In Vitro Regeneration of Capparis spinosa L. by Using a Temporary Immersion System

Seed germination and vegetative and in vitro propagation of Hieracium lucidum subsp. lucidum (Asteraceae), a critically endangered endemic taxon of the Sicilian flora

Hieracium lucidum subsp. lucidum is a critically endangered endemic taxa of the Sicilian flora. It is a relict of the Tertiary period surviving on the cliffs of Monte Gallo (NW-Sicily). This research focused on finding the best protocols for seed germination and vegetative and in vitro propagation to contribute to ex situ conservation. Seed germination tests were carried out using constant temperatures of 15 °C, 20 °C and 25 °C in continuous darkness and an alternating temperature of 30/15 °C (16 h/8 h, light/dark). The seeds had no dormancy, and a high germination capacity (70-95%) was obtained at all tested thermoperiods. The possibility of vegetative propagation of the taxon was evaluated through the rooting capacity of stem cuttings treated or not treated with indole-3-butyric acid (IBA). All cuttings were treated with IBA rooted within 2 months, while only 50% of the untreated cuttings were rooted within a longer time. An efficient protocol for rapid in vitro propagation from leaf portions was developed. The response of explants was tested on hormone-free Murashige and Skoog (MS) basal medium and MS enriched with different types of cytokinins: 6-Benzylaminopurine (BAP) and meta-Topolin (mT) in combination with naphthaleneacetic acid (NAA) and 2,4-Dichlorophenoxyacetic acid (2,4-D) at the same concentration. The combination of mT (2 mg L-1) and 2,4-D (1 mg L-1) in the medium was the most effective and showed the highest percentage of callus induction and the mean number of regenerated shoots. The maximum rate of root regeneration and the maximum number and length of roots were obtained on hormone-free MS and MS enriched with IBA at concentrations of 1 mg L-1. From the results obtained, it can be concluded that H. lucidum subsp. lucidum can be successfully propagated using one of the tested techniques, subject to the availability of the material for reproduction.

Increased Multiplication Rates of Vriesea hieroglyphica (Carriere) E. Morren Through a Temporary Immersion System

The main difficulty for the cultivation and conservation of bromeliad species is the reduced number of propagules and slow growth of many of the species, resulting in a low propagation efficiency. Bromeliad plants are hardy and relatively easy to cultivate, with a high ornamental and ecological importance. Aiming at efficient micropropagation rates of V. hieroglyphica, a highly valued bromeliad, with very low propagation efficiency, a temporary immersion system was used and compared to semisolid and liquid static medium. Cultures obtained from in vitro germinated seeds were used as explants, maintaining their genetic diversity. Micropropagation with this simple temporary immersion system, composed of two autoclavable flasks, each with one opening for the attachment of 22 μm syringe filters, connected by a rubber stopper and an inner glass tube. In the bottom flask, an air valve is attached to the filter, which is subsequently connected to an aquarium pump and a timer and plugged to an outlet. This simple temporary immersion system showed improved micropropagation efficiency and is a method that can also be evaluated for other species.

An Efficient Method of Pennisetum × advena 'Rubrum' Plantlets Production Using the Temporary Immersion Bioreactor Systems and Agar Cultures

The aim of this study is to develop an efficient method for micropropagation of Pennisetum × advena 'Rubrum'. Agar cultures containing Murashige and Skoog (MS) medium supplemented with 6-benzyl-amino-purine (BAP) in various concentrations (0.5 mg/L to 2 mg/L) and a temporary immersion bioreactor system (TIS) using liquid medium MS with an addition of 1 mg/L BAP were tested. Rooting was performed using ½ MS medium supplemented with different auxin combinations (indole-3-butyric acid IBA and α-naphthalene acetic acid NAA) and activated charcoal. The TIS method was found to be the most efficient, producing 36.9 new plants within four weeks. The resulting plantlets were thin and bright green in color, with no signs of hyperhydricity. The most suitable agar medium yielded 19.5 new plants within eight weeks. For rooting, ½ MS supplemented with 0.5 mg/L IBA and 0.5 mg/L NAA exhibited an 84% rooting rate, whereas the addition of activated charcoal inhibited rooting.

