2023 年 11 巻 p. 121-136
Hemp (Cannabis sativa L.) is a multi-million-dollar industry in several temperate countries. In South and Southeast Asian region, it remains a neglected and underutilised due to several legal, political, and cultural barriers. Therefore, very limited research has been done on value chain of hemp in this region. Nevertheless, as discussions are ongoing on the legalization of hemp in some of the countries in the region, interest in research and development of hemp is growing. The objective of this review is to identify what has been done on hemp in the region and outline the potentials and challenges in adopting hemp as an industrial crop in tropical South and Southeast Asia. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to select and review research articles. Out of the 12,210 studies, 36 were selected for review and analysis. The results demonstrate the potential of hemp in the South and Southeast Asian region in terms of genetic diversity, growth habits, environmental and health benefits, and value-added products. To motivate the commercial cultivation, several key aspects were identified that includes development of region/location specific cultivars, introduction of site/cultivar specific management practices and development of proper market facilities. The review concludes that hemp can be a potential candidate for crop diversification across South and Southeast Asia.
The early human gave up capturing and collecting food around 10,000 years ago and moved to grow plants by themselves. Since then, different types of crops species and cultivars shaped the civilizations, economy, and the lifestyles of human [1]. Out of the several hundred to thousand species of crops that are currently cultivated, hemp (Cannabis sativa L.) is one of the earliest domesticated crops with around 10,000 years of archaeological evidence [2]. An intimate history was shared by Cannabis plant and humans that last for the millennium [3].
In agronomical terms hemp is categorized as both oil and fiber crop, although it is a narcotic plant according to the pharmacological classification [4]. Hemp is also an industrial crop with a billion-dollar industry in different parts of the world. However, hemp is a multipurpose crop with more than 25,000 products distributed over several submarkets that include agriculture, automotive, food and beverages, construction, personal care and textiles [5]. Some of the products/value added products of hemp are shown in Figure 1. In Figure 1, the parts of hemp that have industrial related applications and properties are shown inside the circle (flowers, leaves, fibres from stem, roots, seeds, and insect repellent properties) while the industrial uses of each plant parts/ properties are shown outside the circle. For example, flowers and seeds can be used for production of cosmetics, extract essential oils, and leaves are used to extract Cannabinoid (CBD) and Tetrahydrocannabinol (THC) in pharmaceutical industry. Insect repellent properties can be used to produce pesticides.
Figure 1: Industrial uses of different parts of hemp plant (Cannabis sativa L.)
After it’s domestication in China, hemp was introduced across the world [6, 7]. Currently, it is mainly grown in temperate countries and according to the FAOSTAT database, the seed yield data are available for 6 countries; Chile, China, Iran, Russian Federation, Turkey and Ukraine [8]. Industrial cultivation and experiments have been reported from USA [9, 10], China [11], Italy [12], Europe and several other countries [13, 14]. Cannabis for medicinal purposes has been partially or fully legalized in 36 countries [14]. A hemp renaissance within last three decades has led to extensive research work on different aspects of its development such as agronomy [15], industrial properties [16], energy source [17], environmental benefits [18], suitability assessment [13, 19], pharmaceutical value [20, 21, 22] and many more [23].
A thorough search of the relevant literature yields limited hemp research in the South and Southeast Asian region. However, there is ample evidence that hemp is of interest in the region. Cultivation of traditional fiber hemp was reported among tribal people in Thailand [24, 25]. There is a growing interest on Cannabis research in Malaysia [26]. The traces of illegal Cannabis cultivation have been reported from other tropical countries that include Sri Lanka [27], India [28] and Indonesia [29]. It is also used as a traditional and folkloric medicine for aphrodisiacs and treatments for pain in Sri Lanka and India. In India it has been used in Ayurvedic medicine since 3rd to 8th centuries BCE for treatment of phlegm, diarrhea and catarrh [30]. Using a crop modelling approach, Wimalasiri et al. [13] showed that hemp has characteristics of a crop for the future in Malaysia due to its comparatively higher economic returns under both current and future climate.
Due to its cultural and political barriers, very limited research has been done on hemp in the South and Southeast Asian region. However, unexploited potential exists on hemp as an agricultural commodity in tropical environments. Therefore, the objective of this review is to study the potentials and challenges of hemp (Cannabis sativa L.) as an industrial crop in tropical South and Southeast Asia using a systematic approach.
Review of the literature was done according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [31, 32].
