Growth, Development and Suitability for Kent of Mango Rootstocks on Soil Substrates Collected under Anacardium occidentale L., Khaya senegalensis (Desv.) A. Juss and Mangifera indica L., in Casamance, Senegal

With an overall contribution of nearly 4 billion CFA francs to Senegal’s in-come, providing 23,000 employments more than 50% are women in 2021, the mango sector has shown its importance in the Senegalese economy even if the potential remains largely under-exploited. Thus, the study on the main local varieties remains an important perspective. This work carried out in the farm of the agroforestry department concerns the growth and development of four varieties (Pince, Kouloubadaseky, Sierra Leone and Diourou) on different soils (Mangifera indica, Anacardium occidentale and Khaya senegalensis). This work aims to contribute to the knowledge of the most cultivated varieties in Casamance. It is also a question of seeing the response of these varieties to grafting with the Kent variety. An experiment was conducted for one year with a split plot design consisting of 4 replicates (blocks). Each block contains 4 plots and each plot contains 3 sub-plots with 20 plants each. The parameters measured were: diameter at the collar, height, number of leaves, biomass, number of growth units and grafting success rate. The Sierra Leone variety showed the best growth results in terms ± 29.44%). Anacardium occidentale soil substrate gave the best growth in height (39.73 ± 5.54 cm) while the substrate collected under M. indica L produced a greater number of leaves (13.14 ± 3.64) and grafting success rate (71.12% ± 37.25%). The Khaya senegalensis substrate recorded the highest values in biomass production (61.00 ± 35.93 for fresh biomass and 25.25% ± 15.74% for dry biomass).


Introduction
Mango is the 7th most produced fruit in the world. Its production is over forty-five million tons in 2014 [1]. This production represents about 23% of the world's tropical fruit production, the main ones being banana, mango, pineapple, papaya, and avocado [2] [3]. The global production volume of mangos, mangosteens, and guavas reached 55.85 million metric tons in 2019, an increase from around 53.41 million metric tons in 2018 [4] behind the banana crop 106.7 Mt, apple 80.8 Mt, grape 77.2 Mt, and citrus 71.5 Mt [5]. Mango production is important in Senegal both for the local market and for export [6]. Indeed, Senegal exported 24,000 T of mango fruits in 2021 to European Union, Marocco and Arabic countries [7]. However, mango production is constrained by a number of problems: irregularity of production with alternating years of high and low production, heterogeneity of fruit at harvest (in terms of size or taste quality), and phenological asynchronisms with agronomic and phytosanitary impacts on production [8]. In Casamance, in addition to the above-mentioned problems, the mango sector faces several difficulties such as: the organization of producers, the proliferation of the fruit fly [9], the aging of orchards [10] [11] [12]. This is due to the fact that, in this area, populations depend for a significant part on forests and trees to satisfy various needs. With population growth, these resources are being depleted. Fortunately, many farmers would like to plant trees, but it is difficult to obtain high-quality seedlings. The production of basic information on germination, growth and development of local Mangifera indica varieties [13], as well as their suitability for grafting a semi-early variety such as Kent, could contribute to improving farmers' incomes. In addition, the use of litter from the main cash crop plantations in Casamance (Mangifera indica and Anacardium occidentale), but especially from forest species such as Khaya senegalensis (Desv.) A. Juss. would allow to improve growth performance in nurseries [13] at lower cost.
The general objective of this study is to contribute to a better knowledge of the local varieties of M. indica most widely grown in Casamance. Specifically, it aims to:  Evaluate the growth and development capacities of these local varieties on

Materials
Mangifera indica L, Anacardium occidentale L and Khaya senegalensis substrates were used as soil in pol to grow mango seeds. Then, the collected soils were sieved to remove all impurities. Then, they were put in the sheaths. In addition, the blocks, plots and treatments were set up and marked with labels. The seeds were sown on July 27, 2019. Weeding was done every week. Mango nuts of varieties were used as biological material during the study. The varieties are: Sierra Leone, Diourou, Pince and Kouloubadaseky. All the nuts come from the locality of Mlomp in the department of Oussouye. The nuts are identified morphologically. Diourou and Kouloubadaseky nuts have veins following furrows or canaliculi more pronounced in the former than in the latter. The veins follow shallow to superficial grooves in the Sierra Leone and Pince nuts ( Figure 1).

