WILD/WEED BETA POPULATIONS IN THE IMPERIAL VALLEY, CALIFORNIA

Abstract

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 crossfertilize 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 phylogenetic tree (Letschert, 1993; Shen et al., 1998; Villain, 2007). When commercial production areas are adjacent to wild beet populations, gene flow from cultivated beets has the potential to alter the genetic composition of the nearby wild populations (Bartsch and Ellstrand, 1999). Carsner reported populations of B. v. ssp. maritima, B. macrocarpa, and respective hybrids with cultivated beet in the Imperial Valley, California in 1938 and they continue to be identified in California. Plant and root characteristics of Imperial Valley wild beets were compared with collections of B. v. ssp. maritima and B. macrocarpa from European coastlines. The wild beets found in the Imperial Valley differ from typical B. v. ssp. maritima and other wild beets found in California and are most similar to B. macrocarpa (McFarlane, 1975). In 2011, plants were collected from wild Beta populations adjacent to commercial sugar beet fields and while many samples had clear morphological characteristics of B. macrocarpa, several showed B. v. ssp. maritima-like characteristics. This distinction is critical because B. v. ssp. maritima will readily cross hybridize with cultivated sugar beet while B. macrocarpa hybrids occur less frequently and often result in infertile progeny. Further research is needed to evaluate wild beets in the Imperial Valley to understand the origin of populations, determine the species, and explore whether or not gene flow occurs between these wild beets and cultivated beet. Herbarium samples, leaf tissue and seed of weed beet in and around commercial sugar beet fields were collected with the objectives of assigning taxonomy based on morphology and determining genetic variation by genotyping.