Morphological Characterization of Arbuscular Mycorrhizal Fungi Associated with the Rhizosphere According to the Age of Xanthosoma sagittifolium L. Schott Plants in the Field ()
1. Introduction
Xanthosoma sagittifolium L. Schott is ranked among the most important tuberous plants in the world [1] , Africa is the main source of production through Nigeria, Cameroon, and Ghana [2] . This plant is consumed in most African countries and its production is ensured by small farmers with limited resources and mainly women. Formerly classified among neglected plants authors are increasingly giving capital interest to the cultivation of X. sagittifolium [3] [4] . This speculation is a staple food for populations in tropical and subtropical regions, for human and animal nutrition. The leaves and tubers of the plant are the parts mainly consumed. The tubers are rich in minerals such as calcium, phosphorus, potassium, and magnesium [5] [6] . Leaves and flowers contain apigenin, which gives to plant anti-cancer and anti-diabetic properties [7] [8] .
Mycorrhization tests show that an application of allochthonous arbuscular mycorrhizal fungi in X. sagittifolium plants contributes to improving not only their growth but also to boosting the production of seed minitubers [9] [10] . This application of mycorrhizal fungi in propagators also makes it possible to increase the production of PIF seed plants in X. sagittifolium and likewise their growth in the field [11] [12] [13] . However, by concluding that X. sagittifolium is a mycotrophic plant, [9] highlights the hypothesis of calling into question the knowledge of the biodiversity of indigenous arbuscular mycorrhizal fungi associated to the rhizosphere of X. sagittifolium plants. So many questions needed to be answered likewise; are there specific species of arbuscular mycorrhizal fungi associated with the rhizosphere of X. sagittifolium? Do communities of arbuscular mycorrhizal fungi in the rhizosphere vary depending on the soil type, plants age, harvest site, etc.? Do the white and red cultivars of X. sagittifolium establish symbiosis with the same types of arbuscular mycorrhizal fungi species? Exploring the diversity of indigenous arbuscular mycorrhizal fungi in the rhizosphere of X. sagittifolium can depend on the cultivars. That is why this research work focuses on the determination of the different potential genera of arbuscular mycorrhizal fungi associated with the rhizosphere of white and red cultivars in X. sagittifolium. More specifically, the investigations will make it possible to: evaluate the agronomic parameters plants of X. sagittifolium white and red cultivars in the field following the age; the nature of the soils associated with the rhizosphere according to the different harvesting sites; and to determine a morphological characterization of different genus of arbuscular mycorrhizal fungi present in the rhizosphere.
2. Material and Methods
2.1. Study and Sampling Sites
The soil and root sample collection sites used are located in the Central region of Cameroon. The harvests were carried out in Nkometou, (Lékié Department, at geographical coordinates; 4˚5'29'N and 11˚36'16'E, with 600 m of altitude), Olembe (Mfoundi Department, at 3˚56'43'N and 11˚31'46'E, with 690 m of altitude), and Soa, (Department of Mefou and Akono at 3˚59'45'N and 11˚36'49'E, with 680 m of altitude) (Figure 1). These three sites belong to the forest agroecological zone with bimodal rainfall of Cameroon, characterized by a humid equatorial climate.
2.2. Evaluation of Agro Morphological Growth Parameters in X. sagittifolium Plants in the Field According to Harvest Sites
The plant material used consisted of plants of the white and red cultivars of X. sagittifolium with age intervals of 3 - 6, 6 - 9, and 9 - 12 months. These plants were chosen in the field in a randomized manner at each site. The field of each site had a minimum size of 1 ha. For each age group, agronomic growth parameters such as average plant height; the average diameter at the collar of the plants; the average number of leaves, the average leaf area; the average number of roots, and the average weight of the roots [9] [13] [14] , were evaluated on 10 X. sagittifolium plants chosen at random in the field following the harvest sites.
![]()
Figure 1. Geographical location of rhizosphere soil and root sampling sites of Xanthosoma sagittifolium plants.
From these same previously selected plants, the soil of the rhizosphere, as well as root fragments were taken for laboratory analyses.
