1. INTRODUCTION

Plants are considered as a sacred gift of nature to the humankind. It is attributed to their nature of productivity and role playing in maintenance of a healthy environment. Plants have been used for the benefits of human beings in various aspects. For example, man has been growing plants that are used for food, feed, fiber, oil, ornamental, and industrial purposes since time immemorial. Apart from crops, these are also used for oxygen, wood, leaves, fruits, and metabolites produced [1]. Some of these plant products do possess medicinal values, which help in the prevention of medical abnormalities [2]. Hence, they play an important role in maintaining a balanced food chain [3]. Unlike microorganisms and animals, plants cannot move. Thus, it becomes essential for them to get nutrients and growth factors at the site of their growth. The sedentary nature of plants can affect their growth and multiplication in various ways. The availability of nutrients in soil, supporting physical parameters such as temperature, humidity, pH of soil, salinity, water level, and moisture can affect the growth in both supporting and refuting ways [4,5]. Apart from these factors, abnormalities such as diseases, overgrazing by cattle, slash-and-burn of agriculture by humans, forest fires, volcanoes, and insect pests can significantly reduce the number of plants within a region. This may result in either temporary or permanent (in the case of endangered species) loss of crop/plant that can lead to further environment related complications [6,7]. Ancestors used to resolve this problem by preserving seeds with desired qualities. These seeds known as “landraces” were preserved for longer durations and were sown to restore the crop health. Landraces were the wild varieties retaining old set of conserved genes from the ancestral species. The propagation of these units was performed to grow a greater number of plants with same traits [8].

The problem of reduction in the number of plants can be effectively resolved with plant tissue culture (PTC). Various techniques followed in this method of artificial generation of new plants can be used to new and healthy plants with similar characters of the parent plant. This method of generating new plants in artificial conditions is known as “in vitro” approach. The in vitro approach is associated with aseptic culturing of cells, tissues, organs, or whole plant under artificial conditions with reference to nutrition and environment [9-11]. PTC is aimed to produce clones of plants. For the generation of clones, it is essential to facilitate the culture with a suitable environment for the optimum growth and multiplication. These factors create an artificial microenvironment, in which plants grow and multiply. As a result, the generated clones possess true-to-type of selected genotype. Thus, PTC technology is being widely used for large scale multiplication and industry. Apart from research view, techniques of PTC prove to have significant industry potential in the areas of micropropagation, plant quality improvement, secondary metabolite production, disease resistant plant production, and others [12,13]. Small pieces of the tissue (explants) are used to produce thousands of new plants with the help of PTC. This process is completed within a short period of time and space under controlled conditions, irrespective of weather and flowering/pollination season. With the help of PTC, endangered and threatened species can be successfully grown and conserved [14]. This is aided by high degree of multiplication and minimal requirements of sources. In addition to this, PTC is recognized as a most efficient technology for crop improvement by the production of gametoclonal and somaclonal variants. In addition to this, due to the possible occurrence of somaclonal variability, certain callus cultures were able to inherit characters from parent plants. This helps in the commercial production of plants [15]. Production of plants at commercial scale using micropropagation techniques proves to be beneficial over traditional methods such as cutting, grafting, seed, and air-layering. Along with the disease resistant plants, high yields and nutrient rich plants can also be produced with the help of PTC [10,11].

From time immemorial, India has been a rich source of medicinal plants. The richness is attributed to the supporting climate and physical parameters that created natural hubs such as Western and Eastern Ghats with north-eastern hills [16]. With the help of PTC, these species can be identified, screened, and can be cultured with in vitro approach. This helps in regeneration of medicinal plants and may also help in large scale production if required by pharmaceutical industries [17]. The current review was carefully planned considering the lack of literature on the various aspects of PTC industry in India. PubMed and Google search engines were employed to search for the relevant manuscripts related to the recent advances in PTC to identify over 1000 manuscripts resulting from the keyword search. After elimination of duplicates and non-relevant contents, around 60 manuscripts were used to review the findings and to write this article. This review focuses on the emergence of PTC in India and rest of the world along with the followed methods. It depicts the events associated with R&D activities in India, institutions funding the research, private organizations involved with PTC and commercial production of crop plants, medicinal plants, and forest trees. It also deliberates the constraints and remedies need for restoration.

