Growth and flowering physiology, and developing new technologies to increase the flower numbers in the Genus Lilium

The genus Lilium is important as potted plants or cut flowers for horticultural trade and for gardens. However, most of the extensive research on the growth and flowering of this genus was conducted with L. longiflorum Thunb. (Easter lily) forcing large bulbs grown in the field for at least one or two years. Dormancy had to be broken to induce flowering by cold treatment which was given to mature bulbs (vernalization). It would be desirable if the bulb production phase could be bypassed to shorten the total production time, ideally by manipulating the temperature during the bulb programming phase (vernalization methods) and the early greenhouse forcing phase (from potting to flower bud initiation). Information on the physiology of bulb development, controlled flowering, and timing for the Easter, and to certain extent for the Asiatic hybrid lily is readily available. However, information on LA, L. longiflorum x Oriental (LO), and Oriental x Trumpet (OT) hybrid lilies, is not available. The objective of this article is to review factors that control flower numbers and speed of flowering, and to present outlines for producing quality plants of L. longiflorum, L. xelegans, and LA hybrids, starting from seeds, stem bulbils, and tissue cultured plants, respectively, in a year. Detailed information on the production of L. xelegans starting from stem bulbils is presented. Cut flowers of Asiatic hybrid 'Beni no Mai' with 2 to 3 flowers and strong 60 cm stems were produced in less than a year when mature bulbils, weighing about 400 mg harvested 40 to 50 days after flowering, are treated with a sequential temperature treatment (SEQ CD) 14 to 20 days each at 5A degrees C-15A degrees C-5A degrees C. This production period can be divided into plug production phase from potting the treated bulbils shoot emergence lasting about 200 to 230 days and the second phase from shoot emergence to flowering requiring 90 to 100 days. The increase in the number of flowers could result from the increased shoot apex size and not from the changes in soluble and cell wall neutral sugars.