RAPD and ISSR based evaluation of genetic stability of micropropagated plantlets of Morus alba L. variety S-1

Induction of Axillary Bud Swelling of Hevea brasiliensis to Regenerate Plants through Somatic Embryogenesis and Analysis of Genetic Stability

To overcome rubber tree (RT) tissue culture explant source limitations, the current study aimed to establish a new Hevea brasiliensis somatic embryogenesis (SE) system, laying the technical foundation for the establishment of an axillary-bud-based seedling regeneration system. In this study, in vitro plantlets of Hevea brasiliensis Chinese Academy of Tropical Agricultural Sciences 917 (CATAS 917) were used as the experimental materials. Firstly, the optimum conditions for axillary bud swelling were studied; then, the effects of phenology, the swelling time of axillary buds (ABs), and medium of embryogenic callus induction were studied. Plantlets were obtained through somatic embryogenesis. Flow cytometry, inter-simple sequence repeat (ISSR molecular marker) and chromosome karyotype analysis were used to study the genetic stability of regenerated plants along with budding seedlings (BSs) and secondary somatic embryo seedlings (SSESs) as the control. The results show that the rubber tree's phenology period was mature, and the axillary bud induction rate was the highest in the 2 mg/L 6-benzyladenine (6-BA) medium (up to 85.83%). Later, 3-day-old swelling axillary buds were used as explants for callogenesis and somatic embryogenesis. The callus induction rate was optimum in MH (Medium in Hevea) + 1.5 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) + 1.5 mg/L 1-naphthalene acetic acid (NAA) + 1.5 mg/L Kinetin (KT) + 70 g/L sucrose (56.55%). The regenerated plants were obtained after the 175-day culture of explants through callus induction, embryogenic callus induction, somatic embryo development, and plant regeneration. Compared with the secondary somatic embryo seedling control, axillary bud regeneration plants (ABRPs) were normal diploid plants at the cellular and molecular level, with a variation rate of 7.74%.

Thidiazuron Induced In Vitro Clonal Propagation of Lagerstroemia speciosa (L.) Pers.—An Important Avenue Tree

A high throughput regeneration protocol has been developed for Lagerstroemia speciosa through node explants under the regime of various plant growth regulators (PGRs). This protocol can provide an alternative mode to seed-grown plants and minimize the cost–time of regeneration, significantly. Murashige and Skoog (MS) medium containing various combinations of PGRs exhibited a marked stimulatory effect on morphogenesis. Of the various combinations tried, node explant pretreated with thidiazuron (TDZ; 5.0 µM) for 4 weeks and followed with transfer into MS medium containing 1.0 μM 6-benzyladenine (BA) and 0.25 μM α-naphthalene acetic acid (NAA) was reported to be the best treatment as it resulted in a maximum number of 24.5 shoots with an average shoot length of 7.1 cm per explant in 90% of cultures after 12 weeks of incubation. The in vitro-generated shoots rooted satisfactorily in the adopted ex vitro method of rooting, which saves time and cost. Among the different treatments, the greatest rooting percentage (85%) was observed in the 200 μM IBA-treated shoots, with the highest root number (8.7) and length (3.4 cm) occurring after 4 weeks. Four months after being transferred to ex vitro, some of the physiological attributes of the in vitro-propagated plants were examined and compared to the ex vitro plants. Further, analysis of the genetic integrity in tissue culture-raised plantlets along with the parental tree was accomplished through DNA-based RAPD technique. The monomorphic banding pattern obtained by the RAPD primers resulted in a high level of genetic uniformity in regenerated plants.

Biotechnological Advances in Pharmacognosy and In Vitro Manipulation of Pterocarpus marsupium Roxb

Trees are vital resources for economic, environmental, and industrial growth, supporting human life directly or indirectly through a wide variety of therapeutic compounds, commodities, and ecological services. Pterocarpus marsupium Roxb. (Fabaceae) is one of the most valuable multipurpose forest trees in India and Sri Lanka, as it is cultivated for quality wood as well as pharmaceutically bioactive compounds, especially from the stem bark and heartwood. However, propagation of the tree in natural conditions is difficult due to the low percentage of seed germination coupled with overexploitation of this species for its excellent multipurpose properties. This overexploitation has ultimately led to the inclusion of P. marsupium on the list of endangered plant species. However, recent developments in plant biotechnology may offer a solution to the overuse of such valuable species if such advances are accompanied by technology transfer in the developing world. Specifically, techniques in micropropagation, genetic manipulation, DNA barcoding, drug extraction, delivery, and targeting as well as standardization, are of substantial concern. To date, there are no comprehensive and detailed reviews of P. marsupium in terms of biotechnological research developments, specifically pharmacognosy, pharmacology, tissue culture, authentication of genuine species, and basic gene transfer studies. Thus, the present review attempts to present a comprehensive overview of the biotechnological studies centered on this species and some of the recent novel approaches for its genetic improvement.

