Salt Stress Induces Contrasting Physiological and Biochemical Effects on Four Elite Date Palm Cultivars (Phoenix dactylifera L.) from Southeast Morocco.

Understanding the response of date palm (Phoenix dactylifera L.) cultivars to salt stress is essential for the sustainable management of phoeniculture in Tafilalet, Morocco. It offers a promising avenue for addressing the challenges presented by the increasing salinity of irrigation waters, especially because farmers in these regions often lack the necessary knowledge and resources to make informed decisions regarding cultivar selection. This study addresses this issue by investigating the performance of the most relied on cultivars by farmers in Tafilalet, namely Mejhoul, Boufeggous, Nejda, and Bouskri. These cultivars were exposed to a sodium chloride treatment of 154 mM, and their performances were evaluated over a three-month period. We examined the growth rate, photosynthesis-related parameters, pigments, water status in plants, and biochemical compounds associated with oxidative stress, osmotic stress, and ionic stress. Principle component analysis (PCA) effectively categorized the cultivars into two distinct groups: salt-sensitive (Mejhoul and Nejda) and salt-tolerant (Boufeggous and Bouskri). These findings provide valuable insights for farmers, highlighting the advantages of cultivating Boufeggous and Bouskri cultivars due to their superior adaptation to salt conditions. These cultivars exhibited moderate decrease in shoot growth (25%), enhanced catalase activity, a smaller increase in anthocyanin content, and greater enhancement in organic osmolytes compared with salt-sensitive cultivars like Mejhoul (experiencing an 87% reduction in shoot elongation) and Nejda (exhibiting the highest reduction in leaf area). Furthermore, the Na+/K+ ratio was positively influenced by salt stress, with Mejhoul and Nejda recording the highest values, suggesting its potential as an indicator of salt stress sensitivity in date palms.

Analysis of genetic diversity and population structure of Moroccan date palm (Phoenix dactylifera L.) using SSR and DAMD molecular markers.

BACKGROUND: Date palm, oasis pivot, plays a vital socio-economic part in the southern area of Morocco. However, with climate change and drought intensity and frequency increasing, the Moroccan palm grove is threatened with significant genetic degradation. Genetic characterization of this resource is key element for the development of effective conservation and management strategies in the current circumstances of climate change and various biotic and abiotic stresses. To evaluate the genetic diversity of date palm populations collected from different Moroccan oases, we used simple sequence repeats (SSR) and directed amplification of mini-satellite DNA (DAMD) markers. Our results showed that used markers could efficiently assess genetic diversity in Phoenix dactylifera L. RESULTS: A total of 249 and 471 bands were respectively scored for SSR and DAMD, of which 100% and 92.9% were polymorphic. The polymorphic information content (PIC = 0.95), generated by the SSR primer was nearly identical to that generated by the DAMD primer (PIC = 0.98). The resolving power (Rp) was higher in DAMD than SSR (29.46 and 19.51, respectively). Analysis of the molecular variance (AMOVA) based on the combined data sets for both markers revealed a higher variance within populations (75%) than among populations (25%). Principal coordinate analysis (PCoA) and the ascendant hierarchical classification showed that the population of Zagora and Goulmima regions were the closest populations. The STRUCTURE analysis clustering of the 283 tested samples into seven clusters based on their genetic composition. CONCLUSION: The results drawn from this study will orient genotypes selection strategies for a successful future breeding and conservation program, particularly under climate change context.

In Vitro Root Induction from Argan (Argania spinosa (L.) Skeels) Adventitious Shoots: Influence of Ammonium Nitrate, Auxins, Silver Nitrate and Putrescine, and Evaluation of Plantlet Acclimatization.

Argania spinosa (L.) Skeels is an endangered plant species endemic to Morocco. In recent years, attempts to develop in vitro regeneration systems for this species were made. However, rooting and acclimatization of in vitro plants have been a bottleneck for successful propagation. In the present study, the effects of different concentrations of auxins, putrescine, silver nitrate (AgNO3) and ammonium nitrate on the in vitro rooting of adventitious shoots of two argan genotypes "Mejji" and "R'zwa", were evaluated. The highest rooting percentages (86.6% in "Mejji" and 84.4% in "R'zwa") were observed on Murashige and Skoog (MS) medium modified by reducing the ammonium nitrate concentration and supplemented with 1.5 mg L-1 indole-3-butyric acid (IBA), 0.5 mg L-1 1-naphthalene acetic acid (NAA), 2 mg L-1 AgNO3 and 160 mg L-1 putrescine. This medium resulted in the development of a good root system after only 10 days of culture. Plantlet acclimatization was carried out using different substrate mixtures, and high survival rates (100%) were observed when the substrate contained either peat alone or a sand-peat mixture (1:1, w/w). The high percentages of rooting and acclimatization reported in the present study are of high importance for rapid and large-scale propagation of this endangered species.

Antifungal Potential of Phytochemicals against Mauginiella scaettae, the Plant Pathogen Causing Inflorescence Rot of Date Palm.

Date palm (Phoenix dactylifera L.) inflorescence rot caused by Mauginiella scaettae poses a serious threat to date palm in Morocco. The present study aims to determine the antifungal activity of five plant extracts against M. scaettae, including Acacia cyanophylla, Cupressus atlantica, Eucalyptus torquata, Nerium oleander, and Schinus molle and link this effect to their content in phenolics and flavonoids, as well as their antioxidant properties. Plant extracts exhibited significant discrepancies regarding their antifungal activity (p < 0.05). The extracts of E. torquata and C. atlantica had the strongest and dose-dependent manner inhibitory effect against mycelial growth and spore germination. E. torquata and S. molle caused the greatest sporulation reductions of about 88.05% and 36.11%, respectively. In addition, there were significant differences among the examined plant extracts with respect to their total polyphenols (14.52-76.68 mg GAE/g DW), flavonoids (8.75-57.78 g RE/100 g DW), and antioxidant properties as measured by TEAC (74.77-391.23 mmol TE/g DW) and FRAP assays (87.18-474.04 mmol TE/g DW). Strong correlations were found between phenolic compounds and antioxidant activity suggesting that polyphenols play a key role in the observed antioxidant and antifungal activities.

