Introduction

Tea as a plantation crop has been considered as a strong nutraceutical, non-alcoholic and widely consumed beverage after water. It is produced in more than 58 countries and the annual production is 5 million tonnes valued at around $20 billion contributing to rural poverty alleviation and value chain (cultivation- consumption). In India, tea is grown in two distinct regions. Located between 22-27⁰ North, the North Indian tea belt is characterised by a wet and hot summer and a cold, dry winter (Barua, 1989). South Indian tea, located at 7⁰ North latitude, enjoys a tropical climate. In the district of Darjeeling, tea is planted on hill slopes up to a height of 2000 meter above sea level, while in flat valleys of Assam at elevations ranging from few to about 200 meter above MSL. Indian tea industry produces about 1.2 million tons from about 5.64 million hectares of land accounted for 22.7 per cent of global tea production. On an average18 per cent of the total production is exported and balance 82 per cent is consumed within the country. Besides bringing in valuable foreign exchange of US$ 837.33 million (INR 4987.59 crores) (https://www.google.co.in/search) from quality tea of 256.6 million kg during 2017-2018, tea industry is one of the important sources for revenue for the tea growing states. India is the largest producer and consumer of black tea in the world.million people of which 50% are women. Additionally, more than six million people derive their livelihood from ancillary activities associated with the industry (Anonymous, 2017).

Achievements Tea Research in India

The main players in research and extension in Indian tea sector include: Tocklai Tea Research Institute, UPASI - Tea Research Foundation (TRF), Darjeeling Tea Research & Development Centre (DTRDC) and Institute of Himalayan Bioresource Technology (IHBT), Palampur are four major research institutes carrying out tea research in India. Despite, National Tea Research Foundation (NTRF) jointly set up by Tea Board, tea industry and National Bank for Agriculture & Rural Development (NABARD) provides funds for universities/Institutes involved in innovative tea research. Their mission is to promote, develop and encourage research connected with cultivation, production, processing, machinery, marketing, package of tea and allied products of tea, socio-economic aspects and health benefits of tea through tea research organizations/bodies/institutions/ universities by providing financial grants to them.

 

Tea industry in North East India started dabbling in adhoc researches in 1888 (Bamber, 1902) and set up a full-fledged research station in 1900 A.D. In North East India, Tea Research Association popularly known as TRA Tocklai. Tocklai Tea research institute (TRI) is the oldest and the largest tea research institute in the world. It looks after the research and development needs of the Assam and North Bengal tea industry. United Planters’ Association of southern India (UPASI) has established Tea Experimental Station at Davershola in 1927. At present UPASI TRF comprises the Tea Research Institute at Valparai. In Kangra Valley, the State Govt. of Himachal Pradesh started tea research station in 1936 but the efforts at practical research have been augmented only in 1986 when Institute of Himalayan Bioresource Technology (IHBT), Palampur under CSIR started functioning (Kankani, 1987). Darjeeling Tea Research and Development Centre (DTRDC) were established in 1977 at Kurseong to provide R & D support to the Darjeeling tea Industry. The increase in productivity from 424 kg/ha in 1900 to about 2153 kg/ha (2017) is a reflection of the impact that Tocklai, UPASI and other research institutes have had on the Indian tea industry. The major research breakthroughs as reported by Tocklai, UPASI, IHBT, DTRDC are listed in table 1 to 4.

The current priority areas of research and service to the Indian tea industry include:

