Jatropha curcas is a shrub of Euphorbiaceae family and native to Central America and Mexico (Heller, 1996; Agnieszka et al., 2013; Sawadogo et al., 2015). It is well-known by African people, who use it for delimiting farms and concessions. In recent years, because of its biofuel potentials, the species is considered as a solution to deal with climate change, energy insecurity and to fight against  poverty   in   rural   areas  by  generating  income especially for women (Terren et al., 2012; Guittet and Massimiliano, 2015).

In Burkina Faso, J. curcas plantations are widespread through out the country’s phytogeographic zones (Bazongo et al., 2015); Tiendrebeogo et al., 2016a). However, the seed yields and seed oil content are variable and generally weak, reducing its economic potential and  making its culture a risk company (Singh et al., 2010; Kumar and Singh, 2014). These constraints justify the need of a varietal improvement which require the identification of high oil content in local ecotypes in order to optimize profitability of the species and to boost the J.curcas sector (Guittet and Massimiliano, 2015). Unfortunately, data on the characterization of local varieties in Burkina Faso are limited. Yet, previous works in Burkina Faso (Sama et al., 2013; Tiendrebeogo et al.,2016b) and the world (Rao et al., 2007, 2011; Kaushik et al., 2007)have highlighted a wide range of variability in seed traits and oil content depending on phytogeographic conditions. Therefore, regarding the different phytogeographical areas in Burkina Faso, large variability of seed traits and oil content is expected and some accessions may have better oleaginous potential. Moreover, these studies have shown that there is a positive correlation between J. curcas seeds weight and its oil content. In addition, the authors reported that heavy J. curcas seeds have better vigor at emergence and the seedlings grown from heavy seeds have better growth. Thus, assessment of the natural variability of seed traits and oil content of the species could help in identifying accessions with better seed trait and would be an important step for improvement programs (Kumar and Singh, 2014; Tiendrebeogo et al., 2016b). In Burkina Faso, the lack of data on morphological variability and seed oil content of J. curcas strongly limits such perspectives. In fact, the level of seed oil production of local accessions of J. curcas is still poorly understood. Despite the considerable economic potential of the species, limited research has focused on the variability of seed traits and oil content of the J. curcas seeds in Burkina Faso. Researches on the species have focused on the species physiology and biology (Tiendrebeogo et al., 2016a). However, information regarding the extent and pattern of genetic variation in J. curcas of local accessions is limited barring a few recent studies undertaken by Sama et al. (2013) and Tiendrebeogo et al. (2016b). The present study aims at characterizing the morpho-metric traits and the oleaginous potential of seeds of the accessions of J. curcas in Burkina in order to identify the performant accessions. Such accessions would be very capital for improvement and breeding programmes for a durable production of biodiesel containing J. curcas.

 

The study involved a total of 40 accessions of J. curcas L. collected in different sites of Burkina Faso. The characteristics of accessions are presented in Table 1. The collection was carried out based on a climatic gradient with a rainfall ranging from 500 to 1200 mm. The collection sites belong  to  southern  Sudan,  northern  Sudan,  sub-Sahelian and Sahelian zones (Figure 1). In each site, fruits were collected in plantations or hedges of J. curcas at least 5 years older, between July and September 2016. In each plantation or hedge, ripe fruits of ten (10) plants distant at least 10 m were randomly selected. All the fruits collected in the same plantation or hedge were gathered to form an accession. Afterward, fruits were dried under ventilation in the laboratory, decorticated manually and bagged in kraft envelopes without any pretreatment and stored at room temperature.

 

 

 

Characterization of traits variability and seed oil content

Variability of seed traits

For each accession, five batches of ten (10) seeds were randomly selected for the measurement of their morphological parameters (length, width and thickness) using an electronic Vernier caliper (precision of 0.01 mm) and ten seeds weight using an electronic balance (precision 0.01 g).

