Temperature effects on bulb growth and inflorescence development of Lachenalia cv. Ronina

Abstract

Lachenalia cv. Ronina, a new flower bulb variety developed by the ARC-Roodeplaat Vegetable and Ornamental Plant Institute, has excellent characteristics as a flowering pot plant, but information on cultivation practices is limited. Temperature is the most important environmental factor regulating the growth cycle of this flower bulb, therefore three temperature regimes, representing a cool, moderate and warm winter climate, were chosen to manipulate floral development. During this study the bulb structure, development and growth were determined during the bulb preparation phase (year 1) and subsequently the morphology of the bulb was evaluated during the pot plant phase (year 2). Regarding the bulb structure and development, cultivar Ronina has a typical rhythmic, sympodial, modular growth. Bulb growth and module formation is affected by temperature. The low (L TR) and moderate (MTR) temperature regime, which represent the cool and moderate winter climate in South Africa were found to be the best temperature regimes for bulb production. The high (HTR) temperature regime caused bulbs to develop faster, but flower abortion occurred. At the end of the bulb preparation phase, daughter bulbs were observed in the axils of the leaf bases in bulbs of all three temperature regime treatments. Additional inflorescences from underdeveloped growth modules were detected in the axils of the inner leaf bases of bulbs of the high temperature regime. The bulbs as well as the roots are the main sinks for the carbohydrates, whereas the inflorescence and especially the leaves are the main source for soluble sugars. Due to the more stable temperature that was applied in the growth cabinets, the flowering date of bulbs in all three treatments flowered two months earlier than plants growing in the open. During this production phase, simultaneous flowering occurred more within bulbs that were subjected to the LTR during the bulb preparation phase. These bulbs also produced broader leaves with more spots on and better quality inflorescences with a longer keeping ability than those of the higher temperature regimes. A correlation was found between the leaf number and the number of inflorescences of plants in the pot plant phase, grown from LTR treated bulbs. The bulb fresh mass/size at the end of the bulb preparation phase cannot be used as a reliable criterion to predict the quality of the pot plant. By examining the bulb structure at the end of the bulb preparation phase, the quality of the pot plant can be predicted.