Summary
Population structure, the physical arrangement of related and unrelated individuals, can have profound effects on the apparent outcrossing rate (\(\hat t\)) in a plant population. However, detailed experimental investigations of the impact of population structure on \(\hat t\) are few. We compared the apparent outcrossing rates of experimental populations of grain sorghum with seed families spatially arranged in stratified and overdispersed treatments. Using alcohol dehydrogenase allozymes as genetic markers, \(\hat t\) was calculated for each of the treatments at two locations over three years. For all six comparisons, the overdispersed treatment yielded significantly larger apparent outcrossing estimates than the stratified treatment. In one case, the difference was over five-fold. Site-specific and time-specific differences were small compared to treatment differences. Whether natural structuring plays a role in altering the effective outcrossing rates of natural populations has been addressed by only a few descriptive studies; structuring effects appear to have an impact in only about half of such studies. The sample is still too small to make any generalizations.
Population structuring can also be of significance in plant breeding programs. Controllable variation in \(\hat t\) values of the magnitude reported herein may be useful in optimizing selection methods for quantitative characters in experimental plant breeding populations. Further work is under way to determine the effects of the variation in apparent outcrossing rates on genetic gains from selection.
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References
Antlfinger AE (1982) Genetic neighborhood structure of the salt marsh composite, Borrichia frutescens. J Hered 73: 128–132
Brim CA, Stuber CW (1973) Application of genetic male sterility to recurrent selection schemes in soybeans. Crop Sci 13:528–530
Brown AHD (1975) Efficient experimental designs for the estimation of genetic parameters in plant populations. Biometrics 31:145–160
Brown AHD, Marshall DR, Eldridge KG (1975) Estimation of the mating system of Eucalyptus obliqua L'Herit using allozyme polymorphisms. Aust J Bot 23:931
Clegg MT (1980) Measuring plant mating systems. Bioscience 30:814–818
Ellstrand NC, Torres AM, Levin DA (1978) Density and the rate of apparent outcrossing in Helianthus annuus (Asteraceae). Syst Bot 3:403–407
Ellstrand NC, Lee JM, Foster KW (1983) Alcohol dehydrogenase isozymes in grain sorghum (Sorghum bicolor): evidence for a gene duplication. Biochem Genet 21:147–154
Empig LT, Gardner CO, Compton WT (1972) Theoretical population gains for different population improvement procedures. University of Nebraska Exp Stn Misc Pub 26 (revised), pp 1–22
Ennos RA, Clegg MT (1982) Effect of population substructuring on estimates of outcrossing rate in plant populations. Heredity 48:283–292
Foster KW, Jain SK, Smeltzer DA (1980) Responses to 10 cycles of mass selection in an inbred population of grain sorghum. Crop Sci 20:1–4
Hamrick JL (1982) Plant population genetics and evolution. Am J Bot 69:1685–1693
Jan-Orn J, Gardner CO, Ross WM (1976) Quantitative genetic studies of the NP3R random-mating grain sorghum population. Crop Sci 16:489–496
Levin DA (1978) Some genetic consequences of being a plant. In: Brussard PF (ed) Ecological genetics: the interface. Springer, Berlin Heidelberg New York, pp 189–212
Levin DA, Kerster HW (1974) Gene flow in seed plants. Evol Biol 7:133–220
Phillips MA, Brown AHD (1977) Mating system and hybridity in Eucalyptus pauciflora. Aust J Biol Sci 30:337–344
Riccelli-Mattei M (1968) Estimation of genetic parameters related to mating system in populations of sorghum (Sorghum bicolor (L.) Moench). PhD Thesis, University of California, Davis CA,
Ritland K, Jain S (1981) A model for the estimation of outcrossing rate and gene frequencies using n independent loci. Heredity 47:35–52
Ross WM, Kindler SD, Hackerott HL, Harvey TL, Sotomayor A, Webster OJ, Kofoid DK (1977) Registration of RP1R and RP2B Sorghum germplasm. Crop Sci 17:983
Sanders TB, Hamrick JL (1980) Variation in the breeding system of Elymus canadensis Evolution 34:117–122
Schoen DJ (1982) The breeding system of Gilia achilleifolia: variation in floral characteristics and outcrossing rate. Evolution 36:352–360
Shaw DV, Allard RW (1981) Analysis of mating system parameters and population structure in Douglas-fir using single-locus and multilocus methods. In: Proc Symp Isozymes North American Forest Trees and Insects. Gen Tech Rep PSW-48, pp 18–22. Pacific Southwest Forest and Range Exp Stn, Berkeley, Calif, For Serv USDA
Shaw DV, Allard RW (1982) Estimation of outcrossing rates in Douglas-fir using isozyme markers. Theor Appl Genet 62:113–120
Shaw DV, Brown AHD (1982) Optimum number of marker loci for estimating outcrossing in plant populations. Theor Appl Genet 61:321–325
Shaw DV, Kahler AL, Allard RW (1981) A multilocus estimator of mating system parameters in plant populations. Proc Natl Acad Sci USA 1298–1302
Vasek FC (1967) Outcrossing in natural populations.3. The Deer Creek population of Clarkia exilis. Evolution 21:241–248
Vasek FC (1968) Outcrossing in natural populations. A comparison of outcrossing estimation methods. In: Drake ET (ed) Evolution and environment. Conecticut, Yale University Press, New Haven, pp 369–385
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Communicated by P. M. A. Tigerstedt
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Ellstrand, N.C., Foster, K.W. Impact of population structure on the apparent outcrossing rate of grain sorghum (Sorghum bicolor). Theoret. Appl. Genetics 66, 323–327 (1983). https://doi.org/10.1007/BF00251167
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DOI: https://doi.org/10.1007/BF00251167