Gamma irradiation induced effects on in vitro shoot cultures and influence of monochromatic light regimes on irradiated shoot cultures of Dendrobium sonia orchid

Breeding of ornamental orchids with focus on Phalaenopsis: current approaches, tools, and challenges for this century

Ornamental orchid breeding programs have been conducted to develop commercially valuable cultivars with improved characteristics of commercial interest, such as size, flower color, pattern, shape, and resistance to pathogens. Conventional breeding, including sexual hybridization followed by selection of desirable characteristics in plants, has so far been the main method for ornamental breeding, but other techniques, including mutation induction by polyploidization and gamma irradiation, and biotechnological techniques, such as genetic transformation, have also been studied and used in ornamental breeding programs. Orchids are one of the most commercially important families in floriculture industry, having very particular reproductive biology characteristics and being a well-studied group of ornamentals in terms of genetic improvement. The present review focuses on the conventional and biotechnological techniques and approaches specially employed in breeding Phalaenopsis orchids, the genus with highest worldwide importance as an ornamental orchid, highlighting the main limitations and strengths of the approaches. Furthermore, new opportunities and future prospects for ornamental breeding in the CRISPR/Cas9 genome editing era are also discussed. We conclude that conventional hybridization remains the most used method to obtain new cultivars in orchids. However, the emergence of the first biotechnology-derived cultivars, as well as the new biotechnological tools available, such as CRISPR-Cas9, rekindled the full potential of biotechnology approaches and their importance for improve ornamental orchid breeding programs.

Tissue Culture in Ornamentals: Cultivation Factors, Propagation Techniques, and Its Application

Ornamentals come in a variety of shapes, sizes, and colors to suit a wide range of climates, landscapes, and gardening needs. Compared to demand, a shortage of plant materials and diversity force the search for solutions for their constant acquisition and improvement to increase their commercial value, respectively. In vitro cultures are a suitable solution to meet expectations using callus culture, somatic embryogenesis, protoplast culture, and the organogenesis of protocorm-like bodies; many of these techniques are commercially practiced. Factors such as culture media, explants, carbohydrates, plant growth regulators, and light are associated with the success of in vitro propagation. Techniques, especially embryo rescue and somatic hybridization, are widely used to improve ornamentals. The development of synthetic seed allows season-independent seed production and preservation in the long term. Despite the advantages of propagation and the improvement of ornamentals, many barriers still need to be resolved. In contrast to propagation and crop developmental studies, there is also a high scope for molecular studies, especially epigenetic changes caused by plant tissue culture of ornamentals. In this review, we have accumulated and discussed an overall update on cultivation factors, propagation techniques in ornamental plant tissue culture, in vitro plant improvement techniques, and future perspectives.

Gamma Radiation Induced In-Vitro Mutagenesis and Isolation of Mutants for Early Flowering and Phytomorphological Variations in Dendrobium 'Emma White'

In vitro mutagenesis offers a feasible approach for developing new orchid cultivars through genetic manipulation. In the present study, protocorm-like bodies (PLBs) were exposed to gamma rays (10, 20, 40, 60, 80 Gy) to study in vitro growth responses and induction of mutants in Dendrobium ‘Emma White’. Both proliferation and regeneration of PLBs decreased progressively with increasing doses, except for a significantly enhanced growth response at 10 Gy. The optimal dose of gamma radiation for mutagenesis was found in the range 10 to 25 Gy based on the growth reduction curve. Analysis using a high-throughput cell analyzer revealed a significant reduction in nuclear DNA content at > 40 Gy doses. At 10 Gy treatment, the growth attributes, such as root length, plant height and leaf number, were significantly increased by 36%, 26% and 20%, respectively, compared to the control. This increase was significant over other tested doses as well. Testing of random amplified polymorphic DNA markers revealed the presence of detectable polymorphism among gamma mutant plantlets with a polymorphism information content value at 0.41. The gamma-ray-induced earliness in flower development was observed within 294 days post ex vitro growth of 10 Gy mutant compared to the control plants flowered after 959 days. Our results highlight the significance of gamma radiation in inducing enhanced growth, morphological variations and early floral initiation in Dendrobium, providing a basic framework for mutation breeding and improvement of orchids.

Gamma ray-induced tissue responses and improved secondary metabolites accumulation in Catharanthus roseus

