1. INTRODUCTION

Potato (Solanum tuberosum) as the fifth most important crop in the world (Good Seed Ventures, 2021), along with native potato (Solanum sp), Oca (Oxalis tuberosa Molina), Olluco (Ullucus tuberosus Caldas) and Isaño (Tropaeolum turosum Ruíz & Pav.) are considered foods of high nutritional value (Choquechambi et al., 2019). Andean native cultivars of potatoes and minor tubers, represent a diverse range of tuberous crops of economic and nutritional importance in Bolivia (Cipotato, 2023). The Andean region hosts a diverse array of tuber cultivars, each characterized by unique flavors, colors, and adaptability to different production zones (Calliope et al., 2018). These cultivars could play a pivotal role in enhancing food diversity, rebuilding global food system (CPAD, 2023), a crucial aspect considering that, out of approximately 30,000 edible plant species, only around 30 support the human diet (FAO, 2015). Embracing these varied cultivars can significantly enrich our food supply. Additionally, minor tubers, such as oca and isaño, contribute to the region's agricultural biodiversity, offering unique profiles that enrich the local diet. This extraordinary genetic diversity plays a crucial role in food security and cultural heritage, which today faces unprecedented genetic erosion pressure (Malice and Baudoin, 2009).

Potatoes are notable for their rich complex carbohydrates, dietary fiber, and essential vitamins and minerals (Karan, 2023), offering energy support, and contributing to immune function (Chandrasekara and Josheph Kumar, 2016). Native potatoes are rich in bioactive compounds, polyphenols, anthocyanins, flavonoids, carotenoids, and minerals, such as potassium, iron, zinc, phosphorus, and magnesium (Ligarda-Samanez et al., 2023). Andean minor tubers are gaining recognition as functional foods due to their abundance in carbohydrates, dietary fiber, and essential nutrients such as vitamins and minerals. This nutritional profile is attracting consumers in several countries, thereby promising added value for the local farmers involved with these crops (Leidi et al., 2018).

Minimal research has explored the mineral content of native potatoes and minor tubers. Understanding the variability in their mineral composition holds the key to enhancing our knowledge and addressing hidden hunger among vulnerable communities. The limited utilization of these crops is rooted in the lack of comprehensive understanding of their nutritional value and applications. Through detailed analysis of their mineral nutrient composition and identification of their unique characteristics, we can unlock their potential for nutritional breeding programs. This endeavor will not only enrich our understanding of their dietary significance but also fortify food security and resilience against climate change. Furthermore, it will highlight their importance in sustainable agriculture and the preservation of genetic diversity, offering insights into their broader role in strengthening global food systems and conserving biodiversity.

The purpose of the present study was to examine the mineral element composition of commercial potato, native potato, oca, isaño and papa lisa selected locally from the representative diversity of tuber crops in Bolivia. A second goal was to identify association of the mineral composition to specific and intrinsic characteristics of tuber species under study.

MATERIALS AND METHODS

Study area. The study took place in Bolivia, a country that holds a great variability of native potatoes and minor tubers (Oca, Olluco and Isaño), crops that play a fundamental role in the cultivation and evolution of a wide array of diversity through natural processes and human selection over millennia.

Plant materials. They were used samples from four commercially important potato varieties (Desiree, Puka Huaycha, Marcela, and Huaycha), eight indigenous potato cultivars deeply embedded in the Bolivian food culture and prevalent in local markets (Saqampaya, Waycha ADG, Sipankachis, Nameless 1, Canastilla, Nameless 2, Iscayachi, and Sakampaya), four Oca cultivars (Chismi Negro, Kellu Apilla, Wari Chuchuli, Kowi), two Isaño cultivars (Isaño and Isaño Jaspeado), and three Papa Lisa cultivars (Ravelo Lisa, Lisa Oca, and Sorata Lisa). All the genetic material was collected at a local market in Bolivia, comprehensive detail in Table 1. The collected samples were washed with distilled water and dried at room temperature. The collected tuber was identified based on the few days after harvesting.

