Studies on the premature bolting of the chicory cultivar 'Daliva'

The flower Initiation and bolting responses of the extra-early F-1 hybrid chicory cultivar 'Daliva' (Cichorium intybus L. var witloof) were investigated under controlled daylength and field conditions at Knoxville, TN (35°, 53'N and 83°, 57'W). Histological sectioning and biochemical screenings from apical shoot tips for soluble sugars (glucose, fructose, and sucrose) and total free amino acids prior to and after floral transition, in addition to various plant size measurements, were conducted.

Under controlled daylength (10 hours light) for 143 days, pot grown plants did not exceed 22 leaves and no plants initiated a floral transition. After 143 days similar plants were subjected to long photoperiods (>14 hours) for up to 15 days. Over the 15 days of long photoperiods six harvests were made but no floral initiation was found. Total amino acids from all shoot tips ranged from 15 to 30 mg / g dry weight (DW). Soluble sugars leached from apical shoot tips followed no apparent trends. Glucose and fructose each ranged from 25 to 120 umol / g DW while sucrose ranged from 30 to 130 umol / g DW. Immediately after the imposition of the long day photoperiods the total free amino acid level in the shoot tips appeared to rise.

In a field experiment, some field grown 'Daliva' chicory sown on 29 May had signs of bolting within 90 days. Vegetative meristems appeared flattened, even sunken beneath the overarching leaf primordia while induced meristems were domed and hemispherical in shape; this is consistent with other reports from the Cichorieae.

In vegetative shoot tips, total free amino acids from shoot tips ranged between 23 and 40 mg / g DW with the maximum value at the middle harvest. Glucose and fructose each were less than 100 umol / g DW and remained steady through three harvests. Sucrose from the same tissue dropped linearly from 450 to near 50 umol / g DW over a 27 day harvest period.

Shoot tips identified as transitional had levels of free amino acids which rose steadily from 15 to 25 to 35 mg / g DW over three harvests within 13 days. From the same shoot tips all sugars also rose steadily; glucose from 90 to 700, fructose from 60 to 260, and sucrose from 10 to 400 umol per g DW. Transitional plants exceeded 33 leaves and had root diameters greater than 20 mm.

A separate field experiment investigating 'Daliva' plant growth and bolting response was begun on 19 June when seeds were planted into an Etowah clay loam. Five weeks later half the plants were mulched with 10 cm of straw mulch. Harvests began 14 days after planting and continued for 14 weeks. Bolting plants were observed after 8 weeks.

Measurements of bolting plants showed that although the mulched plants grew faster and larger they did not bolt with any more frequency than plants in the bare soil. However, a comparison of various plant parameters (leaf number, area, DW, root diameter, root DW and crown diameter) between bolting and non-bolting plants showed that the leaf number differed (PIn summary, these experiments investigated the bolting responses of 'Daliva' chicory and found that the juvenile stage of this cultivar is passed at approximately 30 leaves and thereafter the plant may proceed directly into flowering. Once induced to flower the apical shoot meristem appeared distinctly domed, in contrast to the vegetative meristem which was flattened at the top.