2.3. Sampling and Analysis of Physicochemical Soil Parameters
Each sample of these soils was taken at a depth of 0 - 20 cm using an auger at the level of the rhizosphere of the X. sagittifolium plants. For each age group (3 - 6, 6 - 9, and 9 - 12 months) of the targeted plants in each harvest site, three repetitions were carried out. These soils by age group will then be mixed. 500 g, will be bagged then labeled, and brought back to the laboratory for analysis. Analyzes of the physicochemical characteristics of these soils were carried out at the University of Dschang, by the Soil Analysis and Environmental Chemistry Research Unit of the Faculty of Agronomy and Agricultural Sciences. The physical parameters of the soil (sand, clay and silt contents) and chemical parameters (pH-H2O and pH-KCl), organic carbon (CO) content, total nitrogen content (N), exchangeable base content (Ca, Mg, K and Na), cation exchange capacity (CEC) and assimilable phosphorus content (P Bray II), exchangeable base sum (EBS) and the rate of saturation (V), were determined and analyzed according to the standards of [15] [16] [17] protocols.
2.4. Determination of the Mycorrhizal Status of Plant Root Fragments in X. sagittifolium Histological Analysis and Assessment of Mycorrhizal Status
The root hairs of X. sagittifolium of the white and red cultivars collected in the field at each site were cleaned, drained, and sectioned to a size of 0.5 to 1.0 cm. The protocol of [18] was used. These root hairs were soaked in 10 g∙L−1 KOH for 15 minutes at 90˚C, then rinsed with HCl (10%). The dye used was trypan blue 1 g∙L−1. Microscopic observations were carried out using the HYMEN brand optical microscope at 400X. 100 of these fragments were observed for each age group and per site. Mycorrhizal status was calculated following the scale proposed by [18] . The parameters F%, M%, m%, a%, A%, v% and V% were calculated.
2.5. Extraction, Enumeration, and Characterization of Spores
The method of [19] was used for the extraction and enumeration of spores in the soil. This method is based on sieving the soil through a set of superimposed sieves having different mesh diameters; 0.5; 0.25; 0.125 and 0.0625 µm. 10 mL of pellet from each soil sample sieved according to the age groups (3 - 6, 6 - 9, and 9 - 12 months), will be observed under a binocular magnifying glass with an X40 objective. An exhaustive count of spores for each age group was carried out in the watch glasses. This operation was carried out in 10 fields and an average was calculated based on the number of spores found. Thus, the total number of spores/soil collected was evaluated from the sum of the number obtained in sieves 2, 3, and 4 (0.25; 0.125; 0.0625 µm). Spore density was determined for each soil sample. The different spores resulting from the extraction and enumeration of soils were described morphologically according to the identification keys of [20] , from the International Culture Collection of Arbuscular and Vesicular-Arbuscular Mycorrhizal Fungi [21] , and the European Bank of Glomales. The classification of species was made using the method of [22] . Species diversity was measured using the species richness of the diversity indices of [23] . The Shannon index (H) varying from 0 (a single species, or one species very largely dominant over all the others) to log S (when all the species have the same abundance) was calculated according to the following formula:
Where: S = total number of species; Ni = number of individuals of gender (i) in a given category; N = total number of individuals of all genders in a given category; log2 = logarithm to base 2; H = Shannon diversity index.
2.6. Statistical Analyzes
The results obtained were the subject of a descriptive analysis (Mean ± standard deviation). The results are represented in the form of graphs and tables (Microsoft Excel 2013 software). The IBM SPSS Version 20.0 software was used to carry out the statistical analyses and to compare the means using an analysis of variance (ANOVA) using the Student-Newman-Keuls test at the 5% threshold.
