Comparison of Hemp Varieties Using Random Amplified Polymorphic DNA Markers

to allow cultivation of hemp varieties with a 9–THC content below 0.3%. By 1998 hemp was reintroduced The objective was to study the genetic structure and degree of in practically all of Europe (Bócsa and Karus, 1998), variability of hemp (Cannabis sativa L.) varieties. Six varieties of hemp were analyzed by random amplified polymorphic DNA though in some countries significant resources are still (RAPD) analysis, using 10 plants per variety. The varieties were a being employed to prevent hemp diffusion regardless dioecious landrace, a dioecious selection from it, a cross-bred cultivar, of its 9–THC content (Linacre and Thorpe, 1998). a monoecious variety, a drug strain, and an inbred female line. The Because of the continuous variation of most morphogenetic complexity of each cultivar was investigated by determining logical and biochemical traits within the Cannabis genus, the number of bands produced by the primers used, the number of it would be useful to identify groups on the basis of fixed and polymorphic loci, the average allele frequency, and the their use or origin. A nonbiosystematic classification heterozygosity. A good correlation was found between these paramedistinguishes wild populations from fiber landraces, culters and the genetic origin and breeding strategy of each variety. The tivars, drug strains, and ornamentals (de Meijer, 1995). average polymorphism over all varieties and loci was 97.1%; the single Hemp cultivars are characterized by different degrees cultivar polymorphism ranged from 31.1 to 85.5%. Heterozygosity ranged from 0.05 (inbred female line) to 0.26 (cross-bred Fibranova). of genetic variability because of commercial value, reThe average heterozygosity calculated over all 102 loci and all plants productive biology (dioecious or monoecious), end use, studied was 0.29. The Fst (Wright’s fixation index) value calculated and different criteria employed in breeding. for all loci was 0.48, and only 33.3% of the scored loci had higher Dioecious cultivars (e.g., Italian fiber varieties) are values and can be considered informative for cultivar identification. obligate outbred, and the method used to multiply them A Fisher’s test based on allele frequencies suggested complete differ(open-field pollination) approaches a random-mating entiation among all varieties, with the exception of the Italian dioecondition. This is also true for monoecious cultivars, cious varieties Carmagnola and CS, for which no discriminating alleles which are composed of about 50 to 70% monoecious were found. The correlations among the molecular data and the geplants and 30 to 50% female plants, with a small number netic structure of the different cultivars and the consequences in of male plants. The original monoecious trait occurred relation to variety discrimination in hemp are discussed. spontaneously in material from central Russia (de Meijer, 1995) and the presence of male plants in a monoecious stand must be limited to avoid reversion to the H is a traditional crop in Europe and Asia. It dioecious condition. Monoecious plants freely pollinate belongs to the Cannabaceae family, which comfemale and monoecious individuals during multipliprises two genera: Cannabis and Humulus (hops). Decation. spite hemp s past importance for both the textile and Drug varieties are dioecious, but their genetic backmanufacturing industry, its cultivation declined rapidly ground probably has been narrowed to keep the 9–THC during the sixties primarily for two reasons: strong comcontent high and uniform; drug hemp breeders make petition from cotton (Gossypium hirsutum L.) and synextensive use of plants cloned through in vivo propagathetic fibers and multiple efforts to limit marijuana tion, and of full-sib crosses. It is possible to get partial abuse carried out in virtually all western countries. reversion of sex in female plants (Mohan Ram and Sett, Hemp varieties used for drug consumption, which have 1982), which when self-pollinated leads to the inbred, a high content of the psychoactive compound 9–tetragenetically female lines. hydrocannabinol ( 9–THC), are in many cases not morIn general, current fiber cultivars include open-polliphologically distinguishable from fiber varieties with a nated populations, selections, and F1 and F2 hybrids lower, nonpsychoactive level of 9–THC (de Meijer, with a high degree of genetic variability. Italy was one 1999). of the leading European countries in hemp cultivation Recently, the need for alternative crops has renewed and breeding (Bócsa and Karus, 1998). Italian cultivars interest in hemp cultivation for several reasons: (i) the have the highest fiber quality employed in the textile comparatively low chemical fertilizer input required by industry and range from landraces (Carmagnola), or hemp, (ii) its exceptional disease resistance, and (iii) selections from landraces (C.S., Carmagnola Selezioincreased public perception of the value of natural fibers nata), to cross-bred populations (Fibranova). In other compared with synthetic ones (Montford and Small, countries breeding programs are designed to produce 1999). A number of hemp varieties were included in monoecious varieties, especially useful for pulp and pathe European Union list as eligible for subsidies, and per production and for seed yield (e.g., the French cv. legislation has been modified in almost all countries Fibrimon and its derivatives). These differences in Istituto Sperimentale per le Colture Industriali, Via di Corticella 133, Abbreviations: AFLP, amplified fragment length polymorphism; bp, 40129 Bologna, Italy. Received 4 Aug. 2000. *Corresponding author base pairs; AMOVA, analysis of molecular variance; RAPD, random ([email protected]). amplified polymorphic DNA; RFLP, restriction fragment length polymorphism; 9–THC, 9–tetrahydrocannabinol. Published in Crop Sci. 41:1682–1689 (2001).