2019 ASHS Annual Conference

Once eco-dormancy is fulfilled, ovaries of tart cherry (Prunus cerasus L.) ‘Montmorency’ flowers steadily lose freeze resistance. The progressive accumulation of heat units advances floral buds development. Floral buds are classified by discrete phenology stages between dormancy and anthesis. Each stage has been associated with a critical survival temperature. Although these phenology stages are distinguishable by visual characteristics, they have not been correlated with actual ovary growth. Further, the early phenology stages between dormancy to first swelling and side green-to-green tip have overlapping visual characteristics and, thus, are not easily discernable. The aims of this research were to phenotype reproductive buds and relate changes in their physical properties with ovary growth and development. A secondary objective was to identify proxies for resumed ovary growth following eco-dormancy. Floral buds were collected several times per week near the end of eco-dormancy until anthesis during two consecutive years of 2017 and 2018. Fresh buds were weighed, imaged and relative water content (RWC) was calculated. Entire pistils were extracted from a subset of fresh floral buds and imaged. Ovary diameter and volume were measured using calibrated image analysis software. Seventy to 100 floral buds were randomly selected from each sample population and frozen in a programmable temperature chamber at a rate of 1.5°C per hour. The lethal temperature (LT₅₀) of flowers was determined by a combination of differential thermal analysis (DTA), between dormancy and first swell and visual assessment (oxidative browning between first swell and anthesis). Between dormancy and green tip, ovary volume increased nearly 5-fold and RWC increased from 50% to 80% for both years. The onset of pistil growth occurred during the transition from bud swell to side green. Concomitantly, ~13°C of hardiness was lost during this period, and the phenology stages showed only little visual difference. Relative water content was strongly associated with pistil growth and loss of hardiness and served as an objective indicator of bud development. Most of the physiological changes occurred within the first 150 GDD, with relative water content being the most sensitive predictor of developmental change.