1. Germplasm Resources and Conservation

Tea germplasm resources are the most basic materials for tea breeding and biotechnology. Over the past decades collection, preservation, exploitation, utilization and cataloguing of germplasm have accelerated expanding genetic pool and breeding of new cultivars of the tea producing countries despite improvement of our understanding of the genetic diversity of the tea plant and its related species. The narrow genetic base of tea cultivars is a hindrance to improving productivity due to rapid vulnerability of genetically uniform cultivars. Hence, studying the genetic diversity of the newly improved clones under exploitation is necessary to avoid narrowing the genetic pool (Borthakur et al., 1995; Leonida et al., 2013). Molecular markers, such as RFLP (Restriction Fragment of Length Polymorphism), AFLP (Amplified Fragment Length Polymorphism), RAPD (Random Amplified Polymorphic DNA), CAPS (Cleaved Amplified Polymorphic Sequence), ISSR (Inter Simple Sequence Repeat), SSR (Simple Sequence Repeat), EST-SSR (Expressed Sequence Tags based SSR), and ALPs (Amplicon Length Polymorphisms) etc. were initiated by using RAPD markers with the aim of assessing the genetic diversity of tea cultivars. These markers have been proven to be robust and valuable in the research of genetic diversity and variation, introduction and spread, molecular identification and DNA fingerprinting, molecular phylogenetics, genetic stability and integrity, and the establishment of the genetic linkage map for tea breeding (Ni et al., 2008). Furthermore, characterization of germplasm will assist in varietal improvement of deserved agronomical traits, avoidance of any unwarranted entry in the gene pool, proficient selection, and taxonomic classification of tea based on molecular markers. Economically important characteristics viz. high content of individual and total catechins (Sabhapondit et al., 2012; Jin et al., 2014a) and theanine (Song et al., 2015), low caffeine (Jin et al., 2014b), high yield and quality (Singh et al., 2013), biotic resistance (Liang et al., 2012) have been identified from different germplasm evaluation studies conducted in different tea producing countries.

 

In recent past the genetic diversity is being narrowed down at an alarming rate due to uprooting of old seed grown population and gradually been replaced by clonal cultivars as tea industry prefers improved superior cultivars such as early sprouting, high yield with better quality, suitable for machine harvest etc. Further, situation is worsened by deforestation, shifting cultivation, industrialization, other human activity related to other agricultural production and climate change. The narrowness of the genetic diversity of improved tea cultivars may possibly lead to a decline in production and quality in the future. It is thus utmost necessary to further collect, preserve valuable landraces and their wild relatives for future tea improvement programme before they are lost for ever. In many tea-producing countries systematic evaluation of tea germplasm accessions has been done and elite germplasm with desirable traits have been successfully used in varietal development programme.  Wild species, weedy relatives and polyploid genetic stocks of tea are maintained in a collection at Tocklai TRI, UPASI in south India, Valparai, Coimbatore and in North-West India at the CSIR-IHBT. These stocks are utilized for continuous tea breeding programmes. It is estimated that more than 2100 and 1250 accessions are maintained at Tocklai TRI and UPASI respectively (Das et al., 2012). Large number of commercially important South Indian, North Indian clones/accessions, Darjeeling garden selections and some other collections are being maintained at the germplasm block of DTRDC experimental farm.

 

Today, no world-sourced collections of tea exist, and the local collections and crossbred populations that have been described in the literature so far have not, in general, been made available to the wider research community (Bennetzen, 2019). It is estimated that more than 600 tea cultivated varieties are available worldwide till date (Mondal et al., 2004) of which many have unique traits. Since identification and exploitation of the useful variation from the huge collections of genetic resources is not an easy task, Ma and Chen (2018) has listed out solutions viz. (1) establishment of core and mini-core collections; (2) application of appropriate methods and technologies like linkage and association mapping, comparative genomics and molecular genetics to increase the efficiency of functional gene identification and allele mining; (3) development of databases and sharing of same among researchers; and (4) exchange of germplasm among the tea producing countries to facilitate exploitation of the full potential of genetic diversity in order to develop elite cultivars. 

 

