Rhubarb (
Oxalic acid generally occurs as oxalate salts in plants and humans (Peck et al., 2016). Oxalic acid is considered as the end product in mammalian metabolism, for example, metabolism of some amino acid, glycolate or ascorbic acid (EMEA, 2004). Oxalic acid forms water-soluble salts with Na+, K+ and NH4+ ions or water-insoluble forms with Ca2+, Fe2+ and Mg2+ and from which the calcium oxalate is the most important constituent of kidney stones (Noonan and Savage, 1999). In plants, oxalates exist in partly insoluble forms such as oxalates, free oxalic acid and calcium oxalate (Silberhorn, 2005). Generally, they can be found in relatively small amounts in many plants and their content varies within species and also among cultivars. Nevertheless, genera such as
Although the major functional role usually attributed to L-ascorbic acid is its function as a water-soluble antioxidant, it also plays a role as a precursor of oxalate in many plants (Yang and Loewus, 1975; Williams et al., 1979). Oxalates might be a final product of L-ascorbic acid degradation in food. On the other hand, it was proven that L-ascorbic acid is also metabolized by pathways other than those resulting in oxalate formation (Knight et al., 2016). Oxalate-accumulating plants (e.g. spinach, wood sorrel, shamrock) produce oxalic acid from dehydro-L-ascorbic acid, an oxidation product of L-ascorbic acid-1-(14)C (Yang and Loewus, 1975). The results of a study on
Abnormal intake of L-ascorbic acid could also be a significant risk factor for the development of kidney stones as well as the oxalates themselves (Knight et al., 2016).
According to the TRIDGE database, the highest export values reached 959.7 million USD in China, followed by Belgium, Spain and Mexico (approximately from 523 million to 430 million USD). Next is Poland and the Netherlands at export values up to 300 million USD. Egypt, France, Turkey and the United States reached export values of around 100 million USD in 2023 (TRIDGE database, 2023).
The present study is focused on the evaluation of L-ascorbic and oxalic acid content during the harvesting period of three rhubarb species (
The influence of
Description of
No. | Plant ID1 | Species | Cultivar | Propagation2 | Origin |
---|---|---|---|---|---|
1 | 42H7500001 | Jara | V | CZ | |
2 | 42H7500003 | Victoria | V | GB | |
3 | 42H7500004 | Dawes Chalenge | V | USA | |
4 | 42H7500005 | The Sutton | V | GB | |
5 | 42H7500006 | Holsteiner Blut | V | D | |
6 | 42H7500008 | – | G | GB | |
7 | 42H7500011 | – | G | GB | |
8 | 42H7500012 | – | G | UA | |
9 | 42H7500014 | – | G | BG | |
10 | 42H7500016 | Timperley Early | V | GB | |
11 | 42H7500020 | – | G | PL | |
12 | 42H7500023 | – | G | GB | |
13 | 42H7500025 | Glaskins Perpetual | G | GB | |
14 | 42H7500030 | Krupnochereshkovyj | V | RUS | |
15 | 42H7500044 | – | V | CZ | |
16 | 42H7500047 | – | V | CZ |
Plant ID according to GRIN CZECH database (GRIN Czech, 2023).
Propagation V—vegetative, G—generative.
Meteorological data were recorded with automatic sensors located near the experimental field. Recorded data comprise the amount of precipitation (mm), air temperature (°C) and sunshine duration, defined as the number of sunny hours. The long-term average values (2015–2021) of selected climate characteristics and the values of the studied period (2022) are shown in Table 2 (CHMI, 2022).
Selected climate characteristics for Lednice location.