Cytokinin-Based Tissue Cultures for Stable Medicinal Plant Production: Regeneration and Phytochemical Profiling of Salvia bulleyana Shoots

Salvia bulleyana is a rare Chinese medicinal plant that due to the presence of polyphenols lowers the risk of some chronic diseases especially those related to the cardiovascular system. The present study examines the organogenic competence of various combinations and concentrations of plant growth regulators to develop an efficient protocol for in vitro regeneration of S. bulleyana via leaf explants, maintaining the high production of active constituents. The purpose of the study was also to assess the possibilities of using a cytokinin-based regeneration to effectively produce therapeutic compounds. The adventitious shoot formation was observed through direct organogenesis on media with purine derivatives (meta-topolin, mT and benzylaminopurine, BAP), and through indirect organogenesis on media with urea derivatives (tidiazuron, TDZ and forchlorfenuron, CPPU). The highest regeneration frequency (95%) with 5.2 shoots per explant was obtained on leaves cultured on Murashige and Skoog (MS) medium containing 0.1 mg/L naphthalene-1-acetic acid (NAA) and 2 mg/L BAP. Following inter simple sequence repeat (ISSR) marker-based profiling, the obtained organogenic shoot lines revealed a similar banding pattern to the mother line, with total variability of 4.2–13.7%, indicating high level of genetic stability. The similar genetic profile of the studied lines translated into similar growth parameters. Moreover, HPLC analysis revealed no qualitative differences in the profile of bioactive metabolites; also, the total polyphenol content was similar for different lines, with the exception of the shoots obtained in the presence of CPPU that produced higher level of bioactive compounds. This is the first report of an effective and rapid in vitro organogenesis protocol for S. bulleyana, which can be efficiently employed for obtaining stable cultures rich in bioactive metabolites.

Hemidesmus indicus L. Br.: critical assessment of in vitro biotechnological advancements and perspectives

Hemidesmus indicus (L.) R. Br. ex Schult., commonly known as Indian sarsaparilla or Anantamul, is an ethnopharmacologically important medicinal plant from the family Apocynaceae. Biosynthesis of an array of bioactive compounds such as methoxybenzaldehydes and their derivatives has been accountable for its intensive medicinal attributes. Low seed setting, over-exploitation from natural habitat and a need for selection and preservation of elite germplasms yielding higher levels of bioactive compounds have led researchers to enquire the standardization of micropropagation techniques and quantitative estimation of phytochemicals from H. indicus. The present work aims to have a comprehensive account on micropropagation in H. indicus, a comparative estimation of biotic and abiotic factors, viz. elicitors and precursors playing a crucial role in H. indicus tissue culture, a critical appraisal of applied protocols to nullify embellished claims and a discussion on future perspectives. The review also highlights the comparative effect of different plant growth regulators as well as their combined role in rhizogenesis, callogenesis, base callus formation, callusing and somatic embryo-mediated indirect organogenesis, outcome of explant selection, contribution of abiotic (temperature, photoperiod, moisture, inorganic molecules) factors, role of carbon source, application of sterilization techniques and associated success rates, role of factors essential for acclimatization and secondary metabolite production, synthetic seed production and genetic transformation techniques. The compiled information along with individual study details, respective outcome and variability of reports will aid in proper assessment of cited standardized tissue culture protocols in H. indicus especially in relation to secondary metabolite production. Moreover, the assessment of applicability of different methodologies in this aspect will aid in the selection of high-yielding germplasms or chemotypes which is not only profitable for industrial application but also important for basic and applied preclinical and clinical research studies. KEY POINTS: • Critical and updated assessment on in vitro biotechnology in Hemidesmus indicus. • Biotechnological advancement via Agrobacterium-mediated transformation. • Key shortcomings and future research directions Graphical abstract Effect of biotic and abiotic factors on Micropropagation and secondary metabolite synthesis in Hemidesmus indicus.

