Wild blueberries are managed on a two-year production cycle, meaning that the plants need to grow for two years for a harvestable crop. During this time, wild blueberry floral buds need to go through three dormancy stages before flowering. Please see previous blogs for more detailed information on the first two dormancy stages, para- and endo- dormancy. Once the blueberry buds have met their para- and endo-dormancy requirements they can enter ecodormancy, which is normally late winter to early spring. Once ecodormancy requirements have been met, then the buds will flower. Wild blueberry producers currently use ecodormancy requirements, based on growing degree days (GDD), to try and predict when the buds will open, and pollinators are needed in the fields. Knowing the requirements that are needed for ecodormancy could help with predicting wild blueberry bloom and allow for more precise placement of managed pollinators for more efficient use of this limited resource.

Wild Blueberry Phenology in the Crop Year - Ecodormancy

Ecodormancy is the second winter dormancy stage of floral buds, where the reaction leading to growth control is driven by external environmental cues, such as warm temperatures⁵. Ecodormant buds will not flower normally, meaning that only some of the buds will open when placed in growth adequate conditions, and the ones that do open will take longer to do so. Ecodormancy will prevent the floral buds from opening until the growing conditions are adequate for flowers, therefore protecting them from fluctuating conditions in the spring. Ecodormancy release relies on an accumulation of warm temperatures and the most common way of measuring the accumulation of warm temperatures is with GDDs⁵.

Ecodormant wild blueberry floral buds in early Spring (© John MacDonald 2024)

GDDs are a measure of accumulated daily heat units during which the plant has potential to be physiologically active and is measured using daily mean temperatures¹. Accumulations of heat units for ecodormancy begin when endodormancy is released. Currently, there are limited experimental results for when endodormancy is released for wild blueberries. Therefore, GDD accumulations for ecodormancy begin at a selected calendar date³, which is currently April 1^st for wild blueberries. Most GDD models include a base and upper temperature threshold, specific to different organisms, at which development may be delayed due to unfavorable growing conditions³. GDD models can be used to predict many crop phenological events, such as pest life cycles for applications of pesticides and floral bloom for placement of pollinators.

GDD models have been created in Nova Scotia to predict phenology of weeds, such as yellow toadflax (Linaria vulgaris), spreading dogbane (Apocynum androsaemifolium), and red sorrel (Rumex acetosella)^2,9,10. GDD models have also been created for predicting flowering in highbush and lowbush blueberries^4,6. More specifically, wild blueberry ramet emergence, tip-dieback, and flowering prediction models have been created in Nova Scotia⁸. The existing model for wild blueberry flowering, however, requires revisions to include early flowering wild blueberry genets and the timing of endodormancy release.

Wild blueberry field during ecodormancy in early Spring (© John MacDonald 2024)

Perennia Food and Agriculture Corporation, Nova Scotia’s technical food development agency, currently has an application called Farm Weather on the Farm Data Tools Website.  This tool will easily calculate GDD accumulations at weather stations, including 55 on wild blueberry fields, throughout Nova Scotia. Please make an account on Farm Data Tools and check out this very useful resource (Farm Data Tools – Farm Data Tools).

The placement of pollinators on wild blueberry fields during bloom can be difficult to plan. Learning more about the phenology stages of wild blueberries, such as endo- and eco-dormancy requirements, may help to create predictive models for the placement of pollinators. These models, based on GDD, could allow more efficient use of managed pollinators, improve wild blueberry production, and support honey bee health.

Written by John MacDonald, ATTTA Seasonal Apiculturist

 

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email abyers@perennia.ca

 

References:

1. Baskerville, G.L. and Emin, P. (1969) ‘Rapid Estimation of Heat Accumulation from Maximum and Minimum Temperatures’, Ecology, 50(3), pp. 514–517. Available at: https://doi.org/10.2307/1933912.

2. Blatt, S., De Clerck-Floate, R. and White, S.N. (2022) ‘Development of a growing degree-day model to estimate Linaria vulgaris shoot emergence and prospects for improving biological control efforts’, Invasive Plant Science and Management, 15(1), pp. 9–15. Available at: https://doi.org/10.1017/inp.2022.6.

3. Carlson, J.D. and Hancock, J.F. (1991) ‘A Methodology for Determining Suitable Heat-unit Requirements for Harvest of Highbush Blueberry’, Journal of the American Society for Horticultural Science, 116(5), pp. 774–779. Available at: https://doi.org/10.21273/JASHS.116.5.774.

