Temporal Aspects of Vernalization and Flowering in Long-day Storage Onion

Abstract

<jats:p>Vernalization is an important step for floral initiation in onion (<jats:italic>Allium cepa</jats:italic>), but our understanding of the minimum vernalization time for long-day storage onions to gain floral competence is limited. A series of time course experiments were conducted over 4 years to determine the effects of vernalization time on sprouting, scape emergence, and flowering in ‘Cortland’, ‘Sherman’, and CUDH2107. We found an endodormancy period is present in the bulbs of these cultivars that lasts for 8 to 10 weeks. In addition, these three accessions achieve optimum uniform scape emergence after chilling for 14 weeks at 10 °C. On average, when bulbs were chilled for 14 weeks, it took 96.8 ± 15.6 days from planting to flowering in all accessions evaluated. As storage duration under vernalizing temperatures increases, the time to sprouting, scape emergence, and flowering decrease. Furthermore, the variance in time from sprouting to scape emergence was greatly reduced between 10 and 12 weeks of storage for ‘Cortland’ and CUDH2107, and between 12 and 14 weeks for ‘Sherman’. After 10 weeks of chilling, each additional week of storage resulted in an average decrease in time to flowering of 4.1%. We also observed large percentages of bulbs flowering without receiving any vernalization. This observation supports our finding that the relationship between vernalization and flowering in long-day storage onion is facultative rather than obligate. These findings help define the relationship between dormancy, vernalization, and flowering in long-day storage onion.</jats:p>

Annualization of the Long Day Onion Breeding Cycle through Threshold Vernalization and Dormancy Disruption

“…While the treatment seems to have been effective at mitigating losses from disease pressure, the effect on root initiation was not as strong as in previous years. Uniformity in rooting time among varieties was poor relative to previous work and the performance of "Cortland" and "Sherman" was consistent with results reported by D'Angelo and Goldman [14] for the year 2015, which was also a year with high disease pressure. This observation supports an earlier observation that a 4-h hydrogen peroxide treatment may be less effective at breaking dormancy in bulbs that were subject to high disease pressure [14].…”

“…We have previously demonstrated that treatments with 10-30% hydrogen peroxide solutions serve to promote uniform endodormancy release and root initiation in "Cortland" and "Sherman" bulbs [14]. In this study, CUDH2107, "Sherman", and WEOS1 bulbs treated with a 15% hydrogen peroxide solution were effectively released from endodormancy as expected, with an average of 13.3 days to visible root growth.…”

“…Utilizing these findings, we demonstrated that a 2 to 4-h exogenous treatment of 15-20% hydrogen peroxide was highly effective at initiating uniform root growth in endodormant bulbs, thus signifying the release from endodormancy [14]. Bulbs treated in this way could then be subjected to precise lengths of vernalization, thereby reducing the overall time to flowering.…”

“…Fifteen bulbs were sampled from each variety and treated with hydrogen peroxide to force the release of bulb endodormancy. We have previously demonstrated that hydrogen peroxide can break bulb endodormancy when treated with 10-30% solutions for 2 to 4 h [14]. Due to a hail storm late in the season, we were unable to sample 15 bulbs from 4 of the varieties: W419B, W205A, W455A, and "Cortland".…”

“…We previously determined that long day onion varieties can achieve uniform scape emergence with an optimum chilling time of 12 to 14 weeks at 10 °C [14]. Through the course of this work we identified and quantified an endodormancy period that is present in the bulbs of these varieties and lasts for 8 to 10 weeks [15].…”