2 Genome Mapping

Genome mapping helps to decode the genetic controls linked to different characters of tea that govern its yield, quality and other attributes. In the past two decades, genome researchers have faced enormous difficulties due to lack of genetic information but in the last two years several genomic resources for tea have made possible some important achievements in this area (Wang et al., 2018; Dolgin, 2019). In tea, the processed tender shoots are rich in secondary metabolites like polyphenols, amino acids and alkaloids. These secondary metabolites are regulated by various pathways. The secondary metabolic biosynthesis, biotic or/and abiotic stress, pest and disease stress are controlled by a number of genes composed of complex regulatory networks (Wang et al., 2018). Meanwhile, Xia et al. (2017) reported the first genome sequence of the cultivated tea (Camellia sinensis var. assamica) (Assam type) with an extraordinary large size of 3.02 billion base pairs in length. It provides and contributes a deeper understanding of the complex evolution and the functions of key genes associated with stress tolerance, tea flavour and adaptation. Further, exploration of the tea genome revealed what Dr. Xia and colleagues called “jumping genes”. These genes are sequences within the genome where the genes have essentially copied themselves in a variety of location. This duplication, which make up approximately 67 per cent of the genome sequence, which is a part of the reason why the actual size of the genome is so extensive. Xia’s team believes that these jumping genes, some of which may have been the result of cultivation and may have helped the plant adapt to climate change, and other environmental stressors. Later, Wei et al. (2018) presented sequence of the genome of Camellia sinensis var. sinensis (China type), with a size of 3.1 billion base pairs in length which provide information on how tea plants produce the abundant and diverse flavonoids and theanine that synergistically contribute to tea palatability and health benefits. Sequencing of the tea genome and identification of functional genes provides the foundation for extracting all the genetic information needed to help breed and speed up development of new varieties of tea. Further, this is an important milestone for tea researchers since it provides a deeper understanding of the complex evolution and the functions of key genes associated with stress tolerance, tea flavour and adaptation. Many of the secondary metabolites that contribute to tea drinking quality are known, such as theanine and catechins. Many candidate genes for the biosynthetic pathways leading to these compounds are now identified by this study (Xia et al., 2017). It may be possible to breed for increases of specific target metabolites and down regulation of branches leading away from target metabolites. Mukhopadhyay and Mondal (2018) opined that genetic transformation of tea has immense potential although it has some negative effect (e.g. allergen contamination) from consumer end. However, black tea is heated at 120⁰C during manufacturing process and at this temperature toxin or foreign protein if present in transgenic tea will be degraded. Further, techniques are available to remove those marker genes, broadly called as marker-free plant production. A recent gene-editing technique CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) will be a novel and powerful approach to develop the transgenic product. India, which recently launched its tea genome sequencing multi-institutional project aims to develop climate-smart tea plantations wherein it aims to establish the whole genetic make-up of India tea, in addition to molecular methods like DNA fingerprinting and DNA barcoding. A four-year on-going genome project is being supported by the NTRF, Kolkata, India. Further, UPASI, TRI, has also identified the value of genome mapping of the Camelia sinensis cultivars. Currently, the researchers are embarking on one of the largest genomes sequencing projects and looking at several aspects of the plant’s genome including the metabolic aspects to help determine the features that can help the plant adapt to abiotic and biotic stresses. The potential benefits from this research are extensive including being able to outline key gene markers which could then be used in plant breeding programmes. Mondal et al. (2019) decoded TV-1, an Assam variety, assembled in 2.93 Gb size consisting of 14,824 scaffolds and covering 97.66% of the predicted genome size 3.0 Gb. This decoding will help out to determine the genetic variations among Indian tea cultivars and the baseline data will assist to identify the genes having agronomic importance. Further, the data will be useful for future research related to genetic improvement of Indian tea. However, Wang et al. (2018) emphasized some issues on the improvement of future tea genome research. These are: 1. Making of authentic reference genome and perfection of the gene annotations. 2. Conducting more re-sequencings on some trait-specific cultivars and obtaining exact genetic regulation information of desirable traits. 3. Getting more molecular markers and establishing a highly saturated genetic map to identify locations of quantitative trait locus. 4. Creation of a high-efficiency genetic transformation system and/or gene editing technology to fulfil gene function homological identification and directional improvement of tea plant traits.

 

