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An olive breeding program was started in Tunisia in 1993 in order mainly to improve the fatty acid composition of the local cultivar ‘Chemlali Sfax’. ‘Zeitoun Ennour’ is a new cultivar obtained from a cross between ‘Chemlali Sfax’ and the local dual-purpose use cultivar ‘Chemchali Gafsa’. The morphological study of this cultivar showed that eleven characters dealing with fruit and endocarp differed from ‘Chemlali Sfax’, mainly regarding to their respective weights. This new cultivar had the same sensitivity to Verticillium dahliae Kleb and earlier bearing than the original variety. Its olive production was considered as high as for ‘Chemlali Sfax’ but with partial self-compatibility and late maturity. The new cultivar realized a net improvement in comparison with the original cultivar particularly regarding its fatty acid composition with very high oleic acid content (>75 %) and low palmitic and linoleic acid contents (

The identification of drought-tolerant olive tree genotypes has become an urgent requirement to develop sustainable agriculture in dry lands. However, physiological markers linking drought tolerance with mechanistic effects operating at the cellular level are still lacking, in particular under severe stress, despite the urgent need to develop these tools in the current frame of global change. In this context, 1-year-old olive plants growing in the greenhouse and with a high intra-specific variability (using various genotypes obtained either from cuttings or seeds) were evaluated for drought tolerance under severe stress. Growth, plant water status, net photosynthesis rates, chlorophyll contents and the extent of photo- and antioxidant defenses (including the de-epoxidation state of the xanthophyll cycle, and the contents of carotenoids and vitamin E) were evaluated under well-watered conditions and severe stress (by withholding water for 60 days). Plants were able to continue photosynthesizing under severe stress, even at very low leaf water potential of −4 to −6 MPa. This ability was achieved, at least in part, by the activation of photo- and antioxidant mechanisms, including not only increased xanthophyll cycle de-epoxidation, but also enhanced α-tocopherol contents. “Zarrazi” (obtained from seeds) and “Chemlali” (obtained from cuttings) showed better performance under severe water stress compared to the other genotypes, which was associated to their ability to trigger a higher antioxidant protection. It is concluded that (i) drought tolerance among the various genotypes tested is associated with antioxidant protection in olive trees, (ii) the extent of xanthophyll cycle de-epoxidation is strongly inversely related to photosynthetic rates, and (iii) vitamin E accumulation is sharply induced upon severe chlorophyll degradation.

Olive is one of the oldest cultivated species in the Mediterranean Basin, including Tunisia, where it has a wide diversity, with more than 200 cultivars, of both wild and feral forms. Many minor cultivars are still present in marginal areas of Tunisia, where they are maintained by farmers in small local groves, but they are poorly characterized and evaluated. In order to recover this neglected germplasm, surveys were conducted in different areas, and 31 genotypes were collected, molecularly characterized with 12 nuclear microsatellite (simple sequence repeat (SSR)) markers, and compared with 26 reference cultivars present in the Tunisian National Olive collection. The analysis revealed an overall high genetic diversity of this olive&rsquo, s germplasm, but also discovered the presence of synonymies and homonymies among the commercialized varieties. The structure analysis showed the presence of different gene pools in the analyzed germplasm. In particular, the marginal germplasm from Ras Jbal and Azmour is characterized by gene pools not present in commercial (Nurseries) varieties, pointing out the very narrow genetic base of the commercialized olive material in Tunisia, and the need to broaden it to avoid the risk of genetic erosion of this species in this country.

Climate changes are expected to have a great and negative impact on agriculture in Mediterranean region. In this region, olive industry plays a key role at regional and national level as in Tunisia. With expected increasing temperature, the impact of climate change on the phonological behavior of the olive cultivars was evaluated in the main production region in central Tunisia (34°56′08″N, 10°36′54″E) during 2005–2015.The relationships between the budburst and flowering dates and climatic variations were investigated for the main local (Chemlali, Chemchali, Oueslati and Chetoui) and foreign (Koroneiki and Arbequina) olive cultivars to state their adaptability to warm area climate. Chilling was computed as chill portions (CP) from October to budburst using Dynamic Model, whereas heat accumulation was quantified as growing degree hours (GDH) from budburst to the beginning of flowering. As a result, variable budburst and flowering dates of olive cultivars were obtained related to the climatic conditions occurring each year. ‘Chemlali’ and ‘Arbequina’ seemed to be the precocious cultivars with an average budburst date of DOY-71 (March-12), whereas ‘Chemchali’ and ‘Koroneiki’ were the most late with an average budburst dates of DOY-80 and DOY-81 (March21-22). The beginning of flowering occurred from DOY-93 (3-April) to DOY-126 (6-May), where ‘Chemchali’ seemed, also, to be the latest one. Winter chill impacted significantly olive flowering with a positive correlation between flowering date and chill accumulation. A tendency for advancing flowering of local and foreign olive cultivars occurred subsequent a lack of winter chill. Trends for increasing heat accumulation with increasing chilling were observed in exponential manner to achieve flowering of olive cultivars. Moreover, winter temperature, appeared to be one of the most important variables in determining flowering time of olive cultivars mainly when quarterly and monthly mean temperatures were considered. In conclusion, this investigation is the first database concerning olive cultivars originated from different geographical areas and grown in a warm area. It revealed that olive cultivars behaved differently with contrasting chilling and heat accumulations and in years with extreme climatic conditions. It will be more interesting to consider the important genetic diversity of olive tree to mitigate the harmful effect of increasing temperature in the future.

