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Jules Janick and Irwin L. Goldman

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Min Wang and Irwin L. Goldman

Genetic relationships among 37 accessions of Beta vulgaris, including 21 table beet, 14 sugar beet, and two Swiss chard (Beta vulgaris ssp. cicla) accessions, were evaluated using randomly amplified polymorphic DNA (RAPD). Genetic distance was estimated based on the presence or absence of polymorphic RAPD bands. Multidimensional scaling plots of genetic distance values revealed that table beet inbred lines from the University of Wisconsin Table beet Breeding Program clustered in an intermediate position between sugar beet breeding lines and standard table beet germplasm, likely because of their origin from an introgression program designed to incorporate sugar beet genes.

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Lynn Maher and Irwin L. Goldman

The earthy flavor of table beet is due to an aromatic terpene derivative called geosmin. It has been hypothesized that geosmin presence in beet is due to geosmin-producing bacteria such as Streptomyces spp. that exist in the soil. However, recent findings suggest that beet may produce geosmin endogenously without microbial influence. The purpose of this study was to determine whether such endogenous production of geosmin occurred in beet by making use of an aseptic tissue culture (TC) environment to remove potential microbial influences on geosmin production. Four table beet accessions (‘Bull’s Blood’, ‘Touchstone Gold’, ‘W364B’, and ‘Pacemaker III’) were grown in three separate TC experiments and in the greenhouse and measured for geosmin concentration via gas chromatography–mass spectrometry (GC-MS). Sequencing of 16S ribosomal RNA was used to identify potential microbial contaminants in TC. Operational taxa units (OTUs) classification resulted in RNA sequences with homology to bacterial RNA of either chloroplast (98%) or mitochondria (2%) origin. Other OTUs identified were considered within the range of sequencing error. In 15 of the 16 TC–grown samples used for the 16S rRNA aseptic validation and in all the greenhouse-grown plant samples, geosmin was detected. Geosmin concentrations from bulked beet tissue of each accession were higher in the TC environment than the greenhouse environment. The lack of microbial detection in the TC environment and the subsequent identification of geosmin from beets grown in the aseptic environment is a strong indication that geosmin is produced endogenously by beets. This finding raises several interesting questions about the functional significance of this molecule for Beta vulgaris.

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Veronica L. Gaertner and Irwin L. Goldman

Half-sib recurrent selection programs were initiated at the University of Wisconsin-Madison in 1978 and 1995 to increase betalain (betacyanin and betaxanthin) concentration in red and yellow table beets (Beta vulgaris L. ssp. vulgaris), respectively. Cycles of selection from both the red and yellow table beet breeding programs were evaluated for pigment and total dissolved solids (TDS) distribution in five tissue sections (outer, middle and center zones of the root; leaf and petiole) in two environments (early and late planting) during 2002. Betaxanthin concentration increased with the later planting date in the majority of the tissue zones in the yellow and red table beet populations. Absolute pigment concentration of the outer root zone increased the most over cycles of selection: 46.6 mg/100 g fresh weight (FW) betaxanthin and 201 mg/100 g FW betacyanin for yellow and red populations, respectively. However, the greatest rate of gain was in the center and middle tissue zones. Selection based on the outer 2 cm of root tissue has effectively increased pigmentation of the entire beet plant. A correlated response to selection in leaf and petiole tissue was measured for pigment concentration in both populations. The contribution of each tissue zone to total pigment concentration of the beet plant remained constant throughout cycles of selection averaging 39%, 25%, 25%, 6%, and 5% for outer, middle, center, petiole and leaf tissue zones, respectively. Across all table beet populations, pigment concentration of the outer root zone was 55% and 62% higher than middle and center zones, respectively. TDS of the outer root zone was 10% and 12% higher than middle and center zones, respectively.

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Thomas C. Koch* and Irwin L. Goldman

Carotenoids (provitamin A) and tocopherols (vitamin E) are powerful antioxidants in plants and in the human diet. Carrot (Daucus carota) has been selected for increased levels of carotenoids, contributing to its orange color and reported health benefits. Selection for increased tocopherol has shown success in seed oils, but little progress has been made in the edible portions of most vegetable crops. HPLC measurement following a simultaneous heptane extraction of both compounds has shown a significant (P ≤ 0.001) positive correlation of α-tocopherol with α-carotene (r = 0.65) and β-carotene (r = 0.52). To increase both the tocopherols and carotenoids in plants, 3 populations have been established from select open-pollinated varieties grown in 2002. These populations consist of half-sib families with these differing selection schemes: based strictly on increased α-tocopherol levels; an index to increase α-carotene, β-carotene and α-tocopherol; and a random population in which no selection is occurring. After one cycle of selection, populations were grown on muck soil during the summer of 2003. Compared with the random population, an increase of 24.68% in α-tocopherol concentration was recorded for the population selected strictly on α-tocopherol while increases of 8.47% in α-tocopherol, 9.31% in α-carotene and 7.31% in β-carotene were recorded for the population with index selection. The continuation of these carrot populations shows promise to produce carrot germplasm with improved human nutritive value.