Period | Average day temperature (°C) | The sum of precipitation (mm) | Sum of sunshine (hr) |
---|---|---|---|
May 2015–2021 | 15.1 | 56.3 | 208.0 |
June 2015–2021 | 20.5 | 46.8 | 269.9 |
July 2015–2021 | 21.6 | 64.8 | 260.9 |
May 2022 | 16.8 | 26.4 | 270.9 |
June 2022 | 21.1 | 76.9 | 296.4 |
July 2022 | 21.6 | 46.3 | 290.6 |
According to the agrochemical analyses of the soil from the experimental field in 2022, the nitrogen content was 0.146%, the content of phosphorus was 37.794 mg · kg-1 and the potassium content was 198 mg · kg-1. The calcium and magnesium contents were 4961 mg · kg-1 and 198 mg · kg-1, respectively. The pH (H2O) of the soil at a depth of 0.3 m was 7.71. The area of cultivation of each accession was 2.9 m2. Plants were grown without additional irrigation.
Sixteen accessions of
Classification of leaf petiole morphological data and selected substances content (Turečková et al., 2001).
Trait | Description |
---|---|
Leaf – petiole skin colour above base | 1 = green, 2 = rose, 3 = red stripped |
Leaf – petiole skin colour at the base | 1 = green, 2 = rose, 3 = red stripped, 4 = red, 5 = dark red |
Leaf – shape of petiole base in cross-section | 1 = oval, 2 = reniform, 3 = semi-circular |
Leaf – surface of petiole lower (abaxial) side | 1 = smooth, 2 = ribbed |
Leaf – flesh colour at the petiole base | 1 = green, 2 = green to white, 3 = green to rose, 4 = red to dark red |
Leaf – petiole thickness (diameter) (mm) | 1 = very small (<20), 3 = small (20-25), 5 = intermediate (26-30) |
Leaf – petiole L-ascorbic acid content (mg · kg-1 FW) | 1 = very low (<50), 3 = low (50-150), 5 = intermediate (151-250), 7 = high (251-350), 9 = very high (>350) |
Leaf – petiole oxalic acid content (mg · kg-1 FW) | 1 = very low (<1500), 3 = low (1500-2500), 5 = intermediate (2501–3500), 7 = high (3501-4500), 9 = very high (>4500) |
Leaf – petiole total soluble solids content (%) | 1 = very low (<2.0), 3 = low (2.0-3.5), 5 = intermediate (3.6-5.0), 7 = high (5.1-6.5), 9 = very high (>6.5) |
FW, fresh weight.
The concentration of L-ascorbic acid was determined by the modified high-performance liquid chromatography (HPLC) method according to Arya et al. (2000). Three parts were taken from each petiole - the basal, central and upper parts - and pooled and then homogenized. For analyses, 10 g of the mixture was mixed in the blender with 20 mL of 0.1 M oxalic acid. The homogenate was filtered and adjusted with 0.1 M oxalic acid to a volume of 100 mL. Then 20 mL of the mixture solution was centrifuged at 3500 rpm for 10 min. The supernatant was filtered through a microfilter (PVDF (polyvinylidene difluoride membrane) 0.45 μm) and used for the determination (ECOM, 1999). The analyses were performed by RP-HPLC (reversed-phase high-performance liquid chromatography) (ECOM, Czech Republic) at 254 nm using a UV-VIS (ultraviolet visible) detector on column (C18). All samples were evaluated in three technical replicates. The amount of L-ascorbic acid was expressed as mg · 100 g-1 FW.
In a 4-year evaluation, the standard titration with the potassium permanganate method as described by Karamad et al. (2019) was used. In 2022, a more precise method to quantify oxalic acid content was applied. The content was determined by a modified HPLC method according to Rahman et al. (2007). The petioles were cut, dried at 70°C in a forced-air dryer for 48 hr and ground into a powder. The sample (0.5 g) was extracted by 15 mL of 1 M hydrochloric acid solution. The sample suspension was heated in a bath of boiling water for 18 min. After cooling, the mixture was filtered, rinsed with distilled water and adjusted to 50 mL. The filtrate of the acid extract was adjusted to pH 3.0 using a 5 M sodium hydroxide solution. The filtrates were further filtered through a syringe filter with a 0.45 μm hydrophilic membrane before analysis by RP-HPLC (ECOM, Czech Republic). A 10 μL sample was injected at a column (C18) using a mobile phase of 15 mM NaH2PO4 (pH 2.7), a flow rate of 0.5 mL · min-1 and a wavelength of 210 nm. Measurement of each accession was performed in three technical replicates. The amount of oxalic acid was expressed as mg · 100 g-1 FW.
