A Belated Green Revolution for Cannabis: Virtual Genetic Resources to Fast-Track Cultivar Development
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REVIEW published: 29 July 2016 doi: 10.3389/fpls.2016.01113 A Belated Green Revolution for Cannabis: Virtual Genetic Resources to Fast-Track Cultivar Development Matthew T. Welling 1, Tim Shapter 1, 2, Terry J. Rose 1, Lei Liu 1, Rhia Stanger 1 and Graham J. King 1* 1 Southern Cross Plant Science, Southern Cross University, Lismore, NSW, Australia, 2 Ecofibre Industries Operations Pty Ltd, Maleny, QLD, Australia Cannabis is a predominantly diecious phenotypically diverse domesticated genus with few if any extant natural populations. International narcotics conventions and associated legislation have constrained the establishment, characterization, and use of Cannabis genetic resource collections. This has resulted in the underutilization of genepool variability in cultivar development and has limited the inclusion of secondary genepools associated with genetic improvement strategies of the Green Revolution. The structured screening of ex situ germplasm and the exploitation of locally-adapted intraspecific traits is expected to facilitate the genetic improvement Edited by: Jaime Prohens, of Cannabis. However, limited attempts have been made to establish the full extent of Polytechnic University of Valencia, genetic resources available for pre-breeding. We present a thorough critical review of Spain Cannabis ex situ genetic resources, and discuss recommendations for conservation, Reviewed by: pre-breeding characterization, and genetic analysis that will underpin future cultivar Ryan C. Lynch, University of Colorado Boulder, USA development. We consider East Asian germplasm to be a priority for conservation Giuseppe Mandolino, based on the prolonged historical cultivation of Cannabis in this region over a range Council for Agricultural Research and Economics, Italy of latitudes, along with the apparent high levels of genetic diversity and relatively *Correspondence: low representation in published genetic resource collections. Seed cryopreservation Graham J. King could improve conservation by reducing hybridization and genetic drift that may [email protected] occur during Cannabis germplasm regeneration. Given the unique legal status of Specialty section: Cannabis, we propose the establishment of a global virtual core collection based on This article was submitted to the collation of consistent and comprehensive provenance meta-data and the adoption Crop Science and Horticulture, of high-throughput DNA sequencing technologies. This would enable representative core a section of the journal Frontiers in Plant Science collections to be used for systematic phenotyping, and so underpin breeding strategies Received: 29 April 2016 for the genetic improvement of Cannabis. Accepted: 13 July 2016 Keywords: genetic conservation, industrial hemp, marijuana, phenotypic variation, plant breeding, cannabinoids Published: 29 July 2016 Citation: Welling MT, Shapter T, Rose TJ, Liu L, INTRODUCTION Stanger R and King GJ (2016) A Belated Green Revolution for Cannabis: Virtual Genetic Resources Cannabis, an erect annual herb and member of the Cannabaceae family, is monotypic and to Fast-Track Cultivar Development. characterized by a single species Cannabis sativa L. (Small and Cronquist, 1976). Plants are diploid Front. Plant Sci. 7:1113. (2n = 20) with an estimated haploid genome of ∼830 Mb (Van Bakel et al., 2011). The extant doi: 10.3389/fpls.2016.01113 genepool is thought to be comprised primarily of domesticated or feral populations, cultivars, Frontiers in Plant Science | www.frontiersin.org 1 July 2016 | Volume 7 | Article 1113 Welling et al. Belated Green Revolution for Cannabis and selections (Small and Cronquist, 1976), with a subset having This deterioration in conservation of industrial hemp genetic been subject to steep selective gradients toward phenotypes resources is not consistent with the intrinsic functionality or for specific end-uses (Mandolino and Carboni, 2004; Potter, agricultural value of the species. The long pericyclic and phloem 2014; Small, 2015a). Cannabis has been cultivated in Eurasia fibers in the bast fraction of the culm (stem) have high tensile over several thousand years (Li, 1974; Bradshaw et al., 1981; strength, and were used for millennia as the predominant source Murphy et al., 2011; Herbig and Sirocko, 2013) and has since of fiber for the production of rope (Murphy et al., 2011). They radiated from this region and been subject to prolonged artificial have also been used in the textile and paper industries (Amaducci selective pressures in Africa (Duvall, 2016) and North and South et al., 2014), as well as in fiber mat thermoplastics for automobile America (Small and Marcus, 2002), and is now cultivated globally manufacture (Pervaiz and Sain, 2003). The woody core or hurd (Salentijn et al., 2014). Plants are diecious and obligate outbred, (shives) within the xylem vascular tissue, comprising up to although some fiber forms are monecious (Faeti et al., 1996). This 70% of the stem biomass (De Meijer, 1994), has also found has contributed to a high level of hybridization between pre-, minor low value use in the production of lime-hemp concrete, post-, and de-domesticated populations (Gilmore et al., 2007), a light composite building material (De Bruijn et al., 2009), as and therefore few if any intact wild populations are thought to well as animal bedding and garden mulch (Pervaiz and Sain, exist (Small and Cronquist, 1976). 