Crop wild relative
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A crop wild relative is a wild plant related closely enough to a crop to pass useful genes to it. In the working definition proposed by Nigel Maxted and colleagues in 2006, it is "a wild plant taxon that has an indirect use derived from its relatively close genetic relationship to a crop", the relationship being set by membership of the crop's gene pools or taxon groups.[1][2]: 56 Breeders draw on these plants for traits such as resistance to pests and diseases. They are held in gene banks and protected where they grow.[3]
John McPartland and Ernest Small named two wild-growing relatives of the drug-type domesticates of Cannabis in 2020.[4] Whether these or any other cannabis populations are wild in the strict sense is disputed. Some authors hold that the wild-growing plants studied so far descend from crops. Others report wild populations in China and think wild relatives likely in remote parts of Asia.[5][6][7]
Ranking the relatives
Two schemes sort a crop's relatives by closeness. The gene pools of Jack Harlan and Jan de Wet rank a relative by how easily it crosses with the crop. The taxon groups of Maxted and colleagues rank it by taxonomic distance, for the many crops with too little crossing data.[8][3] At the close end both schemes stay inside the crop's species: GP1b holds the wild or weedy forms of the crop and TG1b the other members of its species. In grapevine the wild relative is a subspecies of the crop, and olive has wild, weedy and cultivated forms within one species.[3]
The number of crop wild relatives depends on where the line is drawn. If every species in a crop's genus counts, about 21 per cent of the world's flora qualifies, and with wild food plants that comes to 50,000 to 60,000 species worldwide. If only the closest relatives of major and minor food crops count, a working estimate is about 700 species.[3] The Harlan and de Wet inventory holds 1,667 taxa for 173 priority crops, with the most in western Asia, then China and south-eastern Europe.[9]
Genes taken into crops
By 2007 breeders had been using genes from wild relatives for more than 60 years, and cultivars containing such genes were being released at a steadily rising rate. Pest and disease resistance stayed the main emphasis, though a wider range of characters was being introduced. Wheat and tomato, whose relatives had long been used, were the crops most likely to gain new genes in this way.[10] In tomato, five genes for resistance to tomato yellow leaf curl virus came from wild species, and crosses with Solanum pimpinellifolium and another wild tomato led to a 20 per cent rise in yield and soluble solids.[11]
Reem Hajjar and Toby Hodgkin judged the contribution of wild relatives to be less than might have been expected, given better crossing methods and larger holdings of wild accessions.[10] Use is uneven between crops. Possible reasons include how well the plants cross, how closely they are related, how fertile the offspring are, whether the relatives are conserved and available and whether funding exists where they grow.[11]
Collecting and protecting them
A global collecting programme for threatened landraces and wild relatives began in 1975 under the International Board for Plant Genetic Resources. Its more than 1,000 missions in more than 130 countries, most of them before 1995, gathered about 220,000 samples.[3] The International Treaty on Plant Genetic Resources for Food and Agriculture of 2001 asks its parties to promote in situ conservation "of wild crop relatives and wild plants for food production, including in protected areas".[12]: art. 5.1(d)
Gene banks hold few samples of many wild relatives. In a global model of 1,076 taxa related to 81 crops, 313 taxa had no accessions and a further 257 had fewer than ten.[13] Across 23 crop gene pools, leaving out the international CGIAR gene banks, wild relatives made up an unweighted average of 9.6 per cent of accessions, from none for coconut, which has no known wild relatives, to 33 per cent for grass pea.[3]
Of 600 wild relatives native to the United States, more than half may be endangered in their natural habitats.[14] Conserving such plants where they grow keeps them exposed to changing selection, which should generate and favour new variation.[3] This in situ conservation still happens mainly passively, in protected areas with no active management of the plants.[2]: 13 Wild relatives often grow in disturbed and human-made environments, and these are rarely designated as protected areas.[2]: 194 A genetic reserve is an area designated for the active, long-term conservation of such wild populations.[2]: 17 The effectiveness of in situ work is reported to be more uncertain than that of gene banks, and the two can be combined in complementary conservation.[3]
