Sihem Ben Maachia

In date palm orchards, bunches heavily infested by Oligonychus afrasiaticus and covered with dense webbing may coexist on the same palm with neighboring bunches that remain visually healthy and apparently uninfested. This study aimed to determine whether these healthy fruits already express biochemical and structural traits consistent with a systemic induced defense response. Visually healthy date fruits were collected from bunches borne by heavily infested palms, lightly infested palms, and non-infested control palms. Fruits were analyzed for physicochemical, biochemical, and color parameters in order to compare healthy fruits associated with infested palms against fruits from control palms. Healthy fruits associated with heavily infested palms showed clear shifts compared with controls. Flavonoid content increased from 5.85 to 8.34, total polyphenols from 41.32 to 68.82 mg/100g FW, and exocarp firmness from 23.79 to 29.17 N. Sugar content was also higher in fruits from infested palms (7.17 g/100g FW in heavily infested palms and 7.93 g/100g FW in lightly infested palms) than in controls (3.93 g/100g FW). In contrast, pH decreased from 5.8 to 5.4 and water content from 78.6 to 72.3%. Color traits were affected, especially chroma, which increased from 7.75 in controls to 38.57 in fruits from heavily infested palms. Principal component analysis clearly separated the groups, with flavonoids, polyphenols, sugars, exocarp firmness, and chroma as the main discriminating variables. These results support the hypothesis that infestation of some bunches by O. afrasiaticus may trigger a systemic defense-like response in the palm, allowing neighboring still-uninfested bunches to acquire a protective biochemical and structural status. Phenolic compounds, firmness, and color traits therefore appear to be promising markers of induced resistance in date palm.

Manganese (Mn) deficiency is a major factor underlying brittle leaf disease in date palm, yet its root-centered mechanisms under field conditions remain poorly understood. Nine mature palms (three per health category: healthy, asymptomatic Mn-deficient, and BLD-affected) were assessed for soil chemistry (pH, salinity), root Mn concentration and hydraulics, canopy pigments and chlorophyll fluorescence (F_v/F_m), as well as metabolic responses. Elevated soil pH and variable salinity significantly constrained root Mn uptake and water conductance, leading to a ~60% decline in root Mn, a 20% reduction in root water content, an 80% loss of chlorophyll, and a 26% decrease in F_v/F_m. These changes induced strong metabolic reprogramming, including a twofold rise in glucose, increased protein content, and a tenfold enhancement in peroxidase activity. Asymptomatic palms already displayed early declines in pigments and fluorescence, highlighting their diagnostic value. This study demonstrates that soil-driven Mn deficiency impairs root function and cascades to canopy physiology and metabolism, offering realistic avenues for rhizosphere management and early field diagnosis in arid oases.

Background: In Tunisia, the date palm mite Oligonychus afrasiaticus McGregor (Acarina: Tetranychidae) is one of the most important pests of the date palm Phoenix dactylifera L. (Arecaceae). The control of Oligonychus afrasiaticus in Tunisian oases requires the use of safe and effective acaricides. Methods: In this study, the toxicity of pesticides (sulfur, hexythiazox, bifenazate and spinosad) against O. afrasiaticus in date palms was investigated in the field. The aim of this study was also to evaluate the dissipation of bifenazate, hexythiazox and spinosad in date fruits by the QuEChERS method. Result: Bifenazate was effective with a reduction of 90.2 and 89.4% of O. afrasiaticus motile forms and eggs, respectively, up to 21 days after application of this insecticide. Within 21 days of spraying, hexythiazox was an effective acaricide, reducing eggs and motile forms to 98.5% and 82.5%, respectively. Spinosad was effective for up to 14 days. Under the conditions of the Tunisian oases, the sulfur toxicity applied in July may remain effective for less than 14 days after treatment. Regarding, the dissipation of tested pesticides, the results showed that bifenzate deposited faster in date fruits than hexythiazox and spinosad. The initial deposition of bifenzate and spinosad decreased and was no longer detected after 7 and 14 days, respectively. Hexythiazox was detected at harvest when the date fruits were treated twice, but the residues were lower than the residue levels recommended by the European Union. These results would be useful to improve the control of O. afrasiaticus based on the efficacy, persistence and toxicity of these pesticides.