3 Impact of Climate Change

Currently global warming is one of the major environmental problems due to climate change. Tea is an ideal model perennial plant for studying the effects of climate change due to its wide distribution, stable ecosystem, quality parameters, and long economic life. Tea is a rain-fed mono-cropping system and has been found that tea would be one of the crops most adversely affected by climate change (Ochieng et al., 2016). Many tea growing countries viz. China, India, Kenya and Sri Lanka etc. have witnessed significant change in climate in the last few decades (Han et al., 2018a; Bhagat et al., 2016a; ITC, 2014; Wijeratne, 1996). In India, the main tea-growing areas of Northeast India, Assam and West Bengal, showed a steady increase in mean temperature with the average minimum temperature having increased by about 1.3°C over the last 100 years. Further, the annual precipitation has steadily declined. For example, annual precipitation in the south bank region at the Tocklai TRI of Assam has declined by more than 200 mm in the last 96 years. Dutta (2014) applied predicted models derived by WorldClim and IPCC4 and found that the possibility of an increase in average temperatures by 2⁰C in Northeast India in 2050 but not much variation in rainfall pattern as compared to today. Increasing temperatures, enrichment of ambient CO₂, changes to annual rainfall and its distribution pattern, coupled with major shifts in other meteorological parameters have a profound impact on growth and yield of tea. It has been observed that climate change influences tea yields by altering precipitation levels, increasing temperatures, shifting the timing of seasons and encouraging insect pests (Nowogrodzki, 2019). In a study on the suitability of the tea growing regions in 2050 and 2070, it has been reported that tea growing areas in Assam could drastically reduce drastically by 2050 (Bhagat et al., 2016b; ITC, 2014). Hence, facing an unpredictable fate and with the knowledge that climatic conditions are likely to worsen. They have further reported that South bank region; parts of upper Assam and Cachar are the suitable regions (very good and excellent suitability) whereas north bank region is comparatively less suitable (good/marginal suitability). However, the predicted probability distribution of Assam tea by 2050 will reduce drastically and could shift towards comparatively higher and cooler altitude areas. Darjeeling also not immune to the effects of climate change, which has already negatively impacted tea cultivation on several levels. A study conducted at DTRDC demonstrated that the temperatures in the region for last 20 years have risen by 1⁰F (0.51°C); the annual precipitation has decreased by 152.50 cm, and, more than a 16% reduction in relative humidity (Patra et al., 2013). Further, Edwin Raj et al. (2017) reported a land ecological suitability evaluation (LESE) map of tea production regions of South India which was based on geographic information system (GIS). The total area of the study covered 1,08,901 ha including three districts and five regions. Highly suitable regions were mainly located in the northern regions of the Anamalais and the Nilgiris along with the eastern regions of Vandiperiyar and Munnar. Regions deemed very suitable were located in east border of Anamalais and Munnar and the central regions of Udhagamandalam and Gudalur. Very marginal to marginal areas were located in the southern and southwest regions of the Nilgiris viz., Gudalur and Udhagamandalam. These areas have arguably the greatest need for new crop varieties that are tolerant to extreme climate especially to drought. Further, the quality of tea is also severely affected due to changes in the environment (Bhagat et al., 2016b). Some of the specific climate change impacts and challenges for the tea sector listed out in table 5.

3.1 Adaptation and mitigation options

The climate mitigation challenge involves reducing the negative impacts of tea systems throughout the entire value chain. The GHG (Green House Gas) like CO₂ is produced during burning of fossil fuels and deforestation. Methane is produced from cattle as well as during the decomposition of organic waste. Further, nitrous oxide emits GHG during fertilization of tea field (ITC, 2014; Ahmed, 2018). The summary of environmental impacts of tea and possible mitigation measures at different stages of tea industry listed out by Wajiratne (2018) are presented in table 6.

Climate change results in negative economic and social consequences for the tea stakeholders and they are in urgent need of adaptation practices against climate change. Chang and Brattlof (2015) have recommended adaptation measures for tea cultivation. These are • planting drought and stress tolerant tea cultivars or improved seed varieties and grafted plants; • planting of a basket of cultivars in one land; • conservation of soil and soil moisture  by physical methods and other agronomic practices; • diversification of marginal lands as energy/timber plantation and thatch banks (green manure); • diversifying production, including changing low-yielding tea land from tea to other crops that can thrive in poor soil and in tea-growing areas; • intercropping tea with tree crops, like rubber, and/or other food crops; • organic cultivation; and • water conservation and rain water harvesting; and focus on tea production in marine climate zones.. The cost benefit analysis of these mitigation and adaptation measures prior to implementation would need to be undertaken.

