Chemical and Morphological Phenotypes in Breeding of Cannabis sativa L.
Gianpaolo Grassi and John M. McPartland
in S. Chandra et al. (eds.), Cannabis sativa L. – Botany and Biotechnology, Chapter 6, 2017, 137-160.
Doi : 10.1007/978-3-319-54564-6_6
This chapter has two parts. The first part details five characters that contribute to phenotypic diversity in Cannabis. Cannabinoids can be assayed by quantity (dry weight percentage of cannabinoids in harvested material) or by quality (the THC/CBD ratio, or chemotype). Cannabinoid quality is largely genetic, possibly monogenic. We dissect the monogenic inheritance model (two alleles at a single gene locus). Essential oil is composed of volatile, aromatic terpenoids. Terpenoid content varies between different varieties. Hemp seed oil consists of polyunsaturated fatty acids, including omega-6 and omega-3 fatty acids, which are under genetic control. Protein has received less attention than oil, despite hemp’s value as a protein supplement. Bast fibers are phloem (sap-conducting) cells in stalks. The second part presents the current breeding status of phenotypes for various uses. Breeding for fiber production includes monoecious cultivars, dioecious cultivars, high percentage of primary fiber, fast-retting phenotypes, and unique morphological markers in low-THC plants. Selective cross-breeding for cannabinoids includes prevalent-THC, prevalent-CBD, and cannabinoid-free plants. Relatively few cultivars have been bred specifically for seed production.
A century ago, Italian farmers grew over 100,000 ha of industrial hemp annually (Ranalli and Casarini 1988). Seed for sowing was self-produced by the farmers. Breeding was by mass selection, where many individuals with desirable phenotypes were selected and their seeds harvested. Taller and thicker females were left in the field after complete fertilization because harvesting was done by hand. Local improvements gave rise to many landraces named after the province where they came from, such as Ferrara, Bologna, Modena, Rovigo, and Carmagnola.
Professional breeders began to crossbreed diverse landraces, subjected them to recurrent selection, and created the first hybrid Cannabis cultivars. Dewey (1928) crossed Ferrara with an inbred Chinese landraces to select ‘Ferramington.’ In Hungary, Fleischmann (1931) inbred landraces from Bologna and Ferrara to create ‘F-hemp.’ In Italy, Crescini (1934) introduced crossing and selfing, using both genders, to study morphological variants in Carmagnola and non-Italian varieties. Hirata (1927) made the first studies on monoecious hemp derived from the ‘Karafuto’ landrace in Japan. In the Soviet Union, Grishko (1935) initiated work that led to monoecious hemp. And in Germany, Neuer and Sengbusch (1943) fixed the monoecious trait, and increased fiber content. Their efforts gave rise to ‘Fibrimon,’ a parent of modern cultivars from France (‘Férimon,’ ‘Fédora,’ ‘Félina,’ ‘Futura,’), Ukraine (‘Juso 11’), Poland (‘Beniko,’ ‘Białobrezskie’), Hungary (‘Uniko B’), and Romania (‘Secuieni 1’).
Plants with unique morphological traits may serve as easy-to-see markers of low-THC crops. Savelli (1932) described Ferrara plants with leaflets webbed into palmate lobes, which Crescini (1956) named the pinnatofidofilla mutation. Allavena (1961) isolated plants with pinnatofidofilla and monofilla (“simple leaf”) while he bred ‘Fibranova’ from Carmagnola, Turkish, and German lines (Fig. 6.1a, b).
de Meijer (1999) provides an excellent summary of 20th century breeding, more extensive than ours here. He describes traditional Italian cultivars, claimed by Clarke and Merlin (2013) as “practically unavailable,” which is not true. Thanks to Bruno Casarini, three industrial hemp varieties are still available: ‘Carmagnola,’ ‘C. S.’ (Carmagnola Selezionata) and ‘Fibranova.’ Their lines remain pure and original because they have been multiplied in alternative years at the experimental station of CREA in Anzola Emilia (Bologna).
Because of space limitations, we refer the reader to other chapters in this book for prerequisite information. See Ernest Small and David Potter for basic anatomy underlying phenotypic variation. For more on genomics and molecular markers, see the chapters by Jonathan Page, Chiara Onofri and Giuseppe Mandolino.