Conduct of the Experiment
Field preparation began with clearing and staking of the plots. The nuts were sorted after a flotation test with water to determine the good seeds. The nuts were plunged into a wheelbarrow filled with water, the floating nuts were eliminated and those at the bottom of the wheelbarrow were selected for sowing [13].      To evaluate the biomass, the plants were divided into aerial and root parts.
The root part was well separated from the substrate. After rinsing with water, the roots were wrapped with tissue paper to absorb the water before weighing. The aerial part was divided into stems, branches and leaves. These measurements were made at the Agroforestry and Forest Ecology Laboratory at UASZ (Figure 4).

Grafting Technic Used
Grafting of the Kent variety was used. The grafts came from orchards of Djibelor and Diabir around Ziguinchor district. The grafts in stop of growth are better for a fast recovery. A pruning is done before starting the grafting itself. The double slit method was used for all treatments. It is a method that allows for proper welding and maximizes the chances of success in Mangifera indica. Grafted plants were fellow-up to see the recovery. A regular monitoring was done every 3 days to observe the recovery and remove the buds from the rootstock variety. When recovery is noted, the plastic band was removed at the top of the graft not to block the evolution of the new shoots on the scion. The new shoots of the rootstock are regularly removed to avoid competition with the scion. Successful grafted plants were counted for each plot to calculate the success rate using the following formula. Successful grafting rate per plot = (number of successful grafted plants per plot)/(total number of grafted plants per plot) * 100.
Data (number of leaves, height, collar diameter, number of shoots, number of growth units, biomass and successful grafting rate) was collected in the field, entered and processed on the Excel spreadsheet ( Figure 5). The collected data were analyzed with the XLSTAT and Rplus softwares. Analyses of variance (ANOVA) were performed at the 5% threshold and comparison of means tests with Fisher's test. A principal component analysis (PCA) was performed to identify the correlations between the different variables studied (number of leaves, height, diameter, number of shoots, water content, central growth units) but also to characterize the varieties.

Diameter at the Collar
As shown in Table 1, the collar diameter grown highly in the plant of the 3 varieties than in the variety Pince and the three other varieties (P = 0.006). Indeed, the variety Pince had the lowest diameter (0.384 ± 0.095). The Sierra Leone variety had the largest diameter (0.511 ± 0.090).
As shown in Table 2, the substrates had likely the same effect on the plant diameter (P = 0.588). The interaction between the two factors (variety and substrate) was not significant (P > 0.05) on the plant width growth.   Table 3 presents the variation of the average height according to the varieties.

Plant Height
There is no difference between varieties (P = 0.226). However, the Kouloubadaseky variety has the maximum value (41.90 cm) and the Pince variety the minimum value (31.78 cm). The varieties Kouloubadaseky and Sierra Leone had a faster growth in height than the others. Table 4 presents the effect of the substrate on the plant height. As shown there is no significant difference from between the three types of soil (P = 0.319).
However, Anacardium occidentale potting soil induced 1 cm more of height comparing the other substrates.
The interaction between the two factors was not significant (P > 0.05).       Table 8 gives the fraction of fresh biomass produced by the plants grown on different soils. It appears from this table that the plants yield the same amount of biomass whatever the substrates (for leaf biomass P = 0.234, stem fresh biomass P = 0.277 and root fresh biomass P = 0.337). However, in absolute value, the Khaya senegalensis substrate came first in terms of fresh biomass production for leaves (27.17 g ± 16.13), for roots (14.73 g ± 8.62) and for stems (18.69 g ± 13.34).

