Abstract
The knowledge of the phenotypic variation of cassava (Manihot esculenta Crantz) germplasm allows the estimative of the genetic variability to support the selection of contrasting genitors. Therefore, the aim of this work was to define homogeneous groups of cassava germplasm based on yield traits, disease resistance and root quality using K-means as a non-hierarchical method. Breeding values estimated by Best Linear Unbiased Predictor (BLUP) were used for the cluster analysis. The number of groups was defined according to the stabilization of the smallest within-group sum of squares. Seventeen clusters were defined to represent the diversity of the germplasm, whose number of accessions ranged from 7 (Group 15) to 69 (Group 9). In general, accessions belonging to Groups 1, 4, 7, 12, 15 and 16 showed good agronomic traits, such as high fresh root yield and starch yield (> 60.7 t ha-1 and 18.6 t ha-1, respectively). In contrast, only Group 15 presented low bacterial blight severity. The groups obtained showed strong differences, as evidenced by the within-groups sums of squares values, which ranged from 215.1 (Group 15) to 2,338.3 (Group 8). The K-means algorithm allowed the formation of consistent groups based on yield traits, disease resistance and root quality. Therefore, the K-means algorithm was efficient in the formation of groups with low within genotypic variation, especially concerning large amounts of data, such as in cassava germplasm banks.
Highlights
Cassava (Manihot esculenta Crantz) is the third most important source of calories in Africa, Asia and Latin America and is characterized as a food security crop in these regions, where most crops are often held by small farmers on marginal lands
Many important traits have not even been discovered in this germplasm, but in general the search for new alleles for traditionally important characteristics in the cassava production system, which are increasing productivity, starch content and quality and resistance to drought, pests and diseases, is still an extremely important line of research as a step that precedes their use in breeding programs
Six hundred and twenty-nine accessions from the cassava germplasm bank (CGB) from Embrapa Mandioca e Fruticultura (Cruz das Almas, BA, Brazil) were evaluated. This database consists of landraces and improved varieties resulting from conventional breeding procedures, such as crossing and selection, as well as the selection of local varieties with high yield potential identified by farmers or research institutions
Summary
Cassava (Manihot esculenta Crantz) is the third most important source of calories in Africa, Asia and Latin America (after rice and maize) and is characterized as a food security crop in these regions, where most crops are often held by small farmers on marginal lands. The enormous potential of cassava as a raw material base for a range of industrial products can generate increased interest in the culture and raise the demand and contribute to agricultural transformation and economic growth in developing countries (FAO, 2013). In addition to the productivity and root quality, the crop’s variety as a component of the production system plays an important role in the market diversification due to the starch specific characteristics that allow its use in several areas (ZHANG et al, 2010). Many important traits have not even been discovered in this germplasm, but in general the search for new alleles for traditionally important characteristics in the cassava production system, which are increasing productivity, starch content and quality and resistance to drought, pests and diseases, is still an extremely important line of research as a step that precedes their use in breeding programs
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