The Embryo Lethal System


Outcrossing, wind-pollinated members of the Pinaceae have high self-pollination rates yet produce few selfed seedlings. Avoiding self-pollen capture is incomplete so how are self-pollinated ovules or seeds selectively eliminated? Barriers to selfing have long been considered to be either competition via simple polyembryony and death to selfed embryos during seed maturation. Experimental results show that simple polyembrony is a weak barrier against selfed embryos. By far, the most effective barrier is the enigmatic mechanism(s) that cause recognition and death to selfed embryos. A survey shows that extreme inbreeding depression occurs in some species but not in others so this is not a feature of conifers as a group. Only five of the 11 genera within the Pinaceae (Abies, Larix, Picea, Pinus and Pseudotsuga) have been well-characterized with respect to self-pollinated embryo deaths. Molecular dissection methods have been used to infer severity and distribution of lethal factors; to date, most are semi- lethal rather than fully lethal. These range from partially dominant to overdominant or perhaps balanced lethals.

Some selfed embryos die at all stages of seed development but a second death pattern has been detected in some Pinus and Picea spp species: a large proportion of selfed embryo deaths peak during early embryogeny. Are these dual death patterns present in other genera and if so, what genetic models might account for them? This chapter is a case study which integrates not only what was introduced in previous chapters but also shows how knowledge of the conifer mating system contributes to the broader understanding of eukaryotic systems.


Inbreeding Depression Female Gametophyte Pinus Taeda Lethal Factor Molecular Dissection 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Bernasconi G., T. Ashman et al. 2004. Evolutionary ecology of the prezygotic stage. Science 303: 971–975.PubMedCrossRefGoogle Scholar
  2. Bishir, J. and G. Namkoong. 1987. Unsound seed in conifers: estimation of numbers of lethal alleles and of magnitudes of effects associated with the maternal parent. Silvae Genetica 36: 180–185.Google Scholar
  3. Bramlett, D. and F. Bridgwater. 1986. Segregation of recessive embryonic lethal alleles in a F1 population of Virginia pine. IUFRO Conference on Breeding Theory, Williamburg VA.Google Scholar
  4. Bramlett, D. and T. Popham. 1971. Model relating unsound seed and embryonic lethals in self-pollinated pines. Silvae Genetica 20: 192–193.Google Scholar
  5. Buchholz J. 1918. Suspensor and early embryo of Pinus. Botantical Gazette 66: 185–228.CrossRefGoogle Scholar
  6. Buchholz, J. 1920. Embryo development and polyembryony in relation to the phylogeny of conifers. American Journal of Botany 7: 125–145.CrossRefGoogle Scholar
  7. Buchholz, J. 1922. Developmental selection in vascular plants. Bot. Gaz. 73: 249–286.CrossRefGoogle Scholar
  8. Cavalli-Sforza, L. and W. Bodmer. 1971. The genetics of human populations. San Francisco, Freeman.Google Scholar
  9. Crow, J. 1991. Why is Mendelian segregation so exact? Bioessays 13: 305–312.PubMedCrossRefGoogle Scholar
  10. Dogra, P. 1967. Seed sterility and disturbances in embryogeny in conifers with particular reference to seed testing and tree breeding in Pinaceae. Studia Forestalia Suecica 45: 1–97.Google Scholar
  11. Filonova L.H., von Arnold S. et al. 2002. Programmed cell death eliminates all but one embryo in a polyembryonic plant seed. Cell Death and Differentiation 9: 1057–1062.PubMedCrossRefGoogle Scholar
  12. Fowler, D. 1965a. Natural self-fertilization in three jack pines and its implications in seed orchard management. For. Sci. 11: 55–58.Google Scholar
  13. Fowler, D. 1965b. Effects of inbreeding in red pine, Pinus resinosa Ait. Silv. Genet. 12: 12–23.Google Scholar
  14. Franklin, E. 1969. Inbreeding depression in metrical traits of loblolly pine (Pinus taeda L.) as a result of self-pollination. Ph.D. Dissertation, Raleigh NC., School of Forest Resources, North Carolina State University.Google Scholar
  15. Franklin, E. 1972. Genetic load in loblolly pine. Amer. Nat. 106: 262–265.CrossRefGoogle Scholar
  16. Fu, Y-B and K. Ritland. 1994a. Evidence for the partial dominance of viability of viability genes contributing to inbreeding depression in Mimulus guttatus. Genet. 136: 323–331.Google Scholar
  17. Fu, Y-B and K. Ritland 1994b. On estimating the linkage of marker genes to viability genes controlling inbreeding depression. Theor. Appl. Genet. 88: 925–932.CrossRefGoogle Scholar