3. Results
3.1. Agronomic Parameters Recorded in the White and Red Cultivars of X. sagittifolium in the Field in the Different Harvest Sites Following the Age Month Intervals
The average plant height varied significantly at P < 0.05 by the Student Newman and Keuls Test in plants of the two cultivars of X. sagittifolium. We see that this height increases depending on the age interval and the site (Table 1). Low average height values were recorded for both cultivars between 3 - 6 months of growth. X. sagittifolium plants presented greater average heights at the Nkometou site compared to those of Soa and Olembe. The plants of the white cultivar appear larger than those of the red cultivar. We note significant average values of 133.13 ± 040.60 and 158.73 ± 007.54 cm, between 6 - 9 and 9 - 12 months respectively in the Nkometou site. The average diameter at the collar showed maximum values greater than 7cm at the age interval of 9 - 12 months, in X. sagittifolium plants from the Nkometou site (07.53 ± 01.02 cm) in the cultivar white. In plants of the cultivar, it is 07.74 ± 02.66 and 07.65 ± 01.35 cm, respectively at the age interval of 9 - 12 months, in Olembe and Soa. The average number of leaves did not vary significantly in the Student Newman and Keul Test in all cultivars (Table 1).
Generally speaking, the average leaf area of the leaves increases significantly (P < 0.05) following the age interval for the white and red cultivars (Table 1). At the age interval of 6 - 9 months, this average leaf area of leaves appears very large in both cultivars. A maximum of 1840.52 ± 371.41 cm2 is recorded, at a growth
![]()
Table 1. Variation in agronomic parameters of white and red cultivars of X. sagittifolium plants in the field following age intervals.
Student Newman Keuls tests.
Data sharing the same letter in the same column and for each treatment were not significantly different at the 5% level.
age interval of 9 - 12 months, in plants of the white cultivar of X. sagittifolium, from the Nkometou site. In plants of the red cultivar, it is 3119.33 ± 517.76 cm2 at the age interval of 9 - 12 months at the Soa site. However, the results show an increase in the values of the number and average weight of roots over time (Table 1). The average number of roots varies significantly (P < 0.05) with a maximum value of 106.00 ± 012.72, recorded in plants of the red cultivar from the Nkometou site. However, for the average weight of fresh roots harvested, although it is low for the age interval of 3 - 6 months, it should be noted that the significant values are 316.65 ± 27.13 and 625.42 ± 18.86 g, respectively for plants of white and red cultivars from the Soa site at the age interval of 6 - 9 and 9 - 12 months (Table 1).
3.2. Physicochemical Characteristics of the Soil at Different Sites
The physical properties of the soils studied varied according to the three sites (Table 2). From the analysis triangle of the mineral texture of the soils, we note
![]()
Table 2. Physicochemical analyses of the soils of X. sagittifolium plant rhizosphere in each harvest site. Sand (S%), clay (L%), and Loam (L%) contents. pH (aqueous (pH-H2O) and acid (pH-KCl)), carbon (C), total nitrogen (N), phosphorus (P), organic matter (OM). Exchangeable bases (Ca2+, Mg2+, K+ and Na+); Cation exchange capacity (CEC); Assimilable phosphorus content (P Bray II); Exchangeable Base Sum (EBS), Saturation Rate (V).
that the Nkometou site has a loamy texture, with 23.25% clay, 46.75% silt, and 30% sand. The Olembe and Soa sites have respectively loam-clay-sand textures (31.25% clay, 9.5% silt, 59.25% sand) and loamy-clay (35.75%). % clay, 40% silt, and 24.25% sand). The soils of the different study sites showed an acidic character. The pH of water and hydrochloric acid is between 4.6 and 5.8 (Table 2). The results of these soils from the three X. sagittifolium cultivation sites have an average organic matter content. We record 3.18; 3.54 and 3.89% respectively in Nkometou, Olembe, and Soa. The Nkometou site appears richest in total nitrogen. The C/N ratio is very high at the Soa site with a peak of 4.96 but appears very low in the Nkometou (1.74) and Olembe (1.17) sites. The results also show that assimilable phosphorus was very high in the soil of the Soa site with a value of 168.99%. However, it should be noted that the low value of phosphorus content is recorded at the Nkometou site (5.81%). As for the soil of the Olembe site, it is moderately poor in phosphorus (40.54%). Furthermore, according to the standard proposed by Calvet and Villemin (1986), the three sites have high CEC contents. Furthermore, the sum of exchangeable bases varied very little with normal contents. It is 5.54 (0.03% Na+; 3.21% Ca2+; 0.98% Mg2+; 1.32% K+) for the Nkometou site, 5.6 (0.02% Na+; 2 .45% Ca2+; 1.08% Mg2+; 2.05% K+) for Olembe and 5.22 (0.01 Na+; 2.15% Ca2+; 1.21 Mg2+; 1.85 K+) for Soa.