Applications of Cytokinins in Horticultural Fruit Crops: Trends and Future Prospects

Cytokinins (CKs) are a chemically diverse class of plant growth regulators, exhibiting wide-ranging actions on plant growth and development, hence their exploitation in agriculture for crop improvement and management. Their coordinated regulatory effects and cross-talk interactions with other phytohormones and signaling networks are highly sophisticated, eliciting and controlling varied biological processes at the cellular to organismal levels. In this review, we briefly introduce the mode of action and general molecular biological effects of naturally occurring CKs before highlighting the great variability in the response of fruit crops to CK-based innovations. We present a comprehensive compilation of research linked to the application of CKs in non-model crop species in different phases of fruit production and management. By doing so, it is clear that the effects of CKs on fruit set, development, maturation, and ripening are not necessarily generic, even for cultivars within the same species, illustrating the magnitude of yet unknown intricate biochemical and genetic mechanisms regulating these processes in different fruit crops. Current approaches using genomic-to-metabolomic analysis are providing new insights into the in planta mechanisms of CKs, pinpointing the underlying CK-derived actions that may serve as potential targets for improving crop-specific traits and the development of new solutions for the preharvest and postharvest management of fruit crops. Where information is available, CK molecular biology is discussed in the context of its present and future implications in the applications of CKs to fruits of horticultural significance.

In Vitro Propagation of an Endangered Helianthus Verticillatus by Axillary Bud Proliferation

Helianthus verticillatus (Asteraceae), whorled sunflower, is a perennial species restricted to a few locations in the Southeastern United States. Habitat loss has caused H. verticillatus to become rare, and since 2014, it has been federally listed as an endangered species. As a part of the recovery plan for the restoration and protection of H. verticillatus, an efficient micropropagation protocol based on axillary shoot proliferation was developed. Various concentrations of 6-benzylaminopurine (BAP; 0 to 4.44 µM) were examined for their morphogenetic potential in the regeneration of six genotypes of H. verticillatus from the nodal explants derived from greenhouse-grown plants. Both the BAP concentration and genotype had significant effects on the regeneration capacity of H. verticillatus. Although the induced buds were observed on ½-strength Murashige and Skoog medium without plant growth regulators, a higher rate of induction and bud development were achieved on media with either 0.88 or 2.22 µM BAP, regardless of the genotype. Successful rooting of the induced shoots was achieved within four weeks after the transfer from the induction medium to the fresh ½-strength MS medium, but the rooting efficiency was dependent on the plant's genetic background. Regenerated plantlets, with well-developed shoots and roots, were acclimatized successfully to greenhouse conditions with a 97% survival rate. Simple sequence repeats (SSRs) markers were employed to assess the genetic uniformity of the micropropagated plants of H. verticillatus. No extraneous bands were detected between regenerants and their respective donor plants, confirming the genetic fidelity and stability of regenerated plants. To our knowledge, the protocol developed in this study is the first such report for this endangered species.

Indirect regeneration and genetic fidelity analysis of acclimated plantlets through SCoT and ISSR markers in Morus alba L. cv. Chinese white

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A reliable protocol developed for micropropagation of Morus alba L.cv. Chinese white through indirect regeneration using different explants.

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Friable callus was induced in maximum amounts from leaf and nodal explants on MS media supplemented with 2,4-D and NAA respectively.

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Highest frequency of regeneration was obtained from the leaf and node derived callus on MS media with BAP + TDZ and plantlets were rooted on IBA.

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Genetic homogeneity of in vitro raised plants was confirmed by SCoT and ISSR primers based molecular analysis.

A reliable protocol was developed for in vitro micro propagation of Morus alba L.cv. Chinese white. Initially, friable callus was induced (242.8 and 128.5 mg) from in vivo leaf and nodal explants on Murashige and Skoog’s (MS) medium amended with 4.0 μM/L of 2,4-Dichlorophenoxyacetic acid (2,4-D) and 3.0 μM/L of Naphthalene acetic acid (NAA) respectively within 3 weeks. Shoot regeneration (12.2 and 8.6) was obtained from leaf and node derived callus on 6-benzylaminopurine (BAP) + Thidiazuron (TDZ) at 2.5 + 2.0 and 7.5 + 2.0 μM/L concentrations respectively, after 4 weeks of incubation. In vitro shoots were rooted (90 %) on half strength MS medium with 7.5 μM/L indole-3 butyric acid (IBA) and plantlets were hardened in plastic pots contained farmyard manure, sand and garden soil in 1:1:2 ratio. The genetic stability of plantlets were confirmed by start codon targeted (SCoT) and inter simple sequence repeats (ISSR) primers based molecular analysis.