The mineral content analyses were carried out at the laboratory of Chemical Research (Cochabamba, Bolivia).

Chemical analysis. A photometric method of analysis using Digital Clinical Flame Photometer, model ME-882 from India, was employed to determine the content of potassium (K), sodium (Na), phosphorus (P), boron (B), and nitrogen (N) in tuber samples. In this method, the sample solution is aspirated into a flame, leading to the atomization of the sample. Each element emits light at characteristic wavelengths when exposed to the flame. The Flame Photometer measures the intensity of the emitted light, and the digital readout provides concentration values for each analyzed element in the sample.

Atomic Absorption Spectrometry using the PG990 Atomic Absorption Spectrometer from PG Instruments Ltd, United Kingdom, was employed to determine the concentration of iron (Fe), magnesium (Mg), aluminum (Al), cobalt (Co), manganese (Mn), molybdenum (Mo), and zinc (Zn) in tuber samples, this method involves the absorption of light at specific wavelengths by atoms in the vapor phase. The emitted light from the hollow cathode lamp passes through the vaporized sample, and the absorbed light by the atoms is measured. The obtained data were used to calculate the concentration of the target minerals in the potato sample. All the analysis were conducted following the procedures recommended by Association of official Agricultural Chemists (AOAC), (AOAC INTERNATIONAL, 2023).

To determine the Brix degree and pH in potato, juice free from solid particles was extracted from a representative sample. A few drops were then submitted to the refractometer and pH meter, respectively. For determining the humidity of potatoes using the gravimetric method, a fresh sample consisting of uniform pieces of peeled potatoes was weighted using an analytical balance. Then sample was placed in an oven until a constant weight was achieved. Each dried piece was weighed to calculate the humidity.

Statistical analysis. Descriptive statistics were estimated from the mineral composition of each tuber specie to determine the means, dispersion, and departure from normality. Data from each tuber specie were subjected to analysis of correlation for all combinations of minerals, and analysis of variance (ANOVA) was performed for species for each mineral. Principal component analysis (PCA) of mineral composition and tuber species was performed using standardized (l = 0, r = 1) means in the prcomp function of R (R Core Team, 2023). Briefly, the resulting principal component analysis (PCA) scores for minerals and tuber species were plotted in a biplot, and mineral vectors were drawn from the origin to their corresponding coordinates. An angle formed between two mineral vectors approximated their correlation, with 0° and 180° angles indicating strong correlations (positive and negative, respectively) and 90° angles representing a weak correlation (Yan and Tinker, 2006).

Multitrait Genotype-Ideotype Distance Index, MIGDI graphic analysis was carried out to evaluate the distance between a genotype and an ideotype, in this case considering the composition of the minerals, in such a way as to identify the tuber species that is closest to the ideal composition. The analysis was performed with the METAN package with the free software R (Olivoto et al., 2022).

RESULTS AND DISCUSSION

Mean performance in mineral content of tuber cultivars.

Native potato, the mineral composition of native potatoes revealed significant variations across various elements (Table 1 and Fig. 1). They exhibited a substantial mean nitrogen (N) and potassium content of 2149.9 and 1436.7 mg/100 g respectively, with a relatively low coefficient of variation (CV) of 19.9 and 18.3%. Phosphorus (P) and magnesium (Mg) content were also noteworthy, with means of 182.1 and 114.8 mg/100 g, respectively, with a CV of 17.9 and 23.5%, respectively, these results coincide with those reported by Karan (2023) where in general the high concentration of K in potato cultivars stands out. The sodium content, at 38.29 mg/100g, emerged notably high, yet exhibited considerable dispersion with a CV value of 68.9%. Noteworthy were the average micronutrient levels crucial for addressing hidden hunger, with Iron (Fe) and Zinc (Zn) in native potatoes measured at 4.32 and 1.17 mg/ 100g, respectively. Our study revealed that minerals such as manganese (Mn), copper (Cu), including molybdenum (Mo), and aluminum (Al), exhibit moderate mean values and CV. The native potatoes on average had a pH of 6.2, a sugar content (degrees Brix) of 5.63 g/100g and a relatively high humidity of 77.3% in their composition. In general, it was found that native potatoes stand out for their high concentrations of N, Mg, Al, and Na respectively (Fig. 2). Although potatoes are not inherently high in nitrogen; rather, they are considered a good source of carbohydrates, particularly starch. While potatoes do contain nitrogen, they are not particularly known for being exceptionally high in nitrogen compared to other crops. The high content could be due The nitrogen content in potatoes is influenced by various factors, including soil composition, fertilization practices, and the specific potato species.