  18. Fu, Y.B., D. Charlesworth et al. 1997. Point estimation and graphical inference of marginal dominance for two viability loci controlling inbreeding depression. Genet. Res. 70: 143–153.PubMedCrossRefGoogle Scholar
  19. Gifford, E. and A. Foster. 1989. Morphology and evolution of vascular plants. W.H. Freeman Company, New York.Google Scholar
  20. Griffin, R. and D. Lindgren. 1985. Effect of inbreeding on production of filled seed in Pinusradiata, — experimental results and a model of gene action. Theor. Appl. Genet. 71: 334–343.Google Scholar
  21. Hagman, M. and L. Mikkola. 1963. Observations on cross-, self- and interspecific pollinations in Pinus peuce Griseb. Silv. Genet. 12: 73–79.Google Scholar
  22. Haig D. 1992. Brood reduction in gymnosperms. In Cannibalism: Ecology and Evolution among Diverse Taxa. Edited by M. Elgar and B. Crespi. pp. 63–84. Oxford University Press.Google Scholar
  23. Hauser, T. and V. Loeschcke. 1994. Inbreeding depression and mating distance dependent offspring fitness in large and small populations of Lynchis floscuculi (Caryophyllaceae). J. Evol.Biol. 7: 609–622.CrossRefGoogle Scholar
  24. Hedrick, P. and O. Muona. 1990. Linkage of viability genes to marker loci in selfing organisms. Hered. 64: 67–72.CrossRefGoogle Scholar
  25. Husband, B. and D. Schemske. 1996. Evolution and timing of inbreeding depression in plants. Evol. 50: 54–70.CrossRefGoogle Scholar
  26. Kärkkäinen, K., H. Kuittinen et al. 1999. Genetic basis of inbreeding depression in Arabis petraea. Evol. 53: 1354–1365.CrossRefGoogle Scholar
  27. Kang, H., C. Hardner et al. 1994. Lethal loci and lethal equivalents in willow, Salix viminalis.Silv. Genet. 43: 138–145.Google Scholar
  28. Kormutak, A. and D. Lindgren. 1996. Mating system and empty seed in silver fir (Abies alba Mill.). For. Genet. 3: 231–235.Google Scholar
  29. Koski, V. 1971. Embryonic lethals of Picea abies and Pinus sylvestris. Commun. Institute of Forestalia Fennica 75: 1–30.Google Scholar
  30. Koski, V. 1973. On self-pollination, genetic load and subsequent inbreeding in some conifers. Communicationes Instituti Forestalis Fenniae 78: 1–42.Google Scholar
  31. Krebs, S. and J. Hancock. 1991. Embryonic genetic load in the highbush blueberry, Vaccinium corymbosum (Ericaceae). Amer. J. Bot. 78: 1427–1437.CrossRefGoogle Scholar
  32. Kuang, H., T. Richardson et al. 1999. Genetic analysis of inbreeding depression in plus tree 850.55 of Pinus radiata D. Don. II. Genetics of viability genes. Theor. Appl. Genet. 99:140–146.CrossRefGoogle Scholar
  33. Lande, R. and D. Schemske. 1985. The evolution of self-fertilization and inbreeding depression in plants. I. Genetic models. Evol. 39: 24–40.Google Scholar
  34. Lande, R., D. Schemske et al. 1994. High inbreeding depression, selective interference among loci, and the threshold selfing rate for purging recessive lethal mutations. Evol. 48: 965–978.CrossRefGoogle Scholar
  35. Latta, R. and K. Ritland. 1994. The relationship between inbreeding depression and prior inbreeding among populations of four Mimulus taxa. Evol. 48: 806–817.CrossRefGoogle Scholar
  36. Levin, D. 1991. The effect of inbreeding on seed survivorship in Phlox. Evol. 45: 1047–1049.CrossRefGoogle Scholar
  37. Lewontin, R. 1974. The genetic basis of evolutionary change. N Y, Columbia University Press.Google Scholar
  38. Libby, W., B. McCutchan et al. 1981. Inbreeding depression in selfs of redwood. Silv. Genet. 30: 15–25.Google Scholar
  39. Lindgren, D. 1975. The relationship between self-fertilization, empty seeds and seeds originating from selfing as a consequence of polyembryony. Studia Forestalia Suecica 126: 1–24.Google Scholar
  40. McCune, A., R. Fuller et al. 2002. A low genomic number of recessive lethals in natural populations of bluefin killifish and zebrafish. Science 296: 2398–2401.PubMedCrossRefGoogle Scholar
  41. Mergen F., J. Burley et al.1965. Embryo and seedling development in Picea glauca (Moench) Voss after self-, cross-, and wind-pollination. Silv. Genet. 14: 188–194.Google Scholar
  42. Miklos G. and G. Rubin. 1996. The role of genome project in determining gene function insights from model organisms. Cell 86: 521–529.PubMedCrossRefGoogle Scholar
  43. Morton, N., J. Crow et al.1956. An estimate of the mutational damage in man from data on consanguineous marriages. Proc. Natl Acad. USA 42: 855–863.CrossRefGoogle Scholar
