Talk:Mass selection
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Mass selection covers mass selection as a method and its genetics: choosing plants on their own phenotype and bulking their seed, the response to selection and its dependence on heritability, the difference between choosing only the seed parents and choosing both parents, and the effect of the number of parents kept. It applies these to cannabis. How growers choose and keep seed in practice belongs to Farmer selection and Landrace breeding; the removal of male plants as a field operation to Roguing and Sinsemilla; selection by the environment to Natural selection.
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Discussion
Sources
- Fehr, Principles of Cultivar Development, vol. 1 (1987; 1991 printing), ch. 15 "Recurrent selection", pp. 172–181, and ch. 17, p. 239: the names of the method and the narrow sense of "mass selection"; phenotypic selection as the earliest way of improving cross-pollinated crops and the maize cultivars that farmers' selection of ears produced; J.R. Harlan's selection of side-oats grama; the halving of the expected gain when only the seed parent is selected, and parental control; microenvironmental variation and Gardner's grid of 1961; genetic variation and the number of parents.
- Beavis, Lamkey, Mahama and Suza, "Selection response", in Suza and Lamkey (eds), Quantitative Genetics for Plant Breeding (2023): the selection differential, the response to selection R = h²S and Lush's definition of it (1940), narrow-sense heritability as the regression of offspring on the mid-parent value, and the difference between heritability on an entry-mean basis and narrow-sense heritability.
- Felsenstein, Theoretical Evolutionary Genetics (text of December 2019), pp. 266–268 and 443–449: the effective number of a population with separate sexes; the breeder's equation and selection of one sex; the response as a change in allele frequencies; drift, the selection limit and Robertson's result; natural selection and changing conditions as limits on artificial selection.
- Sudika and Soemeinaboedhy (2022), Journal für Kulturpflanzen 74: 134–141: mass selection as the oldest method and its dependence on heritability and on control of the environment; mass selection by pollination control in maize, with a grid of 100 subplots of 40 plants, and the yield of the population after seven cycles.
- Barcaccia and colleagues (2020), Frontiers in Plant Science 11: 573299: the use of mass selection in breeding drug-type and fibre-type cannabis; wind pollination and outcrossing; the make-up of populations from mass selection; the variation of landraces and the uniformity of clones; the dependence of cannabinoid profile on genotype and of cannabinoid quantity on environment.
- Petit and colleagues (2020), Frontiers in Plant Science 11: 102: broad-sense heritabilities of 28 traits in 123 hemp accessions at three European sites.
- Campbell and colleagues (2019), Agrosystems, Geosciences & Environment 2: 1–11: shares of variance due to genotype, environment and their interaction in hemp cultivars in Colorado.
Terms
- Mass selection is used in a broad sense for any cyclic selection of individual plants on their phenotype, and in a narrow sense for selection of seed plants after open pollination. In the narrow sense, selection of both parents before pollination is called recurrent phenotypic selection. The article uses the broad sense and states which case applies.
- Broad-sense heritability counts all genetic differences between plants or entries; narrow-sense heritability counts only the additive part, which sets the response to mass selection. The hemp figures on the page are broad-sense values among accessions and cultivars.
- Parental control is one-half when only the seed parents are selected and one when both parents are.
Source discrepancies
- Size of the gain from choosing the pollen parent. Fehr and Felsenstein give the expected gain from choosing only the seed parents as half the gain from choosing both. In the maize population of Sudika and Soemeinaboedhy, earlier work by Sutresna (2010), which they cite, found a yield gain per cycle of 14.04 per cent with pollination control and 11.33 per cent without it, where the selection was made on other traits than yield.
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File:Cannabis-mass-selection-response-diagram.jpg(lead), a diagram to be drawn: two bell curves on one horizontal axis labelled "Trait value". The upper curve, labelled "Parents", has its right-hand tail shaded, with marks for "Population mean" and "Mean of the selected plants" and the gap between them labelled "S, selection differential". The lower curve, labelled "Offspring", is shifted right by a smaller amount labelled "R, response to selection". A formula line reads "R = h²S". No numbers, trait or crop names.