Talk:Outcrossing

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Outcrossing covers mating between two different plants and its alternative, selfing, in cannabis: outcrossing as the plant's natural mating system, the heterozygosity it keeps, inbreeding and inbreeding depression, the ways a cannabis plant can be selfed (induced male flowers, hermaphroditic flowers and monoecious hemp) and the crossing of inbred lines for heterosis. The separate sexes that enforce outcrossing belong to Dioecy and Sex determination in cannabis; the movement of pollen and seed between populations to Gene flow; how diversity is divided among populations to Genetic diversity; the production of feminised and hybrid seed as a practice to Feminised seeds and F1 hybrid.

Data verification

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Discussion

Sources

• Barcaccia and colleagues (2020), Frontiers in Plant Science 11: 573299: cannabis as dioecious and wind-pollinated, with outcrossing its only natural means of reproduction; the heterozygous make-up of natural and mass-selected populations; selfing by masculinised branches and its all-female offspring; the variability of seed-grown populations against clones; landrace-by-landrace crosses, inbred parents and true F1 hybrids; heterosis in fibre and drug-type breeding.
• Punja and Holmes (2020), Frontiers in Plant Science 11: 718: hermaphroditic flowers on drug-type plants, their viable pollen and self-pollination; the female offspring of seed from hermaphroditic flowers; selfing and cross-fertilisation in indoor and outdoor crops; the genetic variation of seedlings after one generation of selfing.
• Kurtz, Mahoney, Brand and Lubell-Brand (2020), HortScience 55: 1206–1209: the S1 practice of feminised-seed producers; growth, flowering, flower yield, variegation, variability and expected heterozygosity of a selfed hemp strain against two outcrosses.
• McDonald and Lubell-Brand (2024), HortScience 59: 1795–1799: four generations of selfing in the cultivars Wife and Wilhelmina; dwarfed, infertile and low-yielding selfed plants; F1 hybrids between selfed lines.
• Carlson and colleagues (2021), Journal of Experimental Botany 72: 7694–7709: within-family variation and parental heterozygosity in 23 hemp families; the slow growth of S2 families; monoecious cultivars; inbred parents for hybrid hemp.
• Srikul, Mayong, Matthayatthaworn and Sreewongchai (2026), Agriculture and Natural Resources 60: 600512: S1 and F1 progeny of two accessions of the Hang Kra Rok landrace grown in a plant factory.
• Mishchenko, Kabanets, Kyrychenko, Marchenko and Machulsky (2025), Faktori eksperimental'noi evolucii organizmiv 37: 29–34 (in Ukrainian): self-pollination of single plants of the monoecious cultivars Hlukhivski 58, Hlesiia and Zolotoniski 15 for up to twelve generations, 2008–2023; the use of inbred lines in crosses.
• Sawler and colleagues (2015), PLoS ONE 10: e0133292: cannabis as wind-pollinated, dioecious and highly heterozygous, and the clonal propagation of drug-type strains.
• Felsenstein, Theoretical Evolutionary Genetics (text of December 2019), pp. 219, 231–233, 237, 242–244 and 411–414: the inbreeding coefficient; loss of heterozygosity under selfing and full-sib mating; restoring heterozygosity by crossing lines; recessive deleterious alleles and overdominance; the dominance and overdominance explanations of inbreeding depression; heterosis and its decline in the second generation.
• Davinack, Molecular Ecology & Evolution: An Introduction (2024), pp. 172–174: inbreeding depression and purging.

Terms

• Selfing here covers pollination of a plant by its own pollen and by pollen of a clone of the same plant, as feminised-seed producers practise it. Both give offspring of a single genotype crossed with itself.
• S1, S2 and so on are the first, second and later generations of selfing. The Ukrainian study numbers the same generations I1 to I12, with I0 for the starting plants.
• F1 is the first generation of a cross between two parents, F2 the generation after it. A true F1 hybrid in Barcaccia and colleagues' sense comes from two inbred parent lines; a cross between single plants of two landraces is not one.
• Heterosis and hybrid vigour name the same thing. Felsenstein uses heterosis for the superiority of the hybrid whatever its cause, and overdominance only for the superiority of the heterozygote at a single locus.

Source discrepancies

• Height of the selfed Hang Kra Rok plants. Srikul and colleagues found no evidence of inbreeding depression "for plant height or floral yield", yet their own table gives the S1 plants a significantly lower mean height (78.94 and 74.83 cm) than the F1 plants (87.22 and 88.78 cm); dry flower weight did not differ. Their F1 plants came from crosses between two accessions, so the comparison sets selfing within one accession against crosses between two.
• One generation of selfing and genetic variation. Kurtz and colleagues found lower expected heterozygosity in S1 progeny (0.085) than in progeny of two crosses between strains (about 0.10), using AFLP markers on twelve plants of each cross. Punja and Holmes found no measurable difference in gene diversity between seedlings from hermaphroditic flowers and seedlings from cross-fertilised seed, using six ISSR primers. The two studies used different markers and different plants.
• Wilhelmina S4. McDonald and Lubell-Brand found that the means of Wilhelmina's traits did not change from S1 to S4, while within-line variation fell. They described the S4 plants as uniformly diminutive and likely inbred-depressed from their appearance.

Images reserved in the article

One image has a place in the article but is not yet uploaded:

• File:Cannabis-selfing-heterozygosity-decline.jpg (Outcrossing and selfing), a graph to be drawn: a horizontal axis "Generation" from 0 to 8 and a vertical axis "Heterozygosity remaining" from 0 to 1. One flat line at 1, labelled "Random mating, large population". A second line labelled "Selfing" with points at 1, 0.5, 0.25, 0.125, 0.0625, 0.031, 0.016, 0.0078 and 0.0039 for generations 0 to 8. No crop names or other numbers.