THE EFFECT OF TEMPERATURE ON THE DEVELOPMENT OF HIPPEASTRUM : A PHYTOTRON STUDY

Hippeastrum flowers in the spring, but the exact flowering time can be controlled by applying specific thermal regime to large sized bulbs. To control the flowering time, and improve quality and size of Hippeastrum (Hippeastrum hybridum, cv. Red Lion) bulbs, the effect of temperature regime was investigated. The objectives of this research were to study the effect of ambient temperature on the growth rate of bulbs, the effect of soil temperature on the growth rate of bulbs and the susceptibility of several bulbs\u27 sizes to various thermal regimes. Two sets of experiments were conducted: A phytotron experiment with six day/night temperature combinations and a controlled greenhouse experiment in which five levels of minimum soil temperature treatments were imposed. Temperature had a strong effect on bulb and leaf development. Temperatures of 27℃ were optimal for leaf area development while temperatures of 22℃ were optimal for bulb development. Different patterns of bulb growth rate were found when bulbs of different initial sizes had grown under the same minimum growing temperature (22℃): The small bulbs (initial diameter of 5.4cm) had grown about two cm throughout the season (180 growing days) while the large bulbs (initial diameter of 7.9cm) had grown less the one cm. The growth rate of the other three initial bulb size categories (6.1, 6.7 and 7.3cm) varied between these two rates. A high linear temperature dependent correlation was found between leaf area and bulb size. The distribution of the fresh matter among the roots, leaves and bulbs was also found to be temperature dependent