One of the main constraints in the cultivation of the potato is the cost of producing seed tubers since this can account for between 30 to 50% of the total production expenses. There is a number of potato propagation procedures that are currently being used worldwide to multiply seed potatoes; conventional seed potato production, micro propagation, hydroponics and aeroponics. As aeroponics is still a relatively new technique in South Africa that has not been researched extensively for the production of minitubers, an experiment was done to assess the effects of different harvesting intervals and planting densities on the final yield and quality of potato minitubers. Potato plantlets, cv BP1, were grown aeroponically at two different densities (20 and 30 plants/m2) and four harvest intervals (7, 10, 14 and 18 days). Plants demonstrated a rapid vegetative development at the beginning when supplied with a nutrient solution at an EC of 1.5 mS.cm-1. The interaction between harvesting intervals and plant densities did not influence plant morphological development, minituber quality or yield. Best yield in terms of tuber number were realised when harvesting every 7 days with a total tuber number of 299 per m2 over the growing period; more than twice that harvested in other treatments. Harvesting interval did not have an effect on average individual tuber fresh weight. Plant density did not have any effect on average and total tuber number, neither on the average and total minituber fresh weight. At harvest, minitubers were graded into three classes: small (<20 g), medium (20-40 g) and large (>40 g) and stored for two months at 3oC, 16oC and 25oC. Large minitubers had longer sprouts with an average of 7.9 mm and a higher percentage of firmness. The higher storage temperature of 25oC resulted in tubers with a higher number of sprouts (5.08 sprouts per tuber), longer sprouts of about 11.03 mm and with a sprouting capacity of 61.16%. Harvest interval also influenced the phosphorus and copper concentration in minitubers, both being higher when harvested every 10 days. Size did not influence macro and trace content of the minitubers. Further research can be focused on further evaluating the efficacy of harvest intervals, plant densities and storage temperatures on more cultivars and postharvest potato seed quality.
Key words: potato, aeroponics, harvest interval, plant density, minitubers Stellenbosch University http://scholar.sun.ac.za
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