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Chapter 5: Basic sampling strategies: theory and practice

Jose Crossa
Biometrics and Statistics Unit, International Maize and Wheat Improvement Center (CIMMYT), 06600 Mexico, DF, Mexico
E-mail: j.crossa(at)
Roland Vencovsky
Dept. of Genetics ESALQ/Universidade de Sao Paulo, Piracicaba, Sao Paulo, Brazil
E-mail: rvencovs(at)


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This chapter is a synthesis of new knowledge, procedures, best practices and references for collecting plant diversity since the publication of the 1995 volume Collecting Plant Diversity: Technical Guidelines, edited by Luigi Guarino, V. Ramanatha Rao and Robert Reid, and published by CAB International on behalf of the International Plant Genetic Resources Institute (IPGRI) (now Bioversity International), the Food and Agriculture Organization of the United Nations (FAO), the World Conservation Union (IUCN) and the United Nations Environment Programme (UNEP). The original text for Chapter 5: A Basic Sampling Strategy: Theory and Practice, authored by A. H. D. Brown and D. R. Marshall, has been made available online courtesy of CABI. The 2011 update of the Technical Guidelines, edited by L. Guarino, V. Ramanatha Rao and E. Goldberg, has been made available courtesy of Bioversity International.

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Programmes for conserving genetic resources have collected, received and stored hundreds of thousands of accessions of different cultivated species and their wild and weedy relatives. Collection and regeneration protocols must consider the species (i.e., allogamous, partially allogamous, autogamous and dioecious) to ensure that the sample is representative of the population. Previous studies have used allelic richness as the basic parameter for determining sample sizes for genetic resource conservation. The concept of variance effective population size is important to the measurement of genetic representativeness and has been successfully used in genetic conservation (regeneration and collection). The aim of this chapter is to show how to practically apply the theory developed earlier and to demonstrate its use for answering practical questions that a manager of genetic resource conservation might pose when collecting and regenerating plant genetic resources. This chapter explains strategies for determining efficient sample size in order to maintain the representativeness of the original diversity when collecting and regenerating genetic resources.


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References and further reading

Allard RW. 1970. Population structure and sampling methods. In: Frankel OH, Bennett E, editors. Genetic Resources in Plants: Their Exploration and Conservation. Blackwell Scientific Publications, Oxford, UK. pp.97–107.

Bandel G, Gurgel JTA. 1967. Proporção do sexo em Pinheiro Brasileiro Araucaria angustifolia (Bert.) O. Ktze. Rev. Tec. Serv. Florestal do Est. de S. Paulo. Secr. Agr. Est. S. Paulo 6: 209–220.

Barret SCH, Yakimowsky SB, Field DL, Pickup M. 2010. Ecological genetics of sex ratios in plant populations. Philosophical Transactions of the Royal Society B. 365:2549–2557.

Bawa KS. 1974. Breeding systems of tree species of a lowland tropical community. Evolution 28(1):85–92.

Bawa KS. 1980. Evolution of dioecy in flowering plants. Annual Review of Ecology, Evolution, and Systematics 11:15–39.

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Cockerham CC, Weir BS. 1984. Covariances of relatives stemming from a population undergoing mixed self and random mating. Biometrics 40:157–164.

Crossa J, Vencovsky R. 1994. Implications of the variance effective population size on the genetic conservation of monoecious species. Theoretical and Applied Genetics 89:936–942.

Crossa J, Vencovsky R. 1997. Variance effective population size for two-stage sampling of monoecious species. Crop Science 37:14–26.

Crossa J, Vencovsky R. 1999. Sample size and variance effective population size for genetic conservation. Plant Genetic Resources Newsletter 119:15–25.

Crossa J, Hernandez CM, Bretting P, Eberhart SA, Taba S. 1993. Statistical genetic considerations for maintaining germplasm collections. Theoretical and Applied Genetics 86:673–678.

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Crow JF, Kimura M. 1970. An Introduction to Population Genetics Theory. Burgess Publishing, Minneapolis, Minnesota.

Hernandez CM, Crossa J. 1993. A program for estimating the optimum sample size for germplasm conservation. Journal of Heredity 84:1.

Marshall DR, Brown AHD. 1975. Optimum sampling strategies in genetic conservation. In: Frankel OH, Hawkes JG, editors. Crop Genetic Resources for Today and Tomorrow. Cambridge University Press, Cambridge, UK.

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Vencovsky R, Crossa J. 1999a. Variance effective population size under mixed self and random mating with applications to genetic conservation of species. Crop Science 39:1282–1294.

Vencovsky R, Crossa J. 1999b. Medidas de representatividad. Workshop O Melhoramento de Plantas na Virada do Milenio. Universidad Federal de Vicosa, MG, Brasil.

Vencovsky R, Crossa J. 2003. Measurements of representativeness used in genetic resource conservation and plant breeding. Crop Science 43:1912–1921. doi:10.2135/cropsci2003.1912.

Vencovsky R, Nass LL, Cordeiro CMT, Ferreira MAJF. 2007. Amostragem em recursos genéticos vegetais. In: Nass LL, editor. Recursos Genéticos Vegetais. Embrapa, Brasília.

Vencovsky R, Chavez L, Crossa J. 2011. Variance effective population size for dioecious species. Crop Science (in press).

Viegas MP, Silva CLSP, Moreira JP, Cardin LT, Azevedo VCR, Ciampi AY, Freitas MLM, Moraes MLT, Sebbenn AM. 2011. Diversidade genética e tamanho efetivo de duas populações de Myracrodruon urundeuva fr. all., sob conservação ex situ. Revista Árvore 35(4):769–779.

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Internet resources

MLTR (Multilocos Mating System Program) by Kermit Ritlan (a computer programme for analysing marker data):

Resources for obtaining measures of genetic divergence among collection sites or subpopulations of a species in a given ecogeographic region, and of the level of natural inbreeding:

FSTAT by Jérome Goudet:

GDA (Genetic Data Analyses) by Paul O. Lewis and Dmitri Zaykin:


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