2. HISTORY

The history of PTC dates to early 20^th century when Gottlieb Haberlandt, in 1902 addressed the German Academy of Science on his experiments on in vitro single cell culture. Later, his idea of generating the whole plant from a part, now known as “totipotency” got established, which also gave rise to the artificial growing of isolated plant cells using nutrient solution. This approach resulted in the successful culture of root and stem tips using meristematic cells which were completed later using a completely defined medium by Kolte and Robbins in 1922. With the first plant hormone (indole acetic acid) discovered by Went in 1926 and Vitamin B included as an ingredient in media by White in 1934, embryo culture was successfully developed. Later, embryo rescue from non-viable seeds was also performed. In 1939, Gautheret developed the first callus culture along with White and Nobecourt. Overbeek added the coconut milk and reported the cell division in Datura during 1941. In the context, “nurse culture” was developed with using filter paper as a substrate for plant growth. Whole plant regeneration using shoot tip culture was reported by Ball in 1946 using Lupinus plant. As the principle of PTC was then shifted toward enhancing the plant growth, research was focused to improve the nutrient media with the addition of plant hormones. Miller and Skoog discovered kinetin hormone and reported its use in cell division in 1955. The same duo also gave the concept of hormonal control in the plant organ formation [9,18].

In a similar attempt like Ball from 1946, Reinert and Steward developed bipolar somatic embryo from carrot independently along with unipolar shoot buds and roots in 1959. The conventional method of using coconut water was soon replaced by defined medium, when Murashige and Skoog developed it using micro and macro elements, vitamins, growth regulators, and carbon source in 1962. Before that in 1960, Cocking was able to isolate protoplast by cell wall degradation by enzymatic method. Later in the same year, Kanta and Maheshwari developed test tube fertilization. Using anther culture, Maheshwari and Guha produced first haploid plants of Datura in 1964. Regeneration attempt with carrot plants from single cells of tomato was also successful in 1966. After the isolation of protoplasts by Cocking, Power et al. achieved the protoplast fusion 1970, whereas Takebe et al. developed the first plants from these protoplasts in 1971. As a result, pomato was produced by hybridizing tomato and potato by Melchers in 1978. The recent past which includes 1980s witnessed a dramatic increase in the applications that resolved several problems related with basic biology, forestry, agriculture, and horticulture. Agrobacterium tumefaciens was used to integrate its Ti plasmid in plants by Chilton in 1977. The biotransformation was ubiquitously to generate pathogen resistant plants in following days. Meanwhile, techniques such as cryopreservation and germplasm preservation were also developed. As a result of this, more plants produced, in turn, will help to get more plant products that include secondary metabolites, herbal extracts, and oils. The first attempt in 1950s made by Charles Pfizer Co. US was then extended with Germany and Japan executing feasible industrial application of cell cultures in 1978. The modern wave includes development of shuttle vectors, selectable markers, and direct DNA transferring techniques for incompatible plants. This has resulted in considerable success controlling insect pests, weeds, and diseases. On the other hand, plant quality has been improved by gene transfer techniques, developing biofortified species such as Golden Rice. The next wave of PTC is in progress with applications including agricultural biotechnology, pharmaceuticals, and environmental aspects. Indeed, advancements made with in vitro technology in the last century have gone well beyond the imagination of Haberlandt [9,18].

3. COMMERCIALIZATION: A SCENARIO OF INDIA AND CONTEMPORARY WORLD

The extent of globalization created a surge in requirement of food products as well as medicines. Increased production of medicines also resulted in expansion of pharmaceutical industry, thereby increasing the requirement for raw materials such as plant extracts and chemical compounds [19,20]. Although modern-day PTC involved with the micropropagation, it is limited to lab scale production which greatly differs from commercial or large-scale production. Thus, it becomes important to establish PTC industries well-equipped with all the facilities that permit extensive production of plants to produce plant products required by the pharmaceutical industry.

