Abstract
This study evaluated the effect of osmoregulators and carbohydrates on the maturation and germination of somatic embryos of papaya 'Golden THB'. Cotyledon explants from papaya seedlings germinated in vitro on basal MS medium were cultured on somatic embryogenesis induction medium (IM) containing MS salts, myo-inositol, sucrose, agar and p-chlorophenoxyacetic acid. After 50 days, embryogenic calli were transferred onto maturation media (MM) for 45 additional days. For experiment 1, a MS-based medium supplemented with abscisic acid, activated charcoal and concentrations of PEG 6000 (0; 40; 50; 60 and 70 g L-1) was used, whereas for experiment 2 malt extract concentrations (0; 0.1; 0.2; 0.3 and 0.4 g L-1) were assessed. The normal cotyledonary somatic embryos produced in experiment 2 were transferred to the germination medium (GM). The GM consisted of full-strength MS medium, sucrose, agar and was supplemented with myo-inositol at varying concentrations (0; 0.275; 0.55 and 0.825 mM). The PEG concentrations tested impaired the maturation of 'Golden THB' papaya somatic embryos. The MM, supplemented with malt extract at 0.153 g L-1, promoted the greatest development of normal somatic embryos (18.28 SE calli-1), that is, two cotyledonary leaves produced 36.56 SE calli-1. The supplementation with 0.45 mM myo-inositol provided the highest germination percentage (47.42%) and conversion to emblings.
Highlights
Papaya (Carica papaya L.), a tropical fruit crop, is produced in most tropical and sub-tropical countries, with India and Brazil accounting for 41.2% and 12% of world production, respectively (FAO 2012)
As an alternative to these problems, the in vitro culture of papaya has the potential to be used on a commercial scale, by means of somatic embryogenesis (SE), producing synthetic seeds to be made available to the farmer
Somatic embryogenesis is based on cell reprogramming through the pluripotent expression of somatic cells (Altamura et al 2016); it is a morphogenetic pathway with great potential for massive propagation of various species (Isah 2016, Seifert et al 2016)
Summary
Papaya (Carica papaya L.), a tropical fruit crop, is produced in most tropical and sub-tropical countries, with India and Brazil accounting for 41.2% and 12% of world production, respectively (FAO 2012). In Brazil, ‘Golden THB’ is the main cultivar of the Solo group produced and exported. This cultivar has numerous advantages, such as the low plant height (2.0 to 2.5 m at 2.5 years of age), which facilitates pest and disease control and fruit harvesting; predominance of perfect hermaphrodite flowers and absence of carpelloidy and petandry; highly productive, with uniform, vigorous highly sanitary plants; uniform and pyriform fruits; lightor deep-yellow external coloration, orange to red pulp and firm texture (Feltrin Sementes 2009, Quintal et al 2012). As an alternative to these problems, the in vitro culture of papaya has the potential to be used on a commercial scale, by means of somatic embryogenesis (SE), producing synthetic seeds to be made available to the farmer. The pathway encompasses developmental stages, namely induction, maturation and germination, in which some regulatory substances, a such as growth regulators (auxins, cytokinins, gibberellins and abscisic acid), antioxidants (activated charcoal and polyvinylpyrrolidone), polyethylene glycol (PEG), malt extract (ME), and myo-inositol (MI)
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