The content of total soluble solids was evaluated according to Zbíral (2005). The samples were sliced and pressed, and the extracted juice was dropped on the measuring glass plate of the refractometer. Measurements were then conducted on the digital optical instrument HI 96801 (Hanna Instruments Ltd., USA) measuring refractive index, which was converted to the sucrose sugar concentration (%) in water suspensions. For each sample, three technical replicates (measurements) were performed.
In 2022, a detailed observation of the development of L-ascorbic and oxalic acid content and soluble solids content in rhubarb petioles was done. The evaluation was performed at six-time points: May 3rd, May 17th, May 31st, June 14th, June 28th and July 12th, 2022.
Based on the morphological diversity of the studied
Initially, 17 ISSR primers (Tabin et al., 2016) were screened for polymorphism and finally 15 polymorphic primers (Table 4) were selected for generating ISSR profiles of the
Characteristics of 15 ISSR primers used in the study.
Primer name | Primer sequence (5′→3′) | Ta1 | No. of bands | Product size range (bp) |
---|---|---|---|---|
UBC-807 | AGA GAG AGA GAG AGA GT | 52 | 16 | 250–1100 |
UBC-808 | AGA GAG AGA GAG AGA GC | 51 | 13 | 300–1300 |
UBC-809 | AGA GAG AGA GAG AGA GG | 51 | 13 | 180–1000 |
UBC-810 | GAG AGA GAG AGA GAG AT | 46 | 4 | 220–510 |
UBC-815 | CTC TCT CTC TCT CTC TG | 49 | 3 | 700–1400 |
UBC-817 | CAC ACA CAC ACA CAC AA | 51 | 10 | 650–1300 |
UBC-836 | AGA GAG AGA GAG AGA GYA | 51 | 4 | 200–430 |
UBC-840 | GAG AGA GAG AGA GAG AYT | 48 | 5 | 650–1300 |
UBC-842 | GAG AGA GAG AGA GAG AYG | 52.5 | 5 | 220–680 |
UBC-844 | CTC TCT CTC TCT CTC TRC | 51 | 4 | 580–850 |
UBC-845 | CTC TCT CTC TCT CTC TRG | 53 | 13 | 700–2100 |
UBC-848 | CAC ACA CAC ACA CAC ARG | 52 | 18 | 280–1200 |
UBC-849 | GTG TGT GTG TGT GTG TYA | 49 | 3 | 750–1300 |
UBC-850 | GTG TGT GTG TGT GTG TYC | 52.5 | 4 | 450–1400 |
UBC-884 | HBH AGA GAG AGA GAG AG | 45 | 3 | 490–1000 |
Ta: annealing temperature, B = (C, G, T), H = (A, G, T), R = (A, G), Y = (C, T).
Morphological data analysis was performed based on the six leaf-petiole quality characters obtained for the same input material as for the L-ascorbic and oxalic acid content. The representative values of individual descriptors for each accession were calculated using the 4-year dataset. These data were subjected to distance-based clustering analysis using the unweighted pair-group method with arithmetic averages (UPGMA) and Jaccard’s similarity coefficient by the FreeTree v.0.9.1.50 software (Hampl et al., 2001). The phylogenetic tree was visualized by FigTree v1.4.4 (Rambaut, 2010) software.