Due to the above factors, commercial application of PTC was first established in US with micropropagation of orchids in 1970s. Since then, the industry has witnessed tremendous support and global expansion. The number of production units as well as number of plants has been increased from 1985 to the present [21]. The current scenario depicts the presence of enough scope for the expansion of commercial PTC as the demand far exceeds production, with an estimated 15 billion USD market per annum. The global biotechnology business is estimated to be approximately 150 billion USD, of which 50–60% is attributed to agri-business which raises annual demand of tissue culture products by 10%. During 1990, production increased from 130 to 500 million plants, where five major commercial units produce 15–20 million plants per annum. Although it appears like PTC industry is nearly halted in developed countries due to increased production charges, in case of developed countries like India, the production is quite stable because of the lower wage scales. This leads to the production of plants at cheaper costs. The Western Europe has a capacity to produce 212 million plants, with 37 units producing more than 1 million plants per annum. Netherlands produces about 62 million reengineered plants every year with 67 commercial units. In Germany, the production raises up to 8 million with 21 functional units [22].

The first commercial tissue culture in India was established in 1987. It was named as A.V Thomas Company, Kerala. Cardamom plants containing superior genotypes of selected variety were clonally propagated by them to bring out the plant improvement. The production of these plants was done in small scaled laboratory-based industry, which was developed indigenously and released by the National Chemical Laboratory (NCL), Pune, India. This technology was refined to make the methods oriented toward more production, economically feasible, and quality service with the help of a UK based firm [23]. In 1988, the second plant was started, an Indo-American Hybrid Seeds at Bengaluru, Karnataka. They were reported with the hybrid flowers and vegetables nursery with imported PTC laboratory and green houses. By 1988, 4 units were working in India, and it was flowed by a rapid rise till 1996 to around 50 laboratories across the country. Even though the number rose to 105, due to lack of financial support it was reduced to 70–75. With this, Indian micropropagation industry has raised from 5 million to 190 million in course of 8 years from 1988 to 1996. The current scenario of Indian subcontinent shows that the facilities created have made our units competitive to those from leading countries such as US and Netherlands. Indian units need to work on generating unique products based on demand in both domestic and international markets to remain in profitable side and to earn essential foreign exchange [22].

4. INDIAN MICROPROPAGATION UNITS INVOLVED IN COMMERCIAL PTC

5. STATUS OF RESEARCH AND DEVELOPMENT IN INDIA

5.2. Assistance to Commercialization of PTC

The research and development activities are run by an array of institutions and research centers in India. For the smooth run of these units, some assistance is essential. The need of assistance is much appreciated both in terms of technology and economics. It is because India had only 4 operating units in 1980s, while rest of the world produced millions of plants. Even though number of units increased, the output was so minimal to reach up the quantity needed by agricultural and horticulture market needed [22]. Newer technologies, instruments and trained staff are required to run a commercial PTC hub. In addition to this, financial support is also an essential thing, as the handling of instruments and chemicals is expensive. There are number of schemes launched by Government of India and other states to promote the commercial production of PTC.

5.2.1. Ministry of agriculture

Financial assistance up to Rs. 21 lakhs for public sector and Rs. 10 lakhs for private sector commercial units is provided by the Department of Agriculture and Cooperation under the Ministry of Agriculture, Government of India, with a maximum of 20% of the project cost. A subsidy of 50% is provided by various state Governments under development of fruits scheme for purchasing banana plants grown with tissue culture. A national facility for quality control and diagnosing virus has been set up by Government of India in Delhi, which operates with the help of five satellite centers responds to the needs of tissue culture industries in various parts of the country. In addition, under Small Farmers Agri-business Consortium (SFAC), Ministry of Agriculture provides loans up to Rs. 50 lakhs for small scale PTC laboratories run by farmers through cooperative societies [33].

