Abstract
The fig (Ficus carica L.) is one of the oldest fruit trees cultivated in Tunisia. Djebba region is located in the northwest of Tunisia. It is very famous by fig culture. Many specific fig genotypes are very appreciated locally and nationally. Taking into account these considerations, Djebba fig cultivars are subject of label products, namely, “Djebba figs.” This study was focused on fig germplasm characterization of 17 cultivars in Djebba region based on morphological and pomological traits. Results revealed a large variability within the local fig germplasms. The comprehensive analyses of all the data permitted to distinguish some particular genotypes as distinct cultivars, and groups of cultivars as polyclone varieties. It was possible to discriminate six distinct cultivars and two groups of multiclone varieties (Soltani and Thgagli) with different degrees of polymorphism. Hypotheses of homonymy and synonymy were suggested for some cultivars. The diversity is currently threatened by genetic erosion. Measure of conservation is necessary to be undertaken.
1. Introduction
The common fig (Ficus carica L., 2n = 26) belongs to the family Moraceae, with over 1400 species classified into about 40 genera. The genus Ficus contains about 700 species, mainly found in the tropics and currently classified into six subgenera [1]. Nowadays, the common fig grows wild in the Mediterranean Basin where it has been cultivated for its edible fruits for millennia in close association with olive and grapevine [2]. Three types of figs are grown commercially [3]: the common type that develops fruit parthenocarpically, the Smyrna type that requires pollination with pollen from caprifigs (caprification), and the San Pedro type that produces a first crop parthenocarpically and a second crop only after pollination. Total world fig production is over 1 million tons and 70% is produced in Turkey, Egypt, Greece, Iran, Morocco, Spain, and USA. Turkey produces nearly 25% of the total production [4].
In Tunisia, fig biodiversity is very high, and many niches are well suited for fig production. Despite its socioeconomic and historical importance, fig tree was considered as a secondary crop. Fig trees are grown all over the country, with more than 2,500,000 trees occupying about 33800 ha. The total annual production is about 27.000 mile tons [5]. Figs are mainly consumed as fresh fruits. A small portion is sun dried and little quantities are used for jam and alcoholic beverage production [6]. Tunisian fig cultivars are numerous and well adapted to local agroecological conditions [7]. Some are of the common type. Many others are of Smyrna type [8]. It should be stressed that several studies have reported the use of pomological traits in a number of Tunisian ecotypes collected from different zones [9]. Thus, 65 cultivars were described by Minangoin [10], 22 cultivars by Valdeyron and Crossa-Raynaud [11], and 28 by Lahbib [12]. It is noteworthy that a number of these cultivars have been destroyed as a consequence of the intensive urbanization in recent decades. Moreover, severe genetic erosion is also threatening the remaining germplasm. Thus, available information about the ancient landraces is very limited [6].
In order to preserve fig genetic resources, several prospections and alternative strategies for genetic resources management were considered. Pomological and morphological traits as well as molecular markers were used to analyse genetic diversity and characterize local cultivars [8, 13–19]. Recently, various studies on fig genetic resources are continuing across the country. But no research results have been reported so far on northwest fig germplasm. This study is part of a project of the “Union Tunisienne de l’Agriculture et de la Pêche” aiming to establish a label to Djebba’s fig. The objectives are (i) identification of different fig cultivars grown in Djebba area and (ii) analysis of genetic diversity within the germplasm.
2. Materials and Methods
2.1. Plant Material and Study Area
This study concerned the region of Djebba (altitude, 700 m; latitude, 36° 40′N; longitude 9°0′E) located at the northwest of Tunisia. The climate is subhumid with mild winter and hot summer. Annual average temperature is around 20°C. Thermal amplitude is about 16.5°C in summer and 8°C in winter. Average annual rainfall is about 600 mm. The morphological and pomological variability was studied on adult fig trees of 17 local cultivars (one tree per cultivar) grown in this region (Table 1).
2.2. Morphological and Pomological Traits
Morphological and pomological parameters were chosen according to the fig descriptors [20]. On branches, 13 parameters related to the dimensions of shoots and internodes were measured (Table 2). For each cultivar, measurements were made after fall of leaves on six shoots per tree. For leaves, 16 parameters related to the lamina and petiole were measured on 20 mature leaves per tree and cultivar (Table 2).
On fruits (second crop), 16 parameters related to the size, external and internal appearance, and juice quality were taken into account (Table 2). During the harvesting period, pomological measurements and chemical analysis carried out on samples of 20 mature fruits per tree and cultivar were randomly collected. Total soluble solids (°Brix) were determined with a digital refractometer, PR-101 ATAGO, and Norfolk, and titratable acidity (citric acid %) was determined by titrating fig juice with 0.1 M NaOH.
2.3. Statistical Analysis
For all parameters, analysis of variance (one-way ANOVA) was used to determine differences between cultivars. Comparison of the mean values was made using the Duncan’s multiple range test (). Multivariate relationships among cultivars were revealed through a principal component analysis (PCA) using a correlation matrix derived from the significant characters. The squared Euclidean distance was used to perform cluster analysis. Statistical analyses were computed using SPSS 13.0 statistical software.
