The Origin And Development Of Adventitious Roots Of Cassava(Manihot Esculenta Crantz)

In this study, Manihot esculenta crantz cv.South China8(SC8)and Manihot esculenta Crantz cv.South China9(SC9) were used as experimental materials, The method of tissue culture was applied to obtain the micro-tuber, The occurrence, development and morphological structure of cassava in micro-tuber and tuber have been researched by the method of anatomical technology.The conclusions of this analysis are as follows:(1)In this report, A micro-tuber root regeneration system from stem segment of SC8have been extensively investigated. Adding0.5mg/L NAA.0.5mg/L6-BA and5%sucrose to the MS based medium was most favorable to the in vitro growth of micro-tuber roots. Micro-tuber root can be obtained by two ways:the direct induction and the second induction. By the way of direct induction can much more easily obtain micro-tuber root. The ratio of micro-tuber can reach more than90%. Explant maturity may also affect the induction ability of micro-tuber. The base of stem section was more easily induce micro-tuber than the upper part of stem section.(2)In vitro, adventitious root primordium originated in two locations:the vascular parenchyma cells between the layers and primary phloem, the ray parenchyma. The growth of adventitious root forms2types of root in different development stages:primary fibrous root, fibrous root with secondary tissue. There are two kinds of root forms in different medium types:fibrous root and micro-tuber root. There are epidermis, cortex, and stele in the primary fibrous root; There was a similar periderm in the fibrous root with secondary tissue and it was observed about three or four mouths after be cultured There wasn’t any structure of secondary tissue formed in the whole procession of micro-tuber root induction, the enlargement of micro-tuber root was the results of the increasing of cortical parenchyma cell volume and cell gap.5days after been cultured, a small amount of starch grains occurred in the cortical parenchyma cells and starch accumulated with time passed.(3)Field panting showed adventitious root primordium originated in three locations: bud scars, stipular scars and the incision. Each position of adventitious roots may develop into tubers. The growth of adventitious root can form3types of root:primary fibrous roots, secondary fibrous roots and tubers. There wasn’t any structure of secondary tissue formed and starch accumulated in the primary fibrous roots. Secondary fibrous roots occurred secondary growth, periderm and secondary vascular tissue, in wood ray parenchyma cells and cortical parenchyma cells small amount of starch accumulation happened. Three months later, tubers began to form.Secondary vascular tissue occupies major part of tuber, starch mainly accumulated in the secondary xylem parenchyma cells.(4)There isn’t any difference in morphology between the cassava cultured in vitro and in field, they all formed by epidermis, cortex, and stele. Both appear secondary structure, the difference is that root in vitro conditions formed periderm secondary structure only under specific conditions, but in vitro conditions, cassava roots all have the capability to form periderm, secondary xylem and secondary phloem and other secondary structure. Comparison of starch accumulation between micro-tuber root and field tuber, there is a time and space differences:In the early micro-tuber root, there wasn’t starch accumulation and only a less starch was observed in the cortical parenchyma cells later; Field-grown cassava root’s starch was produced in the primary root after secondary structure beginning to accumulate. The starch mainly concentrated in the secondary xylem, and some located in the cortex and phloem.