Salinity stress has become an increasing threat to viticulture in the Tunisian oasis, and more generally, the characterization of salinity tolerance markers can be of great interest for sustainable grape production. This study investigated some metabolic adaptations in different tissues of the ripe berries of indigenous grapevine cultivars after exposure to salt stress to identify the key traits of salt stress tolerance under oasis conditions. We especially focused on the adaptive responses occurring at the level of amino acids, polyamines, and stilbene phytoalexins in the grape berry skin, pulp, and seeds of six grapevine cultivars differing in phenotypic and ampelographic characteristics. Our data showed that amino acids accumulated strongly in the pulp and skin, while resveratrol, trans-piceid and trans-ε-viniferin, as major phytoalexins, significantly accumulated in the seeds. High salinity was also found to increase both the berry skin and pulp contents of essential amino acids such as threonine, valine, leucine, isoleucine, lysine, methionine, and phenylalanine. The amounts of stilbenes also increased under high salinity in the berry skin of all the studied cultivars. Polyamine homeostasis within the different berry tissues suggested enhanced polyamine biosynthesis rather than polyamine oxidation in response to high salinity. Our principal component analysis revealed a clear discrimination between the cultivars based on their metabolic profiles within the ripe berry tissues under high salinity.

Tunisia is one of the world’s largest producers of olive oil, and it preserves pools of olive genetic diversity that are still unexplored. A recent prospection and collection program of the National Gene Bank of Tunisia (NGBT) focused on the vast oasis of Degache, in the south west part of Tunisia, where 47 samples were collected and genetically characterized through simple sequence repeat (SSR) markers. Identification and authentication of genotypes were obtained through comparison with reference cultivars belonging to the Olive National Collection of Tunisia (IOC) and with cultivars from Algeria, Italia, Syria and Lebanon. Degache olive genotypes showed large genetic variability, a significant diversity from the reference germplasm, and a clear differentiation from modern varieties. The population structure analysis identified four gene pools characterizing genotypes from different area of origin. Two gene pools appear to be more represented in germplasm from southern Tunisia, where environmental conditions at critical plant development phases, are harsher. This suggests that this germplasm might present traits of adaptation useful for breeding to improve resilience to abiotic stresses. Our results will support ex situ and in situ conservation activities of Tunisian olive germplasm pursued by the National Gene Bank of Tunisia.

Traditional agricultural systems are receiving increasing attention at the international level due to their multifunctional role. The Globally Important Agricultural Heritage Systems (GIAHS) programme of the Food and Agriculture Organization (FAO) aims to identify agricultural systems of global importance, preserve landscape, agrobiodiversity and traditional knowledge and apply the principles of dynamic conservation to promote sustainable development. Biodiversity associated to traditional agricultural practices is particularly important, especially in difficult environments, like traditional oases, for ensuring food and nutrition to local communities. We documented landscape and biological diversity associated with traditional agricultural practices in three traditional oases in Tunisia, through a landscape analysis based on land-use survey, and an assessment of cultivated species. Results show that the landscape structure is dominated by agricultural land uses and characterized by a high level of diversification. Agrobiodiversity is high: we identified 20 varieties of date palm, 21 species of fruit trees, 21 vegetable species and two fodder crops. Results highlighted that traditional oases, as other agroforestry and agricultural heritage systems, continue to play a crucial role in maintaining genetic resources and agrobiodiversity. Farmers who, all over the world, still cultivate applying traditional practices are the main actors that practice a real conservation of genetic resources and diversity by maintaining traditional cultivars and a diversified landscape structure. Our methodology, based on the combined assessment of land uses and agrobiodiversity, can be replicated in other agricultural heritage systems to evaluate and measure possible transformations and identify the best strategies for their preservation.

Chemical fruit composition of Tunisian date palm ‘Deglet Nour’ collected at maturation from four different oases in Djerid region