Gerbera micropropagation

Colchicine-mediated in vitro polyploidization in gerbera hybrid

An efficient in vitro protocol for high-frequency polyploidization for the first time in gerbera hybrid (BGC-2019-01) was developed in the present study. Two-week-old in vitro-developed shoots (tips) were treated individually with 0.1%, 0.25% and 0.5% (w/v) colchicine solutions for 4, 6, 8, and 12 h. The colchicine-treated shoot tips were then inoculated on Murashige and Skoog (MS) medium fortified with 1.5 mg/l meta-Topolin for multiple shoot proliferation and later transferred into 1.5 mg/l indole-3-acetic acid-fortified MS medium for rooting of shoots. The ploidy levels of the colchicine-treated and regenerated plantlets along with the non-treated ones were confirmed via flow cytometry analysis and metaphasic chromosome count. The highest frequency of tetraploid plantlets (50%) were obtained when shoot tips were treated with 0.1% colchicine for 4 h. Morphological observations revealed that induced tetraploid plantlets exhibited delayed fresh shoot initiation, fewer but longer shoots, as well as fewer but broader leaves. Likewise, the study of stomata revealed that in comparison to their diploid counterparts, the tetraploid plantlets exhibited less frequent yet significantly larger stomata, and higher number of chloroplasts. The tetraploids were recorded with significantly higher chlorophyll, carotenoid, and anthocyanin content during the photosynthetic pigment analyses. During ex vitro acclimatization and field growth, the tetraploid plants exhibited delayed proliferation but with higher vigor and thickened broad leaves. The genetic uniformity among the diploid and the tetraploid plants was confirmed using conserved DNA-derived polymorphism (CDDP), directed amplification of minisatellite-region DNA (DAMD), inter simple sequence repeats (ISSR), and start codon targeted (SCoT) polymorphism marker systems. The tetraploids developed in the present study would be of immense importance for the genetic improvement of gerbera as far as its ornamental values are concerned.

Changes in Endogenous Phytohormones of Gerbera jamesonii Axillary Shoots Multiplied under Different Light Emitting Diodes Light Quality

Light quality is essential in in vitro cultures for morphogenesis process. Light emitting diodes system (LED) allows adjustment as desired and the most appropriate light spectrum. The study analyzed the influence of different LED light quality on the balance of endogenous phytohormones and related compounds (PhRC) in in vitro multiplied axillary shoots of Gerbera jamesonii. Over a duration of 40 days, the shoots were exposed to 100% red light, 100% blue light, red and blue light at a 7:3 ratio with control fluorescent lamps. Every 10 days plant tissues were tested for their PhRC content with the use of an ultra-high performance liquid chromatography (UHPLC). Shoots’ morphometric features were analyzed after a multiplication cycle. We identified 35 PhRC including twelve cytokinins, seven auxins, nine gibberellins, and seven stress-related phytohormones. Compounds content varied from 0.00052 nmol/g to 168.15 nmol/g of dry weight (DW). The most abundant group were stress-related phytohormones (particularly benzoic and salicylic acids), and the least abundant were cytokinins (about 370 times smaller content). LED light did not disturb the endogenous phytohormone balance, and more effectively mitigated the stress experienced by in vitro grown plants than the fluorescent lamps. The stress was most effectively reduced under the red LED. Red and red:blue light lowered tissue auxin levels. Blue LED light lowered the shoot multiplication rate and their height, and induced the highest content of gibberellins at the last stage of the culture.

Effect of Three Types of Ion Beam Irradiation on Gerbera (Gerbera hybrida) In Vitro Shoots with Mutagenesis Efficiency

Gerbera in vitro shoots were irradiated using three types of ion beams with different line energy transfers (LETs) to investigate the effective LET and absorbed doses for mutagenesis. Furthermore, genomic mutation analyses were conducted on the obtained mutants. Survival rate analysis showed a lower lethal dose 50% (LD₅₀) with ion beams with higher LETs. Trait/morphological mutations exhibited changes in the color and shape of petals and male sterility. Irradiation conditions with the highest growth change and trait/morphological mutation rates in each ion were C irradiation at 10 Gy, Ar irradiation at 5 Gy, and Fe irradiation at 5 Gy, with a range of absorbed dose of around LD₅₀ to about 10 Gy lower. The highest trait/morphological mutation rate was 14.1% with Ar irradiation at 5 Gy, which was one of the criteria for ion beam irradiation of gerbera in vitro shoots. Furthermore, the genomic mutation in the flower color, petal shape, and male sterile mutants were confirmed by genotype analysis using Genotyping by Random Amplicon Sequencing-Direct technology. This is the first study to report the efficient production of gerbera mutants that could be analyzed. Our findings may lead to more efficient gerbera mutant production and analysis technology.