2.1 Data acquisition and analysis 2.1.1. Search strategyThe electronic search was conducted with the terms of hemp or marijuana or Cannabis or Cannabis sativa or Cannabis indica or Cannabis ruderalis AND potentials or AND opportunities AND challenges or constraints AND agriculture or agronomy OR crop OR income generation or multipurpose or fiber or environmental benefits or biomass or herb or livestock or genetic resources OR genetic diversity OR Cannabinoid/cannabidiol (CBD) or Tetrahydrocannabinol (THC) or phytocannabinoids AND South Asia (Bangladesh, Bhutan, India, Pakistan, Nepal, and Sri Lanka) or South East Asia (Brunei, Burma (Myanmar), Cambodia, Timor-Leste, Indonesia, Laos, Malaysia, the Philippines, Singapore, Thailand and Vietnam) in Science direct, Scopus (Scopus Elsevier Properties, S.A, USA), Web of science core collection (Clarivate analysis, Philadelphia, PA), biological collection and Agricultural and environmental sciences data bases. The additional hand searched articles and bibliographies associated with this publication were included in references. The search criteria are available in Appendix A.
2.1.2. Eligibility criteriaThe main selection criterion was peer reviewed publication that are published in English and analyse the potentials and opportunities for hemp cultivation related to South Asian and Southeast Asian countries until August 2021. Publication in other languages, other countries, conference abstracts and review articles were excluded due to limited number of available articles.
All search results were exported to the EndNote X9.3.3 (Clarivate analysis, Philadelphia, PA) and duplicates were removed. Manual duplicate removal and pre-sorting was carried out in Excel. The data extracted were author, year of publication, the aim of publication, result and methodology, potential, drawbacks and future trends, country, keywords. Figure 2 shows an overview of the decision process that was used to identify proper research articles.
Figure 2: Overview of the methodology used in the search process, identification, screening and inclusion
The preliminary search retrieved 12,210 studies while duplicate removal led to only 10,203 studies. Out of them, 9140 articles were removed by applying exclusion criteria. Reasons for exclusion were relevance, not related to South or South East Asian countries, focused on pharmaceutical development, sociology, full text inaccessibility and lack of specificity. Then 52 articles were retrieved for analysis and 16 articles were removed due insufficient information (n = 3), inaccessibility (n = 1), focus only on medical properties (n = 6), and not related (n = 6). Finally, thirty-six (36) articles were selected for the review after accessing the full text. The main findings on potentials and constraints/drawbacks on hemp as an industrial crop in tropical South and Southeast are tabulated in Table 1 and 2.
Pharmaceutical properties, diverse range of products (multipurpose crop), phytoremediation, higher productivity and economic benefits, and climate suitability and higher yield potential were identified as the key potentials of hemp as an industrial crop in tropical South and Southeast Asia. The major constraints were legal barriers, competition from similar products (especially for fiber), health effects and addiction (Table 1 and 2).
Out of the selected papers (36), 6 papers were published before year 1990, 4 during 1991–2000, 6 during 2001 to 2010 and 20 after year 2010. Comparatively higher number of related published in the last decade which shows the growing interest of Cannabis in the study region. The number of published papers in each year is available in Appendix (Figure A1). The corresponding authors of 16 papers (44.4%) were from the countries in the South and Southeast Asian region.
3.1 Genetic diversity/ varieties/ accessionsThere are three main types of Cannabis around the world. The utilization of these three types/varieties are dependent on their chemical composition and the agronomic traits of the plants. Cannabis plants with more than 0.5 percent Δ 9 - tetrahydrocannabinol (THC) are classified as drug-type plants according to Cannabis classification on forensic and legal purposes [57]. Any plant that exceeds 1.00 in the phenotypic index (%THC + % Cannabinol)/%CBD is considered a drug Cannabis while the value is less than 1.0, the plant is non-drug Cannabis. The delta-9 tetrahydrocannabinols content of Cannabis sativa, which is also considered as the industrial hemp, is less than 0.3% [60]. Out of the 104 cannabinoids that have been identified, most of the pharmacological activities are ascribed to the Tetrahydrocannabinol (THC) [55]. Genotypes containing less than 0.2% of THC are allowed for cultivation in Europe, which most of them contain non-psychoactive cannabinoids such as CBD [56]. French origin Futura 75 which yields comparatively higher fiber content was also recommended as a cultivar suitable for mountainous regions, which allows the expansion of the cultivation in hilly areas [56]. Depending on various genetic, agro-environmental and the crop management practices that includes harvesting time, storage and drying conditions, the concentration of the cannabinoids can vary [57]. The industrial hemp (C. sativa) is grown for its fiber or for developing medicine.