3. Results
3.1. One-Way ANOVA
The average values of parameters measured on branches are shown in Table 3. Analysis of variance showed highly significant differences between cultivars for all parameters except terminal bud diameter (TBD). The study of morphological characteristics of fig tree shoots allowed the differentiation in biology of some cultivars such as Zidi (ZD1), Zidi Artab (ZD2), and Nemri (NMR). Moreover, the most discriminating variables were terminal bud length (TBL), 1-year-old shoot length (S1Y), and 2-year-old shoot length (S2Y).
The averages of characters related to leaf are shown in Table 4. Analysis of variance showed highly significant differences between cultivars for all parameters. The variability of leaf characteristics was very important and allowed the distinction between some cultivars for several parameters such as leaf shape, leaf margin dentation, and leaf dimensions (LS, LMD, LL, and LW), petiole color (PC), and the depth of basal and lateral sinus (DBS and DLS1, DLS2, DLS3, DLS4).
The averages of characters related to fruit are given in Table 5. Analysis of variance showed highly significant differences between cultivars for all parameters. The most discriminating variables were fruit weight (FW) and fruit dimensions (FL, FD).
3.2. Principal Component Analysis
Principal component analysis(PCA) was performed taking into account shoots, leaves, and fruits. The eigenvalues obtained by PCA indicate that the first three components provide a good summary of the data. They explained 51.91% of the total variability. The first component, PC1, had large positive loading for shoot length of the two years (S1Y and S2Y), lengths of the 1st, and 2nd internode on S1Y (L1N1Y and L2N1Y), diameters of the 1st, and 2nd internode on SY2 (D1N2Y and D2N2Y), depths of basal and lateral sinus (DBS, DLS1 and DLS2), leaf dimensions (LL and LW), fruit weight and diameter (FW and FD), and ostiole diameter (OD) and negative loadings for petiole color (PC), fruit external color (EC), and total soluble solids (TSS). It represented 26.46% of the total variation (Table 6). This component separated the cultivars Zidi (ZD1) and Nemri (NMR) from Soltani Abiadh (SAB), Thgagli Akhder (TAK), and Khenziri (KNZ) based on shoot length, fruit size, depth of sinus, and ostiole diameter. It allowed the distinction of cultivars Bouharrag (BHR) and Wahchi (WAH) from ZD1 based on petiole color, fruit size, and total soluble solids (Figure 1). The second component, PC2, explained 13.67% of the variability observed. It is positively correlated with fruit length and shape (FL and FS), fruit neck dimensions (NL and ND) and negatively correlated with terminal bud length (TBL), 1-year-old shoot length (S1Y), and fruit cavity (FC). This component allowed the distinction of cultivars Zergui (ZRG), Bouhouli (BHL), Garaï (GRI), KNZ, and TAK from SAB, Soltani Ahmar (SAH), and Hemri (HMR) on the basis of fruit shape, fruit neck, and cavity (Figure 1). The third component, PC3, accounted for 11.78% of the total variability estimated from shoots, leaf, and fruit traits. It is positively correlated to the apex shape (AS), fruit length (FL), and titratable acidity (TA), and negatively correlated to the internode diameter of shoots of the two years (D1N1Y, D2N1Y and D1N2Y, D2N2Y), shape of lobes (SL), depth of basal sinus (DBS), and pH. This component allowed the differentiation of cultivars Fawari (FAW), SAB, and HMR with thin shoots and acid fruits from cultivars Boukhobza (BKB), BHR, ZRG, and SAH presenting thick shoots and low acid fruits (Figure 1). The projection of cultivars in the 1–3 plot exhibited the distinction of some cultivars with particular traits such as ZD1 and Zidi Artab (ZD2) and others which are grouped together and having similar characters such as (SAB, WAH, and KNZ) and (BKB, BHR, and ZRG) (Figure 1).