4. Kirk, A.K. and Isaacs, R. (2012) ‘Predicting Flower Phenology and Viability of Highbush Blueberry’, HortScience, 47(9), pp. 1291–1296. Available at: https://doi.org/10.21273/HORTSCI.47.9.1291.

5. Lang, G.A. et al. (1987) ‘Endo-, Para-, and Ecodormancy: Physiological Terminology and Classification for Dormancy Research’, 22.

6. NeSmith, D.S. and Bridges, D.C. (1992) ‘Modeling Chilling Influence on Cumulative Flowering: A Case Study Using `Tifblue Rabbiteye Blueberry’, Journal of the American Society for Horticultural Science, 117(5), pp. 698–702. Available at: https://doi.org/10.21273/JASHS.117.5.698.

7. Rieger, M. (2006) Introduction to Fruit Crops. Haworth Food & Agricultural Products Press.

8. White, S.N., Boyd, N.S. and Van Acker, R.C. (2012) ‘Growing Degree-day Models for Predicting Lowbush Blueberry (Vaccinium angustifolium Ait.) Ramet Emergence, Tip Dieback, and Flowering in Nova Scotia, Canada’, HortScience, 47(8), pp. 1014–1021. Available at: https://doi.org/10.21273/HORTSCI.47.8.1014.

9. White, S.N., Boyd, N.S. and Van Acker, R.C. (2015) ‘Temperature Thresholds and Growing-Degree-Day Models for Red Sorrel (Rumex acetosella) Ramet Sprouting, Emergence, and Flowering in Wild Blueberry’, Weed Science, 63(1), pp. 254–263. Available at: https://doi.org/10.1614/WS-D-14-00048.1.

10. Wu, L. et al. (2013) ‘Spreading Dogbane (Apocynum androsaemifolium) Development in Wild Blueberry Fields’, Weed Science, 61(3), pp. 422–427. Available at: https://doi.org/10.1614/WS-D-12-00156.1.

Successful pollination of wild blueberry crops is dependent on managed pollinators. Studying phenology stages throughout the life cycle of wild blueberry crops could help with efficiencies around the use of these pollinators. Time between emergence and tip dieback in the sprout year will determine what the stem can support in the crop year.  Evaluation of these phenology stages could support a prediction model, using sprout year data, for the numbers of pollinators required in the crop year. Wild blueberry phenology stages in the crop year include two winter dormancy periods, known as endodormancy and ecodormancy, as well as flowering, fruit set, and harvest. With a better understanding of the dormancy periods of wild blueberries, a prediction model for timing of bloom and pollinator placement may be determined earlier in the crop year to help with pollinator efficiencies.

Wild Blueberry Phenology in the Crop Year - Endodormancy

Endodormancy is the first of two winter dormancy periods that are needed for wild blueberry buds to resume normal growth in the spring, and it is driven by internal cues within the plant [5]. Wild blueberry buds become endodormant to withstand cold temperatures and dehydration and prevent buds from opening throughout the winter when growth conditions are not adequate. Endodormancy is initiated by cold temperatures late in the summer and short daylength helps to accelerate this process. Cold temperatures in the fall also help acclimatize the buds to withstand freezing temperatures throughout the winter [1,6]

Endodormant wild blueberry plants (©John MacDonald 2024)

There are many changes happening internally when the buds go endodormant, including but not limited to the bound-to-free water status and hormone levels. The water goes from a free state to a bound state with macromolecules when the buds go endodormant. Also, the two most important hormones that are related to dormancy are abscisic acid (ABA) and gibberellin (GA). There is an increase in ABA within the plant during the initiation of endodormancy, which suggests that ABA plays an important role in endodormancy initiation. There is an increase in GA and decrease in ABA during endodormancy release, suggesting that GA plays an important role in endodormancy release [7].

The release of dormancy is regulated by the accumulation of cold temperatures, which is known as the chilling requirement. This can be calculated as chilling hours, which is an accumulation of temperatures between a lower and upper threshold (e.g., between 0 and 7°C) [3]. In contrast, chilling unit models are created to consider the reduced efficacy of temperatures below or above an optimum value and hence account for the reduced or negative effects of certain temperatures. The chilling requirement of wild blueberries is estimated at 1000 hours of temperatures less than 0°C [9,12], but limited results are available to confirm this assumption.

Endodormant buds will have a delayed and reduced growth rate compared to non-dormant buds when placed in growth adequate conditions, therefore dormancy must be satisfied to have adequate flowering and fruit set [10]. Knowing the chilling requirement for endodormancy release can give insight into the timing and intensity of bloom. The state of dormancy in wild blueberry floral buds can be determined by sampling floral buds throughout the winter, while the buds are receiving more chilling hours, and evaluating them in a greenhouse or laboratory.

