Xylem Functionality Is Not a Direct Indicator of Apple Preharvest Fruit Drop

Apple ( Malus × domestica ) growers can incur significant economic losses when fruit drop before they be harvested [preharvest (PFD)]. In some years and cultivars, more than 30% of potential yield lost. Growers frequently apply plant bioregulators to reduce PFD, either via delay in maturity [aminoethoxyvinylglycine (AVG), 1-methylcycolpropene] or inhibition production cell hydrolysis enzymes the pedicel [naphthalene acetic acid (NAA)]. Finding a physiological indicator PFD would allow assess susceptibility PFD. Due its lignification, xylem is believed last tissue break down pedicel, leading To determine whether loss functionality used as an potential, studies were conducted 2020 2021 with ‘Red Delicious’ treated AVG (132 µL·L −1 ), NAA (10 ethylene-producing compound [ethephon (150 2020, 200 2021)] generate range potentials. Xylem was assessed cortex. Internal ethylene content (IEC), indices, rates quantified weekly throughout harvest period. Expression genes encoding for MdEG1 MdPG2 relate abscission mechanisms. 2021, reduced compared untreated control by decreasing IEC. Although ethephon did not result higher fruit, but 2021. For all treatments both years, there linear decrease measurement Cumulative exponentially decreased neared zero climacteric rise began. Concurrent IEC increase expression AVG-treated fruit. lost at similar rate had lower . These results indicate that sole direct The concurrent / supports previous research indicating these two may serve markers