Mouaad Amine Mazri

Micropropagation of Date Palm: A Review

Somatic embryogenesis and organogenesis are the two pathways of choice for rapid and large-scale propagation of date palm. They have been successfully used for the micropropagation of elite genotypes and have proved their effectiveness for the commercial production of many cultivars. Nevertheless, regeneration through somatic embryogenesis or organogenesis in date palm is still difficult to achieve for recalcitrant genotypes and is often hampered by certain physiological disorders. In the present review, we report the results of a number of studies carried out on date palm micropropagation. It also describes different factors that influence each stage of somatic embryogenesis and organogenesis and the main problems encountered during these two micropropagation processes.

Effects of plant growth regulators and light intensity on the micropropagation of date palm (Phoenix dactylifera L.) cv. Mejhoul

The present study aimed to determine the best combination of plant growth regulators (PGRs) and light intensity in order to improve organogenesis of date palm (Phoenix dactylifera L.) cultivar Mejhoul. Organogenic cultures obtained from shoot tip explants were cultured on half-strength Murashige and Skoog (MS/2) medium supplemented with various combinations of two auxins: 2-naphthoxyacetic acid (NOAA) and indole-3-acetic acid (IAA) at 0, 0.2, or 0.4 mg L−1and two cytokinins: kinetin and 6-(dimethylallylamino) purine (2iP) at 0, 0.4, or 0.8 mg L−1 under different light intensities. Our results revealed that after 3 months of culture, the combination of 0.2 mg L−1 NOAA, 0.2 mg L−1 IAA, 0.4 mg L−1 2iP, and 0.4 mg L−1 kinetin was the optimal for shoot proliferation (12.8 shoot buds per explant), with low levels of hyperhydricity (20.0%), tissue browning (20.0%), and precocious rooting (30.0%). The present study showed also that darkness and low light intensity (500 lux) significantly increased the incidence of precocious rooting while high light intensities (2,000 – 3,000 lux) decreased shoot bud proliferation and stimulated shoot elongation and greening. The optimal light intensity during the multiplication phase was 1,000 lux (13.2 shoot buds per explant, 15.0% greening, 25.0% precocious rooting). Shoot elongation and rooting occurred on PGR-free MS/2 medium then the plantlets were transferred to a greenhouse where 88.0% survived after 3 months. Our results are beneficial for the efficient and large-scale propagation of the elite and endangered date palm cultivar Mejhoul.

Effects of plant growth regulators and carbon source on shoot proliferation and regeneration in date palm (Phoenix dactylifera L.) ‘16-bis’

Summary The aim of this study was to optimise in vitro culture conditions for the date palm (Phoenix dactylifera L.) cultivar ‘16-bis’. The effects of various combinations of plant growth regulators (PGRs) and sources of carbon in the growth medium on shoot proliferation and growth were evaluated. The PGRs used were indole-3-butyric acid (IBA), 2-naphthoxyacetic acid (NOA), 6-benzylaminopurine (BAP), and kinetin (KIN), each at 0, 2.5, or 5.0 µM. The carbon sources used were sucrose, sorbitol, or mannitol, each at 10, 20, 30, 40, or 50 g l-1. Explants cultured on 1.0× Murashige and Skoog (MS) medium supplemented with 2.5 µM IBA plus 2.5 µM BAP and 20 g l–1 sucrose showed the highest rate of shoot proliferation (22.3 shoots per organogenic cluster). Higher concentrations of PGRs increased the frequencies of hyperhydricity and precocious rooting. Carbon source and its concentration affected almost all of the parameters measured. The highest rate of shoot proliferation was on 1.0× MS medium containing 20 g l–1 sucrose. The frequency of precocious rooting increased with higher concentrations of carbon source. The proliferated shoots were transferred onto PGR-free 1.0× MS medium supplemented with 10, 20, 30, 40, or 50 g l–1 sucrose, sorbitol, or mannitol for elongation and rooting. Those grown on 1.0× MS medium containing 40 g l–1 sucrose showed the strongest growth and development, and the highest rate of survival (92.5%) after the plantlets were transferred to a glasshouse. These results will be useful for producing large numbers of ‘16-bis’ date palm plants to restore Moroccan palm groves decimated by bayoud disease.