Micropropagation of Endemic Endangered Taxa of the Italian Flora: Adenostyles alpina subsp. macrocephala (Asteraceae), as a Case Study

The conservation of endangered, rare, and endemic plant species is based on in situ and ex situ conservation strategies. When in situ conservation alone is not sufficient to guarantee the survival of the species, ex situ techniques are adopted in support. This study aimed to develop an efficient micropropagation protocol for Adenostyles by evaluating the effect of different plant growth regulators on leaf explants. Adenostyles alpina subsp. macrocephala (Asterace) is a perennial herbaceous plant endemic to Calabria (Southern Italy). The genus Adenostyles includes three species confined to the mountains of the Mediterranean and southern Europe. For callus induction, media supplemented with different concentrations of Benzylaminopurine (BAP) (0.5, 1, 2, and 3 mg L^-1), Naphthaleneacetic Acid (NAA) (1 mg L^-1), and 2,4-Dichlorophenoxyacetic Acid (2,4-D) (1 mg L^-1) were tested. Shoot regeneration and proliferation were obtained in media supplemented with BAP (1, 2, and 3 mg L^-1) and NAA (1 mg L^-1). Root induction was obtained in media supplemented with IBA (0.25, 0.50, and 1 mg L^-1) and NAA (0.25, 0.50, and 1 mg L^-1). Statistically significant differences in callus induction and shoot regeneration were observed between the various media tested. The medium containing Murashige and Skoog (MS) supplemented with 3 mg L^-1 of BAP and 1 mg L^-1 of NAA showed the highest percentage of callus induction and increased shoot regeneration. The regenerated shoots showed more effective root induction in the hormone-free MS medium and in the presence of Indole-3-Butyric Acid (IBA) at concentrations of 0.25, 0.50, and 1 mg L^-1. These results can be used as a basis for the preparation of a micropropagation protocol for different taxa of Adenostyles, as well as other species of Asteraceae specialized to the Mediterranean mountain habitat.

Somatic embryogenesis of Arabica coffee in temporary immersion culture: Advances, limitations, and perspectives for mass propagation of selected genotypes

Culture in temporary immersion systems (TIS) is a valuable tool for the semi-automation of high frequency somatic embryogenesis of coffee. This system allows the intermittent exposure of explants to liquid medium in cycles of specific frequency and duration of immersion with renewal of the culture atmosphere in each cycle. TIS have revolutionized somatic embryogenesis of coffee plants as an alternative for scaling up and reducing costs associated with labor-intensive solid media culture. In Central America, somatic embryogenesis is employed on a commercial scale to produce F1 Coffea arabica hybrids. In Asia and Africa, somatic embryogenesis is used for the multiplication of selected genotypes of C. arabica and C.canephora. Somatic embryogenesis of coffee plants is considered a model system for woody species due to its biological versatility and low frequency of somaclonal variation. Nevertheless, the success of somatic embryogenesis for mass propagation of coffee plants depends on the development, optimization, and transfer of complementary technologies. Temporary immersion using the RITA^® bioreactor is, so far, the best complementary tool for somatic embryogenesis of Arabica coffee for a single recipient with simple changes in liquid media. Likewise, high volume bioreactors, such as 10-L glass BIT^® and 10-L flexible disposable plastic bags, have been successfully used for somatic embryogenesis of other coffee species. These bioreactors allow the manipulation of thousands of embryos under semi-automated conditions. The protocols, advantages, and benefits of this technology have been well documented for organogenesis and somatic embryogenesis pathways. However, adaptation in commercial laboratories requires technical and logistical adjustments based on the biological response of the cultures as well as the costs of implementation and production. This review presents the historical and present background of TIS and its commercial application and, in particular, pertinent information regarding temporary immersion culture for C. arabica somatic embryogenesis. The main limitations of this technology, such as hyperhydricity, asynchrony, and developmental abnormalities, are examined, and a critical analysis of current knowledge regarding physiological, biochemical, and molecular aspects of the plant response to temporary immersion is offered. Further, perspectives are provided for understanding and solving the morpho-physiological problems associated with temporary immersion culture of coffee plants. Systematic Review Registration.

Temporary immersion systems (TISs): A comprehensive review

The temporary immersion systems (TISs) have been widely used in plant biotechnology. TISs have different advantages from the point of micropropagation and production of secondary metabolites over other continuous liquid-phase bioreactors. The current work presents the structure, operation mode, configuration type, and micropropagation or secondary metabolite production in TISs. This review deals with the advantages and disadvantages of TISs and the factors affecting their performance. Future research could focus on new designs based on CFD simulation, facilitating sterilization, and combining TISs with other bioreactors (e.g., mist bioreactors) to make a hybrid bioreactor.