One way dormancy release can be evaluated is a change in water status or hormone levels using intricate laboratory techniques. Another simpler and cheaper method that will yield similar results is known as forcing buds in a greenhouse. This is done by observing the rate of buds opening after a determined amount of time [4,8,11] or observing the number of buds opening after a determined amount of time [2,7]. Dormancy release is considered to have occurred when plants exposed to more chilling hours exhibit similar rates of buds opening.

Endodormant wild blueberry plants (©John MacDonald 2024)

After endodormancy is released, we then have ecodormancy, flowering, and fruit set. Currently wild blueberry producers and beekeepers use April 1st as an approximation of when endodormancy is released and ecodormancy starts in the Maritimes. This is inaccurate as the accumulation of chilling hours or units will vary from year to year, based on endodormancy requirements. Therefore, determining when endodormancy is released in wild blueberries will give a better approximation as to when flowers will open and help with efficiencies in placing pollinators for optimal fruit set.

Check back in the following weeks for part two of Wild Blueberry Phenology in the Crop Year – Ecodormancy and Flowering.

Written by John MacDonald, ATTTA Seasonal Apiculturist

 

Connecting with ATTTA Specialists

If you’d like to connect with ATTTA specialists or learn more about our program, you can:

visit our website at https://www.perennia.ca/portfolio-items/honey-bees/

Email abyers@perennia.ca

 

References:

[1] Deslauriers, A. et al. (2021) ‘Cold acclimation and deacclimation in wild blueberry: Direct and indirect influence of environmental factors and non-structural carbohydrates’, Agricultural and Forest Meteorology, 301–302, p. 108349. Available at: https://doi.org/10.1016/j.agrformet.2021.108349.

[2] Ferlito, F. et al. (2021) ‘Assessment of chilling requirement and threshold temperature of a low chill pear (Pyrus communis L.) germplasm in the Mediterranean area’, Horticulturae, 7(3), p. 45. Available at: https://doi.org/10.3390/horticulturae7030045.

[3] Fraisse, C.W. and Whidden, A. (2010) ‘Chill accumulation monitoring and forecasting’, Electronic Data Information Source, 2010(AE452). Available at: https://doi.org/10.32473/edis-ae452-2010.

[4] Guak, S. and Neilsen, D. (2013) ‘Chill unit models for predicting dormancy completion of floral buds in apple and sweet cherry’, Horticulture, Environment, and Biotechnology, 54(1), pp. 29–36. Available at: https://doi.org/10.1007/s13580-013-0140-9.

[5] Lang, G.A. et al. (1987) ‘Endo-, para-, and ecodormancy: physiological terminology and classification for dormancy research’, HortScience, 22(3), pp. 371–377.

[6] Li, C., Junttila, O. and Palva, E.T. (2004) ‘Environmental regulation and physiological basis of freezing tolerance in woody plants’, Acta Physiologiae Plantarum, 26(2), pp. 213–222. Available at: https://doi.org/10.1007/s11738-004-0010-2.

[7] Li, Y. et al. (2022) ‘Comparative transcriptomic analysis provides insight into the key regulatory pathways and differentially expressed genes in blueberry flower bud endo- and ecodormancy release’, Horticulturae, 8(2), p. 176. Available at: https://doi.org/10.3390/horticulturae8020176.

[8] Norvell, D.J. and Moore, J.N. (1982) ‘An evaluation of chilling models for estimating rest requirements of highbush blueberries (Vaccinium corymbosum L.)’, Journal of the American Society for Horticultural Science, 107(1), pp. 54–56. Available at: https://doi.org/10.21273/JASHS.107.1.54.

[9] Rieger, M. (2006) Introduction to fruit crops. Haworth Food & Agricultural Products Press.

[10] Schuchovski, C. and Biasi, L.A. (2021) ‘Dormancy of floral buds of rabbiteye blueberry in a mild winter climate’, Brazilian Archives of Biology and Technology, 64, p. e21190755. Available at: https://doi.org/10.1590/1678-4324-2021190755.

[11] Spiers, J.M., Marshall, D.A. and Braswell, J.H. (2004) ‘Chilling requirement studies in blueberries’, Small Fruits Review, 3(3–4), pp. 325–330. Available at: https://doi.org/10.1300/J301v03n03_09.

[12] Yarborough, D.E. (2012) ‘Establishment and management of the cultivated lowbush blueberry (Vaccinium angustifolium)’, International Journal of Fruit Science, 12(1–3), pp. 14–22. Available at: https://doi.org/10.1080/15538362.2011.619130.