| The flavor profile of table beet is dominated by the earthy-flavored terpene derivative geosmin. Geosmin can be a desired characteristic in beet or a deterrent to the consumption of the vegetable. Geosmin is also produced by Streptomyces spp., various cyanobacteria, and fungi often found in soil and water environments. A long-held presupposition suggests that geosmin production in beets is due to an association with geosmin-producing microbes in the soil. This dissertation presents the results of breeding and experimental efforts to disentangle the source of geosmin production in table beet. Bidirectional half-sib recurrent selection for geosmin concentration over four breeding cycles resulted in the development of low (LGC) and high (HGC) geosmin concentration populations. From Year 1 to Year 3, the LGC mean shifted from 17.3 to 4.3 microg geosmin kg--1 tissue and the HGC mean shifted from 22.3 to 33.8 microg geosmin kg--1 tissue. Selected families in Year 4 continued this trend after evaluation, demonstrating that table beet is responsive to selection for geosmin concentration.;To separate the influence of potential geosmin-producing microbes from geosmin production in planta, four beet accessions were grown in an aseptic tissue culture environment. Lack of microbial contamination was demonstrated by sequencing 16S ribosomal RNA to identify potential contaminating microbes. Operational taxa units (OTUs) returned from this analysis were identified as either chloroplast (98%) or mitochondria (2%), demonstrating that beet plants free of microbes were capable of endogenous geosmin production. Geosmin was detected in 15 of the 16 tissue culture-grown beet samples used for the 16S rRNA aseptic validation. Geosmin concentration was higher in tissue culture grown beets than those grown in a greenhouse environment. A BLAST analysis of the recently published Beta vulgaris genome for geosmin synthase from Streptomyces coelicolor resulted in two hypothetical proteins functionally annotated as either isoprenoid or terpene synthases.;The successful bidirectional selection efforts for low and high geosmin concentration and the identification of geosmin in aseptically grown beets is a strong indication that geosmin is endogenously produced by beets and is a heritable trait. As such, geosmin concentration is another selectable trait for beet breeders to consider. |
