Talk:Genetic contamination

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Discussion for: Genetic contamination • View • Links • Related changes

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Page scope

Genetic contamination covers the harm or unwanted change that foreign alleles bring to a population someone wants to keep: the idea of seed purity, swamping and its outcomes, landraces beside modern varieties, the claims made for cannabis, and what is done to keep populations apart. The movement of alleles belongs to Gene flow; their incorporation into a lineage, and the genetic evidence for it, to Introgression; the damage done by mating among relatives to Inbreeding depression; the loss of variation by any cause to Genetic erosion; the history of the Moroccan crop to Cannabis in Morocco.

Data verification

Record source conflicts, dating problems and sources not used here. Keep narrative content on the article.

Discussion

Sources

• Ellstrand (2014), American Journal of Botany 101: 737–753: breeders' pollen contamination, seed purity, swamping, outbreeding depression and the statement that gene flow is not a problem in itself.
• Rhymer and Simberloff (1996), Annual Review of Ecology and Systematics 27: 83–109, on extinction by hybridisation and introgression.
• Potts, Barbour, Hingston and Vaillancourt (2003), Australian Journal of Botany 51: 1–25, on genetic pollution of native eucalypts.
• Todesco and colleagues (2016), Evolutionary Applications 9: 892–908: demographic and genetic swamping and a survey of 143 cases.
• Bitocchi and colleagues (2009), Molecular Ecology 18: 603–621, on maize in central Italy. Bellucci and colleagues (2013), PLOS ONE 8: e83891, on barley in Sardinia.
• McPartland and Small (2020), PhytoKeys 144: 81–112: the introductions into centres of diversity and the extinction claim.
• Bachir and colleagues (2022), Cannabis and Cannabinoid Research 7: 603–615; Chouvy and Afsahi (2014), International Journal of Drug Policy 25: 416–423; Boudouah (2017), Revue Tidighin 6; Chouvy (2024), International Journal of Drug Policy 129: 104479: the Rif.
• Wenger and colleagues (2020), American Journal of Botany 107: 1423–1432: hemp seed. Welling and colleagues (2016), Frontiers in Plant Science 7: 1113: crossing at regrowing and isolation distance.

How far the cannabis evidence goes

The figures for introgression into landraces beside modern varieties are for maize and barley. These are comparisons of collections made decades apart. None of the cannabis sources gives a comparable figure for the share of introduced alleles in a landrace population, in Morocco or in Central and South Asia.

Whether cannabis behaves like either crop is open. Maize is outcrossing and barley sets its own seed; cannabis is dioecious and wind-pollinated.

The cannabis claims of contamination rest on reported introductions, field observation of replaced crops, resin and plant chemistry, and a few gene sequences. McPartland and Small's list cites Beisler (2006), Casano (2005), Cherniak (1982), Lamb (2010), Clarke and Merlin (2016), Clarke (1998), Peterson (2009) and Sharma (1988); these are given through McPartland and Small. Reports of hybrids being grown in a place do not by themselves show that their alleles have entered the local population.

Todesco and colleagues' survey covers mostly crosses between species in the wild, and cannabis is not among the groups it discusses. Whether genetic swamping or outbreeding depression has occurred in any cannabis population is not settled by these sources.

Replacement and introgression in the Rif

Chouvy and Afsahi (2014) report replacement of the crop, which they estimate from sight in the field. Bachir and colleagues (2022) and Boudouah (2017) report change in the local plant. A field sown entirely with hybrids is not by itself evidence of hybridisation with kif. Boudouah states the effect of the pollen without a measurement. Bachir and colleagues cite Clarke and Merlin (2016) for "rare", for the 1980 introduction and for the acquired traits.

Chouvy and Afsahi's footnote on the kif landrace holds that it can be assumed to have become an inbred line long ago. Chouvy (2024) treats it as a heterogeneous, open-pollinated landrace.

The dates differ with what is being dated: Bachir and colleagues give 1980 for the introduction of Central Asian genetics; Chouvy and Afsahi give the early 2000s for the first hybrids seen in the Rif and the mid-2000s for the switch.

Purity

"Pure" is the word of the sources quoted: buyers in Boudouah, the "pure" landrace of Bachir and colleagues, the genetic purity of certified seed in Wenger and colleagues. Chouvy (2024) argues against treating a landrace as fixed.

Terms

• Genetic contamination is used by Ellstrand for seed stocks and by McPartland and Small and Bachir and colleagues for landraces.
• Genetic pollution is the term of Potts and colleagues.
• Genetic swamping and genetic assimilation are one thing in Ellstrand. Todesco and colleagues distinguish genetic from demographic swamping.