Plant material

‘Zeitoun Ennour’ is a new olive (Olea europaea L.) cultivar obtained in a crossbreeding program in Tunisia. It was derived from a cross carried out in 1993/1994 between ‘Chemlali Sfax’ (female) and ‘Chemchali Gafsa’ (male), two cultivars from different geographical origins: ‘Chemlali Sfax’ from Sfax in the center-wast of Tunisia and ‘Chamchali Gafsa’ from Gafsa in the center-west of Tunisia. ‘Chemchali Gafsa’ showed better fatty acid composition when compared to ‘Chemlali Sfax’, the most widely adopted olive cultivar in Tunisia as reported by (Grati-Kamoun & Khlif, 2001).

The cross was performed by pollination of flowers on bagged branches with fresh pollen grain and forced growth of seedlings was carried out in a greenhouse to shorten the juvenile period. Seedlings were planted in two open fields during 1997-1998 with a density of 1250 trees/ha (4 x 2m spacing): the experimental station of the Olive Institute at Sfax (Central Tunisia, lat 34° 44′ N, long 10° 46′ E) and the Research Station of ‘Taous’, which is about 26 km from Sfax (lat 34° 56′ N, long 10° 36′ E).

The first crop was obtained in 2000 and seedling evaluation was carried out for three consecutive harvest seasons. The original seedling of ‘Zeitoun Ennour’ was selected mainly on the basis of its fatty acid composition. After vegetative propagation by semi-hardwood stem cuttings (2002 to 2004), propagated trees of ‘Zeitoun Ennour’ together with other selected seedlings were planted in a comparative trial since 2005 at 6 × 4m spacing and irrigated conditions at the experimental farm of ‘Taous’ in the region of Sfax.

Methodology

The evaluation of ‘Zeitoun Ennour’ and the check ‘Chemlali Sfax’ in this trial was done for three trees per cultivar during three years (2013-2015) on the following characters:

Data analysis

For each morphological character, the type having the highest mean value over three years was attributed to the cultivar. Bearing earliness can be very early (< 3 years), early (3 years), medium (4 years), late (5 years) or very late (> 5 years). The ripening date corresponding to maturity index 3.5 can be in late autumn (early maturity), early winter (medium maturity) or late winter (late maturity).

Variance analysis was made for olive production and Verticillium tolerance considering years and plants as replicates respectively. For pollen compatibility, variance analysis was undertaken for each cultivar to compare fruit sets from self-pollination and free pollination considering years as replicates. For oil chemical characters, variance analysis with years as replicates was carried out for each fatty acid.

All data analyses were performed using the statistical procedures in XLSTAT 11.0 and the separation of means was done by Duncan test at 5 % level.

Morphological characterization

The morphological evaluation of the new cultivar is presented in Table 1 and Figure 1. Leaves of ‘Zeitoun Ennour’ were mostly of elliptic-lanceolate shape and flat longitudinal curvature similar to the original cultivar.

Fruits of the new cultivar were asymmetrical, with a truncated base and rounded apex, medium weight, central maximum diameter, few lenticels, and without nipple. At maturity stage, the location of colour change start was uniformly across the whole epidermis and the colour at the end of maturity was black.

‘Zeitoun Ennour’ had asymmetric endocarp with medium weight, elliptic shape, a round base, pointed apex, its maximum diameter toward the apex, rugose surface and regular distribution of grooves. The apex termination was without mucro.

This cultivar differed from the typical of ‘Chemlali Sfax’ in more than half of the scored fruit and endocarp traits, (11 traits in total), especially regarding their respective weights, where ‘Zeitoun Ennour’ scored higher (> 2 g and > 0.3 g respectively) than ‘Chemlali Sfax’ according to IOC norms (International Olive Council, 1997). Chemlali Sfax was previously shown to have low fruit and endocarp weights (Barranco et al., 2000; Trigui & Msallem, 2002).

Despite the evidence of the subjectivity of the morphological description, it can be concluded that the new cultivar showed substantial genetic differences from ‘Chemlali Sfax’.Laaribi et al. (2014) reported wide genetic diversity observed within and between olive tree seedlings issued from the same Tunisian breeding program.

