Genetic Structure of a Rare Interspecific Hybrid of <i>Vincetoxicum atratum </i>and <i>V. pycnostelma </i>(Apocynaceae–Asclepiadoideae)

Yamashiro Tadashi, Yamashiro Asuka, Maruoka Michiyuki, Kobayashi Tomiki, Maki Masayuki

doi:10.18942/apg.202104

Hybrids of Vincetoxicum atratum and V. pycnostelma (Apocynaceae–Asclepiadoideae) have been rarely recorded. To date their admixture populations have never been analyzed genetically. We analyzed a putative hybrid population of V. atratum and V. pycnostelma and six populations of the parental species based on 12 polymorphic microsatellite loci and morphometric analyses of 17 morphological characters. The STRUCTURE analyses of 12 microsatellite DNA variations correctly assigned pure V. atratum and V. pycnostelma populations to distinct clusters (q > 0.9). Four of 32 samples from the hybrid population had admixed genotypes. Hybrid class assignment by NewHybrids classified these four admixed individuals into the F₂ hybrid class. Principal component analysis (PCA) of 12 floral and 5 leaf characters separated V. atratum and V. pycnostelma into two clusters. The plots of two hybrid individuals available for PCA fell into an intermediate space between the clusters of the two species. The findings indicate that interspecific hybridization between V. atratum and V. pycnostelma can result in fertile F₁ hybrids. Because hybrid populations typically consist of parental and backcross individuals, the population examined here was unusual in being dominated by F₂ individuals. Postzygotic reproductive isolation between the F₁ hybrid and the parental species appears to the best explanation for the dominance of F₂ individuals in the hybrid population of V. atratum and V. pycnostelma. Artificial crossing experiments are necessary to confirm backcross sterility.

Genetic Structure of a Rare Interspecific Hybrid of <i>Vincetoxicum atratum </i>and <i>V. pycnostelma </i>(Apocynaceae–Asclepiadoideae)

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