Rapid plant regeneration in industrially important Curcuma zedoaria revealing genetic and biochemical fidelity of the regenerants

The present investigation was carried out to establish an efficient and reproducible micropropagation protocol for the production of morphologically, genetically and chemically uniform plants of Curcuma zedoaria. Axillary bud explants of C. zedoaria were inoculated into MS basal medium supplemented with various combinations and concentrations of 6-benzyladenine (2.2-22.2 µM, BA), kinetin (2.3-23.2 µM, Kin), indole-3-acetic acid (2.9-11.4 µM, IAA), α-naphthalene acetic acid (2.7-10.2 µM, NAA) and adenine sulphate (33.9-203.6 µM, Ads). Almost 95% of rhizome buds sprouted on MS medium supplemented with 13.3 μM BA, 5.7 μM IAA and 63.9 μM Ads giving rise to an average of 12.89 ± 0.02 shoots within 6 weeks. However, the maximum number of roots (25.8 ± 0.07 roots per explant) was obtained on half strength MS medium supplemented with 7.4 µM of IBA after 4 weeks of inoculation. Morphological characteristics were similar in both conventionally propagated and micropropagated plants. Additionally, genetic homogeneity of in vitro plants was further confirmed through ISSR and flow cytometry analysis. A total of 27 ISSR primers were screened, out of which 13 ISSR primers generated 58 monomorphic and reproducible bands thereby confirming the genetic uniformity of obtained plants. The mean 2C DNA content of the mother plant (2.96 pg) was similar to that of in vitro derived plants (3.07 pg). Gas chromatography-mass spectrometry (GC-MS) analysis showed similarity in the qualitative profile of chemical constituents of essential oil and high-performance liquid chromatography analysis revealed no significant differences in curcumin content in the tissue culture regenerants and mother plants of C. zedoaria. Therefore, the present micropropagation protocol could be effectively employed to generate true to type plantlets of C. zedoaria.

Genetic homogeneity revealed in micropropagated Bauhinia racemosa Lam. using gene targeted markers CBDP and SCoT

Two gene targeted markers i.e. CAAT box-derived polymorphism (CBDP) and start codon targeted (SCoT) polymorphism were applied to analyze the genetic stability of in vitro propagated plants of Bauhinia racemosa Lam. multiplied by enhanced axillary shoot proliferation of mature tree derived nodal explant. Nine randomly selected micropropagated plants of 1 year age were subjected to molecular analysis. The isolated genomic DNA samples were subjected to PCR amplification with a total of 61 primers (25 CBDP and 36 SCoT) out of which 39 primers (21 CBDP and 18 SCoT) produced scorable amplicons. A total of 97 and 88 clear, distinct and reproducible amplicons were produced by CBDP and SCoT primers, respectively. The monomorphic banding pattern obtained through all the tested primers corroborated the true to type nature of in vitro propagated plants of B. racemosa.

Micropropagation, in-vitro conservation and genetic stability studies in pummelo (Citrus maxima)

Pummelo (Citrus maxima L.) is a natural, mono-embryonic and a true fruit species of genus Citrus cultivated widely in India. The study aimed at developing in vitro technique for conservation of Citrus maxima germplasm using shoot tip and nodal section as explants. Various concentrations and combination of hormones were used for successful in-vitro conservation. The shoots sprouted within 9-20 days when inoculated on MS medium supplemented with 0.5 mg/l BAP + 0.1 mg/l NAA growth hormones and above 86% germination was obtained with maximum numbers of shoots (8) and nodes (8.67). Highest shoot elongation (82%) was observed in MS medium supplemented with concentration of 0.6 mg/l GA3 in combination with 0.2 mg/l BAP, shoot length ranged between 1.17 to 6.90 cm and the number of nodes was 2.33-8.33 per plantlet. 1/2 MS medium supplemented with 0.5 mg/l BAP +1.0 mg/l NAA along with 2.5 g phytagel showed best result for rooting (78.33%). The regenerated plantlets did not show any detectable morphological variation at genetic level as evidenced by SSR profiles of plantlets. The developed protocol can be successfully employed for large-scale multiplication and conservation of Pummelo germplasm.

Assessment of genetic fidelity of Fritillaria dagana (Liliaceae) regenerated plants using ISSR markers

ISSR analysis of Fritillaria dagana, endangered ornamental geophyte from the Sayan Mountains, regenerated through direct gemmogenesis from bulb scale tissue was performed. More informative electrophoresis profile with clear and distinct bands was obtained at amplification with (CAC)3GC primer at 56 °C annealing. The genetic fidelity of F.dagana regenerants to maternal plants was confirmed.