Agronomic characterization

An agronomic description of ‘Zeitoun Ennour’ and ‘Chemlali Sfax’ was carried out a the comparative field trial established at the experimental farm ‘Taous’ of the Olive Tree Institute (Table 2).

The new cultivar showed a short juvenility period (3 years) from planting till economic bearing. It can be classified with early bearing in comparison with ‘Chemlali Sfax’ (medium). Yield traits were evaluated on 10-year-old trees during the period 2013-2015, the average yield per tree was classified as high for both cultivars similar what had previously been reported for ‘Chemlali Sfax’ (Barranco et al., 2000; Trigui et al., 2002).

‘Zeitoun Ennour’ displayed late maturity with optimum ripening period occurring in late winter while ‘Chemlali Sfax’ displayed medium maturity.

Regarding pollination mode, fruit set following self-pollination (5.13 %) was significantly inferior to that following crosspollination (9.87 %). Consequently, the new cultivar was found to be partially self-incompatible according to the norms of Barranco et al. (2000). ‘Chemlali Sfax’ had a self-compatible behavior in our study since fruit sets from self-pollination and cross-pollination were statistically similar (11.21 and 10.45 % respectively). The same performance was reported for ‘Chemlali Sfax’ byTrigui et al. (2002) in the centre of origin. Thus, while pollinator trees may not strictly be required in the field with this new cultivar, several pollinator trees planted in the orchards could compensate for the partial self-incompatibility, as suggested byMehri, Mehri-Kamoun, Msallem, Faîdi, and Polts (2003) in these situations. In this case, a study of the flowering period for different olive varieties is necessary to identify the best pollen donor for ‘Zeitoun Ennour’.

With respect to Verticillium dahliae Kleb, our results indicated that ‘Zeitoun Ennour’ and ‘Chemlali Sfax’ had similar levels of tolerance with 65 and 57 % respectively. Consequently, they were susceptible to this fungus. Thus, we suggest propagating this new cultivar with semi hardwood cuttings from healthy trees in order to avoid Verticillium infection. Morever, the best solution in the propagation of this cultivar is to follow the plant certification procedure as outlined in the EU plant health regulation (European Commission, 2016) to ensure the Verticillium free status of olive plants. In fact, Verticillium wilt is the most destructive disease affecting olive orchards in Tunisia (Gharbi, Bouazizi, Cheffi, Amar, & Triki, 2020) and in the world (López-Escudero & Mercado-Blanco, 2011).

Fatty acid composition

The ‘Zeitoun Ennour’ cultivar had a considerably improved fatty acid composition compared to the original cultivar ‘Chemlali Sfax’ (Table 3).

In comparison with the original variety, the mean values of ‘Zeitoun Ennour’ for the three fatty acids were significantly better than the original variety. The concentration of oleic acid, the main monounsaturated fatty acid, was higher for the new cultivar (76.3 %) than the original cultivar (59 %), while the level of palmitic acid, the major saturated fatty acid in olive oil, was significantly lower (10 %) than ‘Chemlali Sfax’ (19.6 %). The content of linoleic acid, another important monounsaturated acid, for ‘Zeitoun Ennour’ was also lower (9.7 %) than ‘Chemlali Sfax’ (16.8 %).

In addition, the fatty acid composition of ‘Zeitoun Ennour’ is within the standard norms reported by the (International Olive Council, 1997), while ‘Chemlali Sfax’ practically has the lowest value of oleic acid and the maximum limit of palmitic acid.

According toD’imperio et al. (2007) and Zarrouk et al. (2009), a healthy olive oil should have high oleic acid content and low palmitic acid content. Thus, we consider that the new selected cultivar ‘Zeitoun Ennour’ realized an important genetic gain in fatty acid composition and could be of great benefit in the Tunisian olive sector (farmers, industrials and oil exporters). From the same breeding program, two other hybrids were released and characterized. Zeitoun Ennwader (Chemlali Sfax/Lucques) and Chemlali Mhassen (Chemlali Sfax autopollinated) were presented, respectively, byBen-Amar et al. (2019) and Guellaoui et al. (2019).