3.3. Mycorrhizal Status of Plant Roots Following Harvest Sites as a Function of Harvest Age Month Interval
The results of the mycorrhizal status assessed varied according to the three harvest sites for the white and red cultivars (Table 3). The value of the percentage of vesicular intensity of AMF appears very low. The highest mycorrhization frequencies (F%) appear at the Nkometou site. The maxima were 75 and 87.33% respectively in the root hairs of plants of white and red cultivars at 6 - 9 and 9 - 12 months. At Nkometou, we note a higher intensity of mycorrhization compared to the Olembe and Soa sites (Table 3). The maxima are 40.73% for the mycorrhizal intensity (M%) for Nkometou red cultivar plants of 3 - 6 months, 61.02% for the mycorrhizal intensity in the root system (m%) at age interval of
![]()
Table 3. Mycorrhizal status of the roots of white and red cultivars X. sagittifolium plants, according to the age interval and according to the harvest site. F%: Frequency of mycorrhizal colonization, M%: Intensity of mycorrhizal colonization, m%: Intensity of mycorrhizal colonization in the root system, a%: Arbuscular content, A%: Arbuscular intensity in the root system, v%: Vesicular intensity of the mycorrhizal part and V%: Vesicular intensity in the root system. Numbers followed by the same letter in the same column are not significantly different in the Newman and Keuls Student Test (5%).
3 - 6, and 6 - 9 months in plants from the Olembe site and 13.55% for arbuscular intensity in the root system (A%) at the age interval of 6 - 9 months for plants of the red Nkometou cultivar.
3.4. Relative Abundance and Diversity Index of Rhizosphere Arbuscular Mycorrhizal Fungi in X. sagittifolium Plants Following Harvest Sites as a Function of Harvest Age Month Interval
Graphs of the relative abundance of AMF spores in the rhizosphere of plants of X. sagittifolium cultivars white and red following the harvest site, several spores vary from one harvest site to another depending on age and cultivar (Figure 2(A) and Figure 2(B); Figure 3). In the white cultivar, the maxima were observed in plants aged between 9 - 12 months. It is 470,280, and 673 spores respectively at the site of Nkometou, Olembe, and Soa. Likewise, the results also show that the minimums were recorded in plants aged 3 - 6 months in Nkometou with a value of 112 spores in 50 g of soil (Figure 2(A)). In the red cultivar, the maxima are
![]()
Figure 2. Relative abundance of AMF spores following the age intervals of the white and red cultivars of Xanthosoma sagittifolium in the three harvest sites.
![]()
Figure 3. Shannon and Weiner diversity index in the three harvest sites.
notably at the age interval of 9 - 12 months (673 spores), 6 - 9 months (331 spores), and 3 - 6 (294 spores) respectively in the plants of X. sagittifolium in Nkometou, Olembe and Soa (Figure 2(B)). Low relative abundance was observed in plants aged 9 - 12 in the Soa site (33 spores). The Shannon and Weiner diversity index in the three collection sites presents a specific diversity of AMF of the rhizosphere in the plants of the white and red cultivars of X. sagittifolium in the Soa site compared to the Nkometou and Olembe (Figure 3).
3.5. Morphological Appearance of the Spores of AMF Associated with the Rhizosphere of Plants of the White and Red Cultivar of X. sagittifolium Following the Age Month Intervals
Observations of AMF spores under a microscope at 200 µm showed significant variation between the spores associated with the rhizosphere of plants of white and red cultivars of X. sagittifolium, particularly in terms of shapes, colors, walls, and slits. spores. 6 genera of AMF have been recorded; Glomus sp. Acaulospora sp., Scutellospora sp., Septoglomus sp. Gigaspora sp., and Funneliformis sp (Figure 4 and Figure 5). In white cultivars, of these six genera, the 5 AMF genera recorded are Acaulospora sp., Glomus sp., Gigaspora sp., Scutellospora sp., and Septoglomus sp. (Figure 4). While in the red cultivar, the results present Acaulospora sp., Gigaspora sp. Glomus sp. Funneliformis sp., and Scutellospora sp. (Figure 5). Glomus sp. spores were the most abundant genera in the rhizosphere of both cultivars at all ages. It also appears most represented at the rhizosphere of X. sagittifolium at Olembe and Soa, compared to Nkometou at the age interval of 6 - 9 and 9 - 12 (Figure 4 and Figure 5).