Relatives named for cannabis
In the classification of Small and Arthur Cronquist, Cannabis has a single species.[15] All its populations can cross and are fully interfertile.[4]: 86 The number of species is a matter of taxonomic dispute. Under the single-species treatment its wild-growing plants belong to the crop's own species, the place of GP1b and TG1b. Hops (Humulus) form a separate genus, which split from Cannabis about 27.8 million years ago on one molecular-clock estimate.[16]
McPartland and Small class the wild-growing relatives of the South and Central Asian drug types as C. sativa subsp. indica var. himalayensis and var. asperrima. Their herbarium specimens of these plants run through an arc of mountains: the Hindu Kush, Karakoram, Pamir and Tian Shan in Central Asia and the Himalaya and the Purvanchal Range in South Asia.[4]: 102 They describe the wild-growing populations of montane India, Nepal and Bhutan as "possibly indigenous" and harvested for fibre, bhang, charas and seed.[4]: 97 Both varieties, in their account, are "very significant potential sources of genes" for the endangered domesticated lines. The study leaves out subsp. sativa, whose wild-type variety has borne the names spontanea and ruderalis.[4]: 86
Regional lists treat the plant in different ways. C. sativa is one of the 289 species on a list for the Kazakh Tien Shan, which also takes in medicinal, fodder and other economically valued plants outside the genera of cultivated crops.[17] In a table of wild relatives of ancient crops in Georgia it stands under GP1A and TG1A, the codes for the cultivated form.[18]: 69
Matthew Welling and colleagues count crop wild relatives, along with locally adapted landraces, as a repository from which diversity can return to domesticated populations.[15] In the pangenome study of Ryan Lynch and colleagues, the plants named C. ruderalis are the supposed source of day-neutral (autoflowering) flowering.[7]
Wild or feral
Cannabis changes form quickly once it leaves cultivation. In Canada, domesticated plants returned to a wild-type form about 50 generations after cultivation was prohibited. McPartland and Small hold that change this fast makes truly wild plants hard to tell from reverted ones, and they separate three kinds of plant outside cultivation: volunteers, which escaped recently and keep the crop's characters; escapes that have readapted to wild existence; and "aboriginal" plants, unaltered by domestication and growing in their indigenous areas.[4]: 86
Several authors doubt that aboriginal plants survive. Small judged in 2015 that wild-growing plants are escapes or the result of thousands of years of exchange with domesticated plants, "making it impossible to determine if unaltered primeval or ancestral populations still exist".[19] McPartland and Small place Cannabis among the crops whose aboriginal populations may not have survived.[4]: 86 Welling and colleagues write that few if any intact wild populations are thought to exist.[15] From the whole genomes of 110 accessions, Guangpeng Ren and colleagues concluded that all the feral plants they studied, those from Central Asia among them, were "historical escapes from domesticated forms". They suggested that pure wild progenitors have gone extinct and said that more sampling was still needed in those areas.[5]: 3
Other authors report wild plants. Qingying Zhang and colleagues sampled 25 wild populations in China between 2011 and 2016, from Inner Mongolia, Jilin, Liaoning, Shandong, Xinjiang, Tibet and Yunnan. They called these "the only distribution ranges of extant wild Cannabis" in the country.[6] Xuan Chen and colleagues describe China as "one of the few countries with wild cannabis plants". Their wild class is made up of plants collected from barren fields and judged by phenotype. In their results they write "wild (or feral)".[20] Shan Gao and colleagues assembled a genome from the Kyirong Gully in Tibet and called the plants wild-type.[21] Lynch and colleagues found that assembly significantly divergent from all the domesticated and feral lines they compared and took this to suggest that wild relatives "still exist in remote regions of Asia".[7]