A highly efficient organogenesis protocol based on zeatin riboside for in vitro regeneration of eggplant

BACKGROUND

Efficient organogenesis induction in eggplant (Solanum melongena L.) is required for multiple in vitro culture applications. In this work, we aimed at developing a universal protocol for efficient in vitro regeneration of eggplant mainly based on the use of zeatin riboside (ZR). We evaluated the effect of seven combinations of ZR with indoleacetic acid (IAA) for organogenic regeneration in five genetically diverse S. melongena and one S. insanum L. accessions using two photoperiod conditions. In addition, the effect of six different concentrations of indolebutyric acid (IBA) in order to promote rooting was assessed to facilitate subsequent acclimatization of plants. The ploidy level of regenerated plants was studied.

RESULTS

In a first experiment with accessions MEL1 and MEL3, significant (p < 0.05) differences were observed for the four factors evaluated for organogenesis from cotyledon, hypocotyl and leaf explants, with the best results obtained (9 and 11 shoots for MEL1 and MEL3, respectively) using cotyledon tissue, 16 h light / 8 h dark photoperiod conditions, and medium E6 (2 mg/L of ZR and 0 mg/L of IAA). The best combination of conditions was tested in the other four accessions and confirmed its high regeneration efficiency per explant when using both cotyledon and hypocotyl tissues. The best rooting media was R2 (1 mg/L IBA). The analysis of ploidy level revealed that between 25 and 50% of the regenerated plantlets were tetraploid.

CONCLUSIONS

An efficient protocol for organogenesis of both cultivated and wild accessions of eggplant, based on the use of ZR, is proposed. The universal protocol developed may be useful for fostering in vitro culture applications in eggplant requiring regeneration of plants and, in addition, allows developing tetraploid plants without the need of antimitotic chemicals.

Micropropagation in the Twenty-First Century

Despite more than a century of research on effective biotechnological methods, micropropagation continues to be an important tool for the large-scale production of clonal plantlets of several important plant species that retain genetic fidelity and are pest-free. In some cases, micropropagation is the only technique that supports the maintenance and promotes the economic value of specific agricultural species. The micropropagation of plants solved many phytosanitary problems and allowed both the expansion and access to high-quality plants for growers from different countries and economic backgrounds, thereby effectively contributing to an agricultural expansion in this and the last century. The challenges for micropropagation in the twenty-first century include cost reduction, enhanced efficiency, developing new technologies, and combining micropropagation with other systems/propagation techniques such as microcuttings, hydroponics, and aeroponics. In this chapter, we discuss the actual uses of micropropagation in this century, its importance and limitations, and some possible techniques that can effectively increase its wider application by replacing certain conventional techniques and technologies.

Biotechnological advances in Lilium

Modern powerful techniques in plant biotechnology have been developed in lilies (Lilium spp., Liliaceae) to propagate, improve and make new phenotypes. Reliable in vitro culture methods are available to multiply lilies rapidly and shorten breeding programs. Lilium is also an ideal model plant to study in vitro pollination and embryo rescue methods. Although lilies are recalcitrant to genetic manipulation, superior genotypes are developed with improved flower colour and form, disease resistance and year round forcing ability. Different DNA molecular markers have been developed for rapid indirect selection, genetic diversity evaluation, mutation detection and construction of Lilium linkage map. Some disease resistance-QTLs are already mapped on the Lilium linkage map. This review presents latest information on in vitro propagation, genetic engineering and molecular advances made in lily.

Competency for shoot regeneration from Arabidopsis root explants is regulated by DNA methylation

Plants exhibit high capacity to regenerate in three alternative pathways: tissue repair, somatic embryogenesis and de novo organogenesis. For most plants, de novo organ initiation can be easily achieved in tissue culture by exposing explants to auxin and/or cytokinin, yet the competence to regenerate varies among species and within tissues from the same plant. In Arabidopsis, root explants incubated directly on cytokinin-rich shoot inducing medium (SIM-direct), are incapable of regenerating shoots, and a pre-incubation step on auxin-rich callus inducing medium (CIM) is required to acquire competency to regenerate on the SIM. However the mechanism underlying competency acquisition still remains elusive. Here we show that the chromomethylase 3 (cmt3) mutant which exhibits significant reduction in CHG methylation, shows high capacity to regenerate on SIM-direct and that regeneration occurs via direct organogenesis. In WT, WUSCHEL (WUS) promoter, an essential gene for shoot formation, is highly methylated, and its expression on SIM requires pre-incubation on CIM. However, in cmt3, WUS expression induced by SIM-direct. We propose that pre-incubation on CIM is required for the re-activation of cell division. Following the transfer of roots to SIM, the intensive cell division activity continues, and in the presence of cytokinin leads to a dilution in DNA methylation that allows certain genes required for shoot regeneration to respond to SIM, thereby advancing shoot formation.