5.2.2. Agriculture and processed food products export development authority (APEDA)

A trans-shipment facility has been established by Government of India under the Ministry of Commerce and Industry at Bengaluru, Mumbai, and New Delhi airports. This facility provides up to 25% of airfreight subsidy in costs to supply tissue culture plants. A subsidy of 50% is given for the development of export promotion, market development, human resource development, feasibility studies, and organization building. It also includes the new infrastructure developments such as refrigerated van and innovative ideas in packing. In addition, financial support is also given for setting up quality control measures and their implementation of ISO 9000 [33].

5.2.3. Department of biotechnology (DBT)

DBT is the principal supporter of research and development projects in India. It functions alongside various universities, laboratories, and research academies for the development and refinement of PTC research. It has established six national centers for the detection and diagnosis of virus and control quality maintenance, which, in turn, deliver the virus-free plants. For the promotion of industrial PTC research, the department has set up micropropagation technology parks (MTPs) [33]. At present, there are two of the parks in National Chemical laboratory, Pune, Maharashtra and Tata Energy Research Institute, New Delhi. These parks are established in order facilitate a solid pavement for transferring novel research techniques to the needy entrepreneurs, working with large scale or commercial PTC. They also aid as a bridge connecting research centers and commercial tissue culture industries to enhance the commercialization of PTC [49]. The services offered by MTPs are given in Figure 1.

Figure 1: Services offered in micropropagation technology parks [Click here to view]

5.2.4. National horticulture board (NHB)

NHB, Ministry of Agriculture, Government of India, was established in 1984 for integrated development of horticulture. This board promotes the healthy development of horticulture industry. A back-ended capital subsidy below 20% of the total cost and up to Rs. 25 lakhs of cost are funded by NHB. It is even extended to the construction of greenhouses [33]. This scheme is greatly helpful to the economically backward farmers and villagers who cannot afford the instrumentation required for the construction of greenhouse.

5.2.5. Financial institutions

Apart from this, financial support is extended by different banks run by Government of India. This will help to establish new culture plants and renewing of the old ones. Centralized banks include State Bank of India, Dena Bank, Bank of Baroda, Central Bank of India, National Bank for Agricultural, and Rural Development (NABARD). Every institution differs from each other in terms of official essentialities [50].

5.2.6. Biotech consortium limited

Under the Indian Companies Act 1956, the Indian government established Biotech Consortium India Limited, supported by Department of Biotechnology, Government of India. This consortium has been involved with the development of technology, syndication of funds, project consultancy, dissemination of information, and training manpower. At present, it has assisted over thousands of clients comprising researchers, research institutes, entrepreneurs, corporate sector, banks, government, and public [50].

5.2.7. State level initiatives

Indian states including Andhra Pradesh, Gujarat, Maharashtra, and Karnataka facilitate financial assistance under agro-industrial scheme, for establishing PTC units. Among these, Government of Karnataka gives a capital subsidy of 20% on all PTC investments [33].

All the above stated facilities have been encouraging the establishment, production, and marketing of tissue culture products in the micropropagation industries. This has enormously helped the farmers and the industrialists to procure the financial as well as technical assistance. This comprehensive approach by the Government and the industries could endeavor to reveal the true potential of Indian PTC industry, which can become a landmark global market in 21^st century.

6. PERSPECTIVES AND PROJECTIONS

The commercial approach to the conventional PTC has resulted in harboring a wide range of techniques that have revolutionized the production thereafter. Since the beginning, all the steps followed in the PTC have been continuously refined by the researchers in search of resultant plants with high yield, resistance to pathogens and environmental aberrations. Although affected by lag of 10 years, the Indian PTC industry has been evolved to equal with its Western counterparts [33,36]. The production of tissue cultured plants has been increased dramatically since the extension of support from the Indian Government in terms of finance and technology. Several applications in agriculture, medicine and forestry have been projected by the PTC. For example, with the advancements in genetic engineering, nutrient enriched crops such as “Golden Rice” have been grown [51]. However, there is an utter requirement of drought resistant crops that may grow with minimal requirement of water. As the Indian climate proves to be harsh for many of the crops especially during summer, drought hit regions could use the benefits from PTC, in terms better varieties of crop plants. Even with the sublime research on major Indian fruits such as banana [52], guava [53], and mango [54], their pharmaceutical importance is not utilized to produce plant-based drugs. The production of plant-based drugs and their marketing at international level needs attention. Apart from crop plants, India is referred as a cradle of medicinal plants. Although many of the agencies have promoted the benefits of these plants in the international market, there is a sublime dependence on synthetic drugs, even with their known side effects [55]. Therefore, attention is needed on the production and marketing of such plants.