3.6. Correlation Study between the Evaluated Parameters
The factor plot of the principal component analysis of the data confirms a positive correlation between agronomic parameters and mycorrhizal status (Figure 6). This linear correlation, thanks to Pearson’s rank coefficient R, indicates a highly significant correlation at 5% at the age interval 9 - 12 months in the three sites, between the parameters; average size of plants, average number of leaves, average leaf surface, average diameter at the collar, average number of roots and average weight of roots, in the white cultivar plants from the Nkometou site and the same in the red cultivar plants from the sites by Olembe and Soa. Furthermore, it appears that all the parameters of the mycorrhization index are significantly correlated with the relative abundance of spores, in white cultivar plants from the Nkometou site, at the age interval, 3 - 6, 6 - 9, and 9 - 12 months. However, the analysis of the Pearson correlation between the physicochemical
![]()
Figure 4. Morphological appearances of the arbuscular mycorrhizal fungi spores associated with the rhizosphere of the white cultivar of X. sagittifolium plants following the age intervals observed with a Leica brand light microscope at 200 µm.
![]()
Figure 5. Morphological appearances of the arbuscular mycorrhizal fungi spores associated with the rhizosphere of the red cultivar of X. sagittifolium plants following the age intervals observed with a Leica brand light microscope at 200µm.
![]()
Figure 6. Pearson correlation between agronomic parameters, mycorrhizal status, and relative abundance. R: red, Bl: white; LA: leaf area; NL: Number of leaves; DC: Diameter of the collar; WR: Weight of Root: NR: Number of roots; RA: relative abundance, F: Frequency of mycorrhizal colonization, M: Intensity of mycorrhizal colonization, m: Intensity of mycorrhizal colonization in the root system, a: Arbuscule content, A: Arbuscular intensity in the root system, v: Vesicular intensity of the part mycorrhizal and V%: Vesicular intensity in the root system.
parameters of the soils, the relative abundance of spores, and the Shannon index, presents a contribution from axis 1 (Fact. 1) of 75.23% and axis 2 (Fact. 2) by 24.77%. That is a total of 100% variability (Figure 7). It, therefore, appears at the
![]()
Figure 7. Pearson correlation between soil analysis parameters, relative spore abundance, and Shannon index. pH (aqueous (pH-H2O) and acid (pH-KCl)), carbon (C), total nitrogen (N), phosphorus (P), organic matter (OM). Exchangeable bases (Ca2+, Mg2+, K+ and Na+); Cation exchange capacity (CEC); Assimilable phosphorus content (P Bray II); Exchangeable Base Sum (EBS), Saturation Rate (V). Relative abundancy (Rel. abundancy) and Shannon index (Shan. ind.).
Soa site, a positive and significant correlation between the parameter’s assimilable phosphorus content, the abundance of spores, and the Shannon index (Figure 7). However, in Olembe, there is a significantly negative correlation for the pH-H2O and EBS parameters.
4. Discussion
The morphological growth parameters varied significantly by the Student’s and Keuls’ Test at P < 0.05. These parameters increase over time in all sites and are important at the Nkometou site compared to the Olembe and Soa sites. In Nkometou, the average plant sizes, collar diameter, leaf area, and number of plant roots presented higher values in the white cultivar compared to the red cultivar. This increase in growth parameters observed would be the result of the physiological response of the X. sagittifolium plants, to the availability of the nutrients necessary for their growth on one hand in the soils of these sites and on the other hand, the presence of microorganisms in these soils which are in symbiosis with X. sagittifolium plants, would contribute to the improvement of their hydromineral nutrition. These beneficial soil microorganisms provide favorable conditions for plant development [24] . The very high average number of roots between 9 - 12 months, in both cultivars and all sites, would explain that at this age, X. sagittifolium plants would need more nutrients to ensure not only its hydromineral nutrition but also storage in tubers. Furthermore, this variation in agronomic growth parameters recorded between month intervals in white and red cultivars, at all sites, could also be the result of variation in physicochemical characteristics such as; the pH, the sum of exchangeable bases, the C/N ratio, etc. in the soils of these different sites. [25] , have also shown that soil pH and hydromineral nutrition significantly influence growth in poplar (Populus tremuloides), jack pine (Pinus banksiana), and white spruce (Picea glauca) seeds grown on sand. According to [26] , the nature and properties of the soil play a critical role in plant growth.