Fresh Biomass
The interaction between the two factors was not significant all fraction of fresh biomass (leaves, stems, branches and roots). Table 9 presents the fraction of dry biomass by variety. The statistical analysis shows a higher significant difference (P = 0.0001) between varieties for the different parts of the plant. The variety Diourou gives the highest dry biomass fractions for stems (8.64 g ± 4.22) while the variety Sierra Leone records the highest value for leaves (12.58 ± 6.75) and roots (7.53 g ± 4.82). The variety Pince has almost half the values recorded for the other varieties, for leaves (5.75 g ± 3.08), stems (3.47 g ± 2.68) and roots (3.56 g ± 1.66). The Sierra Leone variety recorded the highest total dry biomass fraction (28.67 g ± 16.80). Table 10 shows the fraction of dry biomass by soil. Statistical analysis shows that there is no difference between the substrates for the dry biomass of leaves    Regarding the grafting success rate of seedlings there were not interaction between the two factors ("variety" and "ligneous potting soil").

Relation between the variables evaluated and the different treatments
Through the principal components analysis (PCA) carried out, Figure 7 presents the distribution of treatments according to the variables measured on the plants.
The growth in height of the plants is weakly related to the water content or the number of leaves and also the number of growth units. It is closely linked to the diameter at the base and to the amount of dry matter, so varieties that produce more dry matter at the stem, leaf and root, and therefore have good radial growth, are successful in grafting with Kent. The Diourou and Kouloubadaseky varieties seem to be the best rootstocks for Kent and to a lesser extent Siera léone. The variety Pince is the least successful and potentially weakest rootstock for Kent.
The substrates seem to have the same effect on the growth parameters of the seedlings. The emission of growth units seems to be more related to the total biomass (leaf, stem, root), and the diameter of the plant with significant correlations (Table 15). However, the elongation of growth units was not evaluated.

Discussion
The plant height was almost same in all the 4 mango varieties and regarding the substrates. These results corroborate those of Djaha et al., [16], who studied the growth and suitability of two Anacardium occidentale genotypes used as rootstocks in Côte d'Ivoire, and found no significant difference between the different genotypes. This analysis also showed that there was no significant difference in plant height between the different soils (P = 0.319). These results are similar to those of Ndiaye et al. [13] who also showed that the effect of soil substrates was not felt on plant height. Mané, [17] studied the germination and growth of Acacia melifera (Vahl) Benth. on Faidherbia albida (Del.) A. Chev, Elaeis guineensis Jacq. and Anacardium occidentale L. and found a significant difference in seedling height between soils. The height was changing rapidly during the rainy season, which is due to the availability of water; this confirms the statements of Schaffer et al. [18] who showed that environmental factors, temperature and water availability remain the most important in the growth of certain species.
Douma et al., [19] showed the effect irrigation regime on germination and nursery growth of Parkia biglobosa Jacq.
The diameter at the collar measures 4.66 mm in 3 months in Casamance. A higher growth record was reported at Banfora (Burkina) by Bognina [20] A. occidentale L accessions whose plants reach 5.85 mm in 2 months. The diameter growth was different from a variety to another and between treatments. The Sierra Leone variety has a larger diameter than the Pince variety. Similarly, the Kouloubadaseky variety showed a higher difference in diameter on cashew potting soil than on M. indica and K. senegalensis. These results confirm those of Ndiaye et al., [13], who also showed that the Kouloubadaseky variety had a diameter that varied according to the soil fertility. This is confirmed by Giffard [21]

Conclusion
From this study, it appears that the growth and development of four varieties (Pince, Diourou, Sierra Leone and Kouloubadaseky) on substrates (M. indica L., A. occidentale L. and K. senegalensis (Dres.) A. Juss.) and their grafting efficiency with the Kent variety gave good opportunities to farmers. Indeed, the results showed that Sierra Leone variety gives a better growth in diameter and number of leaves, while Kouloubadaseky variety gives a better growth in height.
The variety Diourou gives the best results for all the other remaining parameters.
Even there was no significant difference, the M. indica L. potting soil maintained water content and gave the best results on the diameter and the successful grafting rate; the A. occidentale potting soil gave the best results in height. Finally, the K. senegalensis potting soil gives the best results in terms of biomass production.
Diourou, Kouloubadaseky and Sierra Leone varities responded better Pince when grafted with Kent. M. indica L. and K. senegalensis soils are better in terms of growth of these varieties.