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Christopher J. D’Angelo and Irwin L. Goldman

Vernalization is an important step for floral initiation in onion (Allium cepa), but our understanding of the minimum vernalization time for long-day storage onions to gain floral competence is limited. A series of time course experiments were conducted over 4 years to determine the effects of vernalization time on sprouting, scape emergence, and flowering in ‘Cortland’, ‘Sherman’, and CUDH2107. We found an endodormancy period is present in the bulbs of these cultivars that lasts for 8 to 10 weeks. In addition, these three accessions achieve optimum uniform scape emergence after chilling for 14 weeks at 10 °C. On average, when bulbs were chilled for 14 weeks, it took 96.8 ± 15.6 days from planting to flowering in all accessions evaluated. As storage duration under vernalizing temperatures increases, the time to sprouting, scape emergence, and flowering decrease. Furthermore, the variance in time from sprouting to scape emergence was greatly reduced between 10 and 12 weeks of storage for ‘Cortland’ and CUDH2107, and between 12 and 14 weeks for ‘Sherman’. After 10 weeks of chilling, each additional week of storage resulted in an average decrease in time to flowering of 4.1%. We also observed large percentages of bulbs flowering without receiving any vernalization. This observation supports our finding that the relationship between vernalization and flowering in long-day storage onion is facultative rather than obligate. These findings help define the relationship between dormancy, vernalization, and flowering in long-day storage onion.

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Solveig J. Hanson and Irwin L. Goldman

Earthy aroma and sweet flavor, conferred by the volatile terpenoid geosmin (trans-1,10-dimethyl-trans-9-decalol) and sucrose, respectively, are two essential flavor components of table beet (Beta vulgaris ssp. vulgaris). To elucidate the influence of genotype, growing environment, and fertilizer treatment on geosmin concentration and sucrose [as total dissolved solids (TDS)] in table beet, a field-based genotype × environment study was conducted using a split-split plot design. Four site × year combinations served as whole plots; MgSO4·H2O and CaSO4 comprised split plot fertilizer treatments; open-pollinated cultivars Bull’s Blood and Touchstone Gold, F1 hybrid Merlin, and inbred line W357B constituted split-split plot genotype treatments. Geosmin concentration was measured via gas chromatography–mass spectrometry using headspace solid-phase microextraction, and TDS was measured via refractometry. Variation in geosmin concentration was attributable to a strong genotype effect and significant genotype × year and year × site interactions. Genotypes were observed to have characteristic geosmin concentration and variance, despite being grown in soils with widely divergent physical and chemical properties. While a significant genotype main effect was also present for TDS, it occurred in the context of significant four-way and three-way genotype × environment interactions, plus significant effects of year and year × site interaction. Neither geosmin concentration nor TDS was significantly influenced by fertilizer treatment or fertilizer × environment interactions, averaged across genotypes. Genetics determined a larger proportion of variance for geosmin concentration than TDS in the four table beet genotypes assessed, as reflected in repeatability measurements of 0.90 and 0.43, respectively. This experiment provides support for the primacy of genotype in determining table beet geosmin concentration and a comparatively moderate role of genotype in determining table beet TDS. Thus, genetic manipulation of table beet geosmin could yield cultivars with signature flavor characteristics to serve both niche and mainstream consumer groups, expanding market opportunities for breeders and growers.

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Amy K. Freidig and Irwin L. Goldman

Oxalic acid (C2O4 2–) is a compound of interest as a result of its relationship with kidney stone formation and antinutritive properties. Because table beet [Beta vulgaris ssp. vulgaris (garden beet group)] is considered a high oxalate food, breeding to decrease oxalic acid levels is an area of interest. In this study, a field trial was conducted over 2 years for 24 members of the Chenopodiaceae using two different planting dates to determine if variation exists for both total and soluble oxalic acid levels in roots and leaves. Total and soluble oxalic acid was extracted from homogenized root core and leaf tissue samples and a colorimetric enzymatic assay was used to determine total and soluble oxalic acid levels. Mean values ranged from 722 to 1909 mg/100 g leaf tissue and 553 to 1679 mg/100 g leaf tissue for total and soluble oxalate levels, respectively. Beet cultivar Forono and swiss chard [B. vulgaris ssp. vulgaris (leaf beet group)] cultivar Burpee's Fordhook Giant Chard produced the respective highest and lowest soluble and total oxalic acid leaf levels. Swiss chard cultivars produced 38% less total oxalate compared with table beet cultivars based on overall means. Root soluble oxalate values ranged from 103 to 171 mg/100 g root tissue and total values ranged from 95 to 142 mg/100 g root tissue. Significant variation for both total and soluble oxalic acid levels were detected, indicating progress could be made toward breeding for lower oxalic acid levels in table beet. However, gains in oxalic acid nutritional quality may be limited because it would take a substantial decrease in levels for table beet to be reclassified as a low oxalate food.