2003). Achene (seeds) are also suitable for human and animal The Green Revolution saw the productivity of major crops consumption and contain all essential amino acids (Callaway, such as wheat (Triticum spp.), rice (Oryza sativa), maize (Zea 2004), with the exception of lysine, (House et al., 2010) in a mays), sorghum (Sorghum bicolor), and millet (Pennisetum readily bioavailable form (Malomo and Aluko, 2015), as well as glaucum) increase by 0.5–1% annually between 1960 and 2000 a balanced omega-6/omega-3 essential polyunsaturated fatty acid (Evenson and Gollin, 2003). A large proportion of these gains (PUFA) ratio (Callaway, 2004; Carvalho et al., 2006; Da Porto has been attributed to germplasm improvements initiated by et al., 2012). the Consultative Group on International Agricultural Research In addition to the traditional uses in paper and textile (CGIAR; Hajjar and Hodgkin, 2007), which facilitated genetic industries, a number of novel end-use applications for Cannabis resource exchange, adaptive transfers, and the free flow of are currently being explored. These include cellulosic bioethanol materials and knowledge between research groups (Pingali, which can be extracted from plant biomass and utilized as 2012). However, the genetic improvement of crop-types was a potential transportation biofuel (Finnan and Styles, 2013; not evenly distributed (Evenson and Gollin, 2003). During the Kuglarz et al., 2016). Higher value products being assessed latter part of the twentieth century legitimate crop-types of include cellulose nanocrystals, which have been generated from Cannabis, commonly referred to as industrial hemp, not only low quality fibers (Li et al., 2010) for the development of high- failed to benefit from advances in breeding technologies and performance nanocomposites (George and Sabapathi, 2015), genetic resource utilization, but also suffered significant losses while graphitic carbon nanosheets developed from hemp bast in ex situ conservation (Clarke, 1998; Small and Marcus, 2002; fiber precursors have been shown to have ionic-liquid-based Ranalli, 2004), with likely significant genetic erosion, as has been supercapacitor properties (Wang et al., 2013). documented with the loss of rice wild relatives in China (Gao, The phenolic compounds N-trans-caffeoyltyramine and 2003). cannabisin B (Chen et al., 2012), as well as prenylflavonoids The major contributing factor to the erosion of Cannabis cannflavins A and B (Werz et al., 2014) occurring within seed genetic resources and limited genetic improvement of industrial husks and sprouts, respectively, may have potential nutraceutical hemp has been the status of Cannabis as the source of one of applications. In addition, Cannabis plants produce a group the most widely used illicit drugs (Hall and Degenhardt, 2007). of pharmacologically active terpenophenolic phytocannabinoids Marijuana refers to an informal subtaxa of Cannabis which has (cannabinoids; ElSohly and Slade, 2005; Appendino et al., been selected specifically for its psychoactivity and propensity to 2011). These compounds are currently fueling an emerging accumulate high levels of delta-9-tetrahydrocannabinol (THC; cannabinoid-based pharmaceutical industry (Potter, 2014), with Hewavitharana et al., 2005). The prohibition on marijuana, botanical extracts being safely and efficiently administered which is morphologically indistinguishable from other forms via oromucosal sprays (Izzo et al., 2009) and by electrically- of Cannabis (Small and Cronquist, 1976; Small, 2015a), has driven vaporizers (Lanz et al., 2016). Other terpenoid-related contributed to the decline of industrial hemp (Small and Marcus, compounds that are present at high concentrations in Cannabis 2003; Piluzza et al., 2013; Small, 2015a). In recent years there may also contribute to pharmacological entourage effects (Russo, has been growing public acceptance that medical cannabis has 2011), or have their own specific medicinal applications, such therapeutic applications, which has been particularly prominent as α-humulene which has antifungal properties potentially in a number of states of the USA, along with Australia,