Sampling differs from study to study. Manica Balant and colleagues, for whom the plant's legal status and economic importance make wild-growing populations hard to sample, concentrated on wild-growing plants and landraces from areas sampled little before. Ren and colleagues, in their account, mainly sampled commercial hemp cultivars and drug strains, and sampling bias could be driving differences between the two sets of results. Balant and colleagues proposed that herbarium specimens collected before modern germplasm exchange might "potentially detect some unquestionably wild specimens".[22] Lynch and colleagues called for "careful delineation of wild and feral populations".[7]
The working definition names a "wild plant taxon", while GP1b includes wild or weedy forms of the crop.[2]: 56[3] McPartland and Small hold the wild-growing plants of Asia near the domesticates to be "of special significance" whether or not aboriginal populations survive, since the plant's pollen travels vast distances and makes it likely that they share genes with the crop. The plants may also be the crop's direct ancestors, a point the authors say remains to be ascertained.[4]: 86
Conserving the cannabis relatives
McPartland and Small judged in situ conservation "much preferable" for crop plants and their wild relatives in general. For cannabis they called seed banks "an immediate priority", given "the precarious continued existence of unaltered aboriginal wild populations" in Asia.[4]: 106 Lynch and colleagues wrote that conserving and using Asian hemp and wild cannabis will be critical to breeding.[7] Cannabis is not among the crops listed in Annex I of the Treaty, which sets the crops covered by its multilateral system of access.[12]: 46–49
Other authors and agencies want such plants removed. Canavan and colleagues regard feral cannabis as a possible invader and recommend monitoring for volunteer plants so that these can be removed early.[23] In 2015 the United Nations Office on Drugs and Crime reported 550 hectares of wild cannabis in the Issyk-Kul province of Kyrgyzstan and supported an eradication operation there.[24]
See also
References
- ↑ Maxted, N.; Ford-Lloyd, B.V.; Jury, S.; Kell, S.; Scholten, M. (2006). "Towards a definition of a crop wild relative". Biodiversity and Conservation. 15 (8): 2673–2685. doi:10.1007/s10531-005-5409-6.
- ↑ 2.0 2.1 2.2 2.3 2.4 Maxted, N.; Magos Brehm, J.; Kell, S. (2013). Resource Book for the Preparation of National Plans for Conservation of Crop Wild Relatives and Landraces (PDF). Food and Agriculture Organization of the United Nations.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Engels, J.M.M.; Thormann, I. (2020). "Main challenges and actions needed to improve conservation and sustainable use of our crop wild relatives". Plants. 9 (8) 968. doi:10.3390/plants9080968.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 McPartland, J.M.; Small, E. (2020). "A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives". PhytoKeys. 144: 81–112. doi:10.3897/phytokeys.144.46700.
- ↑ 5.0 5.1 Ren, G.; Zhang, X.; Li, Y.; Ridout, K.; Serrano-Serrano, M.L.; Yang, Y.; Liu, A.; Ravikanth, G.; Nawaz, M.A.; Mumtaz, A.S.; Salamin, N.; Fumagalli, L. (2021). "Large-scale whole-genome resequencing unravels the domestication history of Cannabis sativa". Science Advances. 7 (29) eabg2286. doi:10.1126/sciadv.abg2286.
- ↑ 6.0 6.1 Zhang, Q.; Chen, X.; Guo, H.; Trindade, L.M.; Salentijn, E.M.J.; Guo, R.; Guo, M.; Xu, Y.; Yang, M. (2018). "Latitudinal adaptation and genetic insights into the origins of Cannabis sativa L." Frontiers in Plant Science. 9 1876. doi:10.3389/fpls.2018.01876.
- ↑ 7.0 7.1 7.2 7.3 7.4 Lynch, R.C.; Padgitt-Cobb, L.K.; Garfinkel, A.R.; Knaus, B.J.; Hartwick, N.T.; et al. (2025). "Domesticated cannabinoid synthases amid a wild mosaic cannabis pangenome". Nature. 643 (8073): 1001–1010. doi:10.1038/s41586-025-09065-0. PMC 12286863.
- ↑ Harlan, J.R.; de Wet, J.M.J. (1971). "Toward a rational classification of cultivated plants". Taxon. 20 (4): 509–517. doi:10.2307/1218252.
- ↑ Vincent, H.; Wiersema, J.; Kell, S.; Fielder, H.; Dobbie, S.; et al. (2013). "A prioritized crop wild relative inventory to help underpin global food security". Biological Conservation. 167: 265–275. doi:10.1016/j.biocon.2013.08.011.
- ↑ 10.0 10.1 Hajjar, R.; Hodgkin, T. (2007). "The use of wild relatives in crop improvement: a survey of developments over the last 20 years". Euphytica. 156 (1–2): 1–13. doi:10.1007/s10681-007-9363-0.