Cannabis for both seed and fiber can be grown in South and Southeast Asia which consists of diverse agro-climatic conditions. Due to the lack of genetic materials suited for tropical climatic conditions, the development of suitable varieties is essential to introduce Cannabis in the target study area.
3.2 Growth and Environmental Requirements/ Propagation 3.2.1 Growth requirements/ propagationHemp is an open pollinated plant which contains highly heterozygous seeds [55]. Hemp can be propagated either sexually or asexually [55]. Propagation of hemp through seeds is difficult due to the dioecious nature of the plant and since male and female flowers are on different plants. The plant also shows allogamous (cross fertilization) properties, which resulted in inconsistency in its cannabinoid content and chemical profile if the plants are grown from seeds [55]. Due to the large-scale production of true-to-type plants and their fast propagation, tissue culture techniques are being used to propagate Cannabis [55]. Micropropagation techniques can be used as an alternative to traditional paradigms of propagation and C. sativa improvement [55].
3.2.2 Environmental requirementsHemp is originated in humid and temperate region of the world [55]. Field growing conditions of the hemp has showed that they can be cultivated in the hilly areas with a milder climate ranging from 1,000 to 2,800 m. Generally, Cannabis is found on high northern slopes above 1,000 m and performs well in fertilized fields. It is a hardy crop and the cultivation does not require weeding or irrigation which justifies its cultivation as an economical crop for the future. It is cultivated widely in the temperate climates of Europe and North America, it can be found in tropical Asia [39]. Although few studies reported that hemp is grown throughout the Himalayas below 2500 m which is under temperate Asian conditions [38]. Hemp is gown easily in most climates and it is reported that hemp can enrich poor soils after every crop harvest [40]. Therefore, it is suggested that hemp can be grown in most of the South and Southeast Asian regions industrially.
Due to the lack of legalized cultivation in the region, the climate suitability and growth requirements of hemp were poorly documented. However, using a modelling approach [13], it is shown that industrial hemp can be successfully grown in Malaysia, which is a tropical South Eastern country. Hemp performs well under diverse climate characteristics in Pakistan which include sub-tropical climates [64].
3.3 Environmental benefitsHemp plants are attributed to comparatively higher biomass, a higher tolerance to heavy metal stress and a high metal accumulation ability. Therefore, hemp can be used for phytoremediation in contaminated soils. The ability of hemp plant to accumulate Zn, Cd, Pb, Ni and Cr has been demonstrated in literature, interestingly the high biomass of the plant and the long root system with 180-day short life cycle of hemp make its suitability for enhance the phytoremediation in contaminated soils by waste sludge enriched with heavy metals, industrial wase and municipal wastes. Hemp performs well in poor soils with high pH and clay where other crops fail to grow and yield properly without proper land preparation and soil management [39].
An excellent CO2 sequestering capacity of hemp has been observed due to the high (around 85%) cellulose content [40]. Hemp is a good carbon sequester on which 1000 kg of hemp sequester around 1500 kg of CO2 [40]. Environmental benefits of Cannabis plant are shown in Figure 3. As a summary, these benefits include bio-insecticide (due to secondary metabolites), weed control, phytoremediation, soil quality improvement and environmental purification.
Figure 3: Environmental benefits of Cannabis plants
The hemp leaves are considered anthelmintic; therefore, it is used to cure stomach-pain caused by intestinal worms. Seed oil are used to cure skin burns while the juice on crushed leaves relieves earache [38]. In Sri Lanka, Ayurvedic medicines with varied quantities of Cannabis are readily available [53]. Hemp is a vital medicinal plant with pharmacologic and therapeutic potency [55]. Cannabis is a potential drug for therapeutic purposes due to its analgesic, antiemetic, appetite stimulant and anti-inflammatory properties [55]. The potential of Cannabis in the management of chronic non-communicable health problems such as asthma, cancer, glaucoma, cachexia, HIV/AIDS, hypertension and etc., [40]. In ancient China, Cannabis has been used for its sedative properties in curing pain and illness, countering the effect of evil spirit [40]. Potential used of phytocanabionoids in drug development is a promising area of biomedical sciences. It has been reported that various types of phytocanbiniods extracted from Cannabis plants have unelucidated potential for curing neurodegenerative diseases [65].
