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

Abstract

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.

Molecular Regulation of Storage Root Formation and Development in Sweet Potato

“…Sweet potato roots develop as adventitious roots from the preformed root primordia in the nodal region of stem cuttings or cut sprouts or from the cut ends of stem used as planting material (Togari 1950;Hahn and Hozyo 1983;Belehu et al, 2004;Villordan et al 2009a,b). The number of adventitious roots developing from a single node depends upon the cultivar and may vary between 5 and 10.…”

“…Under conducive conditions such as cool climate (mean of maximum and minimum temperatures between 22 and 26°C) and adequate soil moisture, adventitious roots that have pentarch, hexarch, or septarch stele and a central pith with or without central metaxylem show differentiation of protoxylem, primary cambium, and develop a vascular cambium that joins secondary xylem and phloem as well as parenchyma cells and several circular anomalous cambia are formed around the protoxylem as well as secondary xylem cells (Togari 1950;Esau 1965;Kokubu 1973;Wilson and Lowe 1973;Wilson 1982;Nakatani and Komeichi 1991;Ko et al 1993;Ravi and Indira 1996;Belehu et al 2004). Interstitial cambial strips that are not associated with vascular tissues also develop within the secondary parenchyma and contribute to storage root growth.…”

S-metolachlor and rainfall effects on sweetpotato (Ipomoea batatas L. [Lam]) growth and development

“…Sweetpotato production begins by transplanting stem cuttings (slips). Transplanted slips produce adventitious roots from the nodes and from the cut-end of the slips within few days of transplanting (Belehu et al, 2004;Pardales, 1993). Some of these roots develop into economically important storage roots through proliferation of cambial cells that form starch-accumulating parenchyma cells (Belehu et al, 2004;Ravi et al, 2009;Villordon et al, 2009).…”

Crops that feed the world 5. Sweetpotato. Sweetpotatoes for income and food security

“…Apical cuttings produce more tubers as a result of fewer damaged root primordia, whereas lateral roots originating from damaged preformed root primordia, or directly from adventitious roots, exhibit tetrarch steles and develop into fibrous roots without the potential of developing into storage roots (Belehu et al 2004). Increased numbers of nodes per cutting result in greater numbers of vines per plant, increased vine length and greater tuber yield (Chowdhary et al 1986).…”