Department of Plant Pathology

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Browsing Department of Plant Pathology by browse.metadata.advisor "De Villiers, O. T."

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    The influence of varying ratios of potassium, calcium and magnesium nutrition on quality and storage of potatoes (Solanum tuberosum L.)
    (Stellenbosch : Stellenbosch University, 1993-12) Bester, Gabriel Gerhardus; Maree, P. C. J.; De Villiers, O. T.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: The low calcium concentration of the soils and nutritional imbalances between potassium. calcium and nitrogen have been Identified by the potato industry of South Africa as some of the reasons for Insufficient quality and keeping quality of potato tubers A nutrient fertigation study was conducted under controlled environmental conditions to Investigate the Influence of nutritional Imbalances between potassium. calcium and magnesium (varying cation ratios) on quality parameters One experiment included a boron foliar spray at tuber initiation. Cultivars Hertha. Pimpernel, Up-to-date, Sandvelder and BPI were included in the experiments. Total tuber yield was not influenced to any great extent by different cation ratios. The calcium magnesium mllliequivalent ratio of 26 5 significantly decreased the tuber yield and the calcium: magnesium ratio of 3 6 produced the highest yield under investigation. Potato tuber size grading was improved by an increase in calcium concentration in the different treatments Internal brown spot decreased with an increase in calcium concentration in the different cation ratio treatments. Although the specific gravity, chip colour, fructose, glucose and sucrose concentration of the potato tubers were influenced by the cation ratios, the difference, were not marked. The boron foliar spray applied at tuber initiation increased nitrogen, potassium, calcium and boron, and decreased the copper, zinc and manganese concentrations of potato plants The varying cation ratios influenced the mineral concentration of the potato plants and interacted with cultivars. Haulms and leaves showed a different response to treatments. The varying cation ratios and boron foliar spray resulted in a difference in mineral concentrations in the periderm, cortex and medulla of freshly harvested potato tubers Cultivars differed in mineral concentration in each treatment. Changes in potassium calcium and magnesium concentration of potato tubers during cold storage were influenced by treatments. Sprouting of progeny tubers (physiological quality) of treated plants was influenced by varying cation ratios, boron foliar spray and cultivars Sub-apical necrosis was observed in treatments with the lowest concentration of calcium Sprout mineral concentration was influenced by treatments. especially the calcium and magnesium contents. Susceptibility of potato tubers to Fusarlum so/ani can be influenced by fertilizing with varying cation ratios. The influence of treatments on susceptibility changed with cold storage. Pectin bound calcium and magnesium concentrations were determined in the medulla of potato tubers The pectin bound calcium concentration at harvest and after cold storage, was influenced most and the pectin bound magnesium was less by the treatments. The sugar concentration in the medulla of cold stored potato tubers was mainly influenced by cultivars, the effect of the varying cation ratios being less marked The fructose and glucose concentration increased and the sucrose concentration decreased with cold storage The magnitude of this change in sugar concentration was influenced by cultivar and to a lesser extent by the varying cation ratios The cortex fructose and glucose concentration was higher, and the sucrose concentration lower than that of the medulla The difference in sugar concentration between the cortex and medulla was mainly influenced by different cultivars. This study therefore shows that varying ratios of potassium to calcium to magnesium, a boron foliar spray and different cultivars have a marked effect on potato tuber quality at harvest and after cold storage.