Data of L-ascorbic and oxalic acid content were transformed by the decimal logarithm and analysed by repeated measures analysis of variance (ANOVA) and Tukey’s multiple comparison tests with an α level of 0.05 by the Statistica v.12.0.0 software (StatSoft, USA). The obtained results were examined by residual analysis using the same software. The putative role of L-ascorbic acid as the oxalate precursor in
For genetic analysis, each amplified fragment of the ISSR reaction was scored manually and converted into a binary matrix based on the presence (1) and absence (0) of the respective band. Subsequently, the data were used to construct a difference/similarity matrix based on UPGMA and Jaccard’s similarity coefficient and to construct a phylogenetic tree using FreeTree v. 0.9.1.50 (Hampl et al., 2001) and FigTree v. 1.4.4 (Rambaut, 2010) software. Based on the taxonomical relationships, the accession 42H7500012 (
The gradient for the response data in the ordination analysis was 0.6 units long, and redundancy analysis (RDA) was chosen as a statistical method. The statistical significance of the results was calculated with the Monte-Carlo permutation test (499 permutations). Results are significant at a significance level of
Four-year observation of six morphological characters of petioles and the content of L-ascorbic acid, oxalic acid and soluble solids in 16 accessions of
Data of 4-year observation of
Plant ID | Petiole skin colour above base | Petiole skin colour at the base | Shape of petiole base in cross-section | The surface of the petiole abaxial side | Flesh colour at the petiole base | Petiole thickness diameter (mm) | Petiole L-ascorbic acid content (mg · kg-1 FW) | Petiole oxalic acid content (mg · kg-1 FW) | Petiole soluble solids content (%) |
---|---|---|---|---|---|---|---|---|---|
42H7500001 | 2 | 2 | 2 | 1 | 1 | 3 | 3 | 9 | 5 |
42H7500003 | 2 | 4 | 1 | 2 | 3 | 1 | 3 | 9 | 5 |
42H7500004 | 3 | 3 | 3 | 1 | 2 | 3 | 3 | 9 | 5 |
42H7500005 | 2 | 5 | 3 | 1 | 3 | 1 | 5 | 9 | 5 |
42H7500006 | 2 | 5 | 1 | 2 | 4 | 3 | 3 | 9 | 5 |
42H7500008 | 2 | 4 | 3 | 2 | 1 | 1 | 5 | 9 | 5 |
42H7500011 | 1 | 5 | 2 | 1 | 1 | 1 | 5 | 9 | 5 |
42H7500012 | 1 | 4 | 3 | 2 | 1 | 1 | 3 | 9 | 3 |
42H7500014 | 1 | 1 | 3 | 2 | 3 | 1 | 3 | 9 | 5 |
42H7500016 | 1 | 5 | 2 | 2 | 3 | 1 | 3 | 9 | 5 |
42H7500020 | 3 | 2 | 3 | 1 | 4 | 1 | 3 | 9 | 5 |
42H7500023 | 3 | 4 | 3 | 1 | 2 | 1 | 5 | 9 | 5 |
42H7500025 | 1 | 5 | 2 | 2 | 1 | 1 | 5 | 9 | 3 |
42H7500030 | 3 | 5 | 2 | 2 | 1 | 1 | 5 | 9 | 5 |
42H7500044 | 1 | 4 | 2 | 1 | 3 | 3 | 5 | 9 | 5 |
42H7500047 | 3 | 4 | 2 | 2 | 1 | 1 | 5 | 9 | 5 |
FW, fresh weight.
The majority of the evaluated accessions of
According to the average content of L-ascorbic acid, oxalic acid and soluble solids, evaluated accessions created groups independently of the groups based on taxonomy or morphological characteristics. In the case of L-ascorbic acid, eight accessions (42H7500001, 42H7500003, 42H7500004, 42H7500006, 42H7500012, 42H7500014, 42H7500016 and 42H7500020) showed values of 5–15 mg · 100 g-1 FW, representing a low content of L-ascorbic acid. The value of L-ascorbic acid content reported for
Similarly, in Table 5, the 4-year average of oxalic acid content measured in the harvest season is expressed by a descriptor value according to Table 3. For all accessions, a very high content of oxalic acid (>450 mg · 100 g-1 FW) was found. Significantly lower content was presented by Stoleru et al. (2019) ranging from 256 mg · 100 g-1 to 377 mg · 100 g-1 FW in rhubarb grown in Romania. The oxalic acid content in our study was comparable to experiments from Latvia (Duma et al., 2016) or New Zealand (Nguyen and Savage, 2020). The content of oxalic acid is strongly variable, probably depending on local climate and soil conditions, and taxonomy. Moreover, the variability in content may be affected by the selected analysis type (titration, HPLC, catalytic kinetic spectrophotometry).
