Genetic variation and its relationship to root weight in the sweet potato as revealed by RAPD analysis

The aim of this work was to evaluate the genetic variations of the sweet potato by a random amplified polymorphic DNA (RAPD) assay with emphasis on correlations with morphological traits. Cuttings of superior and inferior lines derived from tissue culture-regenerated plants and asexually propagated plants of the Tainung 57 (TN57) and Tainung 66 (TN66) sweet potato were planted in the field. Three important agronomic traits, top weight, root weight, and root numbers, were measured 3 months after planting. The RAPD-PCR (polymerase chain reaction) technique was used for detecting genomic variations within and between varieties. Of the 160 primers tested in this study, 38 revealed clear and repeatable RAPD polymorphisms. Among the 38 primers, 8 showed consistent amplified band patterns among the plants with variations within and between varieties, while the others indicated polymorphisms within or between varieties. RAPD markers demonstrated a clear association with root weight. However, the presence and absence of these genetic markers did not correspond well with either the top weight or root number. Genetic instability revealed in the selection stress of superior and inferior plants was found to be independent of variety. In addition, both asexual propagated and tissue culture-induced somaclonal variations were observed in this study. Our results show that RAPD is a useful tool for detecting somaclonal variations from varietal and intra-varietal sweet potato for monitoring of DNA changes in somaclonal variants. The identification of regions which are associated with the character of root weight by RAPD markers enables us to use these markers as selection tools to improve root weight in sweet potato.