Multidirectional effects of exposing freesia corms to chilling on flower bud initiation, flower bud development and flower stalk elongation, and cormformation

Corms of Freesia hybrida Hort. 'Cote d'Azur' averaging 6.7 g, which had bee n stored at 30 degrees C for 10 weeks, were potted, exposed to seven temper ature classes from 3 to 21 degrees C for 6 weeks and then transferred to 23 degrees C. Flower buds were observed microscopically at the end of exposur e to 6, 9, 12, 15, and 18 degrees C. The developmental stage of flower buds was most advanced at 12 and 15 degrees C; however, the flower buds initiat ed at 12, 15, and 18 degrees C failed to develop floral parts, and the elon gation of the flower stalks was greatly suppressed upon transfer to 23 degr ees C. Whereas, plants exposed to 9 OC for 6 weeks consequently flowered at 23 degrees C; those exposed to 6 degrees C developed malformed inflorescen ces having abnormally elongated bracts and lacking floral organs. At 23 deg rees C, the epical meristems of plants exposed to 3 degrees C continued to initiate leaf primordia, while those exposed to 21 degrees C formed bract-l ike organs. Daughter corm formation 10 weeks after transferring plants to 2 3 degrees C was most advanced in plants previously exposed to 12 degrees C for 6 weeks. Three directional effects of chilling: 1) direct effect on flo wer bud initiation, 2) after-effect on flower bud development and flower st alk elongation, and 3) direct effect and/or after- effect on corm formation , are discussed.