For the content of soluble solids, the intermediate content (3.6%–5%) was the most prevalent. The results found in Slovakia (3.54–4.37°Bx) (Mezeyová et al., 2021) were close to our values.
The UPGMA analysis based on morphological data created a phylogenetic tree with four main clades, gathering 12 of 13
The first clade (Group I) linked
To evaluate the development of L-ascorbic and oxalic acid, the content of those acids was evaluated in six sampling terms during the year 2022: May 3rd, May 17th, May 31st, June 14th, June 28th and July 12th, covering the common rhubarb harvesting period in South Moravia (Czech Republic). Regarding the climate conditions, values of the average daily temperature and the sum of sunshine did not differ from average values recorded in the last 6 years (2015–2021, Table 2). A different value was determined for the precipitation, where the long-term precipitation in May (56.3 mm) differed from 2022 by almost 30 mm (26.4 mm in 2022). Contrary to the June long-term value of 46.8 mm, the precipitation in 2022 was markedly higher (76.9 mm) (CHMI, 2022). The lowest sum of precipitation was measured in the 2 weeks before the third sampling term (9.5 mm) and the highest before the fourth term (49.7 mm). Some accessions showed a significant increase in L-ascorbic acid content between those two terms. The content of L-ascorbic acid increased by around 50% or more in
The content of L-ascorbic acid developed as follows: in most (10 of 16 accessions), the increase of L-ascorbic acid between the first and second sampling terms was recorded, with the most significant increase in the
Average L-ascorbic acid content in
Taxa | 03/05/2022 | 17/05/2022 | 31/05/2022 | 14/06/2022 | 28/06/2022 | 12/07/2022 |
---|---|---|---|---|---|---|
42H7500012 | 8.76 ± 0.18 | 11.03 ± 0.08 | 10.11 ± 0.30 | 13.36 ± 0.12 | 6.74 ± 0.09 | 25.62 ± 0.37 |
42H7500001 | 15.08 ± 0.34 | 9.28 ± 0.21 | 10.63 ± 0.56 | 15.16 ± 0.24 | 9.59 ± 0.25 | 16.72 ± 0.75 |
42H7500003 | 12.37 ± 0.11 | 13.84 ± 0.10 | 7.69 ± 0.57 | 15.97 ± 0.32 | 8.31 ± 0.39 | 18.72 ± 0.48 |
42H7500004 | 15.15 ± 0.36 | 21.06 ± 0.28 | 18.88 ± 0.46 | 15.24 ± 0.49 | 14.65 ± 0.23 | 18.69 ± 0.20 |
42H7500005 | 16.07 ± 0.12 | 16.12 ± 0.55 | 16.44 ± 0.44 | 29.62 ± 0.38 | 28.08 ± 1.15 | 33.49 ± 0.64 |
42H7500006 | 7.07 ± 0.17 | 17.36 ± 0.36 | 8.75 ± 0.09 | 20.36 ± 0.35 | 13.21 ± 0.03 | 28.24 ± 0.50 |
42F7500008 | 20.98 ± 0.21 | 25.21 ± 0.30 | 27.02 ± 0.06 | 33.53 ± 1.03 | 21.42 ± 0.28 | 32.39 ± 0.22 |
42H7500011 | 12.27 ± 0.23 | 13.88 ± 0.03 | 13.14 ± 0.02 | 18.43 ± 0.21 | 13.15 ± 0.36 | 19.55 ± 0.34 |
42H7500016 | 9.52 ± 0.08 | 11.10 ± 0.26 | 8.90 ± 0.46 | 11.44 ± 0.21 | 11.50 ± 0.21 | 23.20 ± 0.29 |