Thidiazuron (TDZ) induced organogenesis and clonal fidelity studies in Haloxylon persicum (Bunge ex Boiss & Buhse): an endangered desert tree species

Haloxylon persicum (Bunge ex Boiss & Buhse), is one of the hardy woody desert shrubs, which is now endangered and/or nearing extinction. Urban landscape development and overgrazing are the major threats for the erosion of this important plant species. For conserving the species, it is critical to develop an efficient in vitro regeneration protocol for rapid multiplication of large number of regenerants. Leaf explants, cultured on Murashige and Skoog (MS) medium supplemented with different concentrations of thidiazuron (TDZ) (0.5, 1, 2 µM), showed significant difference in bud sprouting and adventitious shoot induction. The highest shoot bud formation was recorded on MS medium supplemented with 0.5 µM TDZ. Shoot tip necrosis (STN), observed after first subculture of shoot buds in same medium, increased in severity with subculture time. Application of calcium (4 mM) and boron (0.1 mM) in combination with kinetin (10 µM) in the subculture medium significantly reduced the intensity of STN. On an average eight shoots/explant were produced by alleviating this problem. ISSR marker analysis revealed monomorphic banding pattern between progenies and parents, indicating the true to type nature of the clones and its parents.

Evaluation of genetic relationship between 15 bamboo species of North-East India based on ISSR marker analysis

The classification of bamboos based on floral morphology and reproductive characters is very hard due to erratic flowering behavior and unusually long reproductive cycle. The application of reliable and effective DNA molecular markers is highly essential to address this problem. In the present investigation, inter-simple sequence repeats (ISSR) markers were employed to study phylogenetic relationship of 15 different bamboos of North-East India. The 10 ISSR primers generated 116 polymorphic loci or scorable bands with average of 11.6 bands per primer. The genetic similarity coefficient ranged from 0.41-0.76 showing high genetic polymorphism among different bamboo species. The phylogenetic tree constructed based on genetic similarity matrix revealed genetic proximity of endemic Bambusamizorameana to other five Dendrocalamus species by clustering into a single group, while Dendrocalamus manipureanus segregated from the cluster indicating its genetic divergent character. Except for Schizotachyum fuchsianum, the three Schizotachyum species viz., S. dullooa, S. pergracile and S. munroi exhibited close genetic affinity by grouping into a single minor clade. Principal coordinates analysis (PCoA) showed distribution of different bamboos species in the plot in accordance to unweighted pair-group method with arithmetic average (UPGMA) cluster analysis. Genetic relationship of 15 different bamboos as revealed from the dendrogram and PCoA analysis reasonably conformed to traditional system of classification though slight disagreement existed. This is the first report on the successful use of ISSR markers in the phylogenetic and genetic variation studies of 15 important bamboos of the region including the endemic bamboo species of B. mizorameana, B. manipureana, D. sikkimensis and D. manipureanus.

Improvement of abiotic stress adaptive traits in mulberry (Morus spp.): an update on biotechnological interventions

Mulberry (Morus spp.), being an economically important tree, is cultivated in China, India, Thailand, Brazil, Uzbekistan and other Countries across the globe, for its leaves to feed monophagous mulberry silkworm (Bombyx mori). The sustainability of silk industry is directly correlated with the production and continuous supply of high-quality mulberry leaves. In India, it is cultivated on large scale in tropical, sub-tropical and temperate regions under irrigated conditions for silkworm rearing. Drought, low temperature, high salinity and alkalinity, being experienced in widespread areas, are the major abiotic stresses, causing reduction in its potential foliage yield and quality. Further, climate change effects may worsen the productivity of mulberry in near future, not only in India but also across the globe. Although traditional breeding methods contributed immensely towards the development of abiotic stress-tolerant mulberry varieties, still there is lot of scope for implementation of modern genomic and molecular biology tools for accelerating mulberry genetic improvement programmes. This review discusses omics approaches, molecular breeding, plant tissue culture and genetic engineering techniques exploited for mulberry genetic improvement for abiotic stress tolerance. However, high-throughput biotechnological tools such as RNA interference, virus-induced gene silencing, epigenomics and genome editing tools need to be utilized in mulberry to accelerate the progress of functional genomics. The application of genomic tools such as genetic engineering, marker-assisted selection and genomic selection in breeding programmes can hasten the development of climate resilient and productive mulberry varieties leading to the vertical and horizontal expansion for quality silk production.