3.3. Cluster Analysis
Morphological and pomological analysis based on different characters showed high polymorphism with 17 fig cultivars. The dendrogram based on squared Euclidian distance clustered cultivars into five major groups (Figure 2). The first cluster was constituted with three cultivars: Zidi, Zidi Artab (ZD2), and Nemri (NMR). ZD2 was the most divergent from the other cultivars (). It is characterized by long internodes, spatulate, and large leaves, deep sinus, and acid fruit juice. The cultivars ZD1 and NMR meet at d = 15.9. They shared the long shoots, large fruits size, and leaves with serrate margin dentation. The cultivar Soltani Abiadh (SAB) formed the second cluster at d = 16.9. This cultivar had the shortest shoots, flattened buds, and cordate leaves with apex acute. The fruits were very long, crackled with high acid juice. The third group, detached at d = 15.9, was constituted with the unique cultivar Fawari (FAW). It is distinguishable, particularly, by short vegetative shoots and internodes, flattened buds, and dark green, large and crenate leaves, with deep sinus and yellow petiole. Fruit shape was oblate producing high acid juice. The cultivar Soltani Ahmar (SAH) formed the fourth cluster at d = 12.85 of the remaining genotypes. It has short and thin shoots with flattened buds. The fruits were relatively small, purple with very thin skin, and give low acid juice with high pH. The leaves were pubescent, serrate with widened lobes and rounded apex. The fifth group consisted of 11 cultivars with a maximum internal dissimilarity level of 10. This cluster was divided into three subgroups. The first subgroup, detached at d = 10, comprised the cultivar Thgagli Akhder (TAK). It is distinguished essentially from the remaining genotypes by small leaves with spatulate lobes, shallow sinus, and short petioles. The second subgroup contained the cultivar Bouharrag (BHR) associated with a level d = 7.85 to the three cultivars Thgagli Abiadh (TAB), Boukhobza (BKB), and Khartoumi (KRT). They are characterized particularly by green leaves with widened lobes, fruits oblate, and sweetened juice. The third subgroup consisted of six cultivars with a maximum internal dissimilarity level of 7.61. Two subsets were identified in this third subgroup. Subset 1 composed of cultivars Garaï (GRI) and Bouhouli (BHL) which associated between them at high level of similarity (d = 2.37) and rejoined the cultivar Zergui (ZRG) at d = 7.61. These cultivars presented conical buds, light green cordate leaves, and oblate fruits without neck. Subset 2 composed of cultivars Khenziri (KNZ), Wahchi (WAH), and Hemri (HMR) having cordate leaves with widened lobes and serrate margin dentation, acute apex, and yellowish green petiole. The fruits give a sweetened juice. WAH and KNZ have the highest level of similarity observed (d = 0.71). The averages values of their main characteristics were similar.
4. Discussion and Conclusions
Morphological and pomological traits considered in this study showed a large variability for Djebba figs. Among the 45 variables analyzed, those of high discriminating level were leaf dimensions, shoot dimensions, petiole color and dimensions, depth of sinus, fruit shape and color, fruit weight and dimensions, ostiole diameter, and juice acidity. Results of the PCA based on shoots, leaf, and fruits traits showed that 51.91% of the total variability is accounted by the three PCs. Studies based on morphological and pomological traits conducted for pomegranate and peach founded, respectively, 49.29% [21] and 63% [22] of the total variability. Characters related to shoots, leaf, and fruits were powerful for studying the genetic diversity of domestic fig in Djebba. Results showed that, among these characters, some were good criteria for discriminating between cultivars. Similar results were reported by Salah et al. [9] in fig collection in the oasis of Nefzaoua and by Chatti et al. [13] in fig collection in Chott Mariem. In addition, morphological study based on the characteristics of fig trees has shown that the first three axes of the PCA amounted to 71.7% and 81.9% of the total variability, respectively, for leaves and fruit traits [15].
The cluster analysis showed high degree of diversity in the germplasm of Djebba fig. Among the cultivars with the same names, there is a similarity between Soltani Abiadh (SAB) and Soltani Ahmar (SAH) and between Thgagli Abiadh (TAB) and Thgagli Akhder (TAK). However, the levels of similarity observed were not always high enough to believe that they are synonymous. Both cultivars Soltani have almost the same characteristics of shoots and leaf and differed mainly by the fruit external color. Both cultivars Thgagli have a significant similarity in terms of shoots and fruit, while they have a divergence in leaf and petiole. Thus, for Soltani and Thgagli, it seems to be “polyclones cultivars” or “multiclones cultivars.” Both cultivars Zidi and Zidi Artab have many differences that were focused on shoots strength developed during the two years. Also, differences were noted for leaves and fruits. The hypothesis of homonymy between these two cultivars could be proposed.
Significant similarities were observed among the cultivars Wahchi (WAH), Khenziri (KNZ), and Hemri (HMR) and between Garaï (GRI) and Bouhouli (BHL) for all morphological and pomological traits. Thus, it seems to be a case of synonymy between these cultivars.
The characters adopted in this study could be used to establish a catalog of local fig cultivars. The concordance between the results of PCA and cluster analysis showed that morphological and pomological analysis can provide reliable information on the variability in fig tree. The overall analysis of all traits brings out a wide diversity in plant material that may have important implications for genetic resources management. This diversity could be due to the antiquity of the culture in this mountainous region and particular cultural practices [7]. More interest has been focused on the diversity since it was known that the domestication of fig tree occurred independently in different areas especially around the edge of the Mediterranean. Thus, it is very interesting to conduct the proper management of these genetic resources. This can be addressed by different tools such as the establishment of ex situ collections. The on-farm conservation can ensure the sustainability of these resources. It is also possible to explore the techniques of tissue culture as an alternative as future protocols for in vitro micropropagation and even cell-cultured fig are already developed [23–26]. Further studies are needed involving chemical, biochemical, and molecular markers [14, 16, 17, 19]. They would clarify the genetic variation at the molecular level in these cultivars.
Acknowledgments
This study is part of research program of the Research Unit on Agrobiodiversity (UR03AGR04) financed by the Ministry of Higher Education, Scientific Research and Technology (Tunisia). Authors would like to thank Mrs. W. Brini for data analysis and technicians and farmers for their efficient collaboration.