Commercial potato, the mineral profile of commercial potatoes included in the study shows predominance of N (1865.0 mg/100g), P (163.1 mg/100g), K (1117.3 mg/ 100g), and Mg (99.3 mg/100g), marking their significance as primary contributors to essential physiological functions (Table 1 and Fig. 1). Moderate levels of Fe (3.51 mg/ 100g), Zn (0.84 mg/100g), and Mn (0.66 mg/100g) were observed, further enhancing the nutritional value of these potatoes. Additionally, trace quantities of Cu (0.21 mg/ 100g), Mo (0.04 mg/100g), Al (0.53 mg/100g), and Na (6.06 mg/100g) complement the mineral composition of commercial potatoes. The commercial potato on average had a pH of 5.9, a sugar content (degrees Brix) of 6.1 g/ 100g and a relatively high humidity of 78.0% in their composition. The relatively high and moderate composition of macro and microelements (N, P, K, Mg, Na, Al, and Fe) were close to the one obtained by Gunko et al. (2023).

Oca, Analysis of the mineral content per 100 grams of this sample reveals outstanding values. High levels of N (527.5 mg/100g) and K (1061.8 mg/100g) stand out, although with notable variability of 92.9% and a CV of 24.1%. Other elements such as P (202.6 mg/100g) and Mg (62.4 mg/100g) show more stable average values. The values of Zn (0.9 mg/100g) and Na (15.4 mg/100g) are moderate, with CV of 26.0% and 34.6% respectively. The pH is recorded at 5.6, and the humidity at 86.9%, both with minimal variability (Table 1 and Fig. 1). The mineral composition of oca tubers exhibited moderate variation, as depicted in Table 2. Notably, nitrogen and potassium emerged as prominent elements. When assessing standardized values, certain trace elements, such as molybdenum and manganese, demonstrated elevated levels.

Isaño, in examining the mineral content per 100 grams, interesting insights emerge. Particularly, N (715.0 mg/ 100g) and K (11621.0 mg/100g) demonstrate noteworthy values, although N displays higher variability at 72.2% compared to K with 5.1% CV. P (221.7 mg/100g) maintains a steady average, while Cu (0.4 mg/100g) and Na (62.6 mg/100g) exhibit high variability at 83.4% and 78.7% respectively. Fe, Zn, and Mn at 5.5, 2.8, and 1.3 mg/ 100g respectively display moderate levels with varying degrees of variability (Table 1 and Fig. 1). Both the pH and Gbrix register at 6.5, showcasing minimal variability, while humidity records at 87.9% with a low CV of 1.9%.

Papa lisa, the mineral composition per 100 grams of papa lisa reveals outstanding values for N (716.7 mg/100g) and K (1297.7 mg/100g), although N shows a higher variability at 45.7% compared to K’s 15.2% CV. P (221.2 mg/ 100g) maintains a consistent average with minimal variability at 1.5% CV. Moderately variable levels are observed for Zn (3.2 mg/100g) and Mg (98.2 mg/100g) with CVs of 21.5% and 22.5% respectively. Cu (0.3 mg/ 100g) and Na (15.5 mg/100g) depict minimal variability at 3.7% and 14.0% CV respectively. Fe, Mn, and Al at 4.9, 1.1, and 0.5 mg/100g respectively, exhibit moderate levels with varied degrees of variability. Furthermore, the pH stabilizes at 6.1 with a 5.0% CV, while both Gbrix and humidity register consistent values of 5.0 g/100g and 86.5% respectively, displaying minimal variability.