3.4.1 Negative health impactThere are ample evidence that young people, even schoolchildren, are abusing these narcotic preparations, posing a hazard not just to their health but also to society [52, 53]. In Nepal, due to its indiscriminate use, few cases have been documented with the need for medical treatment [55]. All Cannabis users were untidy, unkempt, slovenly, and slow. They did not want to mix with anybody other than members of their own group of Cannabis smokers. Their interest was limited to themselves, to the herb, to their akhada’ (places where Cannabis users meet) and to food of a rich and sweet nature such as cakes and sweet drinks. Their physical activity was also limited [55]. Systematic alterations in social behaviour are associated with both acute and daily doses of Cannabis [54]. Among the less experienced users, the inhibition of social interaction was reported due to the marijuana intoxication. Some researchers showed that heavy intoxication is associated with the difficulties in speaking to cognitive impairment due to the pharmacologic properties of Cannabis [54]. “The motivational syndrome” which is characterized by reduction in drive, apathy and difficulty in following routines are some of the social reactions to marijuana [54]. Due to the situational context of use and the associated specific norms, the effects of marijuana are generally internally oriented [54]. One is to make Cognitive experience and more salient non-social activities are pharmacologic effects of marijuana intoxication [54]. Heavy users of marijuana tend to react more to the social context of use compared to the pharmacological effect [54]. When a reasonably high level of marijuana intake is obtained and maintained, results indicate that tolerance to many of the acute and long-term effects of marijuana develops [54]. However, the effect on psychoactive behaviours upon the consumption has been associated with the doses exposed and their post exposure behaviours directly related to the genetic factors of the person exposed and the quantity consumed. The summary of the negative health impact of Cannabis plants is shown in Figure 4.
3.5 Uses/ Value-added productsCannabis is one of the world’s oldest food, fiber, and oil-producing plants (15). With the long history of being known to humans, industrial hemp has been used for a diverse range of applications that include fibers (for cloths and a construction material), seed as a food source and essential oil and secondary metabolites/extractions in pharmaceutical applications [66]. Due to the wide range of applications, the cultivation of industrial hemp is expected to increase in coming years [56]. Some of the other applications include fiber for automotive industry, paper and construction, cosmetics, nutraceuticals, inks and varnishes, plant biomass for bioenergy and animal feed [35, 56]. A special product, more potent and expensive, is called chares. The usual method of using this is by smoking in a funnel-shaped clay pipe, but it is also used in cakes or sweets and drinks [55]. The products of Cannabis can be consumed in a variety of ways; in baked products, smoking, vaporizing and as a tea [57]. Few ethnic regions of Asia use Cannabis as food and fiber in various ways. The indigenous and ethno-botanical uses Cannabis seed, seed oil, seed cake, inflorescence and fiber has been reported in India [38]. When considering all these applications and uses, it is evident that hemp is a multi-purpose crop [56]. Some of the uses of Cannabis plant which are obtained from different plant parts are shown in Figure 1.
Figure 4: Negative health impact of Cannabis plants
Even though traces of Cannabis cultivation have been found in tropical South and Southeast Asian countries, no proper scientific investigation has been carried out in the region. This may be associated with the legal restrictions along with the lack of resources. Some recent simulation using state of the art in data and methods has shown a tremendous potential. The AquaCrop crop model was parameterized to simulate hemp seed and fiber yield in Malaysia which is a promising tool to apply to other countries in the region [51]. Also, using crop and climate modelling, climate and soil suitability and economic assessments, Cannabis was proposed as a crop for the future in Malaysia [13]. The agroclimatic characteristics of hemp is suitable for tropical Malaysia. The higher economic returns are expected under both current and future climates in similar agro-climatic conditions [13].
Cannabis is a multi-billion-dollar industry which is gaining popularity in many parts of the world. Even though this crop is not yet a commercially available crop, it is not a new crop in several South and Southeast Asian countries, as traces of illegal and/ or traditional cultivation is found in some locations [27, 29]. However, both potentials and constraints exist on the introduction and popularization of the cultivation in the region of interest.
The yield and harvest index of industrial hemp varies among locations [19, 67]. Also, it was reported that agroecological conditions have a major impact on the performance of the crop [67, 68]. Due to the legal restrictions, region-specific cultivars do not exist according to the knowledge of authors. Therefore, proper cultivars that are specific for seed and fiber production should be selected/tested for different locations/countries in the region before start the commercial level cultivations. Existing cultivars that are rich in CBDs can also be used in plant breeding programs. Despite the fact that Cannabis has been legalized and approved as an agricultural crop in many countries throughout the world, there is still a lack of public Cannabis germplasm repositories [69] that can negatively affect the promotion of the crop in South and Southeast Asia.
