Phenotypic diversity of plant morphological and root descriptor traits within a sweet potato, Ipomoea batatas (L.) Lam., germplasm collection from 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.