Species of tubers and their mineral content characteristics

To uncover the inherent mineral compositions specific to each species, we conducted analyses including correlation assessments, average comparisons, and multivariate analyses (principal components and biplot) (Figs. 2, 3, 4, and 5).

Correlation. The correlation analysis among mineral contents of tuber species included in the study showed important associations. N exhibited a strong significative negative correlation with Mo (r = -0.70, p=0.000) and moderate correlation with several other minerals like with P (r = -0.56, p = 0.009), Mn (r = -0.52, p = 0.016), and Cu (r = -0.45, p = 0.043). The only positive correlation of N was with Al (0.48, p=0.028). Moderate positive significative correlations were identified for P with Fe (r = 0.47, p = 0.031), Mn (r = 0.46, p = 0.037) and Zn (r = 0.61, p = 0.004). K showed moderate positive associations with Zn (r = 0.46, p = 0.037), Mo (r = 0.44. p = 0.045) and Na (r = 0.45, p = 0.040). isolated correlations were identified for Mn with Mo (r = 0.52, p = 0.015) and Zn with Cu (r = 0.55, p = 0.010). These correlations elucidate potential interdependencies among mineral contents within those tuber species, highlighting some relationships that warrant further examinations with other tools like principal component analysis - biplot.

Analysis of variance. Significant variations were observed in the mineral content among tuber species, as revealed by the analysis of variance. Nitrogen, a vital nutrient, exhibited considerable diversity among species (F(4, 16) = 8.56, p = 0.001), indicating varying nitrogen levels. Phosphorus content showed significant differences across the tuber species (p<0.05), emphasizing distinct variations in phosphorus concentrations. Notably, potassium displayed pronounced variance (p = 0.000), highlighting substantial diversity in potassium content among the studied species. Similarly, Zinc exhibited significant statistical differences (p = 0.000), underscoring marked variations in zinc levels across the tuber species included in the study. Molybdenum and sodium also demonstrated noteworthy differences among species (p < 0.05), indicating diverse levels among different tuber varieties. Conversely, minerals like Mg, Fe, Mn, Cu, Mo, Al showed no statistically significant differences (p > 0.05) among the studied tuber species. These findings underscore the varied nutritional compositions present across different tuber variants, emphasizing their potential variability in fulfilling dietary requirements.

Multivariate analysis. The analysis of principal components and the representation of these in a biplot is shown in Figs. 4 and 5. In it you can see vectors representing the minerals, which depending on their magnitude can be considered very informative, as is the case of the most minerals. Due to the direction of the vectors and the angle they form with each other, robust positive and negative associations can be highlighted. Among which Cu, K, Zn and Fe stand out, clearly aligned to the coordinates of the isaño cultivar and papa lisa as average expression. Fig. 5 can also highlight the inverse relationship presented by the Al and N contents, completely opposite to the directions of the Mo and Mn vectors, representing an almost perfect negative correlation. The scattered points of Mo are much more associated with Mo, while the positions of scattered points for native potato are associated with N and to a lesser extent with Al. The average expression for commercial potato does not have a clear association, the closest being Al. From the configuration of scattered points and vectors of the Fig. 7 shows that cultivars 19 and 21 (papa lisa) are characterized by having a high content of Fe, K, Zn and Cu, a characteristic they share with the isaño cultivar (18). Papa lisa cultivar 20 stands out with the highest Mo content, as well as the papa lisa cultivars identified with 13, 14, 15, and 16. The content relationships can be corroborated with the star graph, where the areas representing the minerals stand out with a greater surface area for tuber species such as papa lisa, isaño and oca.

