Contribution to the Knowledge of Manihot Biodiversity: Study of a Wild Cassava from Paraguay, Manihot takape sp. nov. ^†

Abstract

In Paraguay, the genus Manihot is represented by sixteen taxa, six of which are endemic. The study of wild relatives of Manihot has focused on the search for species related to the cultivated variety, with potential for genetic improvement. Manihot takape sp. nov. is a recently described species, so little information is available about its characteristics. The purpose of this study was to evaluate the centesimal composition and morphologically characterize the wild species Manihot takape sp. nov. in order to contribute to the knowledge of the biodiversity of the genus Manihot in Paraguay. The sample was collected in May 2023 in the Boquerón Department, in the Paraguayan Chaco region. The percent composition was determined in freeze-dried samples using the official methods of the Association of Official Analytical Chemists (AOAC); carbohydrates were calculated by difference. For morphological characterization, the weight, length, and diameter of the tubers were measured. The morphology and size of native starch granules were analyzed by means of scanning electron microscopy (SEM) using a ZEISS EVO 15 device (ZEISS, Oberkochen, Germany) with gold plating and high vacuum observation (10,000×). The results showed a high water content (85 g/100 g ± 1) and a low carbohydrate content (20.1 g/100 g ± 0.90), compared to cultivated varieties. Fiber, ash, and protein values were similar to those of other species of the genus. The tubers weighed 110 ± 1 g, measured 6.56 ± 0.31 cm in length, and had a diameter of 5.56 ± 0.12 cm. The starch granules were truncated spherical, with an average size of 12.5 ± 3.0 µm. This study provides valuable information for the conservation and sustainable use of native genetic resources.

1. Introduction

Cassava is widely recognized as one of the most important tuber crops in tropical and subtropical regions, providing a major dietary source for over 800 million people worldwide. Its origin is traced to Latin America, where it was first utilized by Indigenous populations more than 4000 years ago. Today, cassava is regarded as a staple ingredient in the diet of many developing countries. In 2003, the Food and Agriculture Organization (FAO) designated it as the most important root crop in Africa and a critical source of calories [1].

In Paraguay, cassava production is mainly concentrated in the Eastern Region, covering approximately 99.7% of the total land cultivated with this plant. On the other hand, in the Western Region of the country, only a small area (approximately 0.3%) is devoted to cassava cultivation. It is important to note that cassava cultivation has a significant socioeconomic impact, with national production as an agricultural commodity being reserved essentially for domestic consumption [2].

In Paraguay, the genus Manihot is represented by 16 taxa, of which six are endemic [3]. In 2018, while carrying out fieldwork related to the study of the most important Wild Crop Relatives of the country’s flora, a collection of Manihot was made that could not be assigned to any known species, where herbarium specimens with similar diagnostic characters were found and these had been misidentified as another species of Manihot [3].

It is a subshrub 0.5 to 0.8 m tall, with branched stems from the base where the petiole insertion is basal to slightly peltate, glabrous green to occasionally reddish. The alternate leaves are green and spaced around the stem, with lanceolate to filiform epipulae. The flowers are creamy white with reddish pigmentation. The capsules measure 7 to 15 mm in diameter with a rough to dry surface and are slightly elongated. The seeds are oblong to elliptical, light greenish-gray in color with few dark spots. The roots are thin with subglobose, slightly elongated tubers 5 to 10 cm in diameter. They are woody on the outside and starchy, fibrous, and creamy white on the inside [4].

The new species of Manihot is found in the dry areas of the Paraguayan Chaco, in the departments of Boquerón and Presidente Hayes. The soils in this region are sandy, where the species is common in open wooded savannas [4].

The name takape for the new species comes from the Guaraní language, whose meaning dates back to indicate a particular habitat characterized by a wooded savanna or a very open forest [4]. The purpose of this study was to evaluate the centesimal composition and morphologically characterize the wild species Manihot takape sp. nov. in order to contribute to the knowledge of the biodiversity of the genus Manihot in Paraguay.

2. Materials and Methods

2.1. Raw Material

The analyzed sample of Manihot takape sp. nov corresponds to a species brought from the Department of Boquerón in the Paraguayan Chaco in May 2023.

2.2. Experimental Design

The root peels were removed and then cut into small pieces and lyophilized using LyoQuest equipment at a temperature of −35 °C and a pressure of 0.2 mb for a total of approximately 5 days. These were then stored in pre-labeled bags for later use. Analyses for centesimal composition were performed in triplicate. Granule size measurements were recorded using the average, largest, and smallest diameters of the starch granules (an average of 30 measurements).

