Effects of Storage Temperatures on Endogenous Growth Substances and Shoot Emergence in Freesia hybrida corms1

Abstract

Corms of Freesia hybrida Bailey ‘Moya’ and F. hybrida ‘Maria’ were stored at 2°, 13°, or 30°C immediately after harvest and sampled at 0, 6, or 13 weeks for fresh weight, sprouting ability, free indoleacetic acid (IAA), free abscisic acid (ABA) and conjugated ABA (conj-ABA). High performance liquid and gas-liquid chromatography methods were used for identification and quantification of the extractable IAA, ABA, and conj-ABA. Shoots from corms planted immediately after harvest emerged in 33 to 57 days. It is suggested that freshly harvested F. hybrida corms exhibit physiological dormancy for not more than 4 to 6 weeks and subsequently enter a state of imposed dormancy in storage at 30° or 2°. Physiological dormancy was released more rapidly and corm shoots emerged more rapidly during imposed dormancy when stored at 30° versus 2°. The 30° treatment did not appear to be mandatory for shoot emergence since corms stored at 2° or 13° for 6 weeks emerged within 5 or 20 days, respectively. Extended storage at 13° promoted pupation whereas storage at 30° and 2° prevented pupation. Pupated corms did not emerge when planted. The IAA, ABA, and conj-ABA levels in the corms during storage did not correspond with growth inhibition but rather appeared to relate to the formation of the new corm during pupation.

Localization of Endogenous Growth Substances in Freesia hybrida ‘Moya’ Corms Before and After a Heat Treatment1

“…Rehnstrom (19) using bioassays, showed no auxin (IAAlike growth substance) or inhibitors present in Freesia hybrida corms held at 5°C, slight amounts of auxin and inhibitors present after 2 to 3 weeks storage at 10°, and increased auxin levels in the apical and basal zones as the length of storage at 30° increased. In contrast to Rehnstrom's findings, we found that IAA was present in whole freesia corms; at 2° the level decreased from 10 ng/g fresh weight to 3 ng over a 13 week period (5). IAA decreased at 30° storage from 10 to 4 ng/g fresh weight over a 13 week period while the highest IAA levels were found in newly forming or pupating corms at 13° (4,5).…”

“…In contrast to Rehnstrom's findings, we found that IAA was present in whole freesia corms; at 2° the level decreased from 10 ng/g fresh weight to 3 ng over a 13 week period (5). IAA decreased at 30° storage from 10 to 4 ng/g fresh weight over a 13 week period while the highest IAA levels were found in newly forming or pupating corms at 13° (4,5). In gladiolus, a close relative of freesia, corms of developing plants contained auxin which disappeared at the end of the growing season and reappeared after 2 months of storage at room temperature (22).…”

“…Group 2 corms, representing non-treated tissue, were upon arrival immediately weighed, sectioned (Fig. 1), and extracted for free IAA, free ABA and acid hydrolyzable ABA using the procedures described by Gilbertson-Ferriss et al (5).…”

“…Several studies have reported the presence of ABA and other inhibitors in various storage organs; however, their role in dormancy and sprouting regulation is uncertain (1 ,6 ,1 2 , 1 3 , 16, 19, 20, 21, 24). The level of whole corm ABA decreased during 13 weeks of 30°C storage and did not correlate well with the degree of dormancy in freesia corms (5). Rather, ABA appeared to have a promotive role in new corm formation (4,5).…”

“…The level of whole corm ABA decreased during 13 weeks of 30°C storage and did not correlate well with the degree of dormancy in freesia corms (5). Rather, ABA appeared to have a promotive role in new corm formation (4,5). Aung and De Hertog (2), working with tulip bulbs, reported that total ABA content increased 2 to 4-fold, depending on the cultivar, during the course of the several temperature regimes.…”