A combined pathway of organogenesis and somatic embryogenesis for an efficient large-scale propagation in date palm (Phoenix dactylifera L.) cv. Mejhoul.

An efficient regeneration system via a combined pathway of organogenesis and somatic embryogenesis was developed for date palm (Phoenix dactylifera L.) cv. Mejhoul. Adventitious buds were obtained from shoot-tip explants with a frequency of 53.3% after 9 months of culture: 6 months on half-strength Murashige and Skoog (MS/2) medium containing 14.2 µM indole-3-acetic acid (IAA), 13.4 µM 1-naphthaleneacetic acid (NAA) and 0.5 µM 6-(dimethylallylamino) purine (2iP), and 3 months on MS/2 medium supplemented with 1.1 µM IAA, 1.1 µM NAA, 0.5 µM 2iP, 2.2 µM 6-benzyladenine (BA) and 0.4 µM kinetin. Adventitious bud segments were used as explants to induce somatic embryogenesis, and the effects of different concentrations (22.5, 45, 90, 225 or 450 µM) of 3,6-dichloro-o-anisic acid (dicamba) and 4-amino-3,5,6-trichloropicolinic acid (picloram) were evaluated. The optimal medium for somatic embryogenesis induction was MS medium supplemented with 45 µM picloram and 5 µM 2iP, in which the somatic embryogenesis rate was 70%. For somatic embryo maturation, the effects of sorbitol, mannitol, polyethylene glycol (PEG) and abscisic acid (ABA) were tested. The highest maturation rate (88.6 mature somatic embryos per 100 mg fresh weight callus) was observed on liquid MS medium supplemented with 20 g L-1 PEG. Subsequent somatic embryo germination was achieved with up to 52.0% in MS medium containing 2.5 µM NAA and 2.5 µM BA. The regenerated plantlets were transferred to the glasshouse where 76.0% of them survived.

Somatic embryogenesis from bud and leaf explants of date palm (Phoenix dactylifera L.) cv. Najda.

An efficient regeneration system through somatic embryogenesis was developed for date palm cv. Najda. Adventitious bud and proximal leaf segments cultured on Murashige and Skoog (MS) medium supplemented with various combinations of auxins and cytokinins induced embryogenesis after at least 6 months of culture. Somatic embryogenesis induction seemed correlated with the type of the explant, the induction period and the auxin used. The highest rate of somatic embryogenesis (86.0%) was obtained on bud explants cultured on MS medium supplemented with 45.0 µM 2,4-dichlorophenoxyacetic acid (2,4-D), and 4.5 µM kinetin or 4.5 µM 6-(dimethylallylamino) purine (2iP). Whereas, low levels of embryogenesis were obtained on media supplemented with 1-naphthalene acetic acid (NAA) or 2-naphthoxyacetic acid (NOA). Proximal leaf segments showed somatic embryogenesis only when cultured on media supplemented with 2,4-D or picloram. Statistical analysis revealed significant effects of explant type and plant growth regulators (PGRs) combination on somatic embryogenesis. Somatic embryos were germinated successfully on PGR-free MS medium with or without activated charcoal (50.0-60.0 and 26.6-36.6%, respectively), and 80.0% of plantlets survived after transferring to a glasshouse for 6 months. Our results will be useful for large-scale propagation of date palm cv. Najda, characterized by high fruit quality and bayoud disease resistance.

Optimization of medium composition for in vitro shoot proliferation and growth of date palm cv. Mejhoul.

The effects of major mineral salts, L-glutamine, myo-inositol and carbon source on shoot bud proliferation of date palm (Phoenix dactylifera L.) cv. Mejhoul were evaluated. Different concentrations of ammonium nitrate (NH4NO3; 550, 825 or 1650 mg/L), potassium nitrate (KNO3; 633.3, 950 or 1900 mg/L), calcium chloride dehydrate (CaCl2·2H2O; 147, 220 or 440 mg/L), potassium dihydrogen phosphate (KH2PO4; 57, 85 or 170 mg/L), magnesium sulfate heptahydrate (MgSO4·7H2O; 123, 185 or 370 mg/L), L-glutamine and myo-inositol (0.5, 1, 1.5 and 2 g/L), sucrose, sorbitol, mannitol or commercial granulated sugar (10, 20, 30, 40 or 50 g/L) were tested. The highest number of shoot buds per explant (18.7) occurred on the medium containing 825 mg/L NH4NO3, 1900 mg/L KNO3, 220 mg/L CaCl2·2H2O, 170 mg/L KH2PO4, 370 mg/L MgSO4·7H2O as well as 1 g/L L-glutamine, 2 g/L myo-inositol and 30 g/L sucrose. The results showed that the frequency of hyperhydricity significantly increased in media containing 1650 mg/L NH4NO3. The concentrations of L-glutamine, myo-inositol and carbon source significantly affected the number of shoot buds per explant. However, they had no effect on hyperhydricity, tissue browning and precocious rooting. Shoots of 4.5-6.0 cm in length were isolated and transferred onto hormone-free media for elongation and rooting. After 3 months, the developed plantlets were successfully transplanted in a glasshouse and over 90 % survived acclimatization.