3.2. Planting Material

Development of new climate resilient cultivars having high tolerance to heat, cold and drought stress, high resistance to pests and diseases, high nitrogen nutrient use efficiency and high net photosynthesis, especially in response to higher CO₂ concentrations is the priority research area in the face of climate change. For example, tea cultivars with characteristics of deep-growing roots and high metabolite content (e.g. amino acids and sugars) have proved highly resistant to drought (Thiep et al., 2015; Nyarukowa et al., 2016). Integration of physiological, biochemical, molecular breeding and modelling tools can play a major role in the selection of tolerant genotypes. Additionally, better understanding will improve the capacity to enhance the yield or maintenance of yield under hostile environmental conditions (John Sunoj et al., 2017). TRA, Tocklai has been shortlisted planting materials suitable for unfavourable condition like marginal land, drought and poor drainage for Assam and Darjeeling. Recently, TRA released two high yielding and drought tolerant clones viz. TV 34 and TV 35. TV 34 is very good cup quality for CTC and TV 35 is good for both CTC and orthodox tea manufacture.  These two clones are more tolerant to drought over the popular TRA clones used by the tea industry. For the drought prone areas in southern India, clones like UPASI-2, UPASI-9, ATK-1, TRI-2025, UPASI-20, UPASI-26, biclonal seed stocks viz. BSS-1 to BSS-5 are recommended by UPASI TRI. In Kurseong, Darjeeling, B157, P312, T78 and AV2 are comparatively performing well during drought (Ghosh Hajra, 2001). These stress tolerant cultivars may be selected for new planting and replanting in drought prone area. Qian et al. (2018) listed out some key features of the previous studies in tea plants challenged by drought stress. These are (1) smaller and succulent leaves, and thick cuticle and palisade tissue and deep root system; (2) water deficit, impairment in photosynthesis and respiration, stomatal closure, reduction of carbohydrate synthesis, acceleration of proteolysis, changes in lipid components in the normal cell wall structure; (3) protein denaturation of the plant tissues constituents, protoplast condensation, and the loss of cell wall semi-permeability; (4) enhanced free radical content, antioxidative systems, and osmoprotectant contents; (5) changes in the contents of minerals required for nutrition, hormones, polyphenols, and amino acids; (6) and changes in the transcription levels of many regulatory and functional genes. Further, early selective markers at the nursery stage for various biotic and abiotic stresses should be generated to revolutionize tea breeding programme which suffers from lack of selection criteria and long gestation periods. An important observation in drought tolerant clones is the greater proportion of dry matter in the root system as compared to the leaf biomass. Therefore, selections need to be based on higher rate of root growth and root depth in genotypes and consequently select for drought tolerance (Ni et al., 2008).  Recently, Han et al. (2018b) provided a comprehensive overview of stress-induced changes in tea physiology, biochemistry, and quality as well as physiological and molecular mechanisms of stress tolerance and associated stress management strategies in tea ecosystem in the face of climate change.

 

3.3 Improvement in Field Management Practices

Use of chemical fertilizer and pesticides are vital for increasing yield of crop but overuse is degrading the environment. Integrated Pest Management (IPM) has gained widespread scientific recognition in the past decades which comprises strategies aimed at minimising pest damage through the careful integration of available pest control technologies. IPM includes strategies for monitoring pests for early detection, release of predators, manual control, use of bio-pesticides, and discretion on the choice of pesticides to be used (Ghosh Hajra, 2001; 2007; 2018; Mukhopadhyay and Mondal 2017). Further, Integrated Nutrient Management (INM) practice will be the right option as it gives optimum crop nutrition, improve soil health, minimise nutrition loss and other adverse effects on the environment. Promoting organic agriculture (OA), good agricultural practices (GAP) and climate smart agriculture (CSA) production are capable of contributing to climate mitigation. OA is not only enables agriculture-influenced ecosystems to better adjust to the effects of climate change but also offers potential to reduce the emissions of agricultural GHG. Many field trials worldwide show that organic fertilization compared to mineral fertilization is increasing soil organic carbon and thus, sequestering large amounts of CO₂ from the atmosphere to the soil (http://www.fao.org/organicag/oa-specialfeatures/oa-climatechange/en/). Research also shows significant  higher  levels  of soil pH,  total  nitrogen content and  soil microbial biomass, carbon (C), nitrogen (N) and  phosphorus (P) and  their  ratios  to total  organic C, N and  P, respectively observed in organic tea soils (Han et al., 2013). This interprets into better plant nutrient content, increased water retention capacity and better soil structure and thus to higher yields and greater soil resilience (FAO, 2009). Further, higher levels of biodiversity and natural predators observed in organically managed tea gardens (Ghosh Hajra, 2006; 2018; Saikia et al., 2014; Liu et al., 2015).  Difficulties in controlling of pests and the imbalance of nutrients particularly shortage of nitrogen are responsible for decrease in yields by 20-30% (Ghosh Hajra, 2006a). However, organic tea has a 20–50% higher price compared to conventional tea, compensating for the loss in yield. It is thus, promotion of organic tea production is not only beneficial to producers, also offers significant scope for adaptation to climate change. However, future research should examine the following.   