Multitrait Genotype-Ideotype Distance Index. The highlighted genotypes are denoted by red dots on Fig. 6, with a red circle indicating the defined selection pressure threshold (~25%). Notably, within the study, the “isaño jaspeado” cultivar and the innominate native potato cultivar 2 (AXT2) emerged as the key ideotypes concerning their mineral composition. Their respective strengths and weaknesses are discerned through the proportionate representation within the MGIDI index (depicted in Fig. 7). Here, a factor's proximity to the outer edge signifies a smaller contribution, indicating traits closer to the 'ideal' treatment. The central black dashed circle represents a theoretical uniform contribution across all factors. Factor 1 highlights the “isaño jaspeado” cultivar, notable for its elevated levels of K and Na. Factor 2 showcases select native and commercial potatoes, particularly rich in N, Mg, and Mo. Cultivars associated with factor 3, encompassing papa lisa and native potato, excel notably in Cu and Al. Finally, factor 4 encompasses isaño, papa lisa cultivars, and some native potatoes, demonstrating exceptional contents of P, Fe, and Zn.

The distinctive mineral composition identified in tuber species like oca, smooth potato, and isaño through this study underscores significant intrinsic relationships among microelements. This insight enables us to envision a promising scenario for these cultivars, whose biodiversity remains exclusive to the Andes.

CONCLUSIONS

The results of this study demonstrate differences of mineral composition among the bolivian tubers species depending on their genotypes and tuber species, exhibiting an intricate mineral composition, unveiling substantial diversity and nutritional significance across species. Native potatoes emerged as notable candidates, boasting elevated levels of nitrogen (N), potassium (K), phosphorus (P), and magnesium (Mg), accompanied by moderate micronutrient content, particularly iron (Fe) and zinc (Zn). Commercial potatoes displayed prominence in nitrogen (N), phosphorus (P), and potassium (K), with moderate Fe, Zn, and manganese (Mn) levels. Oca stood out with high N and K contents, complemented by stable P and Mg levels. Isaño and Papa Lisa exhibited exceptional concentrations of nitrogen (N) and potassium (K). Detailed correlation analyses uncovered intricate associations among mineral elements within these tuber species, revealing important interdependencies. Variance analysis underscored significant differences in nitrogen (N), phosphorus (P), potassium (K), zinc (Zn), molybdenum (Mo), and sodium (Na) levels among the various tuber species. Multivariate analyses based on standardized data showcased particular mineral profiles unique to each species, emphasizing isaño and papa lisa’s distinct compositions. The Multitrait Genotype- Ideotype Distance Index (MGIDI) pinpointed isaño jaspeado, isaño and unnamed native potato (AXT2) as crucial ideotypes due to their standout mineral compositions. These important findings are letting us to share important information on the diverse and extraordinary mineral compositions existing within bolivian tuber species, offering profound insights into their nutritional significance meanly due to highly demanded micronutrients like Fe and Zn to face hidden hunger. Moreover, these revelations can inform targeted breeding strategies aimed at developing cultivars with specific and desirable mineral profiles, thereby potentially addressing dietary needs and enhancing food security.

적 요

감자를 포함한 오카(Oxalis tuberosa Molina), 오루코 (Ullucus tuberosus Caldas), 이사뇨(Tropaeolum turosum Ruíz & Pav.)와 같은 볼리비아 전통 괴경작물들은 풍부한 영 양성분을 함유하고 있으며 지역 농업 생물 다양성에 기여하고 있다.

볼리비아는 오랜 기간 취약계층 굶주림 문제를 겪고 있으며 최근 이상기후로 인한 전례 없는 유전적 침식의 위협을 받고 있는 상황이다.

이 연구는 볼리비아 괴경식물들의 영양성분분석을 통해 식 량안보 강화 및 기후변화에 능동적으로 대응하며 추후 볼리비 아 감자 육종의 새로운 지표를 제시하고자 함이다.

연구는 감자를 포함한 총 21종의 볼리비아 괴경작물의 전반 적인 영양성분검사를 연관성 및 변동성(correlation and variance)분석, 다변량분석(Multivariate analyses), Multitrait Genotype-Ideotype Distance Index (MGIDI)분석 통하여 주요 미네랄 성분과 그 함량을 분석하였다.

분석 결과들은 볼리비아 괴경식물의 영양학적 가치를 높이 고 볼리비아에 식량안보 관련 중요한 인사이트를 주며 추후 볼리비아 감자 육종 분야에도 주요한 전략 지표를 제공할 것 이다.