2.3. Analysis

2.3.1. Centesimal Composition

For the centesimal composition, all of the results were expressed in g/100 g: the humidity content was determined using a thermobalance with the official method AOAC 32.102 in Precisa Gravimetrics AG model XM 60-HR equipment (Precisa Gravimetric, Dietikon, Switzerland). The ash content was determined with the official method AOAC 923.03 in the muffle model D-2804 equipment (Nabel, Lilienthal, Germany). Protein contents were determined using the official method AOAC (960.52, 12.1.07) in microKjeldahl in model K40 equipment (Behrotest, Düsseldorf, Germany). Lipid content was determined with the official method AOAC 2003.06 in a Goldfish equipment TE-044 model (Tecnal, Piracicaba, Brasil). The Fiber content was obtained using the official method AOAC 985.29 with muffle and micro-Kjeldahl equipment (Nabel, Lilienthal, Germany) (Behrotest, Düsseldorf, Germany). Carbohydrates were determined by difference, taking into account the results obtained in the other determinations [5].

2.3.2. Morphological Characterization

A scanning electron microscope (SEM), model EVO15 from Zeiss, Oberkochen, Germany, was used for the morphological characterization of the starch granules. To perform the sample analysis, a conductive gold coating was applied, which allowed high-resolution images to be obtained, in accordance with the SEM usage regulations of LabioyMat/FPUNA. Once the images were obtained, ImageJ software version 1.38 (Asunción, Paraguay) was used to measure the major and minor diameters of the granules, thus obtaining the dimensions necessary for their analysis.

3. Results and Discussion

3.1. Centesimal Composition

The values obtained from the centesimal composition of the Manihot studied are displayed in

Table 1. Centesimal composition of Manihot takape sp. nov.

Centesimal Composition in g/100 g	Manihot takape sp. nov.
Moisture	86.4 ± 1.2
Protein	0.624 ± 0.041
Lipids	Nd
Ash	0.475 ± 0.048
Fiber	3.32 ± 1.03
Carbohydrates	20.1 ± 0.9

, which shows the moisture, protein, lipid, ash, fiber, and carbohydrate content in g/100 g of food.

In terms of moisture content, Manihot takape sp. nov. has a much higher value (86.4%) than that reported in other studies of cultivated varieties, which is around 54% [6]. The second major component is carbohydrates, which in the Manihot takape analyzed have a value of 20.1 g/100 g, a much lower content than the cultivated varieties reported in the literature [7]. This difference could be due to the water content of each variety.

The value obtained in relation to protein for the cassava analyzed is 0.624 g/100 g. The values found in Manihot do not usually exceed 1 or 5% since it is a species that is not characterized by having a high content of protein in its composition [8,9].

For Manihot takape, the lipid content was undetectable. The total mineral content was found to be 0.475 g/100 g, which is lower than that found in cultivated varieties (1.2 mg/100 g) [7].

In terms of fiber content, values of 3.32 g/100 g were obtained for Manihot takape, slightly below that of other varieties at 4.6 g/100 g. Fiber is an important component found in food and has a positive influence on digestive health for consumers [9].

3.2. Morphological Characterization

Table 2. Morphological characteristics of the root of Manihot takape sp. nov.

Root Weight in g	Longitudinal Diameter in cm	Transverse Diameter in cm
110 ± 1.2	6.56 ± 0.2	5.56 ± 0.2

details the morphological characteristics of the root, and

Table 3. Morphological characteristics of starch granules of Manihot takape sp. nov.

Largest Diameter of the Granule in µm	Minor Diameter of the Granule in µm	Granule Shape
12.5 ± 3	10.7 ± 3.2	oval, round and truncated

shows the parameters described for the starch granules of the Manihot takape root. Microphotographs of the granules of the analyzed sample are presented in Figure 1.

The sample had an average root weight of 110 g, with very similar longitudinal and transverse diameters, between 5 and 6 cm. The granule size ranged from 10.7 to 12.5 μm, with a shape very characteristic of cassava: predominantly oval, round, and truncated, similar to that reported by Hernandez Medina et al. and Sivoli L. et al. [10,11].

4. Conclusions

This study on Manihot takape sp. nov. constitutes a first approach to understanding this wild species recently described in the Paraguayan Chaco. The results obtained reveal significant differences in centesimal composition compared to cultivated varieties, notably a high moisture content and low carbohydrate level, while fiber, ash, and protein values remain within ranges similar to those of other species of the genus. Likewise, the morphological characterization of the tubers and starch granules provides novel and useful information for future comparisons. These findings contribute to the knowledge of the biodiversity of the genus Manihot in Paraguay and provide a basis for the conservation and sustainable use of native genetic resources with potential for crop improvement.