 

• Does development of organic matter in the soil have a significant value in terms of carbon sequestration?

 

• Quantitative and qualitative information on how much carbon sequestrated and GHG emissions reduced, low carbon regulation/standard development, and attend various activities to power the organic movement of sustainability.

 

• Comparative study on carbon credit between organic and conventional tea gardens.

 

GAP is specific methods which take into account environmental, economic and social sustainability for on-farm production, safe and quality food and non-food agricultural products. The beneficial techniques viz. IPM, integrated plant nutrient management (IPNM) and conservation agriculture are applied.

 

CSA is an integrated technique which aims to transform and reorientation of agricultural production systems and food value chains so that they support sustainable development and can ensure food security under climate change.

 

Precision agriculture is a high-tech farming system which is a concept based on observing, measuring and responding to inter and intra-field variability in crops. It uses GPS (Global positioning systems), GNSS (Global Navigation Satellite System) and unmanned aerial vehicles (UAVs), also known as drones to  collect  the  spatial variability of parameters related to crop  yield and  quality,  such  as plant-growing situations, terrain features, soil organic matter, moisture and nitrogen contents and pH. It utilises agricultural inputs by machines and equipment controlled by the Expert Technology System. Precision agriculture is an effective and efficient way of combating climate change, offering considerable savings in natural resources and optimising crop yield and quality (Han et al., 2018a). Drones and connected analytics have a big role to play in precision agriculture and in terms of access to actionable real-time quality data (Anonymous, 2018). Drones can be a great surveillance tool for examining tea fields regularly at a reasonable price. It can be used in the tea gardens to take actions at the initial stage in order to reduce the reaction time and decrease in pesticide and insecticide volume. The UAVs are used to spray the pesticides to avoid the health problems of humans when they spray manually. They can be used easily, where the equipment and labours difficulty to operate. It also helps the spraying job easy and faster (Mogili and Deepak, 2018). Drones can do soil health scans, monitor crop health, assist in planning irrigation schedules, apply fertilizers, estimate yield data and provide valuable data for weather analysis.

 

3.3.1 Irrigation

Tea is usually a rain fed crop but in certain tea districts of North East India including Darjeeling and some parts of South India plants suffer from drought and irrigation is practiced depending on the availability of water and other factors. Sprinkler irrigation systems are the dominant system of irrigation in mature tea. The quantity and frequency of irrigation depends on soil, temperature, root depth, saturation deficits and rate of plant growth.

 

3.3.2 Rain Water Harvesting

It is an accumulation and storage of rainwater for reuse on site, rather than allowing it to run off. Water harvesting structures in valley areas where tea is grown in undulating topography there water can be stored during heavy precipitation in monsoon. However, more emphasis should be given on water resource management at watershed level.

 

3.3.3 Insurance Schemes

In India, small tea growers contributing near half of the national yield may finally going to have insurance coverage against loss incurred due to adverse weather conditions. Recently, the authorities of Tea Board of India had a meet with insurance companies including Agriculture Insurance Company of India Limited (AICIL) and other Small tea growers to plan the modalities. Following introduction in few pilot districts, the insurance scheme will be scaled up to pan-country level in a phased manner.

 

The dynamics of climate change are still poorly understood. In developing countries like India, formulation of research priorities and their development and dissemination of innovative technologies are vital to deal with climate change. Research is required on the interactions between various climate-related stress factors, particularly to quantify the interactive effects of CO₂, air temperature and other environmental variables on crop production. Multiple agricultural, physiological, and molecular innovations for tea at the production level have been identified towards the development of climate-resilient tea systems (Ahmed, 2018). She further opined that research and development is also needed at the farm level on the cost-effectiveness, replicability, and adaptability of tea agroforestry and various good agricultural practices for climate mitigation and adaptation practices in different contexts. Gnanapragasam (2018a) suggested in-depth studies to understand the impact of climate change on the physiology and behaviour of pests, their mitigation, predators and parasites as well as the host plant and the interaction of insects. More in-depth studies are also suggested to develop ET (economic threshold) levels for changing environmental situations and climate conditions. Molecular and biochemical studies should be carried out to help to identify different races/pathotypes (Gnanapragasam (2018b). Collaborative research networks with different tea producing countries would be useful to know the impact of climate change on tea productivity, quality, soil characteristics, pests and disease infestations and socioeconomic implications.

