Effect of ambient temperature on the growth and development of amaryllis (Hippeastrum hybridum Hort.) bulbs

How different day/night temperature affect the growth and development of the vegetative and reproductive parts, including the bulbs of amaryllis (Hippeastrum hybridum) plants in growth chambers for two years was investigated. One-year-old, 2-leafed seedlings were transferred to growth chambers set at 17 °/12°C (low, L plot), 24°/17°C (middle, M plot) and 30/24°C (high, H plot) under natural daylength.1. High temperatures (H plot) hastened the unfolding and elongation of leaves, and increased markedly the growth of mother bulb and daughter bulbs, but the plants did not flower.2. In plants exposed to low temperature (L plot), the leaves were the slowest of the three plots to unfold and elongate; the mother bulbs were slow to enlarge but produced the most daughter bulbs. The temperature favored floral development.3. Middle temperature (M plot) educed intermediate vegetative growth and the enlargement of mother and daughter bulbs. This condition was optimum for flower stalk elongation and flowering.Thus, comparing the responses of amaryllis grown under low, middle, and high day/night temperatures, high temperature favored promotion of mother bulb enlargement, but the moderate and low temperatures were optimum for bulb and flower production.