ABSTRACT: 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.

RESUMO A jabuticabeira (Plinia sp.) é uma frutífera nativa pertencente à família Myrtaceae, de ocorrência espontânea em grande parte do Brasil. A estimativa da divergência genética entre genótipos de populações nativas pode ser útil para a conservação e conhecimento dos recursos genéticos disponíveis, visando a formação de bancos de germoplasma e melhoramento genético da espécie. Com o objetivo de avaliar a diversidade genética de jabuticabeiras identificadas em municípios do Recôncavo da Bahia, foram caracterizados 35 genótipos por meio de iniciadores ISSR (Inter Simple Sequence Repeats). Os 18 iniciadores geraram um total de 463 fragmentos de amplificação, sendo que o número de fragmentos por iniciador variou de 14 a 36, com uma média de 25,72 e polimorfismo de 99,65%. O conteúdo de informação polimórfica variou de 0,13 a 0,33 com média de 0,22 e o poder de resolução do marcador de 4,34 a 15,77, com uma média de 8,67. A análise multivariada possibilitou a formação de cinco grupos de divergência genética, em que a maior distância foi de 0,97 entre os genótipos JCA6 e JSF8 e a menor entre o JMT2 e JCA1 (0,11). A partir da utilização dos marcadores ISSR é possível verificar a variabilidade existente entre genótipos de jabuticabeira avaliados.

ABSTRACT The jaboticaba tree (Plinia sp.) is a native fruit tree belonging to the Myrtaceae family, which occurs spontaneously throughout Brazil. The estimation of genetic divergence among genotypes of native populations can be useful for conservation and knowledge of available genetic resources, in the formation of gene banks and breeding species. In order to evaluate the genetic diversity of jaboticaba trees identified in the Bahia Reconcavo municipalities, 35 genotypes were characterized by ISSR primers (Inter Simple Sequence Repeats). The 18 primers generated a total of 463 amplicons, and the number of initiator fragments ranged from 14 to 36, with an average of 25.72% and 99.65% polymorphism. Polymorphic information content ranged from 0.13 to 0.33 with a mean of 0.22 and the marker resolution power from 4.34 to 15.77, with an average of 8.67. Multivariate analysis allowed the formation of five groups of genetic divergence, where the longest distance was 0.97 between JCA6 and JSF8 genotypes and the lower of JMT2 and JCA1 (0.11). From the use of ISSR markers it is possible to check the variability between genotypes on the evaluated jaboticaba trees.

The geminivirus complex known as cassava mosaic disease (CMD) is one of the most devastating viruses for cassava (Manihot esculenta Crantz). The aim of this study was to use molecular-assisted selection (MAS) to identify CMD-resistant accessions and ascertain promising crosses with elite Brazilian varieties. One thousand two hundred twenty-four accessions were genotyped using five molecular markers (NS169, NS158, SSRY028, SSRY040 and RME1) that were associated with resistance to CMD, along with 402 SNPs (single-nucleotide polymorphism). The promising crosses were identified using a discriminant analysis of main component (DAPC), and the matrix of genomic relationship was estimated with SNP markers. The CMD1 gene, previously described in M. glaziovii, was not found in M. esculenta. In contrast, the CMD2 gene was found in 5, 4 and 5 % of cassava accessions, with flanking markers NS169+RME1, NS158+RME1 and SSRY28+RME1, respectively. Only seven accessions presented all markers linked to the CMD resistance. The DAPC of the seven accessions along with 17 elite cassava varieties led to the formation of three divergent clusters. Potential sources of resistance to CMD were divided into two groups, while the elite varieties were distributed into three groups. The low estimates of the genomic relationship (ranging from -0.167 to 0.681 with an average of 0.076) contributed to the success in identifying contrasting genotypes. The use of MAS in countries where CMD is a quarantine disease constitutes a successful strategy not only for identifying the resistant accessions but also for determining the promising crosses.