The origin and structure of adventitious roots in sweet potato (Ipomoea batatas)

Morphological and anatomical studies demonstrated the root formation characteristics of sweet potato (Ipomoea batatas (L.) Lam.). In this study, the presence and importance of preformed root primordia is recorded for the first time. On the vines, preformed root primordia are present in sets of 4-10 adjacent to the leaf bases, even those of young leaves. Macroscopically, the root tips of preformed root primordia protruding through the cortex and epidermis of the stems are prominent. These root primordia originate from the procambium on both sides of the leaf gap and produce adventitious roots, with pentarch, hexarch or septarch steles. Under normal conditions, storage roots will only develop from thick roots originating from undamaged preformed root primordia on the nodes of cuttings or nodes of newly formed vines, or from wound roots originating from the cut ends of stem or leaf cuttings. Terminal vine cuttings produce more tubers as a result of fewer damaged root primordia. Lateral roots originating from damaged preformed root primordia, or directly from the adventitious roots, exhibit tetrarch steles and develop into fibrous roots without the potential to develop into storage roots. This understanding of the origin, anatomy and morphology of sweet potato roots and the use of terminal vine cuttings with a higher percentage of undamaged root primordia, should improve production practices, which will contribute to improved crop establishment and increased yield.