Factors influencing the phase change and the tuberization process in potato plant under warm lowland and cool highland conditions

Five planting materials, namely: in vitro cuttings, simple leaf cuttings, compound leaf cuttings, sprout cuttings, and tuberlets obtained from four varieties of potato with different genetic backgrounds were evaluated for growth parameters such as plant height, leaf width and length, number of leaves, root length and duration of phase change under cool highland condition. Plants grown from in vitro cuttings maintained the longest juvenile phase indicating that for propagation purposes, in vitro cuttings are ideal planting materials. Among the four varieties, TM-4 which was tallest required the longest time to produce the first and second compound leaf. As to the role of endogenous growth hormones, results showed that gibberellic acid (GA3) did not influence the phase change whereas auxin-like compounds might have a role in regulating the phase change but their concentration was not detected. GA3 increased plant height by lengthening the internodes under both warm and cool growing conditions while stem number was increased only at warm growing condition. Root growth was significantly promoted while fresh tuber yield was significantly reduced. On the other hand, benzyladenine (BA) and chlorethyltrimethylammonium chloride (CCC) induced tuberization. The increase in fresh tuber weight, tuber number and harvest index by BA and CCC was influenced by some endogenous hormones such as indolacetic acid (IAA) and kinetin as indicated by the accumulation of these substances in plants treated with BA and CCC. Among the four varieties, P-7 and Cosima produced the highest fresh tuber yield under warm and cool conditions, respectively. Under warm growing condition, apical disbudding proved to be more effective in increasing stem number, number of tubers and fresh tuber weight than branch disbudding. Under cool growing condition, however, branch disbudding was more effective than apical disbudding. Disbudding increased the fresh tuber yield of P-7 under both warm and cool conditions.