It is applaudable that the government has been doing its best in terms of providing technical and financial assistance. But practicing of PTC in villages and remote areas has not been took off as it was expected. Farmers in village need to be edified about the benefits of PTC through demonstrations by group of scientists and industrialists. Soil health cards and subsequent suggestions to enhance their fruit and crop production through PTC can be distributed to the farmers. Furthermore, the quantification and quality of micropropagation in plants are still been a difficult task. Structural features such as number of leaves, stem calipers, number of shoots at clump, number of roots per plant, and weight and diameter of bulbs have not yet used to define the quality of the plants obtained [56]. Costing of the plants is not yet taken as a serious concern for the competitive production of plants at global level. Professional credibility has not been established by gaining a recognized position in the market. Poor marketing skills and resistance to foreign product sales are not observed [36].

Furthermore, it is known that Indian research institutes have been exchanging the germplasm at national and international levels [57]. In the context, inducing genes that result in good yield and resistance to diseases could help in the robust development of industry. Furthermore, genome sequencing could reveal both harmful and beneficial effects of mutations, which can be dealt for the modification of plant species. Plant proteins have been the center of interest as they possess substantial amount of nutraceutical values. Bioactive peptides from medicinal plants would sure be able to comprise medicinal benefits [58]. Thus, PTC industries need to focus on these aspects alongside secondary metabolites. In total, the PTC industries could be more worthy if they deliberate on parallel ways of scientific research and commercialization at international level.

7. CONCLUSION

Propagation of new plants from PTC results in good commercial prospects in a variety of plant types including crops, fruits, vegetables, and ornamentals. More than 100 species have been reengineered using modern PTC methods in India. It is now estimated that India can produce more than 350 million cultured plants per annum.

With the applications of PTC in plant biology, several problems related to experimental biology can be resolved, which becomes a tedious task with conventional approaches. PTC is already playing a significant role in the maintenance of plant health through dimensions such as genetic engineering, breeding, and afforestation. It has been a boon for the agriculture and horticulture industries due to its numerous advantages such as pest-resistant, disease-free, and virus-free plants. It is noteworthy to mention about production of plants that are resistant to abiotic stresses and plants with biofortified properties have surely changed the direction modern-day agriculture and food production.

Commercial production of plants using PTC industries has immense scope and potential once the production units become free from all the constraints, particularly advanced research facilities, financial aspects, and marketing. Being blessed with diverse agroclimatic zones and availability of cost-effective labor, India, can flourish off the limits with the various sources from the government, as these measures can enable India to retain its self-sufficiency on agricultural production front. Furthermore, with the employment of digital technologies, one can revolutionaries the PTC industry. Development of new software to monitor the plant growth, in addition to introducing mobile apps that could help the farmers and industrialists from collection of explants to the selling the whole generated plant in market. Considering these factors, Indian tissue culture industry, though started a little later, can have its presence felt on the global scenario.

8. AUTHOR CONTRIBUTIONS

All authors made substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; agreed to submit to the current journal; gave final approval of the version to be published; and agree to be accountable for all aspects of the work. All the authors are eligible to be an author as per the international committee of medical journal editors (ICMJE) requirements/guidelines.

9. FUNDING

There is no funding to report.

10. CONFLICTS OF INTEREST

The authors report no financial or any other conflicts of interest in this work.

11. ETHICAL APPROVALS

This study does not involve experiments on animals or human subjects.

12. PUBLISHER’S NOTE

This journal remains neutral with regard to jurisdictional claims in published institutional affiliation.

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