Oil content of the seeds

The seed oil content was determinate according AOAC 960.39 method described by Turinayo et al. (2015). Oil in seeds was extracted in with Soxhlet apparatus for 6 h, using petroleum ether (boiling point of 40 - 60°C) as an extraction solvent. The extracted oil is recovered by solvent evaporation using a rotavapor apparatus to remove the majority of the solvent by rotatory evaporation at 40°C under reduced pressure. The extracted seed oil was weighed. For each accession, the oil content of three samples was determined in triplicate tests in order to enhance accurate statistical inference. The amount of oil in seeds was calculated and expressed as percentage (%) by following formula:

Statistical analysis

The investigated parameters were subjected to one-way analysis of variance at the 5% level. The effect of climatic zones was the first to be evaluated. The Sahelian zone was excluded from this analysis because of the small number of accessions; only two accessions belong to this zone. When there were no significant differences between climatic zones, the traits of the accessions were subjected to a one-way ANOVA. When the ANOVA test showed significant differences in seed traits, the Tukey test (at the 5% threshold) was performed for the ranking of averages. The Pearson test was performed at the 5% threshold to assess the correlation between seed traits. All these statistical analysis were carried out in the R. software. Ward's aggregation method was used to group the accessions. According to Vachon et al. (2005), it is a method of entities partitioning into classes according to their similarity traits. In this classification, each class is a group of entities in which the variance between members is relatively small. The ANOVA results were also used to calculate genetic parameters (variance and coefficient of genotypic and phenotypic variability, heritability of traits studied and expected genetic gain) according to Gbemavo et al. (2015).

 

 

Morphological traits of seeds in relation to accession and the phytogeographic zone

The results of morphological seed traits showed that accession has a significant effect on seed traits (P < 0.001) in opposite to the phytogeographic zone that has no significant effect. Also, the results showed a very great variability of seed morphological traits from one accession to another. Seed length ranged from 17.40 ± 1.14 to 19.30 ± 0.98 mm with an average length of 18.55 mm. The shortest length was recorded in the J4 accession (North Soudan zone) and the highest value in the accession J13 (North Sudan zone). The width varied from 10.86 ± 0.46 mm for accession J4 (North Sudan zone) to 11.86 ± 0.43 mm for accession J31 (Sudanian zone) with an average value of 11.33 mm. The thickness ranged from 7.0 ± 0.17 mm for J18 accession (Sahelian zone) to 9.22 ± 0.22 mm for J35 accession (Sud Sudanian zone), while the weight of 10 seeds ranged from 5.88 ± 0.96 g for accession of J2 (Sudan zone) to 9.60 ± 0.96 g for accession J15 (Sudan North Area). Morphological  traits   of   seeds   were   subjected  to  an Ascending Hierarchical Classification (CAH). This classification allowed the distribution of accessions into four classes and characteristics are presented in Table 2. Class IV is represented only by the J18 accession collected in the Sahelian zone, while the other classes include accessions from different phytogeographic zones. The highest values of traits are observed in class I while the lowest is in class IV.

 

 

Seed oil contents were expressed as a percentage of kernel dry weight and the corresponding accessions. Seed oil contents of the different accessions ranged from 33.83 ± 1.65 to 57.21 ± 2.44% respectively for J1 accession (South Sudan zone) and J7 (Sub-Sahelian zone). The results also show that accession has a significant effect on the seed oil content (P < 0.001), whereas phytogeographic zone has no significant effect. Table 3 shows different ranges of oil content as percentage of mass of dry seeds. The contents are stored in intervals of amplitude 5%.

 

 

Genetic parameters

The genetic parameters have been calculated and results of calculate of genetic variables are  reported  in  Table 4.

