the two parental lines. A RAPD pattern which is consistent with the soybean genotypes segregating for promiscuous nodulation was generated by one decamer, OPB06 (5′-TGCTCTGCCC-3′), indicating the potential of using RAPD markers in selecting for promiscuity in soybean breeding programs.