Seminar_Jimmy Larson_11.16.2020.pdf

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Abstract:
Crop load management is often cited as one of the most critical priorities apple (Malus x domestica L. Borkh) growers face every year. Early in the season growers intentionally remove fruit to increase fruit size, improve storability and reduce biennial bearing – high crop loads suppress flower development for the following year, leading to “on” and “off” years of production. Then, just before harvest, crop loss can occur with premature fruit drop (PFD), crop losses have been estimated to be up to 30%. Elucidating the mechanisms that lead to and developing tools that can predict abscission during these two periods is the focus of my research. I am aiming to better predict fruitlet abscission rates following chemical thinner applications using nondestructive near-infrared spectroscopy. The loss of xylem function by the fruit has been hypothesized as one factor leading to PFD. We created a range of PFD potentials by applying an ethylene biosynthesis inhibitor – Aminoethoxyvinilglycine (AVG) – a synthetic auxin – Napthaleneacitic acid (NAA), both commonly used chemistries to control PFD, and a precursor to ethylene – Ethephon – to assess PFD and xylem function on Red Delicious apples. AVG and NAA both controlled PFD compared to untreated control and Ethephon, although through different modes of action. AVG by suppressing ethylene production and delaying fruit maturity, while NAA presumably by maintaining polar auxin transport through the abscission zone. An acid fuchsin dye infiltration method showed that fruit from AVG treated trees did maintain higher xylem functionality compared to NAA, Ethephon and control treatments. These results open the possibility of developing fruit transpiration based tools for growers to predict PFD susceptibility and time PFD control applications.