Geosmin (2β,6α-Dimethylbicyclo[4.4.0]decan-1β-ol) Production Associated with Beta vulgaris ssp. vulgaris Is Cultivar Specific

Abstract

The characteristic earthy flavor and aroma of table beet [Beta vulgaris ssp. vulgaris (garden beet group)] is due to the presence of geosmin, C₁₂H₂₂O, a volatile terpenoid compound commonly produced by many soil microorganisms. This study screened beet and related subspecies cultivars grown in three different environments (field, greenhouse in nonautoclaved soil, greenhouse in autoclaved soil) to evaluate the effect of cultivar and environment on geosmin level in table beet. There was no significant difference between years or between cultivars grown in autoclaved and nonautoclaved soil, indicating geosmin content may not be primarily attributable to microbial associations. A significant interaction between cultivar and environment was found, but generalizations could be made for high- or low-producing cultivars, demonstrating that geosmin levels were cultivar specific. 'Bull's Blood', 'Chioggia', and sugar beet exhibited the highest geosmin levels. Cultivars grown in the field had the smallest range of geosmin production, from 4.84 to 20.82 μg geosmin (kg root tissue)⁻¹. The high degree of consistency in cultivar performance across years and in ranking for geosmin levels across environments as well as the lack of a significant difference between plants grown in autoclaved and nonautoclaved soil suggests characteristic levels of geosmin may be present in and produced endogenously by cultivars of table beet. It may be possible to establish breeding populations with defined geosmin levels and to identify variety-specific aroma and flavor intensities that would be durable across environments.

Genotype Is Primarily Responsible for Variance in Table Beet Geosmin Concentration, but Complex Genotype × Environment Interactions Influence Variance in Total Dissolved Solids

“…The significant genotype • year interaction for geosmin concentration (Fig. 1) was effectively of a non-crossover nature and driven by the distinct character of 'Bull's Blood', a known high geosmin cultivar (Freidig and Goldman, 2014). 'Bull's Blood' ranked first for geosmin concentration in both 2016 and 2017, and its mean geosmin concentration in both years was significantly higher than means of all other cultivars in both years (all pairwise comparisons P < 0.001).…”

“…To further investigate the effect of root size on geosmin concentration, five roots in each of three diameter grades (<2.5, 2.5-6, and >6 cm) were selected from each 'Merlin' split-split plot in 2016, and a 10-core bulked sample was taken from each size grade as described above. 'Merlin' was selected for analysis by root size because it showed less variation in geosmin concentration between field and greenhouse environments than other commercial cultivars (Freidig and Goldman, 2014). The present study standardized root size across genotypes and environments rather than adding root size as an additional factor in the experimental design, so significant variation in geosmin concentration by root size in 'Merlin'-a genotype documented as less variable than other commercial cultivars-would serve to justify standardization of root size.…”

“…(Goldman, 1996). 'Bull's Blood' and 'Touchstone Gold' possess characteristically high and low geosmin levels, respectively, while 'Merlin' has intermediate geosmin concentration (Freidig and Goldman, 2014); no previous geosmin levels have been measured for 'W357B'. Sites were selected for differing soil types and CEC: soil at Hancock Agricultural Research Station (HARS, Hancock, WI) is Plainfield sand with an average CEC of 1.3 cmol c Ákg -1 , while soil at West Madison Agricultural Research Station (WMARS, Verona, WI) is Griswold loam and Kegonsa silt loam with an average CEC of 16 cmol c Ákg -1 .…”

“…Previous genotype • environment studies of TDS in table beet showed strong environmental effects and limited realized heritability (Goldman et al, 1996), but these estimates were attained using genotypes selected for high pigment concentration rather than commercial horticultural use. In a study of geosmin concentration in table beet, Freidig and Goldman (2014) found highly significant genotype and non-crossover genotype • environment interaction effects, plus a moderately significant environmental effect. The genotype • environment interaction reflected significantly different geosmin concentration between field and greenhouse environments within cultivar, perhaps due to the smaller size of the greenhouse-grown roots.…”

“…Geosmin is known to accumulate in and directly under the root epidermis in table beet (Lu et al, 2003a;Tyler et al, 1978), lending initial support to this hypothesis. However, the presence of geosmin in table beet tissue grown in autoclaved soil (Freidig and Goldman, 2014) and sterile tissue culture (Maher and Goldman, 2018) refutes it. Second, geosmin could be produced within table beet tissue by endophytic microbes.…”