The highest values of phenotypic variation coefficient (CVP) (95.20%) and genotypic variation coefficient (CVG) (77.80%) were recorded for seed oil content. The lowest values of  CVP (7.30%) and CGV (5.50%) were observed with seed length. The lowest value of heritability in the broad sense (46.40%) was recorded in seed length while the other traits of the seeds showed heritability between 56.00 and 73.70%. The genetic gain ranged from 2.24 to 19.93% for the length and seed oil content, respectively.

 

 

Correlation between seed traits

The correlation matrix based on the Pearson coefficient correlation is presented in Table 5. These correlations are positive and significant between the thickness and the width and between the weight and the other morphological traits of the seeds. However, there is no correlation between seed oil content and seed traits.

 

 

Comparative analysis of accessions

The dendrogram plotted on the basis of the morphological features and the seed oil content using Ward’s aggregation method regrouped the 40 accessions into three (03) clusters (I, II and III) (Figure 2) whose composition and average oil contents are shown in Table 6. In this classification, the average oil content of clusters I is 48.81% as compared to clusters II and III that have respectively 32.65 and 39.55%. Class I contains both accessions that have the high values of morphological traits and the highest oil content as compared to those of the other two classes.

 

 

 

 

 

 

 

Hierarchical ascending classification is a powerful tool used to assess the relative contribution of different traits to the total diversity and to quantify the degree of divergence or similarity between accessions. In this study, the Ascending Hierarchical Classification (CAH) based on the oil content and the morphological traits of the seeds showed a breakdown of the forty accessions into three groups. The constitution of groups is independent of the phytogeographic origin of the accessions. Similar results have been reported by Gbemavo et al. (2015)and Tiendrebeogo et al. (2016a). In this study, group I offers a possibility of varietal improvement that could fill the needs of setting up J. curcas plantations for biofuel production. Indeed, for the purpose of varietal improvement in order to establish plantations of J. curcas for biofuel purpose, accessions belonging to group I present the desired seed traits. Although, this study did not show a significant correlation between oil content and morphological traits of seeds, previous studies have shown that high weight seeds are oil-rich, have higher vigor at emergence, and better seedlings growth (Kaushik et al., 2007; Ouattara, 2013). In  addition,   these  seedlings  require  little  maintenance during the installation phase, which reduces the costs of setting up the plantations.

The genetic parameters presented in Table 4 show a small difference between the phenotypic and genotypic coefficients of variation. Similar results have been reported by Ouattara (2013)and Tiendrebeogo et al. (2016a). According to Basavaraj et al. (2017), a small difference between these two coefficients of variation indicates that the characters are not too influenced by the environment.

Indeed, this results show broad sense heritability values between 56.00 and 73.70%. Except the heritability of seed length, all the traits had high heritability values. According to Miftah (2016), heritability is high when its value is greater than 50%. These high values of heritability in the broad sense confirm the low influence of environmental factors on the expression of these characters. The determination of heritability shows that the observed variability is of genetic origin (Tiendrebeogo et al., 2016a). However, according to Kumar and Singh (2014), heritability and genetic gain must be considered together to predict the resulting effect in an improvement program. Indeed, high heritability (broad sense) may be due to the non-additive action of the gene and will only be reliable when accompanied by a high genetic gain (Kumar and Singh, 2014). The results show, in general, low genetic gain values (values between 2.55 and 19.93). The highest value (19.93) was observed for the oil content. This result suggests large potential for the improvement of seed oil content.

 

This study showed that plantations and hedgerows of J. curcas are widespread throughout the different climatic zones in Burkina Faso. The results show a very high variability of the morphological traits and the oil content of J. curcas seeds with certain accessions having good characteristics for these traits. The study also allowed the identification of genotypes of interest for their oleaginous potential that could serve as a basis for selection and breeding programs. The study of the determinism of this variability has revealed that the sources of this variability could be environmental and also genetic. As a result, there are good opportunities for selection and improvement of traits and seed oil production through selection. This study is an introduction of the identification of the best local genotypes with high oil potential.

 

The authors have not declared any conflict of interests.