42H75000201 | 9.50 ± 0.14 | 6.37 ± 0.27 | 15.38 ± 0.11 | 7.06 ± 0.17 | 9.88 ± 0.48 | 13.42 ± 0.09 |
42H7500023 | 6.77 ± 0.21 | 11.76 ± 0.32 | 13.07 ± 0.52 | 12.56 ± 0.16 | 9.05 ± 0.09 | 14.88 ± 0.11 |
42H7500025 | 12.80 ± 0.05 | 14.05 ± 0.32 | 10.16 ± 0.52 | 18.10 ± 0.32 | 11.39 ± 0.30 | 14.79 ± 0.12 |
42H7500030 | 13.48 ± 0.54 | 12.28 ± 0.03 | 6.66 ± 0.09 | 18.88 ± 0.13 | 10.16 ± 0.14 | 23.54 ± 0.31 |
42H7500044 | 13.39 ± 0.60 | 12.54 ± 0.19 | 15.26 ± 0.12 | 21.27 ± 0.13 | 20.27 ± 0.08 | 24.81 ± 0.65 |
42H7500047 | 14.67 ± 0.05 | 10.39 ± 0.14 | 18.59 ± 0.02 | 16.90 ± 0.17 | 18.69 ± 0.07 | 16.84 ± 0.11 |
42H7500014 | 15.05 ± 0.24 | 16.96 ± 0.18 | 12.10 ± 0.06 | 18.04 ± 0.18 | 19.10 ± 0.08 | 22.19 ± 0.24 |
Originally described as
FW, fresh weight.
Oxalic acid content for
03/05/2022 | 17/05/2022 | 31/05/2022 | 14/06/2022 | 28/06/2022 | 12/07/2022 | |
---|---|---|---|---|---|---|
42H7500012 | 670.19 ± 0.02 | 1036.48 ± 0.04 | 1413.99 ± 0.03 | 1636.8 ± 0.02 | 2315.14 ± 0.12 | 1454.68 ± 0.04 |
42H7500001 | 453.79 ± 0.01 | 1375.85 ± 0.02 | 1991.31 ± 0.03 | 1752.99 ± 0.03 | 1504.59 ± 0.02 | 1463.98 ± 0.05 |
42H7500003 | 540.69 ± 0.03 | 616.96 ± 0.02 | 723.53 ± 0.04 | 620.69 ± 0.01 | 1111.35 ± 0.02 | 761.63 ± 0.02 |
42H7500004 | 792.38 ± 0.00 | 1005.73 ± 0.02 | 889.51 ± 0.05 | 981.64 ± 0.05 | 2287.14 ± 0.08 | 711.01 ± 0.04 |
42H7500005 | 598.80 ± 0.00 | 987.47 ± 0.05 | 793.82 ± 0.01 | 843.32 ± 0.06 | 707.70 ± 0.02 | 1317.66 ± 0.11 |
42H7500006 | 354.81 ± 0.02 | 585.79 ± 0.00 | 926.35 ± 0.04 | 1686.64 ± 0.14 | 1050.84 ± 0.01 | 1194.20 ± 0.01 |
42F7500008 | 407.26 ± 0.01 | 448.45 ± 0.01 | 1743.34 ± 0.03 | 1927.36 ± 0.14 | 1281.33 ± 0.08 | 1546.97 ± 0.03 |
42H7500011 | 451.24 ± 0.01 | 456.33 ± 0.03 | 833.45 ± 0.00 | 817.21 ± 0.02 | 700.95 ± 0.01 | 936.17 ± 0.00 |
42H7500016 | 296.99 ± 0.01 | 432.20 ± 0.01 | 402.99 ± 0.00 | 807.39 ± 0.05 | 486.89 ± 0.00 | 699.58 ± 0.01 |
42H7500020 | 460.39 ± 0.01 | 1523.02 ± 0.05 | 1442.98 ± 0.01 | 2034.83 ± 0.08 | 1229.00 ± 0.01 | 1138.73 ± 0.04 |
42H7500023 | 921.14 ± 0.01 | 869.45 ± 0.01 | 861.78 ± 0.01 | 1527.04 ± 0.03 | 539.44 ± 0.04 | 836.12 ± 0.00 |
42H7500025 | 570.38 ± 0.02 | 561.60 ± 0.01 | 656.61 ± 0.01 | 906.80 ± 0.05 | 679.91 ± 0.00 | 689.21 ± 0.00 |
42H7500030 | 436.23 ± 0.01 | 671.23 ± 0.00 | 985.26 ± 0.01 | 1839.81 ± 0.03 | 835.38 ± 0.02 | 881.95 ± 0.01 |
42H7500044 | 942.77 ± 0.03 | 1345.46 ± 0.07 | 1573.44 ± 0.03 | 1691.24 ± 0.04 | 1276.30 ± 0.02 | 1835.46 ± 0.03 |
42H7500047 | 756.72 ± 0.03 | 1473.44 ± 0.05 | 1330.53 ± 0.02 | 1739.93 ± 0.04 | 981.73 ± 0.00 | 972.80 ± 0.04 |
42H7500014 | 811.57 ± 0.03 | 1628.48 ± 0.01 | 1983.39 ± 0.01 | 1974.29 ± 0.07 | 2266.68 ± 0.02 | 1479.83 ± 0.05 |
originally described as
FW, fresh weight.