  44. Muller, H. 1950. Our load of mutations. Am. J. Hum. Genetics 2: 111–176.Google Scholar
  45. Namkoong, G. and J. Bishir. 1987. Frequency of lethal alleles in forest tree populations. Evol. 41: 1123–1127.CrossRefGoogle Scholar
  46. O'Connell, L. and Ritland K. 2005. Post-pollination mechanisms promoting outcrossing in a self- fertile conifer, Thuja plicata (Cupressaceae). Can.J. Bot. 83: 335–342.CrossRefGoogle Scholar
  47. Orr-Ewing, A. 1957. A cytological study of the effects of self-pollination on Pseudotsuga men-ziesii (Mirb.) Franco. Silv. Genet. 6: 179–185.Google Scholar
  48. Ouborg, N. and R. von Treuren. 1994. The significance of genetic erosion in the process of extinction. IV. Inbreeding load and heterosis in relation to population size in the mint Salvia pratensis. Evol. 48: 996–1008.CrossRefGoogle Scholar
  49. Owens J., A. Colangeli et al. 1990. The effect of self-, cross- and no pollination in ovule, embryo, seed and cone development in westen red cedar (Thuja plicata). Can.J. For. Res. 20: 66–75.CrossRefGoogle Scholar
  50. Park, Y. and D. Fowler. 1982. Effects of inbreeding and genetic variances in a natural population of tamarack (Larix laricina (Du Roi) K. Koch) in eastern Canada. Silv. Genet. 31: 21–26.Google Scholar
  51. Porcher E. and Lande R. 2005. Reproductive compensation in the evolution of plant mating systems. New Phytol. 166: 673–684.PubMedCrossRefGoogle Scholar
  52. Ralls, K., J. Ballou et al. 1988. Estimates of lethal equivalents and the cost of inbreeding in mammals. Conserv. Biol. 2: 185–193.CrossRefGoogle Scholar
  53. Remington D. and D. O'Malley. 2000a. Whole-genome characterization of embryonic stage inbreeding depression in a selfed loblolly pine family. Genet. 155: 337–348.Google Scholar
  54. Remington, D. and D. O'Malley 2000b. Evaluation of major genetic loci contributing to inbreeding depression for survival and early growth in a selfed family of Pinus taeda. Evol. 54: 1580–1589.Google Scholar
  55. Ritland K. 1996. Inferring the genetic basis of inbreeding depression in plants. Genome 39: 1–8.PubMedCrossRefGoogle Scholar
  56. Sarvas, R. 1962. Investigations on the flowering and seed crop of Pinus silvestris. Institute Forestalis Fennica Comm. 53: 1–198.Google Scholar
  57. Savolainen, O., K. Kärkkäinen et al. 1992. Estimating numbers of embryonic lethals in conifers. Heredity 69: 308–314.Google Scholar
  58. Sittman, K., B. Abplanalp et al. 1966. Inbreeding depression in the Japanese quail. Genetics 54: 371–379.Google Scholar
  59. Skinner D. 1992. Ovule and embryo development, seed production and germination in orchard grown control pollinated loblolly pine (Pinus taeda L.) from coastal South Carolina. M.Sc. Thesis, University of Victoria, Victoria B.C. Canada.Google Scholar
  60. Sorensen, F. 1967. Linkage between marker genes and embryonic lethal factors may cause disturbed segregation ratios. Silv. Genet. 16: 132–134.Google Scholar
  61. Sorensen, F. 1969. Embryonic genetic load in coastal Douglas fir, Pseudotsuga menziesii var. menziesii. Amer. Nat. 103: 389–398.CrossRefGoogle Scholar
  62. Sorensen, F. 1971. Estimate of self-fertility of Douglas-fir from inbreeding studies. Silv. Genet. 20: 115–120.Google Scholar
  63. Sorensen, F. 1982. The roles of polyembryony and embryo viability in the genetic system of conifers. Evol. 36: 725–733.CrossRefGoogle Scholar
  64. Vogl C. and S. Xu. 2000. Multiple-point mapping of viability and segregation distorting loci using molecular markers. Genetics 155: 1439–1447.PubMedGoogle Scholar
  65. Williams, C., R. Barnes et al. 1999. Embryonic lethal load for a neotropical conifer, Pinus patula Schiede and Deppe. J. Hered. 90: 394–398.CrossRefGoogle Scholar
  66. Williams, C. and O. Savolainen. 1996. Inbreeding depression in conifers: implications for breeding strategy. For. Sci. 42: 102–117.Google Scholar
  67. Williams, C., Y. Zhou et al. 2001. A chromosomal region promoting outcrossing in a conifer. Genetics 159: 1283–1289.PubMedGoogle Scholar
  68. Williams, C., L. Auckland et al. 2003. Overdominant lethals as part of the conifer embryo lethal system. Heredity 91: 584–592.PubMedCrossRefGoogle Scholar
  69. Williams, C. 2007. Re-thinking the embryo lethal system within the Pinaceae. Canadian Journal of Botany 85: 667–677.CrossRefGoogle Scholar
  70. Williams C. 2008. Selfed embryo death in Pinus taeda: a phenotypic profile. New Phytologist 178: 210–222.PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2009

Personalised recommendations