Fruit trees need to store reserves to allow their survival during winter and for bud flush and leaf growth in the following spring. The current study investigated the effects of alternate bearing and flower buds removal on seasonal starch storage and mobilization in leaves, current shoot and one-year-old wood of fruiting and non-fruiting branches of ‘Mateur’ pistachio (Pistacia vera L.) trees in arid land. Four treatments were applied; T0: untreated trees, T1: removal of all flower buds for one year, T2: removal of all flower buds for two successive years and T3: removal of 50% of flower buds for each year. Annual starch storage and mobilization in fruiting and non-fruiting branches of pistachio trees appeared to be driven by crop load, nut development stage and carbohydrate demands. Starch concentrations in leaves, current shoot and one-year-old wood increased slightly in non-fruiting than in fruiting branches of pistachio. In ‘on’ trees (T0 and T3), one-year-old wood starch increased after the initial growth flush, but is mobilized during kernel fill and continued to decrease after nut harvest. Starch mobilization from current shoots of ‘on’ trees during the high demand period of stage III corresponded to the period of flower bud abscission. These results suggested that branch wood starch concentrations represent the overall balance between source and sinks. Subsequent flower buds removal (T1 and T2), leaves accumulated starch during the first and the third stage of nut growth, whereas, gradually increase of starch concentration occurred over the growing season for the current shoots and one-year-old wood. Starch deficiency in current shoots of ‘on’ trees could be responsible for bud drop and finally for alternate bearing. The yield patterns of pistachio trees cv. Mateur have not shown real evidence of alternate bearing in the experimental site. Flower buds removal (T1 and T2) allowed pistachio trees to achieve higher yield potential, while, these two treatments performed the lowest cumulated yield. Removal of 50% of flower buds (T3) did not cause a significant change in yield, compared to untreated trees, in each of the first three years, as well as in the total yield accumulation. When focusing on 2008, this treatment caused a significant increase in yield, compared to other treatments including the control. Current shoot starch status was also higher in 2008 in the 50% fruit removal treatment. If we isolate and focus on the results obtained in 2008, it appears that this treatment can cause more stable yields, possibly through an increase in current shoot starch content. Consequently, under severe climatic conditions of arid land, the annual pruning could be applied to equilibrate flower buds number and to improve the tree starch status.

Key message After applying disbudding treatments, removal of fifty percent of flower bud each year improves dry matter accumulation in fruiting and non-fruiting branches of pistachio trees, which could minimize alternate bearing.

a b s t r a c t Pistachios (Pistacia vera L.) are widely grown in the arid rainfed areas of Tunisia. However, pistachio production is still low with important variation between years. This study investigated the responses of pistachio trees to variable winter chilling and annual precipitation. It was carried out in an experimental orchard of Mateur, the most important Tunisian cultivar in central Tunisia (34◦94� 11�� , 10◦60� 82�� ) for a period of twelve years from 1997 to 2008. Yield correlated poorly with precipitation (varying on the range of 80-300 mm/year during the 12 years) and showed a moderate alternate bearing index of 0.63. However, flowering and nut yield of pistachio trees was a function of chill accumulation computed as chilling hours (CH), chill units (CU) or chilling portions (CP) depending on using Crossa-Raynaud, Utah or Dynamic models, respectively. For Mateur cultivar, the threshold chilling accumulation appeared to be 206 CH, 539 CU or 36 CP depending on the model used. Under this level, pistachio production was clearly affected. Warm winters with low chilling caused erratic floral bud break, delayed flowering, sparse foliage and decreased yield. With inadequate winter chilling, chemical treatments with hydrogen cyanamide (Dormex) at 2 and 4% increased floral bud break, advanced flowering period and improved vegetative growth of pistachio trees in comparison to the untreated control. As a conclusion, better prediction of chill accumulation must be achieved in the warm production region of Tunisia. To that effect, the Dynamic model showed the lowest coefficient of variation compared to the chilling hours and Utah models and seemed to better reflect what is happening on the field under our warm winter regions. © 2013 Elsevier B.V. All rights reserved.

Pistachio germoplasm cultivated in traditional areas of Tunisia presented an interesting genetic diversity. The study was conducted to assess desirable biochemical characteristics from the rich local germoplasm in pistachio ecotypes. Kernel samples of the widely cultivated Mateur cultivar and 89 ecotypes from Sfax and El Guetar localities were collected during 2 years. Oil content and fatty acid composition were assessed. Fat content and fatty acid composition differed significantly among local ecotypes. The mean fat content of pistachio ecotypes ranged from 56 to 78%. Palmitic acid content varied between 7.1 and 12.9%. In addition, stearic acid was found as a minor saturated fatty acid in pistachio kernels; levels varied from 0.7 to 2.8%. Oleic acid content ranged from 56.1 to 80.7% with a significant difference over the different ecotypes. Linoleic acid varied between 8.2 and 29.7%. Mateur cultivar showed slight variations of fat content and fatty acid composition in the localities investigated. Certain ecotypes, such as Loby7 (fat content 78.5%), Sridique1 (80% Oleic, 9% linoleic), Ibala3 (76.8% oleic, 9.5% linoleic) from Sfax, and EPE2 (80% oleic, 8.2% linoleic), BMS3 (79.4% oleic, 9% linoleic), HAB3 (78.6% oleic, 9.9% linoleic), AMMS4 (78% oleic, 11.2% linoleic), and ABT2 (76.8% oleic, 12.1 linoleic) from El Guetar oasis, were distinguished by the interesting oil quality compared with Mateur and foreign cultivars. These results offer opportunities for further genetic improvement of pistachio oil quality.