Sweet potato (Ipomoea batatas L.) is the fifth most important crop in the developing countries after rice, wheat, maize and cassava. The amplified fragment length polymorphism (AFLP) method was used to study the genetic diversity and relationships of sweet potato accessions in the germplasm collection AFLP analysis of 97 sweet potato accessions using ten primer combinations gave a total of 202 clear polymorphic bands. Each one of the 97 sweet potato accessions could be distinguished based on these primer combinations. Estimates of genetic similarities were obtained by the Dice coefficient, and a final dendrogram was constructed with the un-weight pairgroup method using arithmetic average. AFLP-based genetic similarity varied from 0.388 to 0.941, with a mean of 0.709. Cluster analysis using genetic similarity divided the accessions into two main groups suggesting that there are genetic relationships among the accessions. Principal Coordinate analysis confirmed the pattern of the cluster analysis. Analysis of molecular variance revealed greater variation within regions (96.19%) than among regions (3.81%). The results from the AFLP analysis revealed a relatively low genetic diversity among the germplasm accessions and the genetic distances between regions were low. A maximally diverse subset of 13 accessions capturing 97% of the molecular markers diversity was identified. We were able to detect duplicates accessions in the germplasm collection using the highly polymorphic markers obtained by AFLP, which were found to be an efficient tool to characterize the genetic diversity and relationships of sweet potato accessions in the germplasm collection in Tanzania.
In Tanzania sweet potato ranks as the third most important crop after cassava and potato. We studied the phenotypic diversity of morphological plant and root descriptor traits in accessions of the sweet potato germplasm collection of Sokoine University of Agriculture, Morogoro and Sugarcane Research Institute, Kibaha, Tanzania, using phenotypic characters. A total number of 105 sweet potato accessions of different geographic origins were studied in field trials of The Sugarcane Research Institute at Kibaha Tanzania, and data were recorded for 27 phenotypic characters. Estimates of pair-wise phenotypic similarities using the Manhattan coefficient varied from 0.023 to 0.814, with a mean of 0.285. Cluster analysis was conducted using the unweighted pair group method with arithmetic mean (UPGMA) and Principal Coordinate Analysis (PCO). The clustering of phenotypic data resulted in a dendrogram which was discordant with geographic origin and AFLP data. The analysis of variance (ANOVA) revealed highly significant variation among the accessions for 21 out of the 27 characters studied. Phenotypic analyses revealed a wider range of variability than AFLP analyses. Comparison of molecular and phenotypic data using the Mantel test showed a very low correlation (r 2 = 0.0007). Molecular and phenotypic classifications are discordant, and both are necessary to classify the germplasm correctly and to clarify genetic relationships among sweet potato accessions.
Common bean (Phaseolus vulgaris L.) has two major origins of domestication, Andean and Mesoamerican, which contribute to the high diversity of growth type, pod and seed characteristics. The climbing growth habit is associated with increased days to flowering (DF), seed iron concentration (SdFe), nitrogen fixation, and yield. However, breeding efforts in climbing beans have been limited and independent from bush type beans. To advance climbing bean breeding, we carried out genome-wide association studies and genomic predictions using 1,869 common bean lines belonging to five breeding panels representing both gene pools and all growth types. The phenotypic data were collected from 17 field trials and were complemented with 16 previously published trials. Overall, 38 significant marker-trait associations were identified for growth habit, 14 for DF, 13 for 100 seed weight, three for SdFe, and one for yield. Except for DF, the results suggest a common genetic basis for traits across all panels and growth types. Seven QTL associated with growth habits were confirmed from earlier studies and four plausible candidate genes for SdFe and 100 seed weight were newly identified. Furthermore, the genomic prediction accuracy for SdFe and yield in climbing beans improved up to 8.8% when bush-type bean lines were included in the training population. In conclusion, a large population from different gene pools and growth types across multiple breeding panels increased the power of genomic analyses and provides a solid and diverse germplasm base for genetic improvement of common bean.
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