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The effects of paclobutrazol on the vegetative growth, reproductive development, total nonstructural carbohydrate of the shoots, and nutrient mobilisation to the leaves of 'Tommy Atkins' mango (Mangifera indica) trees grown in the Rift Valley of Ethiopia were evaluated during the 2002/03 season. The trees used were characterised by excessive vegetative growth, erratic flowering, and fruiting with declining productivity that validated the evaluation of paclobutrazol. Uniform trees were selected for a randomised complete block design experiment with two methods (soil and spraying) and four rates of paclobutrazol (0, 2.75, 5.50, 8.25 g a.i. per tree) in factorial combinations. There were three blocks and three trees per plot for each treatment. The results showed that application of paclobutrazol at rates of 5.50 and 8.25 g a.i. per tree both as a soil drench and spray applications were effective in suppressing vegetative growth compared with the control. Consequently, the trees from these treatments had higher total non-structural carbohydrate in their shoots before flowering. Compared with the control, trees treated with paclobutrazol had higher results for percentages of shoots flowering, number of panicles produced, percentages of hermaphrodite flowers, yield as well as quality of the fruit. Applications of paclobutrazol did not affect the leaf macronutrient content levels analysed (N, P, K, and Ca), and with the exception of manganese, the micronutrient (Cu, Zn, and Fe) levels of the treated tree's leaves were significantly higher than the control.

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.

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