The results of soil analysis present physicochemical characteristics that differ relatively from one site to another. The soils of the Nkometou site have a loamy texture, compared to those of Olembe and Soa, which are loamy-clay-sandy and loamy-clayey respectively. The textures of these three sites appear suitable for the cultivation of X. sagittifolium. According to [27] and [28] , these soil texture types are easily well-drained and well-aerated. [29] and [30] , showed that growth and optimal tuberization in X. sagittifolium require light soils, rich in organic matter, well-drained, deep, well loosened and having a pH between 5.5 and 6.5. Chemical analyses show that the different soils of the three sites studied have acidic pHs, with values between 5.6 and 5.8 for pH (H2O) and 4.6 and 4.8 for pH (HCl). The majority of Cameroonian soils are acidic [31] . According to [28] , X. sagittifolium plants exhibit optimum growth and production at a pH varying between 5.5 and 6.5 (pH-H2O). However, it has been shown that pH (5.8 to 6.3) is satisfactory for good biological activity and nutritional exchanges in the soil [26] [32] . The soils of these three harvest sites had a C/N ratio < 6, which would reflect the rapid decomposition of organic matter. These soils were very rich in total nitrogen with values all > 0.25. The Olembe site, with a loamy-clayey-sandy texture, had a greater sand richness compared to the other sites and likewise a higher total nitrogen content. [33] emphasize that, in sandy soils, which are soils with great aeration, the mineralization of nitrogen is very rapid. According to the fertility scale for assimilable phosphorus of [34] , the assimilable phosphorus contents varied significantly. The values recorded were 5.81 ppm (Nkometou), 40.54 ppm (Olembe), and 168.99 ppm (Soa). The soils of the Nkometou site appeared poor in phosphorus. [35] , mentioned that the soils poverty in phosphorus and also the impact of acidity on the CEC of the soil are characteristic of tropical soils. In the soils of the different sites studied, the CEC is higher in Olembe compared to Nkometou and Soa. Of the four exchangeable bases determined, the percentage of Potassium (K+) is higher compared to Calcium (Ca2+), Magnesium (Mg2+), and Sodium (Na+). These minerals are involved in important physiological processes for plants: photosynthesis, fruitification, cell permeability, and ionic balances [36] . This high K+ content is very beneficial for X. sagittifolium plants. [36] and [37] showed that potassium not only contributes to strengthening cell walls but also to increasing leaf surface area and consequently, the chlorophyll content of leaves in plants.
The results show that the mycorrhizal status values varied depending on the cultivars and the age range of the plant. The work of [9] showed that X. sagittifolium is a mycotrophic plant. This variation in mycorrhizal status values would be influenced not only by the root renewal that plants make during their growth but also by the properties of the soil. The high (in Nkometou) or low (in Olembe and Soa) mycorrhization frequencies in the two cultivars at all age intervals could be explained by the fact that the mycorrhizal infection is the result of the AMF response. to the effects of hormones emitted by plants. Generally, the high frequency of mycorrhization in plants from 6 - 9 months can be explained by the fact that at this age, the plants already carry out the physiological phenomenon of tuberization (storage). However, this storage in plants requires good photosynthesis. However, in symbiosis, X. sagittifolium plants should also respond in terms of carbohydrate cost to AMF. In plants of the red cultivar, from the Nkometou site, the highest frequency of mycorrhization was observed in plants aged 3 - 6 months. This could be justified by the fact that these plants were located on an anthill. [38] , show that the presence of ants in the soil would influence the symbiosis through the process of bioturbation, which, due to the high temperatures in the anthills, would not only lead to the accumulation of mycorrhiza spores. In the soil, ants and termites act like earthworms; they contribute to the establishment of the symbiosis between plants and microorganisms through the release of phytohormones [39] .
