In North America, wild populations of Beta vulgaris subsp. maritima, Beta macrocarpa, and respective hybrids with cultivated beet are found in California. These likely originated from contaminated seed imported from Europe (Biancardi et al., 2012). Section Beta includes the wild species B. macrocarpa, and B. v. ssp. maritima, and the cultivated sugar beet, Beta vulgaris subsp. vulgaris (Frese, 2010). Successful hybridization amongst species of section Beta varies. Sugar beet will readily cross-fertilize with B. v. ssp. maritima, but there is conflicting evidence for successful hybridization between sugar beet and B. macrocarpa (de Bock, 1986; Bartsch and Ellstrand, 1999; Jung et al., 1993; Frese, 2010). The relationships among the three species of section Beta have been investigated with PCR-based marker and DNA sequencing techniques. Previous research suggests a close relationship between B. v. ssp. vulgaris and B. v. ssp. maritima with a more distant position of B. macrocarpa in the phylogenetictree (Letschert, 1993; Shen et al, 1998; Villain, 2007).
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