Genetic redundancy in cassava (Manihot esculenta Crantz) presents a challenge to efficient management of genetic resources. This study aimed to identify and define the genetic structure of duplicates in cassava germplasm from various Embrapa research units, using single-nucleotide polymorphism (SNP) markers. We evaluated 2,371 accessions with 20,712 SNPs. The identification of duplicates was performed based on multilocus genotypes (MLG), adopting a maximum genetic distance threshold of 0.05. The population structure was defined based on discriminant analysis of principal components (DAPC). A total of 1,757 unique and 614 duplicate accessions were identified. The redundancy of the collections ranged from 17 % (Belém, PA-Brazil) to 39 % (Petrolina, PE-Brazil), with an average of 21 %. This redundancy between different research units is probably due to the historical sharing of accessions, as well as collections carried out in the same region, or even to the intense germplasm exchange between farmers with different genotype names. In terms of genetic structure, the 250 principal components explained 88 % of the genetic variation of the SNP markers and defined the hierarchical structure of the duplicate cassava germplasm in 12 groups. Since heterotic groups have not yet been identified for cassava, crosses between accessions of the 12 DAPC groups may be promising. All MLGs were allocated within the same DAPC group, corroborating duplicate analyses yet still revealing high variability between groups that were quite distinct based on the first two discriminant functions. Our results contribute to optimizing the conservation of genetic resources, together with understanding diversity and its use in crop improvement.

Fonte de financiamento: projeto PROPALMA-Pesquisa, desenvolvimento e inovação em palmáceas para a produção de óleo e aproveitamento econômico de coprodutos e resíduos-Financiado pela FINEP. Conflito de interesse: Os autores declaram não haver conflito de interesse.

Bitter' and 'sweet' cassava are normally distinguished based on the hydrocyanic acid (HCN) content of their roots. Moreover, Brazilian farmers tend to select 'sweet' cassava based on the taste and cooking aspects. The aim of this study was to characterize chemical traits of 'bitter' and 'sweet' cassava roots of the Amazon region and to find genetic relations among accessions based on these traits. Considerable phenotypic variation was detected among the evaluated traits moisture, ashes, total soluble solids, total titratable acidity, pH, total carotenoids, free and total cyanide, crude protein, glucose, fructose, sucrose and starch. Aside from free and total cyanide, the trait means of sugars and moisture differed in 'bitter' and 'sweet' cassava and also differentiated these in different clusters in the dendrogram using the unweighted pair-group method based on arithmetic averages (UPGMA) and in the results of principal component analysis.

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Platonia insignis is a fruit tree native of Brazil with allogamous and asexual reproduction. The production of fruits is mainly obtained by exploitation of natural populations and the impact of genetic structuring on plant production may be evaluated. For this purpose, codominant and multiallelic markers such as microsatellite are the most suitable, but they need to be developed for this species. Thus, the aim of this work was to develop and validate microsatellite markers for P. insignis. We used Roche 454 GS FLX sequencing platform of a single P. insignis genotype and 1702 microsatellite sequences were identified. Based on some pre-requisites, we could develop 50 primer pairs to be tested. Twenty-two primer pairs successfully amplified fragments and they were tested in 31 genotypes of P. insignis that belong to a germplasm bank and were sampled in the northeast of Pará State, Brazil. Thirteen primers were polymorphic and the number of alleles per loci varied from 5 (PI18 and PI27) to 2 (PI08, PI25, PI31, PI33 and PI 37). Expected heterozygosity (H E ) varied from 0.74 (PI27) to 0.12 (PI31) and observed heterozygosity (H O ) varied from 1.00 (PI25) to 0.00 (PI08, PI31, PI33 and PI37). Principal coordinates could separate the genotypes of P. insignis in clusters and we can conclude that the primers can estimate the genetic diversity of P. insignis populations.

O Pará é o maior produtor brasileiro de mandioca (Manihot esculenta Crantz), a qual e destinada principalmente para a obtenção da farinha de mesa, embora a fécula seja o produto mais nobre extraído das suas raízes. O objetivo deste trabalho foi caracterizar as raízes e as féculas de três variedades de mandioca produzidas no estado do Pará. A análise biométrica constatou que não há um padrão de tamanho e de forma para as raízes de mandioca. As féculas obtidas apresentaram elevada pureza em amido (92%) e foram classificadas como "fécula tipo 1", pela legislação brasileira. De acordo com a microscopia eletrônica de varredura, os grânulos de amido das féculas apresentaram forma arredondada e ligeiramente achatada em uma das extremidades, com superfície lisa e tamanhos diferentes para as três variedades. As temperaturas de gelatinização dos amidos das três féculas (T p = 74,4°C) não apresentaram diferença significativa (p  0,05), porém o amido extraído da variedade Pai Ambrósio apresentou a maior entalpia de gelatinização (∆H gel = 5,88 J/g).

Cassava has importance as a source of human and animal food. With the objectives to select promising sweet and bitter cassava varieties for breeding programs, 27 genotypes were characterized in terms of their quantitative and qualitative properties. Roots were harvested from three plants per genotype, washed, peeled, sanitized. Regarding the yield, the storage root number (SRN), and the fresh storage root weight (FSRW), were determined, as well as the root fresh matter content (RFMC), and root dry matter content (RDMC), both expressed as a percentage. Among the cassava genotypes, the protein content ranged from 0.1-0.7%; lipids 0.3-2.1%; moisture 58.0-65.2%; 0.1-1.0% ash; fibers 0.9-1.9%; acidity 1,1-2,7%; pH 6.3-6.8; TSS between 0.8-1.2 ºBrix; glucose 0.1-0.8% and sucrose 0.5-1.0%, except for the fructose and starch contents, which did not vary significantly. The principal component analysis showed that the factors explain 84.2% of the total variability and through cluster analysis, evidencing cluster III for the highest starch yield and cluster I for the highest average of lipids and proteins

Cassava (Manihot esculenta Crantz) is an important crop in Brazil and Pará is the major producer of roots. High temperature and humidity of tropical regions favor the development of various diseases, among them the cassava root rot. The objective of this study was to evaluate the effect of luminosity and culture medium on the mycelial growth and sporulation of Phytopythium sp. associated with different methods of inoculation on cassava roots. In vitro tests for pathogen growth were established in a 2 x 6 factorial design (luminosity x culture medium) with five replicates and the means were compared by t test (P≤0.05). The culture medium containing sweet cassava root produced greater mycelial development and higher pathogen sporulation and it was the most suitable medium for pathogen culture. The culture under absence of light generated better mycelial growth than culture under 12 hour of light. Regarding the type of inoculation, the response was better when deeper injuries were induced.