Flowering and fruiting phenology, and physico-chemical characteristics of 2-year-old plants of six species of Opuntia from eight regions of Morocco

SUMMARY We have described the flowering and fruiting phenology of 14 accessions of six Opuntia species grown in Morocco: O. ficus-indica, O. robusta, O. aequatorialis, O. dillenii, O. leucotricha, and O. stricta. We also determined the physicochemical characteristics of their cladodes. For each accession, we used four-to-20 plants. Two systems were used to measure phenology: the extended Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie (BBCH)-scale and the National Phenology Monitoring System. Five principal stages were described: the development of vegetatively-propagated organs (vegetative buds), the development of flower buds, flowering, fruit development, and fruit maturity. The number of vegetative buds varied significantly among the 14 accessions, while only four accessions produced flower buds. After reaching their final size, fruit lengths varied from 3.40–6.40 cm, while fruit diameters varied from 1.93–3.90 cm. The average cladode number differed significantly among genotypes and varied from 1.75–7.75. There were also significant differences in cladode length (13.75–30.63 cm), width (6.25–17.33 cm), thickness (0.65–1.38 cm), fresh weight (FW; 67.50–766.00 g), and dry weight (DW; 8.75–67.15 g) between species. Water content and ash content, as well as total protein and total sugar concentrations, showed significant differences and were within the ranges of 86.67–92.04% (w/w), 12.97–22.08g 100 g−1 DW, 4.64–11.56g 100 g−1 DW, and 3.22–12.51 g 100 g−1 DW, respectively. Our results will help in the development of agronomic management practices and improve the characterisation, valorisation, and use of cactus pear species grown in Morocco.

Characterization of Genetic Diversity of Cactus Species (Opuntia Spp.) in Morocco by Morphological Traits and Molecular Markers

The genetic diversity within and among 124 accessions of Opuntia spp. collected from different regions of Morocco was assessed using morphological descriptors and molecular markers. Based on 10 morphological traits, the accessions were separated into 3 main clusters; each cluster was containing accessions from different regions and species. Polymerase chain reaction (PCR) was then performed on 22 accessions from different regions and species, with 10 inter-simple sequence repeat (ISSR) primers and one random amplified polymorphic DNA (RAPD) primer. ISSR primers produced 66 bands overall, 64 (96.9 %) of which were polymorphic while 6 bands were generated by the RAPD marker, all polymorphic. The polymorphic information content (PIC) values ranged from 0.62 to 0.97, with an average of 0.82. The dendrogram of genetic differences generated using the unweighted pair-group method using arithmetic averages (UPGMA) method showed 7 different clusters at a similarity of 0.76, which was confirmed by the principal component analysis (PCA). The main conclusion of our work is the high genetic similarity between Opuntia ficus indica and Opuntia megacantha species in Morocco. Our results will be useful for plant breeding and genetic resource conservation programs. arTiClE hisTorY Received: 27 July 2017 Accepted: 5 September 2017

Use of TDZ for Micropropagation of Some Mediterranean Crop Species

Plant tissue culture is now a widely used technology for many applications. Plant growth regulators (PGRs) play an important role in this technology. Auxins and cytokinins are by far the most commonly used PGR classes in plant tissue culture. N-Phenyl-N′-1,2,3-thiadiazol-5-ylurea, also known as thidiazuron or TDZ, is a synthetic PGR and a phenylurea derivative with a strong cytokinin-like activity. TDZ has been successfully used for the micropropagation of several plant species and sometimes was reported to be more effective than adenine-based cytokinins or to fulfil both the auxin and the cytokinin requirement for in vitro growth and differentiation. In this chapter, we will focus on the use of TDZ for the micropropagation of six Mediterranean crop species. Thus, we will report some findings from past and recent studies in which TDZ was employed for in vitro culture and regeneration of Olea europaea L., Citrus spp., Ceratonia siliqua L., Punica granatum L., Ficus carica L., and Prunus dulcis Mill. We will also highlight the specific action of TDZ depending on its concentration as well as the species, the genotype, the explant, and the concentration of the associated PGRs.

Cactus Pear (Opuntia spp.) Breeding

Cactus pear (Opuntia spp.) belongs to the family Cactaceae which is composed of about 130 genera and 2000 species. It is native to the tropical and subtropical regions of America but can be found in different regions of the world with various climate conditions. The fruit is an ovoid-spherical berry that, at maturity, may vary in color. Opuntia ficus indica is the most economically important and widely cultivated species of this genus. Cactus pear is an economically and ecologically important crop with various uses. It is cultivated for human consumption since its fruits are rich in carbohydrates, vitamins, proteins, minerals and antioxidants and have anti-cancer, anti-inflammatory, anti-viral, anti-diabetic and neuroprotective properties. The juice is rich in glucose and fructose and has a potent antioxidant activity. The cladodes of some species are edible as vegetables in salads. They are also used to feed cattle in arid and semiarid lands. The plants are well adapted to drought, high temperatures and low water availability and are able to absorb and hold CO2 excess from the atmosphere. Cactus pear is mainly propagated by cladodes. The breeding programs of this genus aim at the development of spineless cultivars with cold tolerance, high yield and fruit quality, and resistance to diseases and pests. To date, biotechnological tools have been scarcely used for cactus pear improvement. In the present chapter, the main problems, challenges, strategies and objectives of cactus pear breeding are described, and the recent achievements in terms of biotechnology and molecular biology are reported.