Читать книгу Biotechnology of Fruit and Nut Crops - Группа авторов - Страница 158

Clonal propagation of monocotyledonous plants is limited; for example, palms cannot be grafted. Monocotyledonous plants possess a vascular system based on many vascular bundles and lacking a cambium layer (Tomlinson, 1990, 2006; Broschat et al., 2014) that prevents grafting. Traditional propagation of date palm using offshoots is limited since the number of offshoots that develop is usually small, ranging between 1 and 20 per tree, depending on growing conditions and cultivar. This approach is unable to produce large numbers of trees for new plantations. The date palm can only be efficiently propagated in vitro by shoot tip regeneration or by somatic embryogenesis (see below).

Regeneration from shoot tips is performed usually from offshoot hearts that include the apical meristem and the leaf primordia and from immature inflorescences (Abahmane, 2011; Gadalla, 2017; Khierallah et al., 2017). The regenerative nature of the meristematic tissue enables the induction of multiple buds. The process has four stages: (i) initiation of vegetative buds; (ii) their multiplication; (iii) shoot elongation; and (iv) rooting (Zaid and De Wet, 2002a; Abahmane, 2011). Full-strength Murashige and Skoog (MS) medium (Murashige and Skoog, 1962) is the preferred basal medium, although in some studies 1/2 MS medium was preferred. Sucrose, usually at a concentration of 3% (w/v) is the carbon source. Different plant growth regulators are utilized, usually a combination of cytokinins and auxins. A combination of 6-g, g-dimethylallylaminopurine (2iP) and naphthalene acetic acid (NAA) is normal (Gantait et al., 2018). Activated charcoal (0.75–3 mg/l), polyvinylpyrrolidone (PVP) (1–2 mg/l) or other antioxidants are included to scavenge phenolic compounds (Gantait et al., 2018). Growth conditions are usually a 16 h photoperiod with a light intensity of 30–100 μmol/m²/s and 25°C. For rooting, elongated shoots are usually cultured on MS supplemented with 1–7 μM NAA.