Germination and in vitro development of mature zygotic embryos and protein profile of seedlings of wild and cultivated Hevea brasiliensis

The main factors governing Hevea brasiliensis germination and seedling establishment remains unclear. We examined the effect of growth regulators Indole 3-Acetic Acid (IAA) and 6-Benzylaminopurine (BAP), and their interactions on germination and the development of mature zygotic embryos (MZE) and protein profile of Hevea brasiliensis seedlings from wild and cultivated (clone PB 250) genotypes. Embryonic axes excised from seeds (wild and clone PB 250) were inoculated in Murashige and Skoog medium (control) and supplemented with IAA (3 µM) and BAP (6 µM) individually and their combination (3 µM IAA + 6 µM BAP). For both genotypes, the mature embryos displayed a high percentage of germination and establishment, and the seedlings were characterized by protein bands ranging from 7 to 30 kDa. Notably, the wild genotype showed proteins in the 14 kDa range, which may be associated with one of the major rubber elongation factors (REF). The wild and clone genotypes presented different behavior and strategies in relation to the protein profile in the presence of different growth regulators. Although the latex biosynthetic pathway and its mechanisms of regulation still remain largely unknown, our results aid in our understanding of the dynamics of proteins in different rubber tree clones in vitro.

Can the Caper (Capparis spinosa L.) Still Be Considered a Difficult-to-Propagate Crop?

As a perennial xerophytic shrub, characterized by plesiomorphic features, the caper (Capparis spinosa L.) is naturally spread throughout the Mediterranean basin and occupies an important ecological role, as well as an economic one, in traditional and specialized systems for commercial production. This species, in spite of its wide diffusion, is currently considered at risk of genetic erosion, mainly due to overgrazing and overharvesting for domestic uses and for trade. This situation is made more serious because of the lack of efficient propagation techniques, determining the caper as a “difficult-to-propagate species”. In this review, we report the main available sexual and vegetative propagation techniques with the aim of assessing whether, and to what extent, this criticality is still true for caper as a horticultural crop. In terms of seed propagation, germination rates have generally been considered quite low or unsatisfactory, and are also affected by hybridization phenomena that are likely to occur among both the wild and cultivated forms. The seeds show a physiological dormancy that can be lowered by adopting hormonal treatments, but in situ germination remains a critical phase. Vegetative propagation appears quite effective, mostly as related to in vitro techniques that allow caper cultivation that is no longer affected by propagation for an economic dissemination of the species in more intensive orchards. The research needs for Caper spinosa L. as a horticultural crop, especially in the field of genetic improvement and breeding, are also underlined.

In Vitro Rooting of Capparis spinosa L. as Affected by Genotype and by the Proliferation Method Adopted During the Multiplication Phase

The in vitro rooting of three caper (Capparis spinosa L.) selected biotypes, grown in a commercial orchard on the Sicilian island of Salina (38°33′49” N), was performed using—as base material for rooting experiments—shoot explants proceeding from two different in vitro culture systems: solid medium and liquid culture in a PlantForm bioreactor (TIS). The regenerated shoots of each accession were submitted to different auxin treatments (NAA, IBA, IAA - 1 or 2 mg L⁻¹; NAA+IBA 0.75 and 0.25 mg L⁻¹, respectively), supplemented with sucrose or fructose (mg L⁻¹). The highest rooting rate in terms of root percentage (67%) was reached with the explants of the selected accession ‘Sal 39’ proceeding from liquid culture in PlantForm and induced in the MS medium with sucrose, as a carbon source, supplemented with NAA 0.75 mg L⁻¹ + IBA 0.25 mg L⁻¹, after six days in a climatic growth chamber at 25 ± 1 °C in the dark and then placed under a cool white fluorescent lamp, with a PPFD of 35 μmol m⁻¹ s⁻¹ and a photoperiod of 16 h. On the other hand, poor rooting rate was generally achieved under all the tested experimental conditions with the other biotypes, ‘Sal 37’ and ‘Sal 35’, demonstrating the strong role exerted by the previously adopted proliferation method and by the genotype for successful caper in vitro rooting.