A Sampling Strategy for Conserving Genetic Diversity when Forming Core Subsets

Abstract

The grouping of accessions into clusters is achieved by a classification strategy that partitions the original col-When forming core subsets, accessions from a collection are classilection into groups with maximum distances between fied into clusters, and then samples are drawn from the clusters with accessions located in different groups and minimum disthe aim of maintaining the diversity of the collection. In a stratified tances between accessions located in the same group. sampling strategy, the allocation method provides a criterion for determining the number of accessions to be selected from each cluster. Franco et al. (1998Franco et al. ( , 2002 and Franco and Crossa This paper proposes an allocation method (D method) and compares (2002) proposed a sequential Ward-Modified Location it with three other allocation methods (L, LD, and NY methods). In Method (MLM) strategy in which the Gower (1971) these allocation methods, the number of accessions sampled per clusdistance is used as a measure of similarity (or distance) ter is proportional to (i) the mean of the Gower's distance between among accessions considering all continuous and cateaccessions within the cluster (D method), (ii) the logarithm of the gorical variables. The initial groups were formed by the cluster size (L method), (iii) the product of the cluster size times the Ward (1963) method, and then the MLM was used to mean Gower distance (NY method), and (iv) the product of the loga-J. Franco, Facultad de Agronomía, Universidad de la Repú blica, Av.

Quantificação da divergência genética entre acessos de goibeira por meio da estratégia Ward-MLM

“…Diversos trabalhos vêm sendo desenvolvidos, utilizando tal procedimento, como, por exemplo, com milho (GUTIÉRREZ et al, 2003;FRANCO et al, 2005;ORTIZ et al, 2008), nabo-forrageiro (PADILHA et al, 2005), tomate (GONÇALVES et al, 2009), feijão (BARBÉ et al, 2010CABRAL et al, 2010), pimenta/pimentão (SUDRÉ et al, 2010) e banana (PESTANA et al, 2011).…”

Estratégias de amostragem e estabelecimento de coleções nucleares

“…Os métodos de alocação procuram estabelecer o número e tamanho dos grupos, além dos acessos que irão compor os grupos, de acordo com a similaridade desses acessos. Franco et al (2005) avaliaram diferentes estratégias de determinação do número de indivíduos de cada grupo. Os métodos avaliados por Franco et al (2005) foram baseados na intensidade de amostragem, no tamanho do grupo e na diversidade existente entre os acessos, em relação à coleção inicial como um todo.…”

“…Franco et al (2005) avaliaram diferentes estratégias de determinação do número de indivíduos de cada grupo. Os métodos avaliados por Franco et al (2005) foram baseados na intensidade de amostragem, no tamanho do grupo e na diversidade existente entre os acessos, em relação à coleção inicial como um todo. Porém, praticamente, não há estudos relacionando o tamanho da coleção inicial e sua variabilidade com o número de grupos obtidos pela distância entre os acessos.…”

Comparing the efficiency of sampling strategies to establish a representative in the phenotypic-based genetic diversity core collection of orchardgrass (Dactylis glomerata L.)

“…This definition also includes the core collection representativeness of genetic diversity maintained in the entire collection. The representativeness of a core collection could be considered its ability to capture most of the genetic diversity in the entire collection with minimal redundancies (van Hintum et al 2000;Franco et al 2005Franco et al , 2006. This situation occurs when a core collection reflects its genetic variation with the minimum loss of the original genetic diversity and minimal redundancies.…”

“…This situation occurs when a core collection reflects its genetic variation with the minimum loss of the original genetic diversity and minimal redundancies. This definition is required from the conservation and plant breeding points-of-view (van Hintum et al 1999(van Hintum et al , 2000Marita et al 2000;van Raamsdonk & Wijnker 2000;Malosetti & Abadie 2001;Jansen & van Hintum 2007;Pessoa-Filho et al 2010).The published sizes of core collections range from 0.3 to 30% of the entire collection (Li et al 2002;Franco et al 2005;Logozzo et al 2007;Wang et al 2007;Ghamkhar et al 2008;Liu et al 2009) and are typically close to 10% (Brown 1989a, b;Spagnoletti Zeuli & Qualset 1993;Zewdie et al 2004;Amalraj et al 2006), depending on the species, the objective of the core collection, the strategy adopted and, most often, the size of the collection to be sampled (van Hintum et al 2000). Establishing core collections requires specifying an appropriate sampling strategy (van Hintum et al 1999(van Hintum et al , 2000Xu et al 2006).…”