 

4. Pesticide Residue

The hot and moist climatic requirements and the tea ecosystem, which undergoes continuous monocropping are congenial for the infestation of a large number of pests and diseases (Banerjee, 1983) which cause loss and deterioration in both quantity and quality of teas (Sharma et al. 2008). These pesticides inevitably leave residues in the treated crop (Barooah and Borthakur, 2008; Chen and Haibin, 1988; Hou et al., 2013). The presence of pesticide residues in tea is becoming a priority concern for the consumer’s as its accumulation will have a risk to health. In order to protect the consumer’s health and also promote the development of tea industry, the content of pesticide residues in tea should be less than the maximum residue level (MRL).  The MRL is a legal limit and it represents the highest level of a pesticide residue that is permitted in or on food or feed following the use of pesticides in accordance with the good agricultural practices (GAPs). A pesticide after spray on the canopy of the tea plant, most of the pesticide is retained on the leaf surface and constitutes the initial deposit which penetrates gradually with time into the cuticle of the leaf.  It could overcome through Integrated Pest Management (IPM) strategies, where cultural, biological and chemical means are employed in combination for managing a particular pest or disease situation. Recently, Barooah (2018) reviewed the research carried out on the extent of pesticide residues in tea in different tea producing and consuming countries (Table 7).

Pesticides applied on tea plants undergo degradation through growth dilution, rainfall, dew elution, evaporation, photodegradation, thermodecomposition and biodegradation (Chen and Wan, 1988). They have further reported that about 25.2-67% of the pesticides applied to tea foliage could be degraded during manufacturing of tea. In Darjeeling, the residue level of malathion, quinalphos and fenvalerate declined more than 90 % in 7 days after spraying and the percentage caused by growth dilution may be little less than 45 % (Bisen and Ghosh Hajra, 2000). Residues are further reduced substantially during processing of black and green teas (Gupta and Shanker, 2009; Sood et al., 2004).  It has also been observed from different studies that only a proportion of residues detected in the dry tea leaves are in fact transferred into the liquor. Therefore, the actual residues in tea brew should be considered for setting up realistic MRLs of pesticides in tea (El-Aty et al., 2014; Barooah, 2018) which will satisfy all stakeholders and ensure food safety for consumers. The generation of residue data on commonly used existing pesticides from field trials on different locations of the tea producing countries and sharing data would certainly accelerate the upward revision of many default MRLs which are a major obstacle to non-tariff trade (NTBs) today that restrict exports.

5 Product Diversification and Value Addition

Tea is a rich source of polyphenols and now-a-days interest in the possible health benefits of polyphenols, particularly flavonoids, has increased owing to their antioxidant and free-radical scavenging abilities. Presently, the world market price of tea has stagnated with supplies being stable and this situation emphasizes the need for exploring alternative means of increasing profits from tea cultivation. Product diversification of tea through value addition seems to be an important approach to mitigate the impacts of low market price and high production costs (Ghosh Hajra and Yang, 2015; Wachira et al. 2016).

 

Since tea catechin products presently have gained popularity in different countries, therefore, further research on the development of new products with innovative ideas and their dissemination to the domestic and international markets will counter the escalating global competition to a great extent.

 

6 Tea and Health

Over last few decades, the scientific progress in the role of tea in the promotion of health has been remarkable. These advances have been recorded in numerous scientific publications, reviews, and presentations at the international symposiums and conferences. A literature search on PubMed using the key words ‘Tea and Health’ yielded 3831 publications, Tea and Cancer’- 3657 publications, ‘Tea and Diabetes’- 640 publications, ‘Tea and Heart disease’ – 142 publications and ‘Tea and weight control’ – 290 publications. Various studies suggest that polyphenolic compounds mainly catechins and theaflavins present in green and black tea respectively are associated with beneficial effects in prevention of cancers and cardiovascular diseases, particularly of atherosclerosis, coronary heart disease and other chronic diseases (Ghosh Hajra, 2006b; Jain et al., 2006; Khan and Mukhtar, 2013; Preedy, 2012; Hara et al., 2017; Yang, 2018). Yang (2018) suggested need of further research on following aspects.

