TUBER INITIATION IN HYDROPONICALLY GROWN POTATOES BY ALTERATION OF SOLUTION PH

Because tuberization in potatoes (Solanum tuberosum L.) reportedly is inhibited when stolons are immersed in liquid, this study was conducte d to determine the effect of intermittent pH reductions of the nutrien t solution on tuber induction of potatoes in solution culture. Tissue- culture potato plantlets were transplanted into solutions maintained a t pH 5.5. The pH of the nutrient solution was changed to 3.5 and 4.0 f or 10 hours on each of three dates (30, 35, and 40 days after transpla nting). For the pH 3.5 treatment, tubers were observed first on day 42 and averaged 140 tubers per plant at harvest on day 54. For the pH 4. 0 treatment, tubers were observed first on day 48 and averaged 40 tube rs per plant at harvest. At a constant pH 5.5, tubers were observed on day 52 and averaged two tubers per plant at harvest. Plants with the intermittent pH 3.5 had smaller shoots and roots with shorter and thic ker stolons compared to constant pH 5.5. With the intermittent pH 4.0, plants were of similar size, but stolons were shorter and slightly th ickener compared to those from pH 5.5. Mineral composition of leaf tis sues at harvest was similar for the three pH treatments. These results indicate that regulation of solution pH can be a useful technique for inducing tuberization in potatoes.