Morphological and molecular diversity among cassava genotypes

Abstract

-The objective of this work was to characterize morphologically and molecularly the genetic diversity of cassava accessions, collected from different regions in Brazil. A descriptive analysis was made for 12 morphological traits in 419 accessions. Data was transformed into binary data for cluster analysis and analysis of molecular variance. A higher proportion of white or cream (71%) root cortex color was found, while flesh colors were predominantly white (49%) and cream (42%). Four accession groups were classified by the cluster analysis, but they were not grouped according to their origin, which indicates that diversity is not structured in space. The variation was greater within regions (95.6%). Sixty genotypes were also evaluated using 14 polymorphic microsatellite markers. Molecular results corroborated the morphological ones, showing the same random distribution of genotypes, with no grouping according to origin. Diversity indices were high for each region, and a greater diversity was found within regions, with: a mean number of alleles per locus of 3.530; observed and expected heterozygosity of 0.499 and 0.642, respectively; and Shannon index of 1.03. The absence of spatial structure among cassava genotypes according to their origins shows the anthropic influence in the distribution and movement of germplasm, both within and among regions.Index terms: Manihot esculenta, genetic diversity, germplasm, microsatellites, morphological traits. Diversidade morfológica e molecular entre genótipos de mandiocaResumo -O objetivo deste trabalho foi caracterizar, morfológica e molecularmente, a diversidade genética de acessos de mandioca de diferentes regiões do Brasil. Realizou-se a análise descritiva de 12 características morfológicas em 419 acessos. Os dados foram transformados em dados binários para análise de agrupamento e análise de variância molecular. Observou-se maior proporção (71%) de cor branca ou creme do córtex da raiz, enquanto as cores da polpa foram predominantemente branca (49%) e creme (42%). Quatro grupos de acessos foram classificados pela análise de agrupamento, mas não foram agrupados de acordo com sua origem, o que indica que a diversidade não está estruturada no espaço. A maior parte da variação ocorreu dentro das populações (95,6%). Sessenta genótipos também foram avaliados com o uso de 14 marcadores microssatélites polimórficos. Os resultados moleculares corroboraram os morfológicos e mostraram a mesma distribuição aleatória dos genótipos, com ausência de agrupamento quanto ao local de origem. Os índices de diversidade foram elevados para cada região e a maior parte da diversidade foi observada dentro de regiões, com: número médio de alelos por loco de 3,530; heterozigosidade média observada de 0,499 e esperada de 0,642; e índice de Shannon de 1,03. A ausência de estrutura espacial entre os genótipos de mandioca de acordo com suas origens mostra a influência antrópica na distribuição e movimentação de germoplasma, tanto entre como dentro de regiões.

Population Structure and Genetic Diversity in Sweet Cassava Cultivars from Paraná, Brazil

“…However, sweet cassava presents acceptable concentrations (less than 100 mg kg −1 in raw pulp) of cyanogenic glycosides (Kizito et al 2007), so the cultivars with these characteristics are the most important as staple food in developing countries, due to the big importance of reduced amounts of cyanogenic glycosides in food safety. There are reports of a great genetic diversity in sweet cassava in Brazil (Rimoldi et al 2010;Costa et al 2013;Mezette et al 2013;Oliveira et al 2014), mainly in small areas where cultivars are grown by family farmers for their own consumption, in a type of cropping called Bbackyard^ (Zuin et al 2009). These areas of small crops have decreased considerably because of population migration to towns and big cities in the last 50 years (IBGE 2014).…”

Genetic diversity and population structure of traditional sweet cassava accessions from Southern of Minas Gerais State, Brazil, using microsatellite markers

“…For instance, Turyagyenda et al (2012) obtained a value of 0.025 for genetic diversity between the two groups formed by the cassava accessions from Uganda. In addition, Mezette et al (2013) reported that traditional accessions of cassava from different Brazilian regions revealed a low value of Fst equivalent to 0.041. It is plausible that a very low Fst index for cassava accession indicates a reduced overall genetic differentiation due to the random mating between groups or at least among their ancestors (Turyagyenda et al, 2012).…”

“…Genetic diversity can be assessed by using biochemical and morphological markers (Elias at al., 2001;Ortiz et al, 2016), but molecular markers are highly recommended because they provide more detailed information about polymorphism, independently of physiological state of the plant and environmental conditions (Agarwal et al, 2008;Raji et al, 2009). Molecular marker techniques, such as microsatellites (Raji et al, 2009;Monteiro-Rojas et al, 2011;Asare et al, 2011;Turyagyenda et al, 2012;Costa et al, 2013;Mezette et al, 2013;Kawuki et al, 2013;Ndung'u et al, 2014;Fu et al, 2014;Ortiz et al, 2016) have showed satisfactory results for evaluating the genetic diversity and population structure in sweet cassava. Furthermore, microsatellite markers, also known as simple sequence repeats (SSR), are informative due to their multi-allelic nature, codominant inheritance and wide distribution through the genome (Varshney et al, 2005;Raji et al, 2009).…”

Diversity of Cassava (Manihot esculenta Crantz) Cultivars in the Traditional Agriculture of Togo

“…These cultivars usually produce lower yields under optimal conditions than improved varieties but the relative stability of their yields provides food security to households (Barnaud et al, 2007;IFAD, 2013;Swiderska et al, 2011). Several cassava cultivars with different characteristics most often grow together in a single field, suggesting high diversity within this crop (Siqueira et al, 2009;Alves-Pereira et al, 2011), which is important for plant breeding programs (Mezette et al, 2013). However, according to Siqueira et al (2009), studies concerning cassava diversity are scarce when compared with the great ethnical and territorial diversity of populations that grow cassava.…”