 

• More laboratory studies to elucidate the biochemical basis for the reported health effects of different types of tea. The relevance of these findings to human health should be evaluated.

 

• More prospective studies keeping the types and quantity of tea consumption, diet, physical activities, smoking status, genetic polymorphism and other possible interfering factors are in mind.

 

•  More well-designed intervention studies based on strong laboratory data with adequate duration.

 

On-going research into the properties and possible benefits of tea are of tremendous importance to the industry as it struggles to promote tea over other beverage choices and to establish, once and for all, the veracity of the various health claims espoused for tea.

 

7 Conclusion

After long-standing prominence of the USA and Japan in tea research till 1994, the output of their annual research publications stagnated. Simultaneously research output from China, India and South Korea have increased rapidly from about 1995 showing that these countries spearheaded the observed renaissance that characterised tea research after the year 2002. It was revealed that this renaissance coincided with a focal shift where the health aspects took a more central role in tea science over classic tea research after the year 1997 (Wambu et al., 2016). Tea research has huge potential for success with fascinating targets and major tea producing countries have a community of talented scientists. As tea is predominantly an Asian crop, India is a leading global tea producer /exporter has the responsibility to deal with different tea-research issues and further show the way to the researchers. Unfortunately, the following bottlenecks are sometimes hindering the pace of scientific progress in Indian tea.

 

• There is a necessity to change in the ways of research funding system. Presently, tea research in India is almost entirely dependent on government funding which support the industry to be in a better position amidst the rapidly changing global market. It may be worthwhile to mention, that Indian tea research institutes are facing unprecedented financial crises due to curtail of funds and further exorbitant delay in releasing approved fund. For example, Tocklai Tea Research Institute is funded partly by Indian Government and partly by the Tea Industry and the government of India in the past used to allocated INR 15 crore (2114925 USD) and the industry contributed around INR 10 crore (1414900 USD). Now the industry contributes INR 18 crore (2546820 USD) but for the last two years the fund support from government has come down to about 3.5 crore (4930135 USD). This is posing a huge challenge for TRA. Sometimes fund is allocated where multi-institutional participation in tea research is requirement for grants to be awarded. In comparison, Sri Lanka produces about 338 million kg and the government there allocates about INR 15-20 crore (2114925 - 2819900 USD) towards R&D to the Tea Research Institute (TRI) Sri Lanka (1 INR = 2.53 Sri Lankan Rupee (LKR). Kenya produces about 445 million kg and the government provides INR 15-20 crore to the Tea Research Foundation (TRF) Kenya (1 INR = 1.43 Kenyan Shilling (KES). China produces about 2,400 million kg and while the expenditure on R&D is not available for China, the Chinese government entirely funds the R&D efforts of the Tea Research Institute (TRI), affiliated with the Chinese Academy of Agriculture Sciences (CAAS) (P. K. Bezbarua and J. Phukan, 2019, private communication). The tea sector despite the numerous challenges that it faces, the resources expended on R&D is only around one third of that at the national level. This reflects the need to increase R&D investment which would in turn help in realising the research outcomes. It is obvious, absence of a steady and assured funding for research would have undermined the ability of the tea.

 

• Implementation of long-term global collaborative projects with shared experimental designs and “Big data” sharing to facilitate comparison of outcomes across multiple studies. Such partnerships have contributed endlessly to academic and scientific progress. Institutions that choose to provide shared resources will find that the wider research community converges on them, bringing fresh ideas, scientific advances and their admiration. It was observed that the tea researchers, in general, do not have a history of sharing materials or data within or between countries. Such issues are not unique to tea research, either. But they are problematic for tea; in particular, since the field has no international institute or large research community outside Asia that can provide shared resources.

 

• Tea research could be advanced by a more open community that alone would not be sufficient. For example, to improve quality of tea, a deep collaboration between agronomists, geneticists, biochemists and tea tasters will be required.

 

• Researchers should be rewarded for their work. Incorporation of more rewards and appreciation are useful for steady progress of research. The research reward system should recognize scientists’ accomplishments, even when such work does not lead to publications.

 

•  Rigorous evaluation of the tea research organisations and the works of their researchers need to be made performed periodically to measure outcomes. Sometimes organisation having long list of publications indicates significant scientific activity and substantial efforts to communicate results to the stakeholders. But it would be equally important the adoption of research results by the ultimate users.

 

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