The statistical analysis of the influence of taxonomy and harvesting time on the content of L-ascorbic acid showed significant differences for both factors. In the
The content of oxalic acid in the
The ordination diagram (Figure 2) shows relationships between accessions, sampling terms and the content of oxalic acid and L-ascorbic acid. The content of L-ascorbic acid was the highest at the last, sixth, sampling term. The diagram also indicates an obvious negative correlation between oxalic acid content and the first sampling term, representing the lowest content of oxalic acid at the beginning of the harvesting season. Accessions
The measured values of both acids obtained from May to July were evaluated from the perspective of a possible role of L-ascorbic acid as a precursor of oxalate formation in
The analysis based on the molecular ISSR markers clustered 15
Explanatory notes | |||
---|---|---|---|
RR1 | 42H7500001 |
RRhap | 42H7500014 |
RR3 | 42H7500003 |
RR16 | 42H7500016 |
RR4 | 42H7500004 |
RR20 | 42H7500020 |
RR5 | 42H7500005 |
RR23 | 42H7500023 |
RR6 | 42H7500006 |
RR25 | 42H7500025 |
RR8 | 42F7500008 |
RR30 | 42H7500030 |
RR11 | 42H7500011 |
RR44 | 42H7500044 |
RPW12 | 42H7500012 |
RR47 | 42H7500047 |
T1-T6 | Sampling terms 1 to 6 |
Results of RDA ordination analysis evaluating relationships between the content of oxalic acid and L-ascorbic acid and groups based on molecular data (Figure 3) and sampling terms indicate several correlations (Figure 4). Accessions from Group II had a higher content of L-ascorbic acid at the sixth sampling term. A negative correlation between oxalic acid content and Group Ia suggests a lower content of oxalic acid in this group. Conversely, some positive correlation indicating a higher content of oxalic acid was observed in Group Ib and Group III. The results of this analysis can explain the possible effect of taxonomy in a few groups (Group 2, Group 1a) on L-ascorbic and oxalic acid content development during the harvesting season. In other groups, the correlation was weaker. The content of L-ascorbic and oxalic acid in accessions from Group 1c was probably affected by other factors not included in this analysis.
The estimation of phenotypic and genotypic variance plays an important role in plant breeding, the preservation of genetic resources and the food industry, leading to the targeted use of species with a beneficial effect on human health. According to our observaton, the content of L-ascorbic acid, one of the most well-known antioxidant agents, is dependent on taxonomical membership at the level of species but may vary between individual cultivars. A significant impact was also confirmed for the harvesting time, showing an increasing trend of L-ascorbic content during the cultivation season. Based on the level of oxalic acid determined in rhubarb petioles during the harvesting period, the recommended time for the harvest and use of rhubarb petioles in the conditions of the South Moravia region in the Czech Republic is from May to early June. At this time, the content of oxalic acid has decreased and the possible risk of calcium oxalate formation is predicted to be minimalized. The best results were observed for