Results for relative spore abundance varied from site to site. This relative abundance of spores appears very high in plants of X. sagittifolium, with an age interval of 9 - 12 months in the three sites in plants of the white cultivar. However, we note a value of 673 spores/50g of rhizosphere soil in plants from the NKOMETOU site in plants of the red cultivar. This high abundance observed could be explained by the fact that the lower the phosphorus levels in the soil, the higher the quantity of spores appears. Similar results were obtained by [40] , with Bambara groundnut plants. The analysis of this abundance made it possible to understand the richness and diversity of the AMF communities present in each site. This variation could also be attributed to environmental conditions. Moreover, [41] report that this abundance of spores depends on the physicochemical properties of the soil. Likewise, the availability of nutrients in the soil would influence the presence of spores. According to [42] , loamy and sandy soils with nutrient deficiency would have a high number of AMF propagules and species. The variation in spore density could also be attributed to the presence of plant cover, which would contribute to the creation of a vast network of hyphae and interconnections with the roots of host plants, improving not only biomass but also the microbial activity of the soil [43] . The soils of Nkometou and Soa showed a higher quantity of spores compared to the soil of Olembe. Additionally, the soil at the Soa site showed a higher amount of assimilable phosphorus and an acidic pH at a value of 5.6. However, at this pH value, the phosphorus in the soil is in dihydrogen phosphate form, which can be assimilated by the plant. The results of this work reveal a spore density estimated at 5457 spores for the total of 150 g of soil for the three collection sites, this density is significantly higher than that obtained by [44] (around 4045 spores per 100 g of soil) under cowpea cultivation in the different agroecological zones of Benin.
The six AMF genera were identified in the two cultivars of X. sagittifolium in the three study sites following the age intervals. These were the genera Acaulospora sp., Funneliformis sp., Gigaspora sp., Glomus sp., Scutellospora sp., and Septoglomus sp., belonging to three families; Acaulosporaceae, Gigasporaceae, and Glomeraceae. These different types of AMF identified were not present in all the harvested sites. It is noted that, in the rhizosphere of plants with white cultivars, the AMF genera recorded were Acaulospora sp., Gigaspora sp., Glomus sp., Scutellospora sp., and Septoglomus sp. Whereas, in plants of the red cultivar, these are the genera Acaulospora sp., Gigaspora sp., Glomus sp., Funneliformis sp., and Scutellospora sp. The genus Septoglomus sp., was only present in the rhizosphere of X. sagittifolium plants of the white cultivar while Scutellospora sp. only appeared in the rhizosphere of the red cultivar plants. However, the genus Glomus sp. appeared most in the rhizosphere of X. sagittifolium at the sites of Olembe and Soa, compared to Nkometou at the age intervals of 6 - 9 and 9 - 12. The work of [45] showed that the soils of Cameroon are richer in AMF of the genus Glomus sp. Similarly, [46] highlighted the richness of the AMF of Glomus sp. in the rhizosphere of Gossypium hirsutum L. plants in North Cameroon. This abundance of the Glomus sp. genus could be explained by the fact that this species of AMF can multiply or reproduce and adapt to extreme conditions and acidic soils. Furthermore, the Shannon index greater than 1 obtained at the Soa site explains the diversity of AMF observed associated with the rhizosphere of Xanthosoma sagittifolium plants.
5. Conclusion
This pioneering study made it possible to highlight a few genera of AMF associated with the rhizosphere of white and red cultivars of Xanthosoma sagittifolium L. Schott plants in the field. Of the three study sites with different physicochemical properties, it should be noted that the genus of AMF, which was more represent in all age intervals is the genus Glomus sp. The genus Septoglomus sp., was only present in the rhizosphere of X. sagittifolium plants of the white cultivar while Scutellospora sp. only appeared in the rhizosphere of plants of the red cultivar.
Acknowledgments
The authors would like to thank the Laboratory of Plant Physiology and Biochemistry of the Higher Teachers’ Training College of the University of Yaoundé 1 and the Laboratory of Parasitology and Ecology, Faculty of Science, University of Yaoundé I.