Potato mini tuber production afffected by a short-term calcium deficiency
It was previously reported that tuber initiation is restricted in soil-less production systems owing to a lack of mechanical resistance and that a low-pH shock treatment over a 10-h period alleviated this problem. Tuber initiation was investigated under soil-less conditions by growing single-stemmed Van der Plank potato plants in standard aerated nutrient solutions (EC 1.3 mS cm-1, pH 5.5) in two-litre containers. The pH of the nutrient solution was changed by replacing the standard solution with solutions at pH levels of 3.0, 3.5 and 4.0 for 1 0-h periods, 25 and 35 days after transplanting. Apart from these low-pH treatments, a treatment where the nutrient solution was replaced with a solution containing no calcium (pH 5.5) was also included. Tuber initiation under the influence of these treatments was compared to that of a standard nutrient solution. All plants were harvested 45 days after transplanting. A tuber tip with a diameter more than double the diameter of the stolon was regarded as a tuber. Conditions in the greenhouse were favourable for tuber induction. Shock treatments applied at 25 days after transplanting led to the production of more tubers than when it was applied at 35 days after transplanting. A 10 h shock treatment at pH 4 as well as the Ca-free nutrient solution increased the number of tubers per plant from less than 40 on control plants to more than 66 on the treated plants. These results support the hypothesis that a low-pH shock or an induced short term Ca deficiency may damage cell walls or membranes in stolon tips that may enhance tuber initiation.