- ↑ 11.0 11.1 Zhang, H.; Mittal, N.; Leamy, L.J.; Barazani, O.; Song, B.-H. (2017). "Back into the wild—Apply untapped genetic diversity of wild relatives for crop improvement". Evolutionary Applications. 10 (1): 5–24. doi:10.1111/eva.12434. PMC 5192947.
- ↑ 12.0 12.1 Food and Agriculture Organization of the United Nations. International Treaty on Plant Genetic Resources for Food and Agriculture (PDF). Rome: FAO.
- ↑ Castañeda-Álvarez, N.P.; Khoury, C.K.; Achicanoy, H.A.; Bernau, V.; Dempewolf, H.; et al. (2016). "Global conservation priorities for crop wild relatives". Nature Plants. 2 (4) 16022. doi:10.1038/nplants.2016.22.
- ↑ Khoury, C.K.; Carver, D.; Greene, S.L.; Williams, K.A.; Achicanoy, H.A.; et al. (2020). "Crop wild relatives of the United States require urgent conservation action". Proceedings of the National Academy of Sciences. 117 (52): 33351–33357. doi:10.1073/pnas.2007029117. PMC 7776777.
- ↑ 15.0 15.1 15.2 Welling, M.T.; Shapter, T.; Rose, T.J.; Liu, L.; Stanger, R.; King, G.J. (2016). "A belated green revolution for Cannabis: virtual genetic resources to fast-track cultivar development". Frontiers in Plant Science. 7 1113. doi:10.3389/fpls.2016.01113.
- ↑ McPartland, J.M. (2018). "Cannabis systematics at the levels of family, genus, and species". Cannabis and Cannabinoid Research. 3 (1): 203–212. doi:10.1089/can.2018.0039.
- ↑ Sitpayeva, G.T.; Kudabayeva, G.M.; Dimeyeva, L.A.; Gemejiyeva, N.G.; Vesselova, P.V. (2020). "Crop wild relatives of Kazakhstani Tien Shan: flora, vegetation, resources". Plant Diversity. 42 (1): 19–32. doi:10.1016/j.pld.2019.10.003.
- ↑ Akhalkatsi, Maia; Ekhvaia, Jana; Asanidze, Zezva (2012). "Diversity and Genetic Erosion of Ancient Crops and Wild Relatives of Agricultural Cultivars for Food: Implications for Nature Conservation in Georgia (Caucasus)". In Tiefenbacher, John (ed.). Perspectives on Nature Conservation: Patterns, Pressures and Prospects. Rijeka: InTech. doi:10.5772/30286. ISBN 978-953-51-0033-1.
- ↑ Small, E. (2015). "Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization". Botanical Review. 81 (3): 189–294. doi:10.1007/s12229-015-9157-3.
- ↑ Chen, Xuan; Guo, Hong-Yan; Zhang, Qing-Ying; Wang, Lu; Guo, Rong; Zhan, Yi-Xun; Lv, Pin; Xu, Yan-Ping; Guo, Meng-Bi; Zhang, Yuan; Zhang, Kun; Liu, Yan-Hu; Yang, Ming (2022). "Whole-genome resequencing of wild and cultivated cannabis reveals the genetic structure and adaptive selection of important traits". BMC Plant Biology. 22 (1) 371. doi:10.1186/s12870-022-03744-0.
- ↑ Gao, Shan; Wang, Baishi; Xie, Shanshan; Xu, Xiaoyu; Zhang, Jin; Pei, Li; Yu, Yongyi; Yang, Weifei; Zhang, Ying (2020). "A high-quality reference genome of wild Cannabis sativa". Horticulture Research. 7 (1) 73. doi:10.1038/s41438-020-0295-3.
- ↑ Balant, Manica; Vitales, Daniel; Wang, Zhiqiang; et al. (2025). "Integrating target capture with whole genome sequencing of recent and natural history collections to explain the phylogeography of wild-growing and cultivated cannabis". Plants, People, Planet. 7 (6): 1771–1788. doi:10.1002/ppp3.70043.
- ↑ United Nations Office on Drugs and Crime, Regional Office for Central Asia (2015). "UNODC supports the eradication of wild cannabis in Kyrgyzstan". UNODC. Retrieved 13 October 2026.