Even though the environmental benefits of hemp were not widely documented in South and South-East Asia, numerous hemp associated environmental benefits were reported. Hemp has remarkable insecticidal, phytoremediation and carbon capturing properties. Secretory structures (glandular trichomes) of hemp produce essential oils that are made from monoterpenes and sesquiterpenes on which the plant used to repel and/ or entrap insect pests. Therefore, the potential exists on the production of bio pesticides and the insect repellents (mosquitos, houseflies and moth vectors) using essential oils from the hemp plants. Due to resistance to pests and diseases, it can be cultivated without/with the minimum synthetic pesticides, which makes hemp an eco-friendly crop [66]. Furthermore, hemp essential oils have shown antimicrobial, antileishmanial, nematicidal, and allelopathic properties. The essential oils from hemp inflorescence and leaf were found to be effective against 3 insect types namely; the larvae of Culex quinquefasciatus and Spodoptera littoralis and the adults of Musca domestica [66]. Another key importance of hemp essential oils as a natural pesticide is they do not harm the non-target species and nor cause insect resistance. This justifies that hemp is a good candidate for pull-push system in ecological agriculture.
Agricultural decision-making tools and frameworks have been developed and applied in the region of interest for several crops including industrial hemp [13, 70]. With the increased availability of supportive data (climate and soil), crop model applications along with potential yield mapping which assist in agricultural decision making are under development in the region [13, 71]. Further, specific crop models for Cannabis such as Hcrops [19] which was developed in Italy using the SEMoLa framework [72] can be used for yield simulations. However, unavailability of specific crop module in major crop models like Agricultural Production Systems Simulator (APSIM) and Decision Support System for Agrotechnology Transfer (DSSAT) hinders the crop modelling [13].
Other than the regular/conventional agronomic research, new areas related to Cannabis have been exploited. Lyu et al. [73] studied the impact of plant growth promoting rhizobacteria on Cannabis production, its chemical profile and disease resistance which new research avenues in the study region. Moreover, the cultivation in the region can take advantage of advanced research that will increase both quantity and the quality of production that include appropriate fiber and oil characteristics. It also exhibits potential to be used in ecological farming as an insect repellent, since its secondary metabolites can be used for plant based pesticide development [74]. Some countries in this region, especially Sri Lanka are promoting fully organic agriculture [75] and looking for alternatives for synthetic agrochemicals and introduction of hemp will be an added advantage for the organic agriculture concept.
Due to its myriad of benefits, some of the countries with similar climates have legalised cannabis cultivation. Zimbabwe is a good example on which the cultivation was legalised in year 2022 and extensive breading programmes are being carried out. The success stories can be adapted to South and South East Asian countries. The policies and legal aspects related to Cannabis cultivation in South and Southeast Asian countries will be discussed in a separate article.
According to the systematic review, a huge potential on hemp cultivation exists in the tropical South and Southeast Asian region in terms of environmental, health, agronomic and economic benefits. The results suggest that Cannabis should be introduced as a viable crop for the future in the region. To start commercial cultivation, several key aspects should be addressed that includes 1) development of region/location specific cultivars, 2) introduction of site/cultivar specific management practices and 3) development of proper market facilities. Above all, the rules and regulations of respective countries in the region should be relaxed.
Search criteria (example for South East Asia)
2. Title (TI) = (Cannabis OR hemp OR Marijuana*)
3. #1 OR #2
4. TS = (Cannabis* OR potentials OR constrains OR opportunities OR challenges OR income generation) AND (South East Asia*)
5. TI = (Cannabis* OR potentials OR constrains OR opportunities OR challenges OR income generation) AND (South East Asia*)
6. #4 OR #5
7. TS = (Agriculture OR Agronomy OR crop OR industry OR livestock OR biomass) AND (South East Asia*)
8. TI= (Agriculture OR Agronomy OR crop OR industry OR livestock OR biomass) AND (South East Asia*)
9. #7 OR #8
10. TS = Environmental benefits OR multipurposed OR fibre OR pharmaceuticals OR CBD OR THC OR Herb) AND (South East Asia*)
11. TI= (Environmental benefits OR multipurposed OR fibre OR pharmaceuticals OR CBD OR THC OR Herb) AND (South East Asia*)
12. #10 OR #11 AND (South East Asia*)
Search was also carried out with the names of individual South and Southeast Asian countries and Cannabis sativa, Cannabis indica and Cannabis rudealis.
Figure A1: Annual distribution of publications considered in the systematic review
