Assessment of genetic variability of Spigelia marilandica and S. gentianoides using amplified fragment length polymorphism (AFLP) markers and clonal propagation of stem cuttings of S. marilandica, S. gentianoides var. alabamensis, and S. marilandica × S.
Hershberger, Amanda Jannette
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Despite the ecological and ornamental potential of southeastern U.S. native Spigelia, little is known about the intraspecific or the interpopulation genetic variation. Spigelia habitat is becoming fragmented due to human activity, making it imperative to gain an understanding of natural genetic variation among and within species and populations. This study used amplified fragment length polymorphism (AFLP) analysis to determine interspecific and intraspecific genetic variation and to evaluate gene flow. Thirteen populations of two species of native Spigelia, S. marilandica (L.) (SM), S. gentianoides Chapm. ex A. DC. var. alabamensis K. Gould (SGA), and S. gentianoides var. gentianoides (SGG), were analyzed. Based on analysis of molecular variance (AMOVA) and estimates of Nei’s coefficients of gene diversity (HS, HT, and GST), the majority of variation found in Spigelia occurs within populations. Among species and among population variation were low, likely the effect of common ancestry as well as relatively frequent introgression among individuals (and populations) of Spigelia. An unrooted UPGMA phenogram delineated three clades. The significance of these results is discussed in relation to breeding in Spigelia. In addition to the lack of information concerning genetic variation in Spigelia, little is known concerning clonal propagation strategies of SM and SGA. The effects of cutting date, indole-3-butyric acid (IBA) level, and genotype on rooting percentage, root number, and root length were evaluated. Stem cuttings were obtained from five genotypes of SM, one genotype of SGA, three genotypes of SM× SGA F2 hybrids, and two genotypes of SM × SGA F3 hybrids. IBA level significantly affected rooting percentage and root number, but not root length. The SM × SGA hybrids successfully rooted through all months evaluated, while SM and SGA genotypes exhibited a decline in rooting in cuttings taken in Sept. Results suggest that SM and SGA may be successfully propagated by treating stem cuttings taken in May, June, July, or Aug. with 0.3% IBA. Cuttings of SM × SGA hybrids can be taken through Sept. These protocols provide a basis for rapid propagation of Spigelia.