The present study investigated the impact of gamma ray irradiation on callus biomass growth and the yield of vincristine and vinblastine of in vitro grown tissues of Catharanthus roseus. The biochemical alteration underlying the synthesis of secondary metabolites has also been studied and a comparison of yield was prepared. The embryogenic tissues were exposed to 20, 40, 60, 80, and 100 Gy gamma ray doses and the callus biomass fresh weight, the embryogenesis (the embryo numbers, germination, plant regeneration), the alteration of protein, proline, and sugar attributes at different morphogenetic stages were monitored. The callus biomass growth was maximum (1.65 g) in 20 Gy exposed tissues and was less in 100 Gy treatment (0.33 g). The gamma-irradiated embryogenic tissues differentiated into embryos but the embryogenesis % and somatic embryo number per culture reduced with increasing doses. It was least in 80 Gy where very low numbers of embryos were formed (3.45 and 3.30 mean torpedo and cotyledonary embryo numbers per callus mass, respectively) which later germinated into plantlets. Protein, proline, sugar, and different antioxidant enzymes, i.e., superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities, were investigated as the tissues were exposed to gamma ray elicitation/signaling, evoking cellular stress. Increased 80 Gy gamma dose inhibited a 42.73% decrease in protein accumulation at initiation stages of embryogenic tissue. Soluble sugar level also declined gradually being least in 80 Gy treated tissues (14.51 mg gm^-1 FW) compared to control (20.2 mg gm^-1 FW). Proline content, however, increased with increasing gamma doses, maximum at 80 Gy (8.28 mg gm^-1 FW). The SOD, APX, and CAT activity increased linearly with enhanced level of gamma doses and maximum, i.e., 3.91 EU min^-1 mg^-1, 1.71 EU min^-1 mg^-1, and 4.89 EU min^-1 mg^-1, protein activity was noted for SOD, APX, and CAT, respectively, at 80 Gy gamma rays treated tissues. The quantification of vinblastine and vincristine in gamma ray elicitated tissues was made by using high-pressure thin layer chromatography (HPTLC). Somatic embryo-regenerated plant's leaves had the maximum yield of vinblastine (15.13 µgm gm^-1 DW) at 40 Gy irradiation dose compared to control (13.30 µgm gm^-1 DW)-the increased yield % is 13.75. The stem is also rich source producing 11.98 µgm gm^-1 DW of vinblastine. Among the various developmental stages of embryos, vinblastine content was highest in germinating stage of embryos (10.14 µgm gm^-1 DW) compared to other three, i.e., initiation, proliferation, and maturation embryo stages. Similarly, highest accumulation of vincristine (6.32 µg gm^-1 DW) was noted at low gamma irradiation dose (20 Gy) in leaf tissues. The present study indicates that the synthesis of vinblastine and vincristine was growth- and development-specific and the lower 20-40 Gy gamma levels were more effective in enriching alkaloids while higher doses declined yield. KEY POINTS: • Vinblastine and vincristine yield was quantified in in vitro grown tissues and leaves of embryo regenerated Catharanthus roseus after gamma ray treatment. • The accumulation of vinblastine and vincristine was maximum in regenerated leaves; low doses were more efficient in improving yield. • Gamma ray irradiation impacted biochemical profiles, caused cellular stress, and perhaps responsible for improved alkaloid yield.

Use of Gamma Radiation for the Genetic Improvement of Underutilized Plant Varieties

Agricultural biodiversity includes many species that have biological variants (natives, ecotypes, races, morphotypes). Their use is restricted to local areas because they do not fulfill the commercial requirements; however, it is well documented that these species are a source of metabolites, proteins, enzymes, and genes. Rescuing and harnessing them through traditional genetic breeding is time-consuming and expensive. Inducing mutagenesis may be a short-time option for its genetic improvement. A review of outstanding research was carried out, in order to become familiar with gene breeding using gamma radiation and its relevance to obtain outstanding agronomic characteristics for underutilized species. An approach was made to the global panorama of the application of gamma radiation in different conventional crop species and in vitro cultivated species, in order to obtain secondary metabolites, as well as molecular tools used for mutation screening. The varied effects of gamma radiation are essentially the result of the individual responses and phenotypic plasticity of each organism. However, even implicit chance can be reduced with specific genetic breeding, environmental adaptation, or conservation objectives.

An Overview of Orchid Protocorm-Like Bodies: Mass Propagation, Biotechnology, Molecular Aspects, and Breeding

The process through induction, proliferation and regeneration of protocorm-like bodies (PLBs) is one of the most advantageous methods for mass propagation of orchids which applied to the world floricultural market. In addition, this method has been used as a tool to identify genes of interest associated with the production of PLBs, and also in breeding techniques that use biotechnology to produce new cultivars, such as to obtain transgenic plants. Most of the molecular studies developed have used model plants as species of Phalaenopsis, and interestingly, despite similarities to somatic embryogenesis, some molecular differences do not yet allow to characterize that PLB induction is in fact a type of somatic embryogenesis. Despite the importance of species for conservation and collection purposes, the flower market is supported by hybrid cultivars, usually polyploid, which makes more detailed molecular evaluations difficult. Studies on the effect of plant growth regulators on induction, proliferation, and regeneration of PLBs are the most numerous. However, studies of other factors and new technologies affecting PLB production such as the use of temporary immersion bioreactors and the use of lighting-emitting diodes have emerged as new tools for advancing the technique with increasing PLB production efficiency. In addition, recent studies on Phalaenopsis equestris genome sequencing have enabled more detailed molecular studies and the molecular characterization of plantlets obtained from this technique currently allow the technique to be evaluated in a more comprehensive way regarding its real applications and main limitations aiming at mass propagation, such as somaclonal variation.