| Popis: |
Root development and plant dry matter distribution were observed for 16 weeks after planting in cassava (Manihot esculenta Crantz) grown from stem cuttings in controlled-environment chambers with a day–night temperature of 32–27 °C. During an initial phase lasting 6 weeks, axillary shoots and adventitious roots regenerated, while the original cutting lost weight, and total plant weight remained constant. During the second phase from the 6th to the 16th week there was growth of all plant parts including root tubers. Tuber growth accounted for 46% of plant dry matter accumulated over the final 2 weeks of the study. Roots arising from the base of the cutting were more numerous than nodal roots and produced a proportionately greater number of tubers. Differentiation of secondary tissues started at 4 weeks, and root thickening was visible to the naked eye at 6 weeks. Tuber initiation occurred over the 6- to 16-week period in some of the thickened roots and resulted from production of enlarged storage parenchyma cells in place of secondary xylem fibres, along part of the root axis. At 8 weeks, these thickenings became visible to the naked eye as tubers, distinguishable from the thinner "neck" region, which continued to produce normal secondary xylem with little storage tissue. Other roots thickened uniformly along the root axis, by normal secondary growth, and did not initiate tubers. Root tubers grew in size by continued production of storage tissue, increasing tuber width but not length, accompanied by a decrease in sugar content and increase in starch content. |
