Predicting and Elucidating Apple Fruit Abscission with Emerging Technologies
Jimmy Larson, PhD Exit Seminar
Wednesday, January 4, 2023, 10:00 am
(Under the direction of Dr. Tom Kon and Dr. Mike Parker, Co-Chairs)

Join Zoom Meeting: https://ncsu.zoom.us/j/94534892973?pwd=VDhFRE02QjBZNGtwazBxcWhQS0FFZz09
Meeting ID: 945 3489 2973
Passcode: 679180

 Larson.Abstr.pdf

Apple (Malus x domestica L. Borkh.) crop load management is critical for growers to produce optimum yields of high-quality fruit annually. Apple trees produce an overabundance of fruit, if not removed this will result in excessive yields of small, poor-quality fruit, and suppression flower initiation. The intentional removal (thinning) of a portion is needed to increase fruit size of remaining fruit and promote floral initiation. The application of plant bioregulators (thinners) that magnify the tree’s predisposition to shed fruit in response to physiological stress is the most efficient thinning method growers employ. Multiple applications are typically needed to reduce crop load to the desired level; however, the efficacy of a thinner application is difficult to predict. A model using visible and near infrared spectroscopy data was developed to predict fruitlet abscission/persistence following a chemical thinner application in 2021 and 2022 in ‘Honeycrisp’. Combining all data captured between 2021 and 2022, the developed model from each measurement date (days after thinner; DAT) to predict abscission/persistence resulted in prediction accuracies: 0.84 (-1 DAT), 0.90 (3 DAT), 0.90 (5/6 DAT), and 0.93 (9 DAT). Preharvest fruit drop (PFD), occurring proximal to harvest, is the loss of a portion of crop when fruit of some cultivars abscise before reaching marketable maturity; PFD requires additional crop load management. Xylem functionality throughout the harvest period was tracked in 2020 and 2021 in relation to internal ethylene content, fruit maturity, and PFD to determine if loss of xylem functionality is an indicator of PFD potential. Fruit treated with an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), had lower PFD than the untreated control in both years. Loss of xylem functionality within fruit was independent of PFD and fruit pedicel breakdown as functional xylem vessels decreased in the control and AVG-treated fruit. Breakdown of xylem vessels in the pedicel was not the cause of loss of functionality as the untreated control fruit had higher expression levels of hydrolysis enzymes compared to AVG-treated at later time points. Collectively, these research projects aim to aid growers in crop load management decisions by improving prediction of fruit abscission during the thinning and PFD period.