The use of different clustering methods in the evaluation of genetic diversity in upland cotton

Abstract

-The continuous development and evaluation of new genotypes through crop breeding is essential in order to obtain new cultivars. The objective of this work was to evaluate the genetic divergences between cultivars of upland cotton (Gossypium hirsutum L.) using the agronomic and technological characteristics of the fibre, in order to select superior parent plants. The experiment was set up during 2010 at the Federal University of Ceará in Fortaleza, Ceará, Brazil. Eleven cultivars of upland cotton were used in an experimental design of randomised blocks with three replications. In order to evaluate the genetic diversity among cultivars, the generalised Mahalanobis distance matrix was calculated, with cluster analysis then being applied, employing various methods: single linkage, Ward, complete linkage, median, average linkage within a cluster and average linkage between clusters. Genetic variability exists among the evaluated genotypes. The most consistant clustering method was that employing average linkage between clusters. Among the characteristics assessed, mean boll weight presented the highest contribution to genetic diversity, followed by elongation at rupture. Employing the method of mean linkage between clusters, the cultivars with greater genetic divergence were BRS Acacia and LD Frego; those of greater similarity were BRS Itaúba and BRS Araripe.Key words: Gossypium hirsutum L.. Fibre quality. Agronomic characteristics.RESUMO -A geração e avaliação contínua de novos genótipos, por meio do melhoramento genético, é fundamental para a obtenção de novas cultivares. Foi o objetivo deste trabalho avaliar a divergência genética entre cultivares de algodoeiro herbáceo (Gossypium hirsutum L.), por meio de características agronômicas e tecnológicas da fibra, visando à seleção de parentais superiores. O experimento foi implantado na Universidade Federal do Ceará, Fortaleza/CE, em 2010. Foram usadas 11 cultivares de algodão herbáceo, utilizando o delineamento experimental em blocos casualizados, com três repetições. Para avaliação da divergência genética entre as cultivares foi obtida a matriz de distâncias generalizada de Mahalanobis, e em seguida, realizado agrupamento por diferentes métodos, sendo eles o método da ligação simples, de Ward, da ligação completa, da mediana, da ligação média dentro de grupo e da ligação média entre grupo. Há variabilidade genética entre os genótipos avaliados. O método de agrupamento que apresentou maior consistência foi a ligação média entre grupo. O peso médio do capulho apresentou a maior contribuição para a diversidade genética, seguida do alongamento à ruptura dentre os caracteres avaliados. As cultivares de maior divergência genética, usando o método de ligação média entre grupo, foram a BRS Acácia e LD Frego; as de maior similaridade foram a BRS Itaúba e BRS Araripe. Palavras-chave:Gossypium hirsutum L.. Qualidade da fibra. Características agronômicas.*Autor para correspondência 1 Recebido para publicação em 02/06/2012; aprovado em 03/12/2013 Parte da Monografia do ...

Determining genetic diversity in cotton genotypes to improve variability

“…Genetic diversity among the cotton genotypes in this study ranged from 68.64 to 1121.27 (Table 7). This amplitude echoes that of Araújo et al (2014) who found distances of 23.01 to 1172.28 while evaluating the fiber quality and productivity of 11 cultivars resulting only from Embrapa's breeding program. These results indicate the limited genetic base of current cultivars.…”

Genetic diversity analysis based on morphological characters in mulberry (Morus spp.)

“…For analysis of genetic divergence, the genetic distance between the different pairs of genotypes was calculated, employing the generalized Mahalanobis distance as a measure of genetic dissimilarity among the cultivars (Mahalanobis 1936). To estimate this distance, the averages were computed for each of the variables for each cultivar, and then the residual covariance matrix was established, the data transformation matrix, the variance of transformed variables, the averages of uncorrelated variables, and finally the pivotal condensation technique for resolving the dispersion matrix (Araújo et al 2014). From the dissimilarity matrix a cluster analysis was performed using the hierarchical methods of single linkage (nearest neighbor), of Ward, of complete linkage (furthest neighbor), of the median, the average linkage within a cluster and the average linkage between clusters, allowing dendrogram to be produced.…”

“…From the dissimilarity matrix a cluster analysis was performed using the hierarchical methods of single linkage (nearest neighbor), of Ward, of complete linkage (furthest neighbor), of the median, the average linkage within a cluster and the average linkage between clusters, allowing dendrogram to be produced. To validate clusters, that is, to verify the ability of the dendrogram to reproduce the dissimilarity matrix (Araújo et al 2014).…”

Dissimilarity measures and hierarchical methods for the study of genetic diversity on soybean

“…In relation to the number of groups formed it was possible to find that the Euclidean distance showed a greater capacity of differentiation in a group in comparison to the Mahalanobis distance. Araújo et al (2014) comparing the hierarchical methods with 11 cotton cultivars obtained that the nearest neighbor, the furthest neighbor, UPGMA and Ward grouping method also resulted in 90% or more of similarity among the grouped genotypes.…”