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.

Plant breeding efficiency relies mainly on genetic diversity and selection to release new cultivars. This study aimed to identify landraces with favorable characteristics that can be used as parents of segregating populations in common bean (Phaseolus vulgaris L.) breeding programs. Firstly, ten bean genotypes were selected because they showed promising agronomic performance, and the following seven adaptive traits of four commercial bean cultivars were evaluated: i) plant height; ii) diameter of the stem; iii) height of the insertion of the first pod; iv) pod number per plant; v) grain number per pod; vi) weight of a thousand grains and vii) grain yield. The accessions BAF 07, BAF 44, and BAF 45 are promising in terms of increasing plant height, and accession BAF 01, in terms of reducing plant height. The accession BAF 07 was also the most promising in terms of a plant ideotype that combines higher plant height, maximum height of the insertion of the first pod, and increment in grain yield. Moreover, the selection can be made between and within accessions, because genetic variability is also present within landraces.

Os objetivos deste trabalho foram estimar a eficiência da seleção, em populações segregantes de feijoeiro, para a resistência à murcha de Curtobacterium, e indicar o melhor período do ciclo da cultura para se proceder à seleção das plantas resistentes. Foram realizados os cruzamentos convergentes IAC-Carioca Aruã x SCS Guará, IAC-Carioca Pyatã x SCS Guará e IAC-Carioca Pyatã x Pérola, dando origem às gerações F1, F2, F2:3, F3:4, que foram inoculadas com Curtobacterium flaccumfaciens pv. flaccumfaciens isolado 2634. A resistência foi avaliada segundo escala de notas referentes aos sintomas comuns da doença aos 20, 40 e 60 dias após a inoculação. Os resultados indicaram que as gerações segregantes de Aruã x Guará, Pyatã x Guará e Pyatã x Pérola possuem comportamento semelhante em relação à resistência aos sintomas da murcha de Curtobacterium. A seleção foi efetiva para as gerações oriundas de Aruã x Guará e Pyatã x Pérola e o período entre 40 e 60 dias após a inoculação é o mais adequado para seleção de plantas segregantes para resistência.

The objective of this study were both the estimation of the efficiency of selection in segregating populations of common bean for the resistance to Curtobacterium and also the indication of the best time of the cycle to make the selection of resistant plants. To this end, we used converging crosses between IAC-Carioca Aruã x SCS Guará, IAC-Carioca Pyatã x IAC-Carioca and SCS Guará x Pérola, originating filial generations (F1, F2, F2:3 and F3:4) which were subsequently inoculated with Curtobacterium flaccumfaciens pv. Flaccumfaciens, isolate 2634, and evaluated according to a scale related to the common symptoms of the disease at 20, 40 and 60 days after inoculation. The results showed that the segregating generations of Aruã x Guará, Pyatã x Guará and Pyatã x Pérola had similar behavior in relation to resistance to the Curtobacterium symptoms. The selection is effective for the coming generations of Aruã x Guará and Pyatã x Pérola and the favorable